# Flat Response?



## ErinH (Feb 14, 2007)

I know some people love a flat response, and others don't care for it. 

I myself have decided to take the graphs of my speakers output and put them side by side, draw out a "median" line and change my EQ for each band to try to get the speaker outputs to a flat response. I know that this may not be the best application since various things come into play when tuning, but I thought I'd give it a go and post back my results. I'm also going to tune by ear and note the differences. FWIW, I just copy & pasted the graphs into powerpoint and lined them up.

I'm curious to know how you guys tune? Do you go for a ruler flat response maybe with an RTA, or do you only go by what sounds good?


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## chad (Jun 30, 2005)

"Modified flat" I flatten it out then use mild subtractive EQ'ing to get more zing/excitement out of it.

My PA is flat, I use individual instrument EQ to paint the picture I want.

When I mix in the studio it's flat, when I master (esp pop/rock) I have a bit of Zing in the rig to keep me from getting too crazy. I master classical flat, jazz 50/50 depending on what the "artist" wants out of the end result.

Chad

Chad


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## ErinH (Feb 14, 2007)

chad said:


> "Modified flat" I flatten it out then use mild subtractive EQ'ing to get more zing/excitement out of it.
> 
> My PA is flat, I use individual instrument EQ to paint the picture I want.
> 
> ...


Holy crap, now that's how you answer a post: with way more examples than needed! Everyone, quick, take notes. lol


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## mvw2 (Oct 2, 2005)

I've sort of come to like a simple pink noise test, run it and set it"flat" by ear with no EQ band overshadowing the other nor absent. Ear flat?


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## 60ndown (Feb 8, 2007)

if it sounds 'authentic' its good for me.

i guess useing eq or not will depend on speaker choice, amp used and enviroment playback is in.


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## WLDock (Sep 27, 2005)

Keep in mind that, many that like accurate sound don't want peakyness in the response....and while flat can be thought of as a flat line of equal amplitude of all frequencies (Ruler Flat!) that is not how we listen to music.

Many will try to keep the response between bands fairly close (maybe within 9dB?) yet the response may have a slight upward curve on the low end and maybe a slight downward curve on the high end...or vice versa....yet the overall response can be though of as flat OR good overall spectral balance...not ruler flat as in RTA flat...I don't think even die hard classical listeners want their system set like in the car?

TONAL ACCURACY and SPECTRAL BALANCE are what to strive for....not a flat RTA response because lets not forget the other things that make a system sound good...i.e...
*S*taging, *I*maging, *L*inearity, *A*mbience, (not to mention getting tweets, mids, midbasses, subs mounted in different locations to blend)...etc...Sometimes one has to sacrifice a truly flat system to get the best of all worlds in the car. Also, don't forget...some of us have the ability to tune LEFT and RIGHT and EACH speaker independently...more variable into the equation. 

That is what I would tune for...who gives a damn what the curve looks like if everything sounds good and is happenin' ??? 

It's all about the music!  I choose not to vote!


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## chad (Jun 30, 2005)

WLDock said:


> TONAL ACCURACY and SPECTRAL BALANCE are what to strive for....not a flat RTA response because lets not forget the other things that make a system sound good...i.e...
> *S*taging, *I*maging, *L*inearity, *A*mbience, (not to mention getting tweets, mids, midbasses, subs mounted in different locations to blend)...etc...Sometimes one has to sacrifice a truly flat system to get the best of all worlds in the car. Also, don't forget...some of us have the ability to tune LEFT and RIGHT and EACH speaker independently...more variable into the equation.


This is very important because you can have every element in a system out of phase in each passbend except two subs and get the response flat....... IT WILL SOUND HORRIBLE!

Chad


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## demon2091tb (May 30, 2005)

bikinpunk said:


> Holy crap, now that's how you answer a post: with way more examples than needed! Everyone, quick, take notes. lol


Hes in the industry, and he's a recording engineer, (may be wrong on the latter few), but honestly what do you expect......

Personally i tend to generally flat, but with a little rise on the lower end, slight dip 1-4k to keep it from being really sensitive to the vocals, and slightly rising up top.

I do find that overly flat though does make things sound boring.

When you do EQ though, get everything flat like chad said, then cutt from there any peaks, if you boost you need to reset majority of things like gain, etc, to get back to a standardized 0 level setting.

but start flat, get something fairly close to go by, then fine tune by ear, thats the only way....


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## ErinH (Feb 14, 2007)

demon2091tb said:


> When you do EQ though, get everything flat like chad said, then cutt from there any peaks, if you boost you need to reset majority of things like gain, etc, to get back to a standardized 0 level setting.
> 
> but start flat, get something fairly close to go by, then fine tune by ear, thats the only way....


I took the frequency response charts of my speakers out to the car on lunch break and did some tuning. 

Since my midranges are crossed at 5.6k and my right side is mounted about 20 degrees off axis it suffers from off-axis break up which starts around 2k (according to the manufacturer's specs). I had to decrease left & increase right in the 2-6 range. Both L & R had to be brought up from 400-1k. Tweeters had to be brought down quite a bit @ 10 and @ 20k, tough 16k is right on my "average" line I drew.

Now, like I said, none of this tuning was done by ear. It was simply done using the response graphs provided by the manufacturer's. The purpose here was to get the speakers all on a level field and then adjust from there. I didn't have time, however, to adjust the rest by ear, but from the tunings based off the graphs alone the sound is dramatically improved. It could be worse, or it could be better after some tuning by ear but already I'm happy with the response. 

Just my $.02.


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## Whiterabbit (May 26, 2006)

I find trying to set anything flat leads to getting that "I used too much EQ" sound. takes the life out of music, and often eliminates low level midrange. I never set flat anymore.

I have the same problem when measuring left and right sides "even". Worse when I get no appreciable improvement in focus! 

I find the RTA to be a very helpful tool in verifying my ears are hearing what I think they are. The RTA tells me when a particular driver or a particular setting or install leaves a HUGE peak somewhere, where precisely that peak is, and whether or not my tuning method (whether via gain, crossover, T/A, phase, or EQ) is being effective at reducing the peak or filling the sinkhole.

but to what level to EQ or tune? off goes the RTA, only the ear can be used for that.


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## ErinH (Feb 14, 2007)

Suppose I should mention I've never seen an RTA, much less used one.


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## demon2091tb (May 30, 2005)

bikinpunk said:


> already I'm happy with the response.


Thats really all that should matter.......I've done all of mine by ear, but if i had the other stuff on hand i would definently go that route, less time involved, but you don't necessarily get the KNOW the response of the car and which little nuances it has, which effects come from which reflections, etc etc etc.....list could go on, ear is the only way, but RTA, spectrum analyzers, oscilators just make them that much quicker and easier, but the ear still comes back as the reference....


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## MidnightCE (Mar 5, 2007)

Flat with my parametric EQ, then I let some of the midbass back in.

This is usually my goal +/- 3db, and what I did with my Focals.

```
DB
100
90 -------------___
80 --------------------------------------
70 --------------------------------------
60 --------------------------------------
     80 100 200 500 1k 2k 5k 8k 10k 15k 20k hz
```
To compensate for road noise.


However with my Dyns, this is the best I've been able to do:


```
DB
100
90  ______________
80 -----------------------------
70 ------------------------------
60 -------------------------------
    80 100 200 500 1k 2k 5k 8k 10k 15k 20k hz
```
thinking about adding a hu powered pair of tweets so I can get some sound over 10k.


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## chad (Jun 30, 2005)

demon2091tb said:


> Hes in the industry, and he's a recording engineer, (may be wrong on the latter few), but honestly what do you expect..........



Which also limits me as to what I can do in terms of the way a rig sounds  I've heard some fun sounding systems but know that if I got "used to it," and I would, that my performance at work would suffer. Flatish keeps me on the straight and narrow. It's amaing how it all translates. For the longest time I did not have a sub in the truck I drive to and from gigs and as a daily driver. I found quickly that when I added a sub to the truck that I demanded more out of my PA in the low end department. I try to keep my car NOT sounding over the top in terms of hype, yes I have an "over the top" setting for EQ but it's rarely used. Live, my mixing style is representitive of the Marylin Manson albums, Mechanical Animals, and Antichrist Superstar. VERY forward, VERY in your face, and pretty damn loud (RMS wise). The low end is over the top and there's a bunch of energy. And that comes from flattish daily listening, imagine what I would want out of a system if my personal listening was over the top? Not good, I'd be spending more money in recones 



demon2091tb said:


> Personally i tend to generally flat, but with a little rise on the lower end, slight dip 1-4k to keep it from being really sensitive to the vocals, and slightly rising up top.
> 
> I do find that overly flat though does make things sound boring.
> 
> ...


That is EXACTLY how I "voice" things, no matter what it is.

A way I EQ when coming into a "house rig" is flatten out the graphs (EQ's), Put on a known CD or file, and before adjusting to personal taste I go across 31 bands and at each one starting about 100HZ bump it up 3 dB and bring it back down flat, do this for each band, you will QUICKLY find out where the system/room is hot. If I find 3 dB to kill me I back it down 3dB, If it's only mildly annoying then I back it down less. I then bump the volume up a bit and repeat. After I get the annoyances out I'll go for the personal taste thing BUT KNOWING FULL WELL that it's going to be WAY different with a band on the stage. Any boosting I do is usually on the tippy top and MAYBE 40-63 but the 40-63 thing can usually be cured by creative notching from 80-160 whare a lot of rigs become VERY sensitive. Again I shoot for flattish and use the per channel EQ to paint the picture. If I'm mixing a band and find 160 coming off the stage from the bass guitar killing things why would I notch the whole PA, just notch the bass so a 7 string guitar can still blow thru. Same with rooms/cars. If you find a nasty peak right at the XO freq, underlap them more and leave a bit of a "hole" or steepen the slope on one or both drivers. This could presumably leave you with a free band of parametric that you can use elsewhere where you really need it and can't manipulate crossover slopes/frequencies.

Chad


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## ErinH (Feb 14, 2007)

I want your job, Chad.

*dreams*


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## DS-21 (Apr 16, 2005)

Keep in mind that "ruler flat" is basically impossible. Yes, it is possible in some cases to get the 31 points of an RTA to be at the same place at a given SPL, but there's plenty of stuff going on between those 1/3 octave bands.


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## 300Z (Mar 20, 2005)

There is a lot more involved that meets the eye... Freq response, power response, time domain, phase, distortion... all play a role on how we perceive sounds.

Me? When I tune (when I really get serious about it anyway...) I use some well recorded songs that I'm familiar with and spend all the time needed playing with x-overs and EQ and a few other tricks until I get the timbre as close to the real instruments being played as possible, but achieving what I consider my reference level is very difficult and very very few cars that I have heard could pull it right. Car audio is about compromises...


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## demon2091tb (May 30, 2005)

Alot of what i see myself doing lately while tuning, is i had played the ECA V4 percussion disks where it has the straight drum solo's and just work on them constantly.......Get the impact, feeling, omph, zing, depth, and fizzle out of them, then move onto well recorded music, think just the drum tracks can do wonders with a good ear. Then i'll move onto some vocal tracks to make sure that the upper midrange isint harsh or peaky, as natural reflections are horrible for it and firing directions add significantly as well.

Get the Drum solo's that start specifically with the kickdrum then slowly add more then go into a solo.....Wonderful when done correctly.......Then Horns and BigBand for Holy god dynamics and in your face sound.


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## ErinH (Feb 14, 2007)

demon2091tb said:


> Alot of what i see myself doing lately while tuning, is i had played the ECA V4 percussion disks .


I like that perspective. Could you tell me where to look for those discs?


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## demon2091tb (May 30, 2005)

bikinpunk said:


> I like that perspective. Could you tell me where to look for those discs?


Audionutz himself......Search over on ECA, for email, etc, etc. And for pricing information, honestly not sure how many cd's he has out now, i bleieve 25. I have i think 1/2 of them


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## jearhart (Jul 28, 2006)

demon2091tb said:


> Audionutz himself......Search over on ECA, for email, etc, etc. And for pricing information, honestly not sure how many cd's he has out now, i bleieve 25. I have i think 1/2 of them


i think he is closing in on 50, i've got 32 i think

linky
http://www.elitecaraudio.com/forums/showthread.php?threadid=139546


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## JAG (May 6, 2006)

Whiterabbit said:


> I find trying to set anything flat leads to getting that "I used too much EQ" sound. takes the life out of music, and often eliminates low level midrange. I never set flat anymore.
> 
> I have the same problem when measuring left and right sides "even". Worse when I get no appreciable improvement in focus!
> 
> ...


Good answer , and good advice.


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## npdang (Jul 29, 2005)

I think people too often confuse theory and practice. In theory, yes you want a perfectly flat response if you're intent is to accurately reproduce a recording. In practice however, where you put the mic, the type and length of your measurement window, as well as what kind of spatial averaging you're doing, etc. will have a huge impact on the response you measure. In other words, flat with one type of measurement isn't necessarily flat with another type, and especially with a limited device such as an RTA you don't always get the most informative picture.


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## Hobbes26 (Mar 9, 2005)

Flat may be good..... but there are two components to the sound - direct and indirect (reflected).

Sure you can EQ the speaker to be 'flat'. But how do you EQ the room to give you an indirect sound that's flat as well?

Or... is that not what we want to do?


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## ErinH (Feb 14, 2007)

I honestly don't have much of a preference, I suppose.

I just wanted to get perspectives on this topic as it seems I see "flat response" sometimes dictated in other posts (and forums).


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## B&K (Sep 20, 2005)

FFT or 1/3 octave flat? Flat on equal loudness contours, sones, or in standard frequency response? Pink noise or white noise flat? Binaural recording flat or single mic with no body in the vehicle flat? The uncertainty in the measurements that most people make have a huge effect on the results which really affect the answer here. I think with a bit better measurement understanding more people would actually enjoy the flat response when measured correctly, but again the uncertainty in the measurement setup is always a problem. While some frequency coloration can be beneficial, in a perfect environment with a perfect recording I would assume that most of you would actually indeed answer a ruler flat response. Since this isn't very possible in real life however that won't be the case.


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## Hobbes26 (Mar 9, 2005)

B&K said:


> FFT or 1/3 octave flat? Flat on equal loudness contours, sones, or in standard frequency response? Pink noise or white noise flat? Binaural recording flat or single mic with no body in the vehicle flat? The uncertainty in the measurements that most people make have a huge effect on the results which really affect the answer here. I think with a bit better measurement understanding more people would actually enjoy the flat response when measured correctly, but again the uncertainty in the measurement setup is always a problem. While some frequency coloration can be beneficial, in a perfect environment with a perfect recording I would assume that most of you would actually indeed answer a ruler flat response. Since this isn't very possible in real life however that won't be the case.


Flat can be achievable using headphones or earphones, provided the response of the ear is measured beforehand and the music is filtered with the inverse response to give a flat response (including the headphones' response) ... This should be done at narrowband resolutions...

Has anyone tried that before to see if they like it or not?

Like I said before... "Flat" may not really be flat directly from the speaker - when you're doing your measurement, your measurement includes the room response, so you're effectively EQing the speaker+room response.


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## ErinH (Feb 14, 2007)

Hobbes26 said:


> Flat can be achievable using headphones or earphones, provided the response of the ear is measured beforehand and the music is filtered with the inverse response to give a flat response (including the headphones' response) ... This should be done at narrowband resolutions...
> 
> Has anyone tried that before to see if they like it or not?
> 
> Like I said before... "Flat" may not really be flat directly from the speaker - when you're doing your measurement, your measurement includes the room response, so you're effectively EQing the speaker+room response.


I was actually thinking of using headphones to tune, but I dunno. I'm not sure how much I would like it since you can't listen to the entire spectrum. Unless there's some 3-way headphone splitter I'm not aware of? Maybe daisy-chain a bunch of splitters?


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## Whiterabbit (May 26, 2006)

what do you mean? Headphones are often THE reference for tonal accuracy when tuning home and car stereo systems.

What do you mean by a limited spectrum, and how would you use a splitter?


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## ErinH (Feb 14, 2007)

Whiterabbit said:


> what do you mean? Headphones are often THE reference for tonal accuracy when tuning home and car stereo systems.
> 
> What do you mean by a limited spectrum, and how would you use a splitter?


I'm just not sure how to hook up headphones to every output?

Heck, maybe I just don't know how to hook headphones up at all. I thought you would use a mini-jack to RCA splitter for 1 channel (left & right) and if you have 3 channels for midbass, midrange, and tweeter and you wanted to listen to the whole spectrum (all channels) you'd have to have multiple splitters. 

Maybe I'm just making this harder?

I only say you'd need to listen to the spectrum, because it's been my experience (when setting gains) listening to one-channel only doesn't give an accurate description of how the entire system will sound.

Heck, I know I'm probably making it harder than it is, but does what I said even make sense?


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## Whiterabbit (May 26, 2006)

I understand what you are saying now.

The use for headphones is to use them seperately from your signal processor, amplifiers, etc.

You dont have to use your in car CD player, either. you can have them totally separated.

they become a "reference system", in effect.

I suspect most use headphones in their home, then move out to the car to play carstereo games.


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## zfactor (Oct 19, 2005)

i only use a rta anymore for comp use. but i do try to get a somewhat flat response then adjust accordingly to what my ears like. i never listen totally flat though sounds terrible imo...lifeless and drab and def not what the recording was meant to be imo.. i want as lifelike as possible


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## MidnightCE (Mar 5, 2007)

Whiterabbit said:


> I understand what you are saying now.
> 
> The use for headphones is to use them seperately from your signal processor, amplifiers, etc.
> 
> ...



I use amplified sennheiser HD580s. Though I went from car audio to headphones.  I have to say, they sound a bit similar to my Dynaudios... Whereas my Grado headphones sound a bit like my Utopias...

They are fantastic for finding distortion that I "think" I hear. If that makes sense...


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## npdang (Jul 29, 2005)

Please refer to this thread as well on measuring a flat response:

http://www.diymobileaudio.com/forum/showthread.php?t=12096


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## shinjohn (Feb 8, 2006)

bikinpunk said:


> I myself have decided to take the graphs of my speakers output and put them side by side, draw out a "median" line and change my EQ for each band to try to get the speaker outputs to a flat response.





bikinpunk said:


> I took the frequency response charts of my speakers out to the car on lunch break and did some tuning.
> 
> Now, like I said, none of this tuning was done by ear. It was simply done using the response graphs provided by the manufacturer's.


I was a little confused reading this thread.  

In your first post, it sounded like you intended to measure in-car response of each driver separately (of which your setup would obviously have a huge impact), and then use that data to tune up your car. This is similar to N's tutorial he wrote on in-car tuning, which is an excellent read, IMO.

In a follow up post, you mentioned just using "response graphs provided by the manufacturer's."

I see now what you did.  My one comment is that although response graphs from a manufacturer are good for (some) comparative purposes, IMO they are of limited use for in-car tuning. The simple reason is that beyond anything else, the car's transfer function has more impact on system response than any other variable. If you tune strictly to the raw driver's baffled or near-field response, you're likely to be far off from where you would like to be.

I can't knock your approach completely though since cone breakup modes aren't going to move, and a resonance is still a resonance, however you find it. I think it's great to use any and all data at your disposal to get the best result!


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## ErinH (Feb 14, 2007)

shinjohn said:


> I was a little confused reading this thread.
> 
> In your first post, it sounded like you intended to measure in-car response of each driver separately (of which your setup would obviously have a huge impact), and then use that data to tune up your car. This is similar to N's tutorial he wrote on in-car tuning, which is an excellent read, IMO.
> 
> ...



Yea, I know it's somewhat of a flawed method, but I did use it to somehow get all frequencies on a level plane...that being my only way since I don't have access to an RTA. I know things are different in-car, but I figured it was worth a shot. Thanks for not slamming me, as I'm sure others were like "wtf" with that method.


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## shinjohn (Feb 8, 2006)

bikinpunk said:


> Yea, I know it's somewhat of a flawed method, but I did use it to somehow get all frequencies on a level plane...that being my only way since I don't have access to an RTA. I know things are different in-car, but I figured it was worth a shot. Thanks for not slamming me, as I'm sure others were like "wtf" with that method.


No need ever for "slamming" IMO.  We're all learning as we go along. 

The "flat response" question is not an easy one. N is opening my eyes more to measurement related issues in car and I'm anxious to play around with some measurement/data acquisition gear soon.


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## Patrick Bateman (Sep 11, 2006)

300Z said:


> There is a lot more involved that meets the eye... Freq response, power response, time domain, phase, distortion... all play a role on how we perceive sounds.
> 
> Me? When I tune (when I really get serious about it anyway...) I use some well recorded songs that I'm familiar with and spend all the time needed playing with x-overs and EQ and a few other tricks until I get the timbre as close to the real instruments being played as possible, but achieving what I consider my reference level is very difficult and very very few cars that I have heard could pull it right. Car audio is about compromises...


IAWTC










The graph at the bottom is the polar response of a JBL 2470 compression driver mounted on a USD Audio horn that's been treated. The black line is an average of the polar response. (Is that the power response?)

The colored lines are measurements taken at 4.5 degree increments.

In the measurement you can see that the response jumps around a lot, with peaks on the order of 6db, but the average is relatively smooth.

When I first started messing with measurements, I tried to get smooth response at the drivers seat, but I've found that the most natural results are found when I EQ the power response, not the frequency response.

Also, I use a "dual" gate. That's helped improve the accuracy of my low frequency results, without ruining my high frequency results.

(If you use a single gate, you can't have your cake and eat it too. Either you use a short gate that's accurate at high frequencies, or a long gate that's accurate at low frequencies. But in a car, they're mutually exclusive. Hence, a dual gate.)

The graph at the top is the polar and power response of the same horn, but with a stock driver and untreated.


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## npdang (Jul 29, 2005)

Pat... what about a gate length that changes dynamically based upon frequency?


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## Patrick Bateman (Sep 11, 2006)

npdang said:


> Pat... what about a gate length that changes dynamically based upon frequency?


I write software for a living, having to write software for my hobby would turn it into work


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## npdang (Jul 29, 2005)

Patrick Bateman said:


> I write software for a living, having to write software for my hobby would turn it into work


Check out LMS or Praxis... they do something called "adaptive windowing" that you might find useful.


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## LegendJeff (Jun 28, 2009)

I start by setting phase, x-overs, and T/A before even touching EQ. In my experience, EQ more or less patches the problem. Driver placement, Phase, On/off axis is more important to get down first.

From there I use a test disk with 1/3 octave test sounds, listen for peaks or dips and take notes. Then I go back and change what I heard could have been ipmroved. Re-run the disk and I follow the same procedure until I get a subjectively falt response. I guess my method is considered solely by ear.


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## 14642 (May 19, 2008)

The point isn't the WAY you measure, rather it's whether what you measure correlates to what you hear. If you're able to use ANY tool to repeat the procedure of going from a bad-sounding car to a good one, then your measurement is valid. The confusion arises when you attempt to explain that tool to others, so they can use it successfully. 

Npdang's method will yeild a very different target curve at high frequencies than the method I use. One thing is for certain, though, and that is that you understand the tool you use so you aren'tchasing problems that don't exist. I find that 1/3rd octave analysis isn't enough resolution if I'm tuning a single speaker. However, if you tune both sides at once because you don't have separate left and right EQ, using finer resolution will expose a response that doesn't correlate to what you hear because the steep and narrow peaks and dips that result from the constructive and destructive interference are far less audible than the measurement suggests (unless you know what you're looking at). A spatial average helps to reduce those peaks, but a spectral average helps too. IF you're using 1/3rd octave analysis and measuring all the speakers at the same time, then you shold avoid using high Q filters to fix problems and target the general shape instead because the picture of those high Q peaks and dips isn't valid.

Gating the high frequencies is similar to applying a low pass filter to the measurement, so the target curve will have more high frequency attenuation compared to a non-gated measurement because there's no reverberant field in a car because the dimensions are too short. All reflections in a car are early reflections and we have to EQ them. We hear the speaker system's power response. Using a head mic is similar--the head provides high frequency masking, so the target curve would include more attenuation at high frequencies. This is simple to rectify, though, because we localize sounds at high frequencies using level rather than time and the additional reflected sound is added to the direct sound and we hear it as a single event. Simply attenuating the high frequencies with EQ is is the fix, so the measurement difference is just a matter of tool choice. The high frequencies are simple to fix with EQ and so are the very low frequencies. It's 80Hz-3kHz that present most of the difficulties. Fortunately, flat response through most of that region (with some additional output between 80 and 160 and some attenuation at the top of that band and continuing into the top 2-1/2 octaves) sounds correct when each channel is measured with pink noise and an unweighted RTA. 


The OP's poll would be easier to answer if it included the details of the measurement system--"Do you prefer flat response when each channel is measured separately with pink noise and a single micropone placed in the listening position and an unweighted RTA?" If that were the question, my answer would be "no".


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## Oliver (Jun 25, 2007)

Andy Wehmeyer said:


> *The point isn't the WAY you measure, rather it's whether what you measure correlates to what you hear... sounds correct when each channel is measured with pink noise and an unweighted RTA. *
> 
> 
> The OP's poll would be easier to answer if it included the details of the measurement system--"Do you prefer flat response when each channel is measured separately with pink noise and a single micropone placed in the listening position and an unweighted RTA?" If that were the question, my answer would be "no".


*Qualifier for sure ^^^^^*


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## donkeypunch22 (Nov 5, 2008)

Andy Wehmeyer said:


> The point isn't the WAY you measure, rather it's whether what you measure correlates to what you hear. If you're able to use ANY tool to repeat the procedure of going from a bad-sounding car to a good one, then your measurement is valid. The confusion arises when you attempt to explain that tool to others, so they can use it successfully.
> 
> Npdang's method will yeild a very different target curve at high frequencies than the method I use. One thing is for certain, though, and that is that you understand the tool you use so you aren'tchasing problems that don't exist. I find that 1/3rd octave analysis isn't enough resolution if I'm tuning a single speaker. However, if you tune both sides at once because you don't have separate left and right EQ, using finer resolution will expose a response that doesn't correlate to what you hear because the steep and narrow peaks and dips that result from the constructive and destructive interference are far less audible than the measurement suggests (unless you know what you're looking at). A spatial average helps to reduce those peaks, but a spectral average helps too. IF you're using 1/3rd octave analysis and measuring all the speakers at the same time, then you shold avoid using high Q filters to fix problems and target the general shape instead because the picture of those high Q peaks and dips isn't valid.
> 
> ...


Andy,
Many of the posters on this forum use the $100 RTA that Doitor described in May of 2008 (Behringer ECM8000 Microphone + USB Mic Mate + TrueRTA program). Considering that most of us bought the highest resolution of 1/24th octave from TrueRTA, can you help us get a reliable and repeatable measurment with the above system that "correlates to what we hear". In other words, many of us who use the $100 RTA don't fully understand the "tool we are using" and don't want to "chase problems that don't exist". 

From recent posts, I have gathered that early reflections are the enemy (thanks Patrick Bateman), but the $100 RTA gets swamped by all reflections, early and late. Is gating the solution? Or, is there still a way to still get a reliable and repeatable measurment with the $100 RTA that will yield a valid correction? 

If so, please recommend how we should use the $100 RTA tool. I hope you're somewhat familiar with the TrueRTA program, and if you could direct us with the settings you would use that would be great (speed trade off, avergaing, resolution, and if you recommend mic calibration). 

Then how would you place this single mic? 

Would you sit in the car while measuring? 

Then assume that most here on the forum are using 2 or 3 way + sub active systems with L/R EQ capability (Infact, if I may be specific for myself, I am using a 2 way + sub set up with 10 channels of parametric EQ for each channel - Zapco DC amps, and also have available 31 graphic L and R EQ - Alpine H701).

As always, your input is greatly appreciated.


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## ErinH (Feb 14, 2007)

Wow… someone dug this from the deep black abyss! 


I started this thread 2.5 years ago and I’ve learned a lot since then. One thing that is more important than anything else I’ve learned about using an RTA to tune: 
*You can get a flat response (or just about any target curve within reason) MULTIPLE ways and each result will sound different.*
So, just because you have this certain curve, it doesn't mean it's going to sound great.

I can use different x-over settings, different gains, different EQ settings, etc, etc to get a curve (or line) response from one setting to another. The thing you have to realize is that they will all sound different. More proof that a certain curve isn’t the end all be all, because you may get the curve one way and it sound horrible, while another person gets the same curve another way and it sounds great.

It’s just too generic to say that a curve is how you should tune.


Tuning is very iterative. I set up my x-over points based on driver limits and what I hear in a quick test drive of the system. Then I use the RTA to level match all the drivers as close as I can. Then I go to work on the EQ. Then I get in and listen. While listening, I often setup the mic inside the car with me to watch for issues. Ie: a song sounds screechy… I watch the RTA at the certain point in the song that sounds bad and I try to figure out if I can work it with the EQ or gain. Typically 2khz in my car presents issues as does 200-315hz. The RTA will show a large jump from the resonance in these frequencies, so I know to hit those with the EQ. Most can do this by ear, but to me it’s just easier to use an RTA to help you figure this kind of thing out.

After all that, I then do it over again. 

The best results I’ve gotten follow the Fletcher-munsoon curve. Not necessarily to a ‘t’, but within reason. That means that the low end from about 300hz and below has a gradual increase of about 15dB, and the 1-4khz range is cut a bit, while the top end also gets some boost.

There are many methods to achieve this curve. One thing in particular… I notice a lot of people talk about EQ’ing up 10k-20khz. Instead of this, I typically just set the gain to where 16khz is even with the rest of my curve, then I drop from 10khz down to about 4khz so that the tweeter level starts to line up with the midrange level. I don’t know if one is more ‘correct’ than the other, but it’s just a method I use.



If you read this far, I appreciate it.


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## 14642 (May 19, 2008)

Yeah, I'll come up with an explanation in a day or two. It'll be based on 20 years worth of experience in making cars sound good, but it'll likely conflict with a bunch of what's been posted all over this forum. I'm not into mythology nor complexity--just tools and procedures that work.


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## donkeypunch22 (Nov 5, 2008)

Alright!! Thanks, Bikinpunk, and in advance Andy, and anyone else who may have information to share.


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## boundbyglory (Feb 21, 2009)

anxiously awaiting Andy's write-up.


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## vecc205 (Nov 18, 2007)

I'm tuned in waiting for Andy's response


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## 14642 (May 19, 2008)

OK. Sorry for the delay. I don't use True RTA, but they're all pretty much the same and include the same tools. 

We'll start with a few basics here and most of this isn't my opinion. Rather, it's stuff that can either be verified and has been written about by various people who get paid for this stuff because they're scientists. Some of them are people with whom I work and some is available at the LIBRARY.

Anyway, cars are full of reflections and there are all kinds of opinions about what to do with them. Since the dimensions of the car are small, the car doesn't create a reverberant field--all reflections arrive within 20mS of the initial sound. 

Second, when the same sound emanates from a particular source and is also reflected from a nearby source, the difference in arrival time and frequency responses of that sound create comb filtering. At some frequency and at multiples of that frequency, based on the difference in distance from the two sources to the listener, there will be destructive interference. The lowest-frequency null is the widest and each subsequent null (as frequency increases) will be narrower than the one that preceeded it. Hereafter, we'll refer to that width as Q--low-Q is wide and high-Q is narrow. 

Here's a screen shot from an RTA to illustrate this. To simulate this, I've set the RTA to show the sum of left and right, and I've delayed the right by 1mS which is about equal to a foot--1.132', to be more exact.











In the next screenshot, I've increase the delay to 2mS, and you can see that the first null happens at a lower frequency.










In the third screenshot, I've reversed the phase of one channel and it's plain to see that I've moved the null back up, but I've killed the bass response. Switching the phase has put the sound from the two channels back in phase at frequencies where it was out of phase. It's also put the sound from the two channels out of phase at other frequencies. 










Also remember, that in order for two sources, in this case a right and left speaker, to produce a phantom image in between the two speakers, they must both be in phase. If you sit equidistant from a pair of speakers that are in phase, there's an image. If you swap the polarity of one, there's no image, less bass and you hear the speaker locations. If you're not equidistant, and the two speakers are in phase, then you'll hear a phantom image at frequencies where they are in phase, and no image for frequencies where they are out of phase. In the case of the third screenshot, --a pair of speakers located where the PLD is about 2.5' and one speaker's polarity is swapped, there won't be an image at low frequencies and the bass will suck, there won't be an image at 500 Hz and at multiples of that frequency. The comb filtering causes this image "problem" as well as the obvious frequency response problem.

For right and left speakers mounted in the doors, the first and lowest Q null happens in the vocal region. Swapping the phase of one channel can dramatically improve the image for a vocalist, but screws up the bass and screws up the image at higher frequencies.

In the fourth screenshot, I've simulated time alignment by putting the channels back in phase and delaying the other one by 2mS so they match. See, flat response.










OK, now that we're clear on this, let's think a little more carefully. When we minimize pathlengths, we simply move the null to a higher frequency. Shorter PLDs place the null higher and higher until when the PLDs match, there's no null. This exercise also shifts the frequency where we begin to hear the speaker locations to higher and higher frequencies. Hmmm...this means that for a sound that includes midrange and high frequencies that should appear in the center, if the PLDs are close, we'll hear MOST of it in the center and we'll hear the high frequencies in the right and left speakers. When we listen to lots of events all playing at the same time, some of it will appear in the center and some on the right and left. 

We're all so used to listening to small PLDs that we hear those errors as stage width, even though it doesn't exist in the recording. It's kinda nice, because small PLDs don't screw up anything for the fundamental sounds in the recording, but do screw things up for harmonics. That condition adds this sense of space --or width.

OK, the sound we hear in cars and rooms includes reflections, and those reflections also create comb filtering, which change the frequency response and change the image. For the rest of this, remember that reflections from nearby surfaces have short PLDs and from far-away surfaces have longer PLDs. 

For an even more detailed picture of what happens, it's important to consider speaker directivity. Adjacent boundaries will produce reflections for speakers at frequencies where the dispersion is wide, but not where the dispersion is narrow. The angle of incidence equals the angle of reflection, and that's anpther thing to take into account when considering how all of this interacts. We don't have to be concerned with reflections until the sum of all of them reaches our ears, because that's the only place where we hear their sum. 

Finally, in all of this talk of reflections, we have to consider that the sound from the right speaker will be reflected off the left side of the car and sound from the left speaker will be reflected off the right side of the car. This crosstalk partially destroys stereo, as each of our ears hears both speakers and the arrival times are within 20mS. This is worse in cars than in rooms, because the surfaces are closer. That means the intensity (loudness) of the reflections is greater and our perception that they and the initial sound are the same is greater. This is what makes a car sound like a car rather than a much larger space. 

The first rule of equalization is that you can't put energy back into a null caused by destructive interference in the acoustic system. You can remove energy from a peak caused by constructve interference.

The second rule is that high-Q (narrow) peaks and dips are less audible than low-Q peaks and dips. When we listen to music, our ability to perceive high-Q peaks and dips is further decreased because the chances that a particular sound happen at precisely the right frequency, thereby energizing the high-Q peak or dip is reduced. In essence, this means that there may be no need to smooth the TOP of the comb, but the bottom of the comb is a problem. Plus, many listeners like the way tht top of the comb sounds, because it adds a sense of width. 

FWIW, this delay between the channels is used by music producers to provide a sense of spaciousness or a separation of the sound in right and left channels. 

OK. I'm clicking "sumbit reply" here and I'll continue in another post--this too much work to lose by pressing the wrong key.


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## 14642 (May 19, 2008)

There's a bunch of talk here about the benefits of adaptive windowing to eliminate the reflections from the measurement, but I don't think it's a very valuable procedure and it just adds complexity to the process. 

Applying a window to the response is most often used as a way to make anechoic measurements in a non-anechoic space. Essentially, you just set the window to exclude the sound from the reflections, but the frequency at which the resolution becomes so poor that the measurement isn't useful depends on the size of the window. In cars, the boundaries are close so the window has to be small. We can't make full-bandwidth anechoic measureements using this process in a car that are useful because that frequency will be high. An adaptive window allows us to make an anechoic measurement at high frequencies but not at low frequencies. All this means is that we won't be looking at the highest part of the comb--it'll appear flat and the additional energy that the reflections will provide won't appear in the measurement. We'll have to adjust our target curve to compensate for the lack of energy, but we won't be tempted to equalize those peaks and nulls. Instead, it's sufficient to just NOT EQ the high-Q peaks and nulls at high frequencies and not add the additional complexity of the adaptive window.

There are other ways to obscure the peaks and nulls-one is spectral averaging and the other is spatial averaging. I find that a combination of the two is most useful. It's easiest with multiple mics, but it can be accomplished with a single mic, as well. 

I'm going to go eat some breakfast--I'll continue this later.

Understanding spatial averaging is next.


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## Oliver (Jun 25, 2007)

Andy Wehmeyer said:


> There's a bunch of talk here about the benefits of adaptive windowing to eliminate the reflections ...
> 
> Instead,* it's sufficient to just NOT EQ the high-Q nulls at high frequencies *and not add the additional complexity of the adaptive window.
> 
> ...


Thanks Andy !


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## Askspot (May 22, 2009)

What's great about an RTA however not needed, especially if you are on the clock ie an installer or like me a PRO Audio installer for buildings; is that it gives you a starting point. For personal things you don't have to have an RTA, but it is nice to have a starting point if you want to eventually get fussy with it. It's nice to start out with a nice solid base (or known quantity) then you can adjust for your ear. It's just nice to see how the speaker reacts in the environment they are in. my $.02 as well  There are some products out there in the pro audio market that will automatically adjust your EQ kind of like that Alpine Imprint system that did it. I tell my customers use it as a starting point then adjust it so it sounds good to you. Also lets face it! those auto eq's are not typically perfect in any way and tend to over exaggerate the room response. IMHO  I find those individuals that are tuning the response for having the speaker off-axis as being just great I think it's neat and it requires developed experience to do that. I too have individual control over each speaker in the car and EQ  hehe I love it, however I find all of this car audio stuff just crazy sometimes in the fact what you need to do to get a really good sound. Very challenging in the environment the speaker is.


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## Askspot (May 22, 2009)

Andy Wehmeyer said:


> There's a bunch of talk here about the benefits of adaptive windowing to eliminate the reflections from the measurement, but I don't think it's a very valuable procedure and it just adds complexity to the process.
> 
> Applying a window to the response is most often used as a way to make anechoic measurements in a non-anechoic space. Essentially, you just set the window to exclude the sound from the reflections, but the frequency at which the resolution becomes so poor that the measurement isn't useful depends on the size of the window. In cars, the boundaries are close so the window has to be small. We can't make full-bandwidth anechoic measureements using this process in a car that are useful because that frequency will be high. An adaptive window allows us to make an anechoic measurement at high frequencies but not at low frequencies. All this means is that we won't be looking at the highest part of the comb--it'll appear flat and the additional energy that the reflections will provide won't appear in the measurement. We'll have to adjust our target curve to compensate for the lack of energy, but we won't be tempted to equalize those peaks and nulls. Instead, it's sufficient to just NOT EQ the high-Q nulls at high frequencies and not add the additional complexity of the adaptive window.
> 
> ...



Hey Andy nice to meet you. I am a JBL Pro dealer in the pro sound market. How would you say making this 12volt stuff sound good compared to a good pair of pro speakers is!  It's more confusing haha


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## Askspot (May 22, 2009)

Quick Question for all of you RTA users. I have an Audio Control Analyzer at my disposal and it has a pink noise generator. I then run the pink noise through the aux in on my Kenwood Excellon. Does it make more sense to burn a good WAV. file of pink noise to I am actually EQing to the pre EQ of the deck. I feel like when I use the generator I get mixed results and feelings about how it sounds compared to when I use a good CD in the player and just pick it up on the Mic. Give me your .02 please


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## 14642 (May 19, 2008)

Probably doesn't matter so long as the output of the RTA has sufficiently low impedance. It does matter that you don't try to analyze and EQ both channels at once, though...we'll get to that, but you may be able to pick up on why that's a problem from the posts above.


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## ErinH (Feb 14, 2007)

I personally prefer to use the aux input as it just makes it easier on me. No need to get in and out of the car to pause/play, and even with a remote sometimes you have to make sure you're lined up to the IR path.

I don't see why you should have different results from the CD to the aux input unless you have some serious FR issues in the sources. 
But, also make sure that the generated pink noise is the same as what you would burn. There are variations such as correlated (mono) or non-correlated (stereo).
It's possible the two use a different pink noise. I've actually unknowingly used two different types before and the difference is enough to be very audible when tuning... or maybe it was just pure coincidence. Either way, I still only use the program's generator because I can control it from outside the car. 

IOW, make sure you're comparing apples to apples.

$.02





Andy Wehmeyer said:


> Probably doesn't matter so long as the output of the RTA has sufficiently low impedance. *It does matter that you don't try to analyze and EQ both channels at once, though*...we'll get to that, but you may be able to pick up on why that's a problem from the posts above.


Good point.


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## Askspot (May 22, 2009)

Andy, Thank you! I've been doing the Pro Audio thing for about 8 years now, but there is sooo much to learn!! I do it every day. Would you suggest Pinking only one side in a large room as well. I always feel like I need to pink both of them at once to get a balanced output.


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## Askspot (May 22, 2009)

Hey sounds great! I actually have an Alpine PXA-H700? yeah so I can control 28 or 30 or 31 ( I can't remember) >_> bands of eq on each ch. so I will pink each ch. separately while i'm in the driver's seat. I love that controller I have a double Din radio spot so I have my Kenwood and then the controller right under it! That way if my buddies get in the car I can press the other program so it sounds "ok" for both of us. ( LOVE THAT) 



bikinpunk said:


> I personally prefer to use the aux input as it just makes it easier on me. No need to get in and out of the car to pause/play, and even with a remote sometimes you have to make sure you're lined up to the IR path.
> 
> I don't see why you should have different results from the CD to the aux input unless you have some serious FR issues in the sources.
> But, also make sure that the generated pink noise is the same as what you would burn. There are variations such as correlated (mono) or non-correlated (stereo).
> ...


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## Askspot (May 22, 2009)

By the way. ROADHOUSE......GHOST (Family guy hahah I saw the swaz on your pic)



Askspot said:


> Hey sounds great! I actually have an Alpine PXA-H700? yeah so I can control 28 or 30 or 31 ( I can't remember) >_> bands of eq on each ch. so I will pink each ch. separately while i'm in the driver's seat. I love that controller I have a double Din radio spot so I have my Kenwood and then the controller right under it! That way if my buddies get in the car I can press the other program so it sounds "ok" for both of us. ( LOVE THAT)


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## CraigE (Jun 10, 2008)

Andy, THANK YOU!
Your posts are greatly appreciated.


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## donkeypunch22 (Nov 5, 2008)

Thanks Andy, I've read your posts three times now, but keep it going. Eventually it will make sense.


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## 14642 (May 19, 2008)

Hey Donkeypunch.
I went back to edit the original post to make it clearer and discovered that after working on it for an hour, my time to edit has passed. Sorry to take up a bunch more space, but here it is again, including the edits and additional information. Please start at the begining.

OK. Sorry for the delay. I don't use True RTA, but they're all pretty much the same and include the same tools. 

We'll start with a few basics here and most of this isn't my opinion. Rather, it's stuff that can either be verified and has been written about by various people who get paid for this stuff because they're scientists. Some of them are people with whom I work and some is available at the LIBRARY.

Anyway, cars are full of reflections and there are all kinds of opinions about what to do with them. Since the dimensions of the car are small, the car doesn't create a reverberant field--all reflections arrive within 20mS of the initial sound. That means, we hear the reflections and the initial sound from the speaker as the same event.

Second, when the same sound emanates from a particular source and is also reflected from a nearby surface, we have two sources playing nearly the same sound. The reflection will have a slightly different frequency response and will arrive a tiny bit later. The difference in arrival time and frequency responses of the initial sound and the reflected sound create comb filtering. At some frequency and at multiples of that frequency, based on the difference in distance from the two sources to the listener, there will be destructive interference. The lowest-frequency null is the widest and each subsequent null (as frequency increases) will be narrower than the one that preceeded it. Hereafter, we'll refer to that width as Q--low-Q is wide and high-Q is narrow. 

Here's a screen shot from an RTA to illustrate this. To simulate this, I've set the RTA to show the sum of left and right, and I've delayed the right by 1mS which is about equal to a foot--1.132', to be more exact.











In the next screenshot, I've increased the delay to 2mS, and you can see that the first null happens at a lower frequency.










In the third screenshot, I've reversed the phase of one channel (as if I've listened to the car over and over and "played with the phase of each driver by ear to determine which polarity is correct) and it's plain to see that I've moved the null back up, but I've killed the bass response. Switching the phase has put the sound from the two channels back in phase at frequencies where it was out of phase. It's also put the sound from the two channels out of phase at other frequencies. 










Also remember, that in order for two sources, in this case a right and left speaker, to produce a phantom image in between the two speakers, they must both be in phase. If you sit equidistant from a pair of speakers that are in phase, there's an image. If you swap the polarity of one, there's no image, less bass and you hear the speaker locations. If you're not equidistant, and the two speakers are in phase, then you'll hear a phantom image at frequencies where they are in phase, and no image for frequencies where they are out of phase. In the case of the third screenshot, --a pair of speakers located where the PLD is about 2.5' and one speaker's polarity is swapped, there won't be an image at low frequencies and the bass will suck, there won't be an image at 500 Hz and at multiples of that frequency. The comb filtering causes this image "problem" as well as the obvious frequency response problem.

For right and left speakers mounted in the doors, the first and lowest Q null happens in the vocal region. Swapping the phase of one channel can dramatically improve the image for a vocalist, but screws up the bass and screws up the image at higher frequencies.

In the fourth screenshot, I've simulated time alignment by putting the channels back in phase and delaying the other one by 2mS so they match. See, flat response.










OK, now that we're clear on this, let's think a little more carefully. When we minimize pathlengths, we simply move the null to a higher frequency. Shorter PLDs place the null higher and higher until when the PLDs match, there's no null. This exercise also shifts the frequency where we begin to hear the speaker locations to higher and higher frequencies. Hmmm...this means that for a sound that includes midrange and high frequencies that should appear in the center, if the PLDs are close, we'll hear MOST of it in the center and we'll hear the high frequencies in the right and left speakers. When we listen to lots of events all playing at the same time, some of it will appear in the center and some on the right and left. 

We're all so used to listening to small PLDs that we hear those errors as stage width, even though it doesn't exist in the recording. It's kinda nice, because small PLDs don't screw up anything for the fundamental sounds in the recording, but do screw things up for harmonics. That condition adds this sense of space --or width.

OK, the sound we hear in cars and rooms includes reflections, and those reflections also create comb filtering, which change the frequency response and change the image, just like the two independent speakers in the screenshots above. We can't time align reflections to get rid of the constructive and destructive interference. For the rest of this, remember that reflections from nearby surfaces have short PLDs and from far-away surfaces have longer PLDs when compared to the initial sound fro the speakers which cuts a direct path to our ears. 

For an even more detailed picture of what happens, it's important to consider speaker directivity. Adjacent boundaries will produce reflections for speakers at frequencies where the dispersion is wide, but not where the dispersion is narrow. The angle of incidence equals the angle of reflection, and that's anpther thing to take into account when considering how all of this interacts. We don't have to be concerned with reflections until the sum of all of them reaches our ears, because that's the only place where we hear their sum. 

Let's back up. Relative to the diameter of the speaker, sounds are distributed into the space in which they are emitted differently for different frequencies. This is speaker dispersion and it works like holding your thumb over the end of the garden hose. If the aperature is narrow, the water shoots out in a wide spray. If the aperature is wide, the water comes out in a narrow stream. The stream of water isn't periodic, though and for a speaker we have to consider the size of the aperature (speaker diameter) as it compaares to the wavelength of the sound that's emitted. The condition below applies to every speaker no matter the type or shape.










I've placed a frequency response plot and a polar response plot for an 8" woofer below. These two graphs show basically the same thing, just displayed differently. In the frequency response plot, the attenuation at high frequencies when the speaker is measured off axis is easy to see--the shape of the frequency response is the primary information. 










In the polar response graph below, the frequency response is still displayed, but the shape of the DISPERSION is the primary information. Each colored line represents the shape of the dispersion at a particular frequency. It's easy to see that at low frequencies the sound is radiated in all directions, but as frequency is increased, the sound is radiated into a narrower and narrower space. This is "beaming" and all speakers do it. Different chapes, dustcaps and phase plugs can tweak the SHAPE of the beam and alter the frequency where it starts SLIGHTLY, but nothing will stop it. 










If you study the graph above fo a few minutes, you'll see that below about 1k, aiming this speaker is of very little consequence. The sound is radiated in all forward directions almost equally. As frequency is increased the sound is focused into a smaller area directly in front of the speaker. When we mount this speaker in the car the adjacent boundaries will reflect the sound that is radiated in all directions, but the high frequencies won't be reflected by adjacent boundaries, because they never hit the adjacent boundaries. They will hit the boundaries adjacent to our ears, though. 

In cars, we hear all of the reflections and the initial sound as one event--that means we hear the speaker's power response, which is the average of the frequency response at all angles. If we use the speaker above all the way up to 12k, we'll have a big fat hole in the off-axis response where the high frequencies contain far less reflected sound. If we aim the speaker so that our ears get the high frequency sound the on-axis response will have wide bandwidth, but the reflected sound will lack high frequencies. When we tune the car using an EQ, we'll want to boost the high frequencies to smooth the response, but that'll make the on-axis response too bright. 

It's much easier to make the car sound good if we can make the reflected sound as similar in frequency response to the initial sound. Then, when we EQ, we'll have smoother coverage over a wider listening window.

If you look at the ploar response one more time, it'll be obvious that if we use this 8" woofer at frequencies below about 1kHz, no aiming is necessary. Since midranges and tweeters work the same way, if we can find a tweeter that has good output and good power handling crossed over that low, the 8" can be used in a 2-way. If not, then an additional midrange is helpful. 1k is easy for a 2" or 3" so putting one of those in between the 8" and the tweeter is a good fix for this directivity problem. 

Tweeter aiming can be helpful, since the highest frequencies will begin to beam even for regular 1" domes. If you're using a much larger dome, then aiming the tweeter is important. Check out the polar response of the 1.5" tweeter below:










So, there are a couple of basic ways around this reflection thing in cars. One is to try to minimize them and the other is to "spread the chaos around". Minimizing them is damn difficult if you want to have a car that can be driven. Spreading the chaos around simply means that we try to make all the reflections have similar frequency response so we can EQ them and the sound of the speakers using the same filters. Using the speakers where the dispersion is wide is the way to do this. 

Using horns and big diaphragms for "pattern control" is the way to minimize the reflections from adjacent boundaries, but those adjacent boundaries are responsible mainly for altering the frequency response and not the image. Image narrowing and causing the car to sound like a car is mostly caused by reflections of right channel information from boundaries near our left ear and reflections of left channel information from surfaces on our right. This crosstalk partially destroys stereo, as each of our ears hears both speakers and the arrival times are within 20mS. This is worse in cars than in rooms, because the surfaces are closer. That means the intensity (loudness) of the reflections is greater and our perception that they and the initial sound are the same is greater. This is what makes a car sound like a car rather than a much larger space. This condition is what "Ambisonics" tries to fix. 

I've tried both of these routes to great sound and I find that the "spread the chaos around" method is the most straightforward and because the conditions in the car make this much easier. The cheesy drawing below makes this a little more obvious, if the car is compared to a room. 










The first rule of equalization is that you can't put energy back into a null caused by destructive interference in the acoustic system. You can remove energy from a peak caused by constructve interference.

The second rule is that high-Q (narrow) peaks and dips are less audible than low-Q peaks and dips. When we listen to music, our ability to perceive high-Q peaks and dips is further decreased because the chances that a particular sound will happen at precisely the right frequency, thereby energizing the high-Q peak or dip is reduced. In essence, this means that there may be no need to smooth the high frequency part of the comb, but the low frequency part of the comb, particularly the first (lowest-frequency null) is a problem. Plus, many listeners like the way the top of the comb sounds, because it adds a sense of width by screwing up the phase between the speakers and drawing our attention to the locations. This is very hard to hear in the frequencies that tweeters play, but a bit easier, lower in the midrange. 

FWIW, this delay between the channels is used by music producers to provide a sense of spaciousness or a separation of the sound in right and left channels. 

OK. I'm clicking "sumbit reply" here and I'll continue in another post--this too much work to lose by pressing the wrong key.


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## 14642 (May 19, 2008)

Next, I'll move on to a procedure for tuning using an EQ that provides separate filters for left and right. If you don't have one of those kinds of EQs and just have a stereo EQ that forces you to use the same filters for both right and left, I'll cover using that less-than-adequate tool later.

Once that's all done, I'll explain why multichannel in cars is a big help. After that, you guys will know everything I know about this and I'll have to buy the research people some more lunches so I can have some more info to share.


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## Askspot (May 22, 2009)

So my tweeter's are in the pillars I notice the difference of them being off-axis. I am getting the Hertz HT28's now these are supposed to be better off-axis. Would it be benifical in a big way to make a pod so I can aim them better? I always have to balance the sound over to the left a little bit to center it to my side. Even with a 2.5ms delay. Could it be that I am just not hearing the HF's like the other side is producing? The other problem is, for some reason the passenger side seems much louder on their side meaning coming from the right. They cannot hear the left, however it sounds balanced for me (without TA fyi) Is this because my passengers also drive cars and are just used to being on the left side like myself? So their ear isn't trained to pick up on the left as much?


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## Askspot (May 22, 2009)

I'm kind of excited in that nerdy way 



Andy Wehmeyer said:


> Next, I'll move on to a procedure for tuning using an EQ that provides separate filters for left and right. If you don't have one of those kinds of EQs and just have a stereo EQ that forces you to use the same filters for both right and left, I'll cover using that less-than-adequate tool later.
> 
> Once that's all done, I'll explain why multichannel in cars is a big help. After that, you guys will know everything I know about this and I'll have to buy the research people some more lunches so I can have some more info to share.


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## Askspot (May 22, 2009)

Askspot said:


> So my tweeter's are in the pillars I notice the difference of them being off-axis. I am getting the Hertz HT28's now these are supposed to be better off-axis. Would it be benifical in a big way to make a pod so I can aim them better? I always have to balance the sound over to the left a little bit to center it to my side. Even with a 2.5ms delay. Could it be that I am just not hearing the HF's like the other side is producing? The other problem is, for some reason the passenger side seems much louder on their side meaning coming from the right. They cannot hear the left, however it sounds balanced for me (without TA fyi) Is this because my passengers also drive cars and are just used to being on the left side like myself? So their ear isn't trained to pick up on the left as much?


Ok So I guess doing a pillar doesn't solve the problem of the fact when your sitting in the passenger seat the audio does not come from the left side very much at all even when balanced to the left. Very little difference. I'm beginning to think its because I'm used to being on the left. I took my analyzer and the outputs I get from my DSP unit is on .4 off on the right side that is the right side is .4DB louder....if you can hear that you are a liar IMHO


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## donkeypunch22 (Nov 5, 2008)

Askspot said:


> So my tweeter's are in the pillars I notice the difference of them being off-axis. I am getting the Hertz HT28's now these are supposed to be better off-axis. Would it be benifical in a big way to make a pod so I can aim them better? I always have to balance the sound over to the left a little bit to center it to my side. Even with a 2.5ms delay. Could it be that I am just not hearing the HF's like the other side is producing? The other problem is, for some reason the passenger side seems much louder on their side meaning coming from the right. They cannot hear the left, however it sounds balanced for me (without TA fyi) Is this because my passengers also drive cars and are just used to being on the left side like myself? So their ear isn't trained to pick up on the left as much?


If you look at the polar response figure of the 1.5" tweeter, it would suggest that aiming the tweeter "better" would not make much difference. What would, I think, from what Andy wrote is, "make the reflected sound as similar in frequency response to the initial sound. Then, when (you) EQ, (you'll) have smoother coverage over a wider listening window."

But lets let him finish before we start asking questions.

BTW - Thanks Andy. This is great stuff!!


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## Askspot (May 22, 2009)

donkeypunch22 said:


> If you look at the polar response figure of the 1.5" tweeter, it would suggest that aiming the tweeter "better" would not make much difference. What would, I think, from what Andy wrote is, "make the reflected sound as similar in frequency response to the initial sound. Then, when (you) EQ, (you'll) have smoother coverage over a wider listening window."
> 
> But lets let him finish before we start asking questions.
> 
> BTW - Thanks Andy. This is great stuff!!


Alright, well I was wondering if anyone else had ran into that problem. Like I said both outputs are the same. Just when I sit in the Pass seat it sounds like it's coming more from the right side. Could it be the big bulge in the dash where my gauges are that are reflecting most of the hf away from the pass left ear?


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## keep_hope_alive (Jan 4, 2009)

some of that i knew, and some of it i didn't, and some cleared up questions of how it affects car audio. A++. the edited response and any future responses will be copied in Word and saved. 

great information, great timing. i spent several hours last night with TrueRTA and the H701, first time on a new install. comb filtering is a beyotch.  

in order to counteract some of the comb filtering, i "average" the listening area by quickly moving the mic in a 3D pattern where my head would be, and setting the resolution to slow. the result was a response that didn't suffer from as much comb filtering at mid/high frequencies and allowed me to interpret the RTA so I wasn't trying to fix problems that didn't exist. basically, the integration included time AND space. I also rolled the windows down so I could more accurately interpret the direct sound. i'll worry about a separate preset for windows up vs. windows down later. for now, i'm just trying to evaluate the drivers response in their locations. 

thoughts on that process? (question for the group, not just Andy).


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## DanMan (Jul 18, 2008)

Andy-God bless you and thank you for being so generous with your knowledge.

Anybody reading this that doesn't know-Andy is a true expert and we are blessed with the knowledge he shares with us.


Thanks Andy!


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## nirschl (Apr 30, 2009)

Andy Wehmeyer said:


> Next, I'll move on to a procedure for tuning using an EQ that provides separate filters for left and right. If you don't have one of those kinds of EQs and just have a stereo EQ that forces you to use the same filters for both right and left, I'll cover using that less-than-adequate tool later.
> 
> Once that's all done, I'll explain why multichannel in cars is a big help. After that, you guys will know everything I know about this and I'll have to buy the research people some more lunches so I can have some more info to share.


Wow! I am truly enjoying your posts and greatly appreciate the time and effort you are putting into them. Cheers to you sir! Pete


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## heathw_2005 (Dec 7, 2009)

flat is a good starting point


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## dbiegel (Oct 15, 2006)

Andy, thanks so much for posting all this and sharing your knowledge!

I'm still confused about a couple of things:

1) Wouldn't the polar response of a speaker turn into a total clusterfuck (excuse the francais) when you put it in a car?

For example, I'd think speakers installed behind door panels would have a vastly different polar response because the sound will be affected by the panel, the door enclosure, vehicle transfer function, etc. A tweeter's polar response would vary due to the windshield, dash hump, etc.. plus the effects of baffle, not to mention interior shape, seat absorption, other windows etc etc... 

So once a speaker is in a car, wouldn't you just end up with a crazy looking polar response that varies at each degree of angle in every dimension? What are some ways to deal with this other than endless random experimentation until we find something that happens to sound less horrible? (seems to be the typical method we use!)

2) Whenever I've used the RTA to set time alignment or polarity based on the setting that gives the most "flat" response, it always sounds like crap, as if many frequencies are still out of phase... why does it look so different from what we hear? Is there some way to measure the "phase" between two speakers with a mic and computer? (e.g. to have it tell me that 2k is 180 degrees out of phase but 3k is fine)


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## donkeypunch22 (Nov 5, 2008)

Just checking...


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## 14642 (May 19, 2008)

Sorry I haven't been able to continue this yet. Please stay tuned--getting killed at work.


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## npdang (Jul 29, 2005)

Some very good contributions in this thread. 

Not to rain on anyone's parade, however I would just add that achieving this effect in significantly less hostile environments (like the home) is difficult already... achieving it in the car is next to impossible. I believe DBGIEGEL touched on this point already.

Narrowing dispersion may solve for some problems, but also makes the sound extremely forward and "shut in," which is hardly a reasonable tradeoff Imo.

That being said, I look forward to hearing more from Andy.


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## Patrick Bateman (Sep 11, 2006)

dbiegel said:


> Andy, thanks so much for posting all this and sharing your knowledge!
> 
> I'm still confused about a couple of things:
> 
> ...


While we wait for Andy's response, I'll take a stab at this one.










Sound travels 13.5" in a millisecond. The first five milliseconds are the most important. If you can control reflections and diffractions for that first five milliseconds, it's going to go a long way towards improving the polar response, soundstaging, and intelligibility of your recordings.

Ignore the text in the graph above; it's from one of my projects. But the data in the graph shows the polar response of a seven dollar QSC waveguide loaded by a Celestion compression driver, mounted in the kick panels of my Accord.

In the graph, you can see that the polar response is +/- 3dB from 500hz to 20khz. That doesn't mean the response is flat; *I don't even care if it's flat.* As long as the polar response is consistent, you can simply EQ the whole thing to whatever curve you'd like.

You can only do that with good directivity; otherwise a boost or cut will only improve the response at just one angle.

Hope that makes sense.









Here's the polar response of a direct radiator. This is an eight inch woofer in a sealed box.

As you can see, below 2khz, it's ridiculously bad. By the way, that *isn't* a coincidence. An eight inch piston begins to beam around 2khz, and you're seeing that in the graph. The polar response above 2khz is better than the polar response *below* 2khz *because* of beaming.

IMHO, the solution to the directivity problem in the car is to use waveguides, arrays, or even pistons that are directional. That last option is the one I've been exploring a lot lately, since a large piston has a great deal of directivity. This has been my soapbox lately - I really believe that car speakers *should* beam. We've been using rules in car audio that work for home audio, and that's not a good thing.


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## stereojnky (Mar 17, 2008)

Patrick Bateman said:


> IMHO, the solution to the directivity problem in the car is to use waveguides, arrays, or even pistons that are directional. That last option is the one I've been exploring a lot lately, since a large piston has a great deal of directivity. This has been my soapbox lately - I really believe that car speakers *should* beam. We've been using rules in car audio that work for home audio, and that's not a good thing.


I was under the impression that the reason that you *wouldn't* want beaming was because the speaker would "scream" at the frequencies that it was beaming. Would the solution then, be to just simply lower the intensity at those frequencies to compensate? Say with a "shelf" eq like in the Zapco DC amps which would allow you to lower all frequencies above a certain point? Please elaborate...


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## Patrick Bateman (Sep 11, 2006)

stereojnky said:


> I was under the impression that the reason that you *wouldn't* want beaming was because the speaker would "scream" at the frequencies that it was beaming. Would the solution then, be to just simply lower the intensity at those frequencies to compensate? Say with a "shelf" eq like in the Zapco DC amps which would allow you to lower all frequencies above a certain point? Please elaborate...


A well behaved piston will start to beam at a frequency that's equal to the diameter. For instance, an eight inch woofer with a cone that's about 7" across will start to beam at 1928hz.










When it starts to beam, the energy is focused into a narrow angle. That raises the efficiency on-axis, and lowers it off axis. In a car, that's A Very Good Thing. Basically there's less reflections off the doors, and more efficiency on axis.

All of that is a fact; now for some opinions:

I personally believe that speakers that sound "screechy" are often suffering from a tipped up response *and* high distortion. You can reduce the high frequency energy in the crossover, but there isn't much you can do about the distortion.

In a nutshell, there are a lot of large drivers with light cones, and awful screechy response. But there are also large pistons with well-behaved cones, shorting rings, and ruler flat response. It's easier to make a good small woofer than a good big woofer, because small woofers are better behaved, due to the small cone size.









Also, you can duplicate the directivity of a large piston with an array of small pistons. JBL does this with their K2 speakers. Instead of using a 35" woofer, they use an array of fifteens. The math applies no matter what the size is; if you want the directivity of a fifteen you could approximate it with four eights, or even two.

As for the filter in the Zapcos, I'd just use an inductor and a resistor instead. The filter is about five bucks a side.


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## dbiegel (Oct 15, 2006)

Patrick Bateman said:


> In the graph, you can see that the polar response is +/- 3dB from 500hz to 20khz. That doesn't mean the response is flat; *I don't even care if it's flat.* As long as the polar response is consistent, you can simply EQ the whole thing to whatever curve you'd like.


I appreciate your goal, but doesn't that all depend on the time window you measure with? Are these measurements gated such that they include all the reflections in your car or are they relatively short? Depending on the window you use, the results may be totally different... I'm thinking what we need is a third dimension -- time -- for car audio measurements to correlate better with what we hear. Kinda like a CSD graph, but with off axis measurements as well. What do you think?



> IMHO, the solution to the directivity problem in the car is to use waveguides, arrays, or even pistons that are directional. That last option is the one I've been exploring a lot lately, since a large piston has a great deal of directivity. This has been my soapbox lately - I really believe that car speakers *should* beam. We've been using rules in car audio that work for home audio, and that's not a good thing.


Funny thing is, when I surmised a while back that beaming can be a good (and perhaps even necessary) thing in a car, people were biting my head off because it didn't mesh with home audio principles... The more I've played around with and researched stuff after reading your posts, the more I realize that attention to managing directivity seems to be absolutely critical in a car.. beaming is certainly one tool we can use for that... noone really discussed this stuff before you came around!

My hat is certainly off to you for pioneering the way and pushing our science forward. That said, I still suspect the *time dimension* is the critical missing piece here... Excellent polar response + excellent time response should get us pretty close to a home system.. the rest would be easy to tune with any modern processor.


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## 14642 (May 19, 2008)

Patrick Bateman said:


> While we wait for Andy's response, I'll take a stab at this one.
> 
> 
> 
> ...


Patrick, over what angles are you measuring your response in the graphs above? 
As I wrote earlier, I'm killed at work, but I'll finish my suggestions on Saturday morning.


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## donkeypunch22 (Nov 5, 2008)

I was wondering what the angles were too, Patrick.

As stated before, this is great stuff, and I can't wait till Saturday.


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## niko084 (Dec 16, 2009)

Flat response is just that it's flat, it's boring it has no definition of it's own.

I prefer a certain type of sound, but I like to make sure I get close to the original recording, so I start close to flat and work my way from there.

Being I produce music, I am constantly listening to my monitors which are basically built to be flat, they sound nice but they don't have any personality.


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## traceywatts (Jun 2, 2008)

niko084 said:


> Flat response is just that it's flat, it's boring it has no definition of it's own.
> 
> I prefer a certain type of sound, but I like to make sure I get close to the original recording, so I start close to flat and work my way from there.
> 
> Being I produce music, I am constantly listening to my monitors which are basically built to be flat, they sound nice but they don't have any personality.


That doesnt seem to make much sense to me. are you referring to graphically flat or fletcher-munson flat?


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## niko084 (Dec 16, 2009)

traceywatts said:


> That doesnt seem to make much sense to me. are you referring to graphically flat or fletcher-munson flat?


Studio Monitors "the better ones" are built more fletcher-munson flat.

Obviously some are a bit heavy here and there, or a bit light here and there, but as a general rule they are much flatter than anything most people have heard.


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## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Patrick, over what angles are you measuring your response in the graphs above?
> As I wrote earlier, I'm killed at work, but I'll finish my suggestions on Saturday morning.


Here's the key to my polar measurements:


purple = 45 degrees off axis from the driver
red = 30 degrees off-axis
orange = 15 degrees off-axis
yellow = 0 degrees off-axis

To get at these figures, I do three measurements for every point, and average them. So purple is actually measured at 52.5 degrees, 45 degrees, and 37.5 degrees. You can see an un-averaged curve in the B&C graph. Without doing a spatial average, the data is practically unreadable.

I know this sounds like a lot of work, but I have a jig, I can do a whole set in fifteen minutes. The jig insures that every speaker is measured at the exact same points. If I had nine mics I could do it in five minutes.

One thing that complicates things is that every waveguide and horn that I own is firing off-axis. For instance, the USD horns direct the energy 45 degrees off-axis. That's why you'll generally see more energy in the purple curve. Even though the microphone is 45 degrees off-axis from the speaker being tested, the energy is being directed straight at the mic.

Of course this is all by design, and it's one of the reasons that the QSC waveguide is so special. On axis and off, the response is practically the same. Compare that to the USD, and you'll see why I like waveguides so much.


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## Patrick Bateman (Sep 11, 2006)

dbiegel said:


> I appreciate your goal, but doesn't that all depend on the time window you measure with? Are these measurements gated such that they include all the reflections in your car or are they relatively short? Depending on the window you use, the results may be totally different... I'm thinking what we need is a third dimension -- time -- for car audio measurements to correlate better with what we hear. Kinda like a CSD graph, but with off axis measurements as well. What do you think?


The answer to that questions depends on what you're trying to do. You can set a very short gate to capture the effect of an early reflection. But when you do that, you won't have any usable data below a certain frequency.

For instance, it takes ten milliseconds to measure a 100hz soundwave. (1000ms / 100hz.) But sound travels 135 inches in ten milliseconds. (13.5 inches per second x ten milliseconds.) _So if you're trying to get a good measurement of what's happening at 100hz, your data above that point would be corrupted by reflections due to the long gate._ I generally use short gates, which is why you don't see any low frequency detail in many of my measurements. Even a millisecond or two will give you good detail if you're measuring a tweeter.

That's the fundamental problem with RTAs - they basically ruin all your high frequency data, because they don't gate out those reflections.

With gated measurements, you can get either one. High frequency resolution, or low frequency.

Or better yet, use two gates, and get both. That's what I do. Occasionally I'll use a single gate if I'm trying to "zero in" on a particular band.


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## donkeypunch22 (Nov 5, 2008)

I know your busy Andy, but just checking...

Oh, and Patrick, thanks for giving the angles of your measurments, and for the additional input, too. 

And if you could, Patrick, what are the most common gated time intervals you use?


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## 60ndown (Feb 8, 2007)

a moving vehicle has an inherent noise floor of about 70 db from about 20-500 hz

from 20,000- 500 i aim for flat, from 500-20 i boost by about 70 db.

but i only listen when i drive.


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## 60ndown (Feb 8, 2007)

"Sound travels 13.5" in a millisecond. The first five milliseconds are the most important."

so a snare drum hit im guessing probably lasts (with a little decay) 0.5 - 1 second, so in a vehicle that sound has reflected off everything even the rear glass, in a station wagon.

and thats the shortest sound i can think of, guitar notes and vocals are waaaaaaay longer.

no way to defeat reflections in a vehicle.


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## 60ndown (Feb 8, 2007)

:beerchug:

lol 2007

morning


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## donkeypunch22 (Nov 5, 2008)

just checking, Andy.


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## 14642 (May 19, 2008)

OK. Sorry for the delay. As a matter of review and to redirect this thread a bit, I've pulled the following from an earlier post:

_So, there are a couple of basic ways around this reflection thing in cars. One is to try to minimize them and the other is to "spread the chaos around". Minimizing them is damn difficult if you want to have a car that can be driven. Spreading the chaos around simply means that we try to make all the reflections have similar frequency response so we can EQ them and the sound of the speakers using the same filters. Using the speakers where the dispersion is wide is the way to do this. _

_Using horns and big diaphragms for "pattern control" is the way to minimize the reflections from adjacent boundaries, but those adjacent boundaries are responsible mainly for altering the frequency response and not the image. Image narrowing and causing the car to sound like a car is mostly caused by reflections of right channel information from boundaries near our left ear and reflections of left channel information from surfaces on our right. This crosstalk partially destroys stereo, as each of our ears hears both speakers and the arrival times are within 20mS. This is worse in cars than in rooms, because the surfaces are closer. That means the intensity (loudness) of the reflections is greater and our perception that they and the initial sound are the same is greater. This is what makes a car sound like a car rather than a much larger space. This condition is what "Ambisonics" tries to fix. _

_I've tried both of these routes to great sound and I find that the "spread the chaos around" method is the most straightforward and because the conditions in the car make this much easier. The cheesy drawing below makes this a little more obvious, if the car is compared to a room. _

_







_

_The first rule of equalization is that you can't put energy back into a null caused by destructive interference in the acoustic system. You can remove energy from a peak caused by constructve interference._

_The second rule is that high-Q (narrow) peaks and dips are less audible than low-Q peaks and dips. When we listen to music, our ability to perceive high-Q peaks and dips is further decreased because the chances that a particular sound will happen at precisely the right frequency, thereby energizing the high-Q peak or dip is reduced. In essence, this means that there may be no need to smooth the high frequency part of the comb, but the low frequency part of the comb, particularly the first (lowest-frequency null) is a problem. Plus, many listeners like the way the top of the comb sounds, because it adds a sense of width by screwing up the phase between the speakers and drawing our attention to the locations. This is very hard to hear in the frequencies that tweeters play, but a bit easier, lower in the midrange. _

Patrick's method is different than my method and both work. Patrick's goal is to control both frequency response and directivity (through narrow passbands and pattern control--(horns) and using speakers in the range where they beam) and the method I suggest is the opposite. The reason that they both work is because, as I've suggested before, we don't hear the reflections as separate events. Patrick attempts to eliminate adjacent boundary reflections, and I suggest simply EQing them along with the direct sound. 

It's important to note, that neither method will eliminate the reflections from boundaries close to our ears, and those reflections are the ones that make a car sound small--those reflections contribute crosstalk (left sounds at our right ear and right sounds at our left ear).

OK, so if you're following me, the basics are that we have to have a right and left speaker system that covers the band of frequencies from the crossover point between them and the sub and 20kHz without huge holes in either the on-axis response or the off-axis response. Of course, the off axis response will exhibit gradual attenuation as frequency increases, but it shouldn't have big peaks or dips near any crossover point. Below is a nearly ideal frequency response and directivity index:










Obviously, the red curve is slightly better than the blue one. For the speaker in the graph above, we use a waveguide on the tweeter to match the directivity of the tweeter to that of the woofer at the crossover. A similar curve (a directivity index that's reasonably flat with no peaks or dips) can be achieved by using multiple drivers in the regions where they DON'T beam. This is why I suggest a 3-way system in the front doors.

The frequency response plot below is one for a 2-way component system that doesn't include any measures to match directivity between the drivers. The crossover point between the mid and tweeter is too high (the mid starts to beam off axis). There's no directivity index plotted here, but it would include a peak in the region where the off-axis response shows a dip. 








OK, so now that we've placed a great deal of importance on getting the speaker system right to begin with, here's an example of why that's all good system design practice, but in the end, doesn't matter nearly as much as it might seem. It is important to be sure that the entire bandwidth is covered competently, because we can't put energy into a system if there's no source for that energy--if your speaker system has a big hole at the crossover, you can't get it back.

Below is the near-field respone of the OE speaker in the door of a Mini Cooper. The measurement was taken about a half inch form the grille. Despite the dip at 1k, the response isn't too bad. BTW, I didn't investigate the cause of the dip










If I were building this system, I'd add a 3" mid and cross the 6" at 1kHz. The OE system doesn't include a low pass on the 6" and includes a small tweeter in the top of the door. Anyway, if I close the door and place the microphone at the driver's listening position, this is what the response looks like:










Nice, huh? What's the difference? Reflections and a tweeter. Good luck trying to eliminate all of that--no matter what you do, you'll never get back to the previous graph. The stuff below 1kHz can't be eliminated by anything other than dramatically changing the shape of the interior surfaces and the size of the vehicle. Between 1kHz and about 10kHz, adjacent boundaries contribute to the mess. Above about 10kHz, adding foam and carpet here and there might tame this somewhat, but the benefit isn't worth the effort. 

Fortunately (or unfortunately) the response above is what we hear and it can be adequately equalized. Below is the target response I suggest:










the big problems at lower frequencies have to be fixed. It won't be possible to put energy back into the biggest hole, so the peaks will have to be reduced to match.










At this point, looking at a lower-resolution graph may be helpful--we don't want to be distracted by all of that high-Q stuff at high frequencies. 










. Here are the steps, including selection of a high pass filter frequency:










Of course, this can't be done with a 31-band graphic EQ and that's why those aren't useful. It also can't be done by moving speakers, changing the aiming, swapping the speaker for something better, adjusting the crossover point between the mid and tweeter slightly, adding damping material to the doors, or anything else. EQ is the only thing that will help.

This is why I suggest the method I suggest. 

TA should be set first, especially if you can align the tweeter and mid separately. After TA, set your EQ according to the process above. Once the left and right have been EQed so thay have the same response and the arrival times match, add the sub. EQ the right with the sub. Then turn the right off and EQ the left with the sub. Then, turn on both channels and listen. If you need to make further adjustments, be sure to EQ right and left equally--you're just shaping the response now and you can't equalize frequency reponse problems that appear in the measured response of both channels, measured at the same time (see the lengthy discussion of comb filtering in the previous post). In fact, what you see on the RTA won't even look like what you hear, so don't pay much attention to the RTA of both channels playing at the same time for any frequency above about 150Hz (the region where the sub contributes). 

Also, moving the microophone around a head-sized area will help you determine whether to fix the high-Q peaks at higher frequencies. If they change or go away as you move the mic, don't worry too much about them unless they annoy you when you listen to music. Then, pick the annoying one and get rid of it. 

BTW, we have a new 2-channel auto EQ algorithm that does precisely what I've suggested and it makes even this Mini Cooper with the factory speakers sound GREAT.


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## gutz (Aug 8, 2008)

Great info Andy! Thank you , It was worth the wait
Ill test your method as soon as I finish my mids and tweeters a-pillar install

Im actually using a car-pc , What do you suggest will be the way to go when you have almost unlimited sound proccessing capabilities?
For now im using a simple l/r 12db crossover on all channels
But I would really like to use the resources I have..

For instance I can use a vst plugin called "Electric-Q"
This offers so much options on crossover design and EQ capabilities ( linear phase , minimun phase , fir etc. etc. )
AiXcoustic Creations: Electri-Q (FULL)

Or I can use "Frequency Allocator" which also contains linear phase correction on crossover frequencies
DSP Crossover for PC. Frequency Allocator.

Is all of that even matters in a car with all the enviormental hazzards ( phase issue near the crossover cut-off frequency )?
Would Ill be better of with a simple EQ on left and right channels?

Of course i own a calibrated ecm8000 for testing purposes

Your thoughts would be welcome


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## 14642 (May 19, 2008)

I use electriQ and another crossover called crossover3way, or something like that. Frequency allocator looks pretty cool too. Crossover is far less important than EQ and 4th order slopes are plenty steep enough.

Oh, and yes, all of that does matter. The graph avobe doesn't sound nearly as bad as it looks and following the process I've suggested makes success pretty easy.


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## lucas569 (Apr 17, 2007)

good stuff! ive been tackling car audio for 20 yrs. amazed that i learn new stuff daily.


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## chipss (Nov 13, 2009)

agreed, was an brow raiser for sure...



niko084 said:


> Studio Monitors "the better ones" are built more fletcher-munson flat.
> 
> Obviously some are a bit heavy here and there, or a bit light here and there, but as a general rule they are much flatter than anything most people have heard.


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## gutz (Aug 8, 2008)

Andy Wehmeyer said:


> I use electriQ and another crossover called crossover3way, or something like that. Frequency allocator looks pretty cool too. Crossover is far less important than EQ and 4th order slopes are plenty steep enough.
> 
> Oh, and yes, all of that does matter. The graph avobe doesn't sound nearly as bad as it looks and following the process I've suggested makes success pretty easy.


This one? 
KVR: rs-met Crossover 3-Way - Virtual Effect

It looks like Electric-Q has some great capabilities and it can actually can be used also as a crossover , why do you use the other crossover also?
Would you recommend using "Electric-Q" as the subwoofer crossover + EQ , And "Crossover 3-Way" as the front stage cross + "Electric-Q" for front stage EQ?

Do you prefer 24db Slopes over 12db's? Doesn't it create too much seperation and help you localize where the sound comes from?

How do you set T/A? Impulse Response? Ears? Measurment Tape?
All of the above?


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## CraigE (Jun 10, 2008)

"Of course, this can't be done with a 31-band graphic EQ and that's why those aren't useful."


Andy,
Thanks for the great info.
But, can you go into a little more depth about the 31 band graphic EQ not being useful.


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## 14642 (May 19, 2008)

gutz said:


> This one?
> KVR: rs-met Crossover 3-Way - Virtual Effect
> 
> It looks like Electric-Q has some great capabilities and it can actually can be used also as a crossover , why do you use the other crossover also?
> ...


Actually, in my car, I use the Car PC for a bunch of custom spatial processing and a little bit of EQ, but the real EQ is in the amplifiers--they're OE amps from our OE group that are used in Hynudai cars overseas. There are 120 filters possible in each amp and each amp has 12 channels. I use two of those amps. 

The filters are standard IIR (as opposed to FIR) and include crossovers, peak, notch, all pass, high and low pass shelves and basic delay and Logic7. I use the EQ in the amps for room and speaker EQ--the process I've described above. The same thing could be accomplished in a PC with a multi-channel interface and several instances of ElectriQ or some other EQ and crossover. I added the PC after I had done the othe work (the car originally had a factory radio feeding those 24 channels). I just added the PC so we could evaluate custom DSP as VST plug-ins before adding them to real products.

I use impulse response measurements for setting delays. It's important to turn off low pass filters during the measurements, if you do it that way. No need to time align to the sub. 

I usually use 4th order slopes to minimize interaction between the drivers, which are seldom mounted close to each other and to protect them from too much bass.


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## 14642 (May 19, 2008)

CraigE said:


> "Of course, this can't be done with a 31-band graphic EQ and that's why those aren't useful."
> 
> 
> Andy,
> ...


They just don't allow enough precision, in my experience. They're cool for drawing a nice curve once the real EQ is done--that's why we'll include one in MS-8 on top of the autotune--so you can draw the curve you want to listen to after the more powerful EQ has fixed the system.


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## gutz (Aug 8, 2008)

Sounds great!

Thanks for the tip on the impluse response , ill definatly use that

Any other tips you can give?
Do you match IR on first arrival ( even a null ) , first peak or highest peak?

I also would love to get some info on the custom spatial processing you do on your car-pc , I tried using ARC which implements Audyssey's Multi-EQ but I didn't like the result and it lack customization eq graph..

Is DRC worth messing with in a car ?

I'm learning now how to use HOLMImpluse which seems great taking IR / FR plots
Do you recommend using gated mesurments to filter reflections?

Sorry for all the questions but I really like to figure out the best way to tune my system

Also , A little bit off-topic but are you planning implementing MS-8 Auto tuning technology in a VST or some sort of pc software?

Thanks Andy !


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## 14642 (May 19, 2008)

gutz said:


> Sounds great!
> 
> Thanks for the tip on the impluse response , ill definatly use that
> 
> ...


Usually first peak. I don't use gated measurements and the two super long posts in this thread contain the answer to, "Why not?". 

Measurement tool doesn't matter. They're all based on the same basic principle. Use the one that's easiest. ARTA, Holm, YMEC, SMAART, whatever. 

Audyssey multEQ isn't spatial processing, it's AutoEQ. By spatial processing, I mean stuff like PLII, Logic7, SRS WOW!, or any of those--upmixers. The one I use is a new invention and includes room synthesis and crosstalk cancellation. It'll undoubtedly make it into a produce one of these days.


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## gutz (Aug 8, 2008)

Ok thanks Ill keep my eyes open 

What about WuNgUn approach described here?
http://www.diymobileaudio.com/forum...crossover-linearization-design-56k-death.html

Do you think its a good approach on the subject?

Also earlier in the thread if I remember correctly ( too lazy to go back and check lol ) you described phase ( polarity ) influence on the fr
where is this going in the proccess you have just described? every change you make?

From my little experience when you only messing with the polarity it focuses your stage but at the account of bass fullness and depth of sound or some call it dynamics
I've been a reading couple of thread's on this subject but I can't figure out what to tune for - the focus ( which means phase cancellation i guess? ) or the depth/fullness/dynamics since we have T/A , Or it does nothing to do with it?

Hoping for some clearance on that subject..


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## 14642 (May 19, 2008)

Go back and reread the posts. This question is answered in there.


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## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> OK. Sorry for the delay. As a matter of review and to redirect this thread a bit, I've pulled the following from an earlier post:
> 
> _So, there are a couple of basic ways around this reflection thing in cars. One is to try to minimize them and the other is to "spread the chaos around". Minimizing them is damn difficult if you want to have a car that can be driven. Spreading the chaos around simply means that we try to make all the reflections have similar frequency response so we can EQ them and the sound of the speakers using the same filters. Using the speakers where the dispersion is wide is the way to do this. _
> 
> ...


If I am reading the graph correctly, the output of the JBL system is beginning to beam at 4khz. The reason that it's beaming at 4khz is due to the waveguide on the tweeter. A waveguide with a diameter of 3.375" will accomplish this. (speed of sound / 4000hz = 13500inches per second/4000hz = 3.375")







Here's a pic of the speaker in question. The waveguide is about 6" across. I'm guessing that it's beaming at a higher frequency than expected because the edges of the waveguide are virtually flat.

The most interesting thing about the JBL waveguide is the directivity index. It appears that the speaker is about 4dB "hotter" on axis. This is important, because it implies that the speaker is about 2dB "colder" at 45 degrees off axis.

In other words, you DON'T want to listen to these on axis.









I hope people give JBL proper credit for designing speakers that won't make your car look like ass. This is a QLogic kick panel. See how the woofer and tweeter are pointed up? And see how it robs the driver of valuable leg room?

This isn't necessary. Just design the speaker so that it sounds better *off* axis than *on.* Once you do that, your mounting options become a lot simpler. If I'm reading the graph correctly it appears that carefully aiming the JBL speakers is completely unnecessary. In fact it will actually make the tweeter sound too bright. (And knowing how smart the guys at JBL are, I'll bet they included a switch in the crossover to "cut" the tweeter if people insist on aiming it.)

Basically you throw these speakers in the doors and you're good to go. Or build a simple baffle in the kicks, nothing fancy, and that will work too. No extravagant kick panels required.


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## 14642 (May 19, 2008)

Yup. Patrick is absolutely right. In fact, the owner's manual describes exactly that...if only people would read it...

Here's an illustration from the manual:









And if you're inclined to read the rest, you can find it here:

http://www.jbl.com/resources/Brands...-US/OwnersManual/560GTi660GTiOMrev3_20_07.pdf


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## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Yup. Patrick is absolutely right. In fact, the owner's manual describes exactly that...if only people would read it...


To be honest, I switched to JBL for my new Unity horns. 400GTI for the woofer, and BMS 4540ND for the tweeters.















The top pic is a mock-up of my new waveguides. The pic at the bottom is a JBL model which looks suspiciously similar to the BMS that I use :surprised:


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## donkeypunch22 (Nov 5, 2008)

Thanks Andy and Patrick!! Happy New Year.


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## DynaudioNut (Jan 1, 2010)

great thread!


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## donkeypunch22 (Nov 5, 2008)

Andy,
Can you go further with this image? You touch on the level of attenuation for the "peaks" and "big humps", but can you also include the Q and shape (peak, shelf, etc.) of the filters in your answers on the graph?

And would it be safe to say that you prefer to do your EQing on a 1/6 octave measurement?

Can you do a corrective example on a typical sub-woofer measurement?

Thanks!!!


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## SQHemi (Jan 17, 2010)

Tremendous post, Thank you for the info Andy & Patrick.


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## 14642 (May 19, 2008)

donkeypunch22 said:


> Andy,
> Can you go further with this image? You touch on the level of attenuation for the "peaks" and "big humps", but can you also include the Q and shape (peak, shelf, etc.) of the filters in your answers on the graph?
> 
> And would it be safe to say that you prefer to do your EQing on a 1/6 octave measurement?
> ...


I'm constantly switching the resolution of the graph to see what's actually going on. The filters that I'd use depend entirely on where the EQ is paced in the system and what kind of EQ it is. The Q control on EQs can't be trusted and I find that the best way to do this is to dial in a peak with a parametric band and adjust the frequency so it aligns with the peak to be eliminated, cut the agnitude until the peak is reduced to the target level and then to adjust the Q so adjacent bands are also in line with the target.


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## donkeypunch22 (Nov 5, 2008)

Andy Wehmeyer said:


> I'm constantly switching the resolution of the graph to see what's actually going on. The filters that I'd use depend entirely on where the EQ is paced in the system and what kind of EQ it is. The Q control on EQs can't be trusted and I find that the best way to do this is to dial in a peak with a parametric band and adjust the frequency so it aligns with the peak to be eliminated, cut the agnitude until the peak is reduced to the target level and then to adjust the Q so adjacent bands are also in line with the target.


Thanks Andy, this has been most helpful.


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## nick561 (Jun 25, 2009)

flat dos not sound good to my ear at all


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## 14642 (May 19, 2008)

nick561 said:


> flat dos not sound good to my ear at all


Small spaces require additional bass.


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## Hernan (Jul 9, 2006)

Andy Wehmeyer said:


> Small spaces require additional bass.


Bass or midbass?

Thx for your great contribution to the forum!


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## michaelsil1 (May 24, 2007)

Bump!


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## ErinH (Feb 14, 2007)

OMG! YOU EFFER!!!


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## donkeypunch22 (Nov 5, 2008)

Yeah, this post should now say, "Please don't worry about it. Just go purchase the MS8. Thank you."


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## michaelsil1 (May 24, 2007)

cajunner said:


> draw a flat curve, I dare ya...


______________________


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## tornaido_3927 (Nov 23, 2009)

cajunner said:


> draw a flat curve, I dare ya...


Haha, flat curve. Even the wording doesn't sound good


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## jhmeg2 (Nov 6, 2009)

mine is a little flat... lol


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## michaelsil1 (May 24, 2007)

jhmeg2 said:


> mine is a little flat... lol


Probably sounds overly bright! :wiseguy:


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## jhmeg2 (Nov 6, 2009)

a little but, the silk domes help. its acctualy pretty nice though


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## tornaido_3927 (Nov 23, 2009)

And maybe bass-less? Especially whilst driving?!


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## jhmeg2 (Nov 6, 2009)

I've got plenty of bass.


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## chad (Jun 30, 2005)

Someone is unaware of the studies of Fletcher and Munson.


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## Hernan (Jul 9, 2006)

chad said:


> Someone is unaware of the studies of Fletcher and Munson.


Why are your saying this?

Is not just how we listen?

A relative flat FR and power response are good things on a reproducction system. 

Of course, we don't hear the same at different Levels. Need to EQ this? I think no.

One thing that has a direct relantionship with how some frecuencies are more prone to need some EQ is the earcanal tranfer function. There is natural amplification around 4 and 10k inside the eardrum (around 12dB), so we are very sensitive at these frecuencies. 
This does not means that we have to cut this frecuencies, just pay special attention to them.

I call these the "devil frecuencies". The first thing I do in a car is look at what's happening near 200hz, 4k and 10k.


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## 8675309 (Jan 8, 2007)

flat to start with! Then you must tune off of that! No curve after that you must tune off of ear!


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## matthewo (Jan 31, 2008)

i listen to music thats all around. so even if i tuned it right with one album another album even with the same genre doesnt sound good.

i get a few eq presets with the bitone. 3 time delayed for the drivers ear. and 1 for the passenger. set pretty good for most music. then i use a few slight variations on the eq on my pioneer headunit, depending on the music im playing.

in the real world not all my music is recorded perfect so some tweaking has to be done.


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## 8675309 (Jan 8, 2007)

it has to be equal on both sides of the car to get anything. The Maxima was a driver seat car no matter what you did.



matthewo said:


> i listen to music thats all around. so even if i tuned it right with one album another album even with the same genre doesnt sound good.
> 
> i get a few eq presets with the bitone. 3 time delayed for the drivers ear. and 1 for the passenger. set pretty good for most music. then i use a few slight variations on the eq on my pioneer headunit, depending on the music im playing.
> 
> in the real world not all my music is recorded perfect so some tweaking has to be done.


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## matthewo (Jan 31, 2008)

I cannot say it helps much to time delay the passenger seat when I have the tweeters on axis to the driver

it's not a comp car so I could care less about anything other then the driver which is me 99% of the time. The 1% my wife or other few may drive the car I can use the passenger seat preset


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## mdechgan (Dec 16, 2010)

Treble 0, Bass 0, balance 0, fader 0
Crossover points fixed.
All I usually play with are the tweeter attenuation and gains.
I also don't play around with speaker location because in most installs it become impractical to move the speakers around too much.


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## req (Aug 4, 2007)

neat, found this thread on a google search. repy'd so its in "my threads"

thank you gentlemen.


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## mattyjman (Aug 6, 2009)

great read.... thanks all


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## sqnut (Dec 24, 2009)

Oh NO!!!! We need another discussion on FR like we need a hole in the head.


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## ErinH (Feb 14, 2007)

I started this thread nearly five years ago and it's still kicking!


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## sqnut (Dec 24, 2009)

I know, but its been bumped up just after we got done with that other thread of yours. Seems like you're the resident agent provocateur .........jk


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## mattyjman (Aug 6, 2009)

nah, it just so happens that i am busy reading a ton of stuff to make my current build, the best one ever. erin just asked all the same questions i'm asking, only years ago


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## adrenalinejunkie (Oct 17, 2010)

Overwhelmed. Good job guys.


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## Gary S (Dec 11, 2007)

The only kind of flat response that is good is anechoic. Our brains can separate the sounds of the speakers and late reflections, late reflections don't matter.

The secret to good sound is simple - get a great install, great speakers that measure flat anechoic, the best speaker placement you can (including kick panels) and ditch the EQ. Oh, and add surround sound and a sub and reasonable power.


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## 14642 (May 19, 2008)

No car sounds right without EQ.


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## garysummers (Oct 25, 2010)

View attachment 37054


Andy

Can you elaborate on this target curve and how it was arrived at?

Thanks,

Gary


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## 14642 (May 19, 2008)

garysummers said:


> View attachment 37054
> 
> 
> Andy
> ...


Practice Practice Practice.


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## Woosey (Feb 2, 2011)

garysummers said:


> View attachment 37054
> 
> 
> Andy
> ...


How about this









It all depends of the way of measuring... White noise, Pinke noise.. 

If you look at the graph, the pink noise is more intense down low and less intense above ( if you know what I'm saying )

White noise is leveled more equal ( imo better way to measure )

When RTA pink noise, people cut the low and boost the highs to get it flat ( compensate the curve in my link )

This is why it often sounds thin.... If the measuring is done with white noise ( the measured freqs. all at the same intensity ) is will not sound thin...

my $0.02


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## ErinH (Feb 14, 2007)

Let me add something that keeps getting missed by a lot of folks, including myself at times. 

The idea of flat response is rooted in testing that showed a speaker with flat ANECHOIC response was more liked against others who strayed in some degree from this. Toole's Sound Reproduction book covers this. Flat wasn't measured in the room. But measured anechoically to get a baseline performance amongst multiple speakers. 

And the key is that flat anechoic response is NOT flat RTA response. 

Dot forget to factor in sound power response.


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## Woosey (Feb 2, 2011)

bikinpunk said:


> Let me add something that keeps getting missed by a lot of folks, including myself at times.
> 
> The idea of flat response is rooted in testing that showed a speaker with flat ANECHOIC response was more liked against others who strayed in some degree from this. Toole's Sound Reproduction book covers this. Flat wasn't measured in the room. But measured anechoically to get a baseline performance amongst multiple speakers.
> 
> ...


agreed!

This is possible with MLS signal and gating right? ( quasi anechoic? )


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## 14642 (May 19, 2008)

The Punk is right again. Yes, it can be achieved with gating, but you won't be able to gate in a car at a low enough frequency to be useful because the car is too small. Plus, it isn't necessary. Just EQ to your target in a small space.


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## ErinH (Feb 14, 2007)

Woosey said:


> agreed!
> 
> This is possible with MLS signal and gating right? ( quasi anechoic? )



Not really. Because the environment is too reflective to yield a meaningful quasi anechoic result. Consider how soon your first reflection occurs relative to driver measured. Probably within a cm of the driver if not less. In the case of a reflection at 1cm, this means your measurement must be gated to >5khz (speed of sound/distance). This is equivalent to about 0.18ms. Extremely low. While this may seem fine, you also should factor in the resolution accuracy with a sample of this size. 

Not only is this an extremely ideal example, it includes only one reflection. The car is just too reflective for gating an impulse to be meaningful. I've tried. I've tried a lot. I'm still researching methods but the bottom line is its futile at best. 

And you can't do nearfield because your accuracy in the nearfield is only good up until a point related to driver diameter. For example, a 3/4" tweeter. 5475/(.75/2) = ~1400hz. 
This is the highest frequency accurately measured by nearfield measurement. 

So, the lowest you can measure in the farfield via gating to 0.18 (thus, omitting first reflection) is about 5khz. The highest allowable frequency measured in the nearfield is 1400hz. You then have immeasurable data between 3 octaves (1400-5000). 

http://www.klippel.de/fileadmin/kli...39_Merging_Near_and_Farfield_Measurements.pdf

Consider this: if we can't obtain any better than a cm of reflection free data AT BEST, then windowing is certainly useless for any other driver. 

This is why obtaining impulse response (for the purpose of gating) in a car is meaningless. 


Now, for the fun part... Harmonic distortion results ARE altered by reflections in the measurement. Keep this in mind when you see someone post or discuss obtaining HD measurements in the car. Thy have their place but you have to factor this in during analysis.


Edit: I can't spell on a phone.


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## ErinH (Feb 14, 2007)

To take it one step further, consider the Schroeder frequency. AKA: critical frequency (Fc to keep me from typing it). This is one thing I've been looking into more the past year. This essentially defines the point at which the sound you hear shifts from reverberant to modal. Reverberant means the sound bounces around and the response is an effect of comb filtering relative to the listener moreso than a standing wave or pressure mode created null. Modal means that the response varies greatly from seat to seat (as much as +/-30dB in some cases I've seem). Probably a gross dumbed down explanation but it helps me keep it straight. 
It's all related to the size of the room, location of speakers, and wavelength relation. The more complicated aspect includes the material characteristics (ie: rigidity of drywall in a room, etc). 

What this means for us is that below some given frequency, based on room size and reverberation time (T60), the response changes drastically from seat to seat. Or even position to position. 
Of course, you'd have to define T60... And that's not easy in a car with odd shapes. The only way you can determine Fc is to really measure in the car at multiple locations and look for the point where you start to see a separation in all of the plots. For example, 6 measurements are taken in different locations. You notice that above 800hz the response kind of does the same thing (note: not saying its the exact same but has the same diffuse behavior). Below about 800hz you notice each response varies pretty greatly. This is an indication of Fc location. This does a good job of explaining it:
http://www.soundandvisionmag.com/blog/2012/03/05/schroeder-frequency-show-and-tell-part-1


In a car you'd think Fc matters very little unless your goal is great sound from every seat. You're in the same seat so you're not subject to varying nodes, right? But, the kicker is, according to the equation, the critical frequency increases as the room size decreases. Room size and critical frequency are inversely non-proportional. Why does this matter now? Well, at least to me, this means you have a lot of modal resonance going high in to the mid band. That sucks. And, this is a other reason why averaging a few measurements within a small head window is great. It keeps you from going nuts over the diffuse effects above Fc. 
HOWEVER, at the same time, I wonder just how important it is to consider each measured response before you average in order to give you an idea of modal issues from mic position to position. If Fc happens at a point which is a I've the relationship of widest mic measurements, it seems you'd possibly filter out higher frequency modal issues. Example: IF Fc occurs at 1200hz, which is equivalent to about 11", anything below below this frequency will be averaged together and possibly hide modal issues up high if you have a mic distance delta of >11" in your measurements. Now, realistically, this is probably about the max distance in mic position. But it's something to consider IF you find Fc is high in frequency. Just take Fc and divide it in to the speed of sound. So, 13500/Fc. If Fc is 800hz, then you can move the mic up to a distance of about 17" before you reach a point where your outside f that modal issue. THIS IS ALL THEORY... I have not yet proved or attempted this. In fact, I just thought of it when typing this reply. 
It does also indicate the need to perform Fc determination measurements by placing the mic in various locations in the car; not just the head area. I measured from every seat, center of car, the dash corner and rear shelf corner. Didn't measure from the trunk since the IB wall separates the two cabins. (Side note: IB yields resonance in the trunk as well. Consider it a separate room that's EXTREMELY small. Problems...)


Note, though, his article says 200hz seems to be the breaking point. This is a large room. I chose 800hz because my measurements thus far have shown me this is closer the Fc in my car. But, I really need to revisit this as I'm not sure my analysis and thought process was correct at the time. 


Then there's the idea that on one side you're somewhat nearfield and on the other side you're farfield. Not sayin this for the purpose of high frequency sound propagation but to point out how it seems possible that in an assymetrical stereo situation, does T60 vary? This would have to be measured or I'd have to track down someone who knows this subject well ... Or I do some more research and find its in plain English in the first google return. Lol.


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## jhmeg2 (Nov 6, 2009)

I start with crossover points, time alignment, and gains. Get it ruler flat, then listen and make it sound REAL from there.

but, this is as flat as I could get it.


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## seeguhl (Oct 2, 2013)

awsome thread. Very informative. I learned quite a few new things reading this. Thanks Andy and Patrick.


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