# Improve Your Sound Quality for $80



## Patrick Bateman (Sep 11, 2006)

Someone on another thread asked me how I do my measurements, so thought I'd do a quick "brain dump". This isn't meant to be a "deep dive", just a quick summary of how to do it.

Basically a microphone can sleuth out problems in your system in a matter of seconds, problems that could take hours to detect audibly. I've been building systems for almost twenty years, and even with that level of experience, my microphone is a million times faster than doing it by ear.

Anyways, here's how to fix your stereo for less than a hundred bucks. This is exactly how I do it.


Get a copy of Arta. You can do acoustic measurements with Arta without paying for it. Or support the dude and pay for it. I've heard good things about HOLMImpulse too, which is also free. Stay away from Speaker Workshop, it's free, but it's a p.i.t.a. (It has a great crossover module tho.)
Build a cheap PC and put it in your garage. I had one laying around. The quality of the components doesn't matter at all, even an onboard sound card is good enough these days. I purchased a $200 professional sound card for measurements, and it was no better than the onboard sound card. Modern sound cards are very good.
Get yourself a mic. Nearly everyone uses a Behringer ECM8000. It's $40. If that's too much, build your own. The parts are less than $5.
Get a preamp. I use an M-Audio Audio Buddy. $40 on Ebay. If you don't want to wait for it to come in the mail, you can buy it over the counter at Guitar Center. I think it's about $150 there.

That's the part list. I spent less than $100, but I used a PC I had laying around. You could use a laptop too.

Back in the 80s people would use a RTA, which cost about $1000-$2000. I would discourage the use of an RTA; a PC with Arta or HOLMImpulse does it a lot better. The reason why is that we can "gate" measurements. In a "gated" measurement we are capturing a few milliseconds of sound. This method removes reflections and cleans up the measurement.

If you don't gate the measurement, reflections swamp the response, and the data isn't accurate. Besides screwing up the response, it also tips it towards the bass, since high frequencies are absorbed in the car, and low frequencies are augmented by cabin gain.

So, long story short, use something that can gate the measurements.

Unfortunately gating only gets us in the ballpark. That's why I do polar measurements. Setting the "gate" is a real art. Siegfried Linkwitz has this crazy measurement set up that he uses, even WITH gated measurements. Here's a pic:










The reason you have to use this crazy contraption is that you have to get the speaker far from any boundary, even with a gate. For instance, to get a clean measurement down to 100hz you really shouldn't have anything within a hundred and twelve feet. 

Even getting a half-assed measurement at 100hz requires you to get the speaker eleven feet from any obstructions.

So obviously, this is completely impractical, which is why I use polar measurements. I'll explain how to do that in the next post.


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## Patrick Bateman (Sep 11, 2006)

Okay, part two: Polar Measurements.

As mentioned above, RTAs are low tech these days, particularly if you're measuring midranges and tweeters. Due to reflections in the car, a gated measurement gives you much better data than a RTA.

The problem with the car is that even when you use a gate, reflections are impossible to avoid. Reflections off the windshield, off the dash, off the doors, etc...

That's where polar measurements come into play. With a polar measurement we measure the speaker at multiple points in the car. Standard operating procedure is to do it at 15 degree increments.

When you measure at multiple points, you'll learn when the problem is your speakers, and when the problem is your car. Here's a polar measurement of my own speakers in my own car, using the techniques I describe here:










In the measurement above, you'll see that the peak at 400hz is the same in all the measurements. The peaks at 800hz aren't. Generally, this demonstrates that the peak at 400hz is coming from the driver, or from something near it. In the measurement above the peak and the dip were due to a resonance. Without polar measurements this wouldn't be obvious.

I'll post some pics of the "jig" that I use for polar measurements. It's basically a board that stretches from one side of the car to the other, with long slender arms that the microphone is placed on. The arms are important, otherwise there will be reflections from the board that goes from side to side.

Note that this isn't 100% accurate; a true polar measurement would be done in a arc so that the mic is equidistant from the speaker.

A few months ago I came up with a way to clean up the measurements, I'll describe that in the third post.


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## Patrick Bateman (Sep 11, 2006)

A few months ago I came up with a way to clean up the polars in a car. This is a bit controversial, so don't use this if you don't agree with the ideas behind it.

Basically there are so many reflections in the car, that it's difficult to get a clean measurement. Gating and polars help a lot, but not enough. Standard operating procedure is to do polars at fifteen degree increments.

Based on all that, you would do four measurements using a gate. (0, 15, 30, 45 degrees.) I can do four measurements in under three minutes; it's ridiculously easy.

To take it to the "next level", I do three measurements for each point. For instance, for a measurement at 15 degrees I do one at 7.5 degrees, one at 15 degrees, and one at 22.5 degrees. And then the controversial part, I average those three measurements. Standard operating procedure dictates that you put all of them on the graph, but I prefer to have four averages instead of twelve unique traces on the graph. It's just easier for me to analyze the data. If I was measuring speakers outside, like Linkwitz, I'd put all twelve on the graph. Measurements in the car are just too rough for that IMHO. So this is kind of a cross between a polar response graph and a power response measurement.

To do this in Arta, make a measurement, and then select "set as overlay." You can do this with one measurement or a hundred. Arta can power average your overlays with one click. It's a great program.


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## Patrick Bateman (Sep 11, 2006)

Also, if anyone thinks that doing polar measurements is "over the top", it's really easy. I can literally do a single measurement in under a minute, and a set of twelve in less than fifteen minutes.

Think about it this way, how many times have you listened to your speakers for a solid week, wondering why they didn't sound correct? Wouldn't it be nice to suss that out in a minute?

If fifteen minutes is too long, buy four mics for $160, and set up circuit to switch the mics in and out. Right now the most time consuming part of my measurements is walking ten feet to the car to move the mic.


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## Nathan P (Jun 9, 2007)

I've got a bunch of panasonic omnidirectional mic capsules I bought to build some binaural mics with. From what I remember they are very similar to those used in homemade measurement mikes. Any chance these could be setup for this? I think I have 5 or so left over.

Nathan


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## I800C0LLECT (Jan 26, 2009)

I'm pretty excited...onto craigslist for crappy laptop.


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## Patrick Bateman (Sep 11, 2006)

Nathan P said:


> I've got a bunch of panasonic omnidirectional mic capsules I bought to build some binaural mics with. From what I remember they are very similar to those used in homemade measurement mikes. Any chance these could be setup for this? I think I have 5 or so left over.
> 
> Nathan


I think so. I built some with Panasonic WM-61. Wound up using the Behringer instead, mostly out of laziness.


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## Austin (Mar 12, 2009)

Could you post links to the arta website and HOLMImpulse website please. i could find them through google.


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## ErinH (Feb 14, 2007)

Patrick Bateman said:


> Based on all that, you would do four measurements using a gate. (0, 15, 30, 45 degrees.) I can do four measurements in under three minutes; it's ridiculously easy.
> 
> To take it to the "next level", I do three measurements for each point. For instance, for a measurement at 15 degrees I do one at 7.5 degrees, one at 15 degrees, and one at 22.5 degrees. And then the controversial part, I average those three measurements. Standard operating procedure dictates that you put all of them on the graph, but I prefer to have four averages instead of twelve unique traces on the graph. It's just easier for me to analyze the data. If I was measuring speakers outside, like Linkwitz, I'd put all twelve on the graph. Measurements in the car are just too rough for that IMHO. So this is kind of a cross between a polar response graph and a power response measurement.
> 
> To do this in Arta, make a measurement, and then select "set as overlay." You can do this with one measurement or a hundred. Arta can power average your overlays with one click. It's a great program.


How necessary have you found the additional response measurements to be? Frankly, I’m not so sure I see the need for a total of 12 (3 at each 15* increment), based on my past experiences (as recently as last Friday night). While I definitely agree that multiple stops should be used, I’m not sure I see the necessity for more than a few; I think 15* increments alone are enough. In this case you’re only looking to discern the environment from the speaker, and I believe that 12 measurements could be overkill.
So, have you truly noticed anything beneficial to doing 12 vs. 4-5? 

Speaking of this stuff, I need to get my butt down to radio shack to pick up some motors…


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## Patrick Bateman (Sep 11, 2006)

Austin said:


> Could you post links to the arta website and HOLMImpulse website please. i could find them through google.


ARTA home

HOLMImpulse: Measuring Frequency- & Impulse-Response - diyAudio


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## Patrick Bateman (Sep 11, 2006)

bikinpunk said:


> How necessary have you found the additional response measurements to be? Frankly, I’m not so sure I see the need for a total of 12 (3 at each 15* increment), based on my past experiences (as recently as last Friday night). While I definitely agree that multiple stops should be used, I’m not sure I see the necessity for more than a few; I think 15* increments alone are enough. In this case you’re only looking to discern the environment from the speaker, and I believe that 12 measurements could be overkill.
> So, have you truly noticed anything beneficial to doing 12 vs. 4-5?
> 
> Speaking of this stuff, I need to get my butt down to radio shack to pick up some motors…


It's because I can't use a proper gate.

For instance, let's say you're measuring a tweeter with a crossover at 2.5khz. You only need to capture about five to ten cycles. Just to be generous, you want accuracy down to 1.25khz. Ten cycles at 1.25khz is 8ms.

(1000ms / 1250hz) * 10 cycles = 8ms

In eight milliseconds sound travels 104 inches.

So that leaves you with this dilemna when you're measuring in the car. Either you set the gate to a very short length, and discard accuracy. Or you use a proper gate length, and suffer the reflections.

I like merging three points of data because it helps to smooth out response blips that only exist at one point, while illuminating response problems that exist at ALL points.

In the pic I posted above you can see that with the peak at 500hz; it's in all the polars.


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## SSSnake (Mar 8, 2007)

Patrick,

I understand the logic behind the twelve measurements but have you found that they provide increased accuracy?

I'm all for more data but there comes a point where more is just more not better.


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## ErinH (Feb 14, 2007)

SSSnake said:


> Patrick,
> 
> I understand the logic behind the twelve measurements but have you found that they provide increased accuracy?
> 
> I'm all for more data but there comes a point where more is just more not better.


x2.

This is exactly what I was asking, Patrick. I understand what you're doing. I just don't know if the 12 points are necessary. IME, they are not. I was looking for your own, honest opinion on this matter.


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## ItalynStylion (May 3, 2008)

Patrick, all of this is great material! Keep it coming as this is EXACTLY what this forum needs!


I only have one question about the reasoning behind the gate process. I understand that it is to take a direct measurement of the frequencies before they have time to reflect at the microphone and skew results. However, our ears are the permanent microphones that we have mounted on the sides of our head and they will be receiving these reflections when listening to the music on a regular basis.

Basically, since we will be listening in a sea of reflections, should we not measure them too and adapt FR?


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## ErinH (Feb 14, 2007)

ItalynStylion said:


> Patrick, all of this is great material! Keep it coming as this is EXACTLY what this forum needs!
> 
> 
> I only have one question about the reasoning behind the gate process. I understand that it is to take a direct measurement of the frequencies before they have time to reflect at the microphone and skew results. However, our ears are the permanent microphones that we have mounted on the sides of our head and they will be receiving these reflections when listening to the music on a regular basis.
> ...


I was going to ask the same thing, but I think his post here is about measuring what your speaker is providing so that you can work on anomalies, rather than measuring the overall system output.

If that's not the point of the thread, then... x2.


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## rockinridgeline (Feb 2, 2009)

I think the answer is that our ears and brains are able to differentiate much of the reflections based on time and amplitude of the signal, whereas they get lumped into the RTA response and can skew the measurements. Taking a gated response more accurately shows us what our ears are actually able to discern.


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## ItalynStylion (May 3, 2008)

bikinpunk said:


> I was going to ask the same thing, but I think his post here is about measuring what your speaker is providing so that you can work on anomalies, rather than measuring the overall system output.


Now that I think about it I think you're right. Good call.


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## BigRed (Aug 12, 2007)

why would you want to measure without reflections while the speaker is in your car? unless you are of course trying to address what the reflections do. a simpler method would seem to take the speaker out of your car and measure it without reflections, and then overlay that reading with the one in the car.


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## ErinH (Feb 14, 2007)

BigRed said:


> why would you want to measure without reflections while the speaker is in your car? unless you are of course trying to address what the reflections do. a simpler method would seem to take the speaker out of your car and measure it without reflections, and then overlay that reading with the one in the car.


as I alluded to above, I believe his goal here is to find issues with the enclosure + environment. He specifically talks about resonances. You could find these outside the car, but when you add other structures to the equation you have coupling going on, which could cause some things you don't want. In order for you to discern if it's the speaker/enclosure or the playback (refelctions), you'd gate it, and take multiple measurements from multiple locations as is done in post #2. A good example I can think of would be kicks. The dash can give you a lot of problems that you wouldn't necessarily see if you didn't do a gated measurement.

Again, this is what I assume this thread is about. If not, then I'm with you and Steve.


Edit: Actually, are the polar responses gated? Seems like he's saying that 'gating is impractical so I use polar response'. Well, how are the polar responses done? Sine sweep? Pink noise? Gated? Not gated? 

Patrick, don't take offense at me asking these questions. In fact, your thread comes at a time (if you search back to last week) when I'm actually delving back into using software for system setup again. So, I'm trying to learn about this stuff, too. Although I don't think it should solely be used to tune a system, I do see it being used as a great _tool_ to help you tune and also help you learn. IMO, that's the biggest benefit (learning from tests).


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## ItalynStylion (May 3, 2008)

BigRed said:


> why would you want to measure without reflections while the speaker is in your car? unless you are of course trying to address what the reflections do. a simpler method would seem to take the speaker out of your car and measure it without reflections, and then overlay that reading with the one in the car.


Also true. Tom Nousaine wrote an article about the obtaining of quantitative FR data by way testing without reflections. He describes what is called an anechoic chamber which is an acoustically dead space. He mentions that when that isn't available he does it outdoors much like Siegfried Linkwitz in the picture that Patrick has in the first post. I attached the PDF if anyone is interested in it.


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## Patrick Bateman (Sep 11, 2006)

BigRed said:


> why would you want to measure without reflections while the speaker is in your car? unless you are of course trying to address what the reflections do. a simpler method would seem to take the speaker out of your car and measure it without reflections, and then overlay that reading with the one in the car.


Because all reflections are not created equal.

Reflections which occur in the first few milliseconds are a problem. They make music and speech unintelligible, create peaks and dips in the frequency response, and generate phantom images which quickly wreck the soundstage.

On the other hand, reflections which occur *later* create a sense of ambiance and space which is pleasing.

Anyways, that's why I gate my measurements. I care about early reflections.

For more on this see this:

diyAudio - View Single Post - Geddes on Waveguides

and this:

http://www.diymobileaudio.com/forum...-rta-plots-what-being-heard-2.html#post685872

It's pretty easy to hear the difference; just take a pair of tweeters, throw them into a sphere, mount them a few inches away from any boundary, and listen. Controlling early reflections opens up the soundstage like nothing else can.


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## ItalynStylion (May 3, 2008)

I agree on the topic of early reflections being bad and late reflections giving a nice ambiance effect. I've recently discovered this myself when I built my first pair of Lotus BVR's with a side firing driver and now (most recently) built my first bipoles. My hypothesis is that sound CREATED and not REPRODUCED is not unidirectional and these late reflections are a natural occurrence. Therefore REPRODUCING music without these late reflections would not sound natural at all. 

I was actually chatting with a sales guy in Marvin Electronics last year about room interactions. He was explaining to me the flaws in most rooms like wood/tile floors. I immediately came to the conclusion that a dead flat room (anechoic chamber) would be the pinnacle listening environment. However, he told me that he had been in a room very similar to that and it was NOT at all natural and sounded VERY odd. Thinking about that now I'd guess it was because of the lack of any or minimal reflections. I'd like to experience it for myself though.


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## Patrick Bateman (Sep 11, 2006)

ItalynStylion said:


> I agree on the topic of early reflections being bad and late reflections giving a nice ambiance effect. I've recently discovered this myself when I built my first pair of Lotus BVR's with a side firing driver and now (most recently) built my first bipoles. My hypothesis is that sound CREATED and not REPRODUCED is not unidirectional and these late reflections are a natural occurrence. Therefore REPRODUCING music without these late reflections would not sound natural at all.
> 
> I was actually chatting with a sales guy in Marvin Electronics last year about room interactions. He was explaining to me the flaws in most rooms like wood/tile floors. I immediately came to the conclusion that a dead flat room (anechoic chamber) would be the pinnacle listening environment. However, he told me that he had been in a room very similar to that and it was NOT at all natural and sounded VERY odd. Thinking about that now I'd guess it was because of the lack of any or minimal reflections. I'd like to experience it for myself though.


The first 10milliseconds seem to be the most critical, based on what I've read. That works out to eleven feet. A few years back I was at CES, and Creative Labs was demoing some crappy five channel system for PCs. The whole system was under $150. Because they didn't want people knocking over speaker stands, they'd built a giant PVC ring, and suspended it above the show floor. The speakers were attached to the ring.

So I'm standing there, with five speakers suspended about 10 feet above the floor. The ring itself was about fifteen feet wide. So each speaker is about ten feet apart, and they're equidistant, and they're ten feet off the ground. (that's the key...)

They fired up this $150 set of PC speakers, and it was one of the most convincing images I've ever heard. My jaw dropped! I could close my eyes and pinpoint everything they were demoing...

And it was under $150.

Depresssing.

Anyways, the reason it worked so well is that there were no reflections off *anything* for a solid ten feet in all directions. (The roof of the building is easily 30-40 feet.)

Hell of a demo.


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## rockinridgeline (Feb 2, 2009)

I've spent time in an anechoic chamber used for wireless antenna testing. Shut the door and stand still and you can hear your own heart beat, your breathing. It is a surreal experience.

Sounds in the chamber sound anything other than natural. All natural sound that we hear is accompanied by some sort of reflections. Take those away and it sounds just plain weird. I have not heard music in the chamber, but just the human voice sounds really strange.


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## ItalynStylion (May 3, 2008)

rockinridgeline said:


> I've spent time in an anechoic chamber used for wireless antenna testing. Shut the door and stand still and you can hear your own heart beat, your breathing. It is a surreal experience.
> 
> Sounds in the chamber sound anything other than natural. All natural sound that we hear is accompanied by some sort of reflections. Take those away and it sounds just plain weird. I have not heard music in the chamber, but just the human voice sounds really strange.


I want to try it bad! :laugh:


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## AUr6 (Apr 10, 2007)

excellent thoughts here. I've got to agree that i think the biggest goal here with this type of testing as it seems he stated is to determine whether the driver or the environment is causing any distortion in the tuning of the desired sound stage. 

As far as anechoic chambers go, i've been in one of the big ones where they can fit whole aircraft, and the only way you can talk to someone even close to you is to look directly at them when you speak. all reflections you're used to hearing are completely absorbed/dispersed by the walls/floor/ceiling. It's definitely unlike anything in nature... almost TOO quiet!


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## Austin (Mar 12, 2009)

Could someone post a video of how to use true rta? Ive been reading the manual and it isn't too clear as to how to set it up and use it. or atleast im really confused.


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## DanMan (Jul 18, 2008)

Austin said:


> Could someone post a video of how to use true rta? Ive been reading the manual and it isn't too clear as to how to set it up and use it. or atleast im really confused.


x2

I am using the ECM-8000/MicMate combo recommended a while back. Initially I hoped it would be as simple as adjusting the eq while viewing the RTA in real time to get your desired response curve.

Aside from figuring how to best use the software, the limitations of the hardware(Mic/preamp/soundcard), by the time the sound gets done bouncing around and resonating the interior surfaces, I wonder about the integrity of the measurements.

Somebody with the know-how would be doing a great service to make a tutorial on best using TrueRTA


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## tronik (Sep 1, 2009)

DanMan said:


> x2
> 
> I am using the ECM-8000/MicMate combo recommended a while back. Initially I hoped it would be as simple as adjusting the eq while viewing the RTA in real time to get your desired response curve.
> 
> ...


x3

As a novice, it would be great to at least see a brief writeup on:
a. Setting up the hardware (microphone, sound card adjustments, etc)
b. How to use ARTA/TrueRTA
c. How to interpret the results and using it to adjusting EQ.


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## Patrick Bateman (Sep 11, 2006)

DanMan said:


> Aside from figuring how to best use the software, the limitations of the hardware(Mic/preamp/soundcard), by the time the sound gets done bouncing around and resonating the interior surfaces, I wonder about the integrity of the measurements.


Here's an example of the difference it makes:

When I first got into car audio, the systems I built were fairly complex. One of my cars had Peerless 5" mids up front, with Audax tweeters, and dual 10" subs. The crossovers were all passive, with 24db slopes.

Sounded like absolute **** - it was horrible.

The first system was too bright, and didn't have any midbass.

In an effort to fix this, the next system had *dual* 7" woofers from Seas in the doors, with customer doors I built by hand. Wish I had a picture of that - it looked sharp.

It *still* had no midbass, but it sure played loud. This really pissed me off though - I mean, four 7" woofers shouldn't sound "thin."

Frustrated by these systems, I literally spent a DECADE trying to squeeze ever last ounce of performance out of widebanders, with everything from tiny 3" woofers in the kick panels to ginormous JBL horns under the dash.

The systems that used the widebanders sounded better than the abominations I built ten years ago, but they're not even in the same _ballpark_ as the last three systems I've built.

And it's all because of measurements. It's just preposterously easy to find little glitches and resonances and reflections with a mic. Ten years ago I'd sit in the car four HOURS trying to grok what was going on, now I just measure it and I know the truth in five minutes. Soooooo much easier, soooo much faster.

I wish I still had those cars - if you guys could hear the difference between what I could do with my ears, and what I can do with my ears and a mic, you'd be amazed.


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## ErinH (Feb 14, 2007)

^ so, in the instances where you found the resonances and reflections, how did you fix them? I think that would be beneficial information to discuss and share. It's actually a 'part 2' of this thread, if you will. Finding the issues is good, but if you don't know how to fix them when what's the point?
Know I'm sayin'?


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## Patrick Bateman (Sep 11, 2006)

bikinpunk said:


> ^ so, in the instances where you found the resonances and reflections, how did you fix them? I think that would be beneficial information to discuss and share. It's actually a 'part 2' of this thread, if you will. Finding the issues is good, but if you don't know how to fix them when what's the point?
> Know I'm sayin'?


Fixing the resonances and the holes and the peaks is fairly straightforward, but finding them isn't so easy.

For instance, I added my sub to my system on Sunday. I didn't measure the sub, I just plugged it in. Immediately, it was obvious that there was a hole in the response somewhere.

If this was 1999, I would've sat there in my car, obsessing about the hole in the response, tweaking crossover points on my electronic crossovers, listening, maybe adding a bit of EQ, listening some more, etc...

Since it's 2009, I didn't do that. I grabbed my microphone, measured the response, and looked at it. There was a big hole at 150hz. Then I lowered the gain on the sub amp, dialed in some EQ to fill in the hole, and measured again.

Boom, done, took ten minutes. I fixed the hole in the response in less time than it takes to get coffee before work. (I *did* tweak it a bit by ear after the fact, I don't live and die by what the computers says BTW. Measure first, listen second.)

Now obviously, you can EQ by ear, but it's IMPOSSIBLE to get it perfect. Mics have a sensitivity that exceeds our own ears. When you EQ by ear, you undershoot or overshoot all the time, and wind up with response variations on the order of 3db.

A 3db hump isn't massively offensive, but when you're chasing down perfection, you can't have errors of that order.


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## Patrick Bateman (Sep 11, 2006)

Someone emailed me some questions on how to get results from software, here's a quick summary. I'm putting it in the forums in case anyone else wants the info too.

Anyways, here's the answer, they were basically wondering about whether you should measure one speaker at a time, and which ones should be measured first:


Plug the mic into your preamp, and plug the output of your preamp into your PC. Once you do that, you'll be getting an SPL measurement of your car.

My preamp has a meter which shows if there's too much signal. It turns red if I "overdo it." Keep you're eye on that - if you clip the signal, you're measurements will be garbage.

Technically, you're supposed to measure the voltage across the speaker terminals. I don't do this - I just play the sounds at 90db or so. I do so many measurements that it's not practical to bust out the multimeter every day.

I am using Arta, not any of the packages you mentioned. Having said that, I *believe* that Arta is doing gated measurement with pink noise. I'll have to double check. Arta is ridiculously easy to use, and the measurements are really consistent.

As for what to measure, this is what I do:

#1 - midranges
#2 - tweeters
#3 - midranges AND tweeters
#4 - then I add subs, and set the levels

Measure one speaker at a time - for the most part it isn't necessary to measure in stereo, and stereo measurements will be difficult to interpret.

When you get to the point that you're satisfied with one side of the car, do the other. If you have dual channel EQ, focus on getting the left and the right to match above 1khz. Due to the Fletcher Munson curves, and the mechanics of our hearing perception, we're very sensitive to frequency response mismatches above 1khz.


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## ErinH (Feb 14, 2007)

Patrick Bateman said:


> Fixing the resonances and the holes and the peaks is fairly straightforward, but finding them isn't so easy.
> 
> For instance, I added my sub to my system on Sunday. I didn't measure the sub, I just plugged it in. Immediately, it was obvious that there was a hole in the response somewhere.
> 
> ...


Didn't really answer my question. You kind of just re-said what you've been saying (rta software really helps).

I'm with you on the RTA and software stuff. I tinker with it a lot. You don't have to sell me on it. 

I'm just looking for you to further explain your resonance issues, etc. I'm assuming by your post above that you just use the DSP to work the issues out. Sometimes a DSP can't do a thing, or the downside is that you might catch some of the bad response via G-EQ, you might also pull down things you don't want to pull down. Did you do anything to mechanically fix your system rather than acoustically correct it via DSP? That's the kind of info I think would be beneficial to this thread.


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## Patrick Bateman (Sep 11, 2006)

bikinpunk said:


> Didn't really answer my question. You kind of just re-said what you've been saying (rta software really helps).
> 
> I'm with you on the RTA and software stuff. I tinker with it a lot. You don't have to sell me on it.
> 
> I'm just looking for you to further explain your resonance issues, etc. I'm assuming by your post above that you just use the DSP to work the issues out. Sometimes a DSP can't do a thing, or the downside is that you might catch some of the bad response via G-EQ, you might also pull down things you don't want to pull down. Did you do anything to mechanically fix your system rather than acoustically correct it via DSP? That's the kind of info I think would be beneficial to this thread.


That's actually a really good point. Back in the 70s there were some blowhards that would argue that you could make one speaker sound like another, by simply applying EQ. That doesn't work in the real words because of things like resonances, power response, distortion, etc...

Mechanical resonances are a complete deal-breaker - they will literally ruin a system. It's heartbreaking when you pour weeks or months into a project, and run into a mechanical issue. No amount of EQ will overcome a mechanical resonance.

In the past six months, I've pesonally had two big mechanical problems with the system:


From May until July of this year, I tried to put a set of Unity horns on my dash. A month after starting the project, I was laid off. (I work at home - almost never use my car at all. Makes it easier to do crazy stuff to it.) Giant speakers on the dash are fine when you don't actually *drive the car*. But if the car is going to be more than a conversation starter, I can't have speakers that big on the dash. And since I figured that I'd have to get a day job I scuttled the project... Here's the thread : http://www.diymobileaudio.com/forum/diy-mobile-audio/60146-creating-perfect-soundstage.html
The other mechanical issue with that project was that the two inch midranges would buzz at moderate volumes. As you noted, not something you can fix with DSP or EQ.
After scuttling the project above, I started a new one. I fixed the issue with the buzzing midranges by "dishing out" the baffle. That clears enough room to prevent the cone from hitting the baffle.
The midrange horns in the new system gave me all kinds of grief. Because they're made of fiberglass, they vibrated a bit. Not a LOT, but enough to create a dip and a peak in the response. It took weeks to figure that out; at first I thought it was a problem with the horn's shape, not it's construction. Anyways, read about that here: Creating a Soundstage with Waveguides and Psychoacoustics - Page 4 - diyAudio

As for resonances in the car itself, and sound deadening, that's all but unnecessary due to a peculiarity with waveguides. I could get into that, but it's off topic.

As for DSP, not using it, just an Audio Control EQT, paid all of $60 for it. All the equipment in the entire system combined costs little more than a DSP EQ.

As the system gets closer to perfection, I'll likely upgrade the amps and source, but right now the focus is on the speakers.


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## SSSnake (Mar 8, 2007)

Directivity control is great but once you get low enough in freq it just isn't practical in a car. At this point room treatments or active solutions must be utilized to provide any meaningful improvements. The problem with room treatments is size becomes an issue at low freqs as well. That leaves one investigating active solutions (such as 3 or more channel midbasses - _similar to Geddes' approach for subs in a home _- and phase corrections in addition to the magnitude corrections). 

I guess that I will have to go ahead and build that carputer so that I can try these things out (was waiting for the MS-8 but I keep finding things that I want to do that I am not sure the MS-8 will do). Does anybody know where I can find a good and cheap Dolby PL II vst plugin?


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## exiton (Sep 13, 2009)

Be sure to check out the Dayton mic EMM-6 as it comes with a unique response graph.


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## Patrick Bateman (Sep 11, 2006)

exiton said:


> Be sure to check out the Dayton mic EMM-6 as it comes with a unique response graph.


Just got a flyer for that! My poor mic has seen so much use, I'm half tempted to buy a second one just to be sure the first one still works alright.


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## ErinH (Feb 14, 2007)

could you use that response graph to build your own cal file? Would you trust it enough to?

Good info on the new Dayton mic:
http://www.hometheatershack.com/for...bration-sound-cards/21050-dayton-emm-6-a.html

I believe this is Jim Harris, who has been making the cal'd Behringer mics.

CSL= Jim Harris' Reading
Dayton = Dayton cal sheet


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## Patrick Bateman (Sep 11, 2006)

bikinpunk said:


> could you use that response graph to build your own cal file? Would you trust it enough to?
> 
> Good info on the new Dayton mic:
> Dayton EMM-6 - Home Theater Systems - Electronics and Forum - HomeTheaterShack
> ...


All the calibration files for the ECM8000 show anomalies in the frequency extremes, basically from 10-30hz and from 15khz and up.

When designing a speaker, I find that the most obnoxious peaks and dips occur in the midrange, right where they're most audible.

And luckily, the ECM8000 measures flat as a board at these frequencies.


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## ErinH (Feb 14, 2007)

My ears are most sensitive to 1khz and it's harmonics. I typically have to EQ 2khz down a few notches, too.

I see your point, but I still think that's a bad way about buying a microphone. If I'm spending money on a mic to setup my system with, I want to make sure it's calibrated. I'm worried about the audio spectrum I can hear, which encompasses the portion at which the ecm8000 has drastically varying response (8k/10k). That's why I had mine calibrated.


FWIW, they are now also calibrating and selling the dayton mics.


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## methodsound (Oct 1, 2009)

If I have a sphere with a midrange in it and I want to place it in the car it will most likely be near at least 2 walls if not a corner or 3 walls. How far away from the corners or walls would it have to be in order to avoid introducing early reflections? Is there an angle of dispersion to watch for? Such as avoid reflections for 150 degrees, or 220 degrees? I am wondering if you can use the sphere concept in a spot of the car that also works well for pathlengths such as the kickpanels. Or would the reflection off the floor, firewall, and underdash introduce the same early reflections that the sphere was eliminating?


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## hypnoz (Sep 29, 2009)

Awesome, thanks!


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## jonatbaylor (Aug 20, 2009)

I am going to read this post like 5 more times and hopefully it sinks in after a week


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## mattgw86 (Sep 28, 2009)

jonatbaylor said:


> I am going to read this post like 5 more times and hopefully it sinks in after a week


Yeah, it's quite a bit to soak in all at once.


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## ellaandlou (Oct 4, 2009)

sounds like good stuff


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## Patrick Bateman (Sep 11, 2006)

mattgw86 said:


> Yeah, it's quite a bit to soak in all at once.


I didn't even read the manual to Arta before using it. It's THAT easy. I first started doing measurements with Speaker Workshop about eight years ago, and that program had a very steep learning curve, since you had to build a jig to measure Thiele Small. Arta is more intuitive.

If you have an hour to burn, that's all it takes to learn it.

I've learned a lot more from measuring speakers than I've learned from audio forums on the internet. It's also symbiotic; now that I know how to measure speakers, it's easier for me to understand the comments of guys like Dr Geddes, Danley, Zaph, Mark K, etc...

Engineering is a series of compromises, and measuring loudspeakers helps you to understand which compromises are important, and which aren't. For instance, ten years ago I was fixated on frequency response and bandwidth, because those are the parameters that we see when we simulate designs with WinISD. Now that I actually measure things in the real world, I'm fixated on distortion, diffraction, the power response, reflections, and power handling.

And most importantly of all, simulations will only get you so far. In the real world, there are a ton of variables which a computer can't tell you. But a microphone can.


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## greenh0rn (Sep 14, 2009)

Patrick, thanks for this thread- undoubtedly a great resource for people like myself! Just wanted to see if you could post some pics of the jig that you use for polar measurements in a car.


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## Eastwood (Oct 24, 2009)

Two thumbs up to Patrick for this post. That's what I call thinking outside the square. 

I'll try this on my system when time permits!


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## WRX/Z28 (Feb 21, 2008)

I'm going to come back and read through this a little more later, I skimmed the first post to get the general idea. 

I recently purchased this:

XTZ | Software • Room Analyzer

Thoughts. 

I haven't even played with it yet, so I'm not sure if it does Gated Measurements or not. 

I'll be re-reading everything later on to clarify it, right now my heads a little foggy.


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## less (Nov 30, 2006)

I guess I'm still not seeing how you are making any corrections to your systems sound as a result of your measurements other that the single mention of using an eq to make up for a response bump... Am I missing something?

I've recently purchased the appropriate equipment and am getting started with making measurements - so its important to me to make quality measurement habits - so I appreciate the information on gating and such... I'd still like to know what you actually do in a case for example, where you find from your polar measurements that you have a hump in certain frequency that doesn't occur at all polar points... ok, its a reflection issue... now what?

As for measuring in an anchoeic chamber... well thats cool if I listen in one =) BTW - I was in one the other day and it was just STRANGE - almost made me feel like I was floating in space with no cues to my surroundings. Anyhow, I've seen the plots for my individual drivers and know they are capable of flat response in that environment... but isn't my goal to have a somewhat flat response given the realistic environment that I"m forced to listen in? I get that reflections are bad and confuse imaging... but can we do anything about them by creative installation techniques or damping? 

Lol - the truth is that I'll have to get a degree in acoustical engineering to understand this deeply enough to really make an impact on my sound... or perhaps just to realize how little control we really have.


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## Patrick Bateman (Sep 11, 2006)

less said:


> I guess I'm still not seeing how you are making any corrections to your systems sound as a result of your measurements other that the single mention of using an eq to make up for a response bump... Am I missing something?
> 
> I've recently purchased the appropriate equipment and am getting started with making measurements - so its important to me to make quality measurement habits - so I appreciate the information on gating and such... I'd still like to know what you actually do in a case for example, where you find from your polar measurements that you have a hump in certain frequency that doesn't occur at all polar points... ok, its a reflection issue... now what?
> 
> ...


Ideally I'd like to see the off-axis response decay smoothly and consistently. In the uppper half of this pic is the response graph of my reference, a set of Summas, which I'm listening to right now.










In a car it's not possible to achieve this kind of performance. There are too many reflections.

Even so, we can still take into account the off-axis response. For years there were only a handful of people who were using RTA to tune their car, and many were doing it by ear. Even with an RTA, it was difficult to agree on what "curve" was best. If you look around these forums, you can see there are a lot of people who are still arguing about what response curve is the best.

Now that it's 2009, we have the kind of tools that go way beyond what you can do with an RTA. An RTA can't gate out the echoes. That's one of the main reasons that people end up using a sloping response when they tune with an RTA.

With gated polar measurements we can get a much better idea of what part of the spectrum is coming from the speakers themselves, while gating out a big chunk of the reflections.

But we can't gate them ALL out, the "room" is too small. That's where polar measurements come in. They can help us see if a tweeter is hot on axis, or if a reflection is appearing.

For instance, I've done *hundreds* of measurements in my car, and I consistently see the response go crazy as I get close to the windows. If I was using an RTA, I might blame the speakers. But it's not the speakers - it's the windows. So polar measurements help me isolate the things I can control (the speakers, the enclosure) and the things I can't (deep nulls from reflections off the windows, the sunroof, a midbass dip that's caused by the cabin's dimensions, etc...)


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## Patrick Bateman (Sep 11, 2006)

WRX/Z28 said:


> I'm going to come back and read through this a little more later, I skimmed the first post to get the general idea.
> 
> I recently purchased this:
> 
> ...


Doesn't look like it can do gated measurements. Appears to be an RTA. Check out Arta - it's shareware, easy to use, and you don't even need to pay for it if you don't need to save anything.

I just do screencaps, works for me.

HolmImpulse is supposed to be good too.


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## jimbno1 (Apr 14, 2008)

Patrick - Thanks for your always well thought out and informative posts. I love that you cut out the bull and get straight to the physics behind the reproduction of sound. Even though it is well above my head I try to keep up as best I can.

I find the idea of multiple midbasses intriguing. Do you plan to mix brands? I was thinking if I can shoe horn in JBL 2118 in kicks some how, then pair with JL IB4 8's or 10's in the front doors. The JBL's are much more efficient and should draw the stage forward if I understand your plan.



One other question why not cut the sub freqs to blend better with the midbass?


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## Toastytoy (Jun 9, 2005)

I find this very interesting, it would be very helpful if you can do a little tutorial of how to use ARTA to get a reading, i am having trouble understanding the software.


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## donkeypunch22 (Nov 5, 2008)

*Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

How does one measure 2nd, 3rd, 4th, 5th, and so on harmonic distortion? I have an RTA, but I'd also like to measure harmonic distortion. Is it possible to DIY? Thanks.


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## Dryseals (Sep 7, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

I use SoundEasy. It's a very accurate tool and will do much more than just HD. I've used it now for about the last four years. Google it. It takes some reading and studying to learn all that it can do. But for what it does and the price, you can't go wrong.


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## donkeypunch22 (Nov 5, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*



Dryseals said:


> I use SoundEasy. It's a very accurate tool and will do much more than just HD. I've used it now for about the last four years. Google it. It takes some reading and studying to learn all that it can do. But for what it does and the price, you can't go wrong.


Do you use the SoundEasy in the car, and take your harmonic dist measurments there? Thanks for the reply!


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## Patrick Bateman (Sep 11, 2006)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

I use Arta, and do distortion measurements in and out of the car. Here's my measurement thread:

http://www.diymobileaudio.com/forum...um/65046-improve-your-sound-quality-80-a.html


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## donkeypunch22 (Nov 5, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

Thanks Patrick. I have read that post, but at the time I thought the post was way over my head. Now, I think I understand like 40%!!

Can you tell me more about how exactly you set up your measurments for the ARTA program? I see you don't sit in the car and take measurments, but why not. Your body is a big obsticle, no? 

Also, I have a laptop and the Behringer ECM8000. I use the mic calibration file that came with TrueRTA (is there a better one, and if so can you put up a link?). I guess I need a preamp to output the test tones from the laptop to my car's audio system, so I'll get the one you recomended.

Any other pit falls or pointers with use of the ARTA program, set up of mic, and interpretation of data?

Thanks Patric!


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## Patrick Bateman (Sep 11, 2006)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*




donkeypunch22 said:


> Thanks Patrick. I have read that post, but at the time I thought the post was way over my head. Now, I think I understand like 40%!!
> 
> Can you tell me more about how exactly you set up your measurments for the ARTA program? I see you don't sit in the car and take measurments, but why not. Your body is a big obsticle, no?
> 
> ...


Well I've been doing measurements for about half a decade, and I still screw them up all the time. So there's a long road ahead of you I'm afraid 

That's the bad news.

The good news is that distortion measurements are probably the second easiest measurements to do, and they're VERY revealing. For instance, over the Summer I spent nearly a month pulling my hair out, trying to figure out why the horns under my dash sounded "grungey." A couple of weeks back I ran a distortion measurement, and there it was, as clear as day. There was a big fat resonance in the passband. That's what I was hearing, but I couldn't put my finger on it. Distortion measurements found it in under three minutes.

My Arta configuration is exactly what's in the manual. You can get the PDF from his site. I have an ECM8000 for measurements, plugged into an AudioBuddy for preamp, which is plugged into the inputs of a 24/96 soundcard in a PCI slot on a PC running XP. I've tried three amplifiers, they all performed the same. Basically I keep upgrading amps because I've found that you need a lot of power to do clean measurements of subs outside. No joke, you can hear me for three blocks. 64 watts is LOUD. Especially since I live in a fairly remote area, where a bird chirping is audible.

I don't use a calibration file for the ECM8000, and I haven't calibrated SPL levels properly. That's one of the reasons I typically hack off the top octave from my plots, because that's where the ECM8000 suffers from some droop. The ECM8000 has some droop at 20hz, but getting a good noise floor at low frequencies is a much bigger issue. Because speakers have low sensitivity at 20hz, you need a ton of power to get a clean measurement at low frequencies. Geddes has alluded to the possibility that HOLMImpulse having higher resolution than everything else out there, but I never got a clear idea why, so I never tried it. It uses an alternate measurement technique than Arta and SoundEasy. Whatever you do, don't use Speaker Workshop, because it's measurements are more difficult and less reliable than Arta. (The program WORKS, it's not defective. It's just difficult to get good measurements quickly.)

As for tips on measuring, here's a few:


Buy "measuring loudspeakers" from Joe D'Appolito. I re-read this thing every few years. About 75% of it makes sense to me now. I've read it at least five times.
Stereophile, of all places, has some good articles on loudspeaker measurement. John Atkinson is the man!
Distortion measurements are really easy. Go easy on the voltage at first - I've blown up tweeters doing distortion measurements.
Learn how to do a gated measurement. I know that 50% of the people that use RTAs have been disappointed with the results. Gated measurements work a lot better, and are basically the standard for measurement for those who do not own anechoic chambers. Getting the right combination of sampling rate and window can be tricky. For instance, if you use the Arta default of 48khz, the low frequency accuracy is terrible. Reducing the sampling rate increase accuracy at low frequencies, at the expense of high frequencies. It's a bit of an art. It's not an issue when you measure outside because the number of reflections is about 80% less. Most of the time I use a sampling frequency of 16khz and a gate of about 5-20ms. Sound travels 13.5 inches in a millisecond, so even a 10ms gate is going to have it's share of reflections, due to the interior. But it's a heck of a lot better than an RTA, where reflections overwhelm the signal itself.
The "power response" is basically an average of the "polar response." The polar response is a measurement of the loudspeaker at various angles. I believe that using the power response to adjust levels and EQ is a lot more sensible than using the frequency response, because the frequency response varies everywhere in the cabin. If you'd like to read more about it, buy this : AES E-Library: The Localized Sound Power Method
If you don't want to spend ten bucks on the article above, Geddes has discussed polar and power measurements for years, particularly on diyaudio.

That was a big post!

I hope I haven't scared anyone away from doing measurements. The truth is that the easiest measurements to do are distortion measurements, and measurements in the midrange, where the microphone is accurate and the noise floor is relatively low.

Despite all the scary talk about soundcard sampling rates and gate windows and noise floors, you can almost ignore all that in the beginning. Those concepts become very important as you measure subwoofers, but in the midrange, they're less of an issue. (The wavelengths are shorter and the noise floor is lower.)

And once you measure a loudspeaker or two, a light bulb is going to go off above your head, and you'll realize that the midrange is where it's at. Despite everyone obsessing over tweeters and subwoofers, the problems are in the midrange. That's the frequency range where you have six drivers overlapping, all kinds of phase issues, and reflections that are beyond obnoxious. At high frequencies you get a lot of absorption and reflection from the cabin, and making bass in a car is ridiculously easy. But the midrange? Ohhhh that's a tricky frequency to correct.


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## gutz (Aug 8, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

Patrick i need to read your last post again and again before it all sink in 
thanks for sharing your knowledge

i wanted to know why youre not using a calibrated ecm8000
doesn't it throw off your all measurments?
here are the variations between different ecm8000 ( from hometheatershack )









it looks like its essential to get it calibrated
thats why i ordered a calibrated one couple of days ago ( i also have a non-calibrated one )
btw its on sale now at cross-spectrum ( black friday ) 
Cross·Spectrum - Calibrated Behringer ECM8000 Microphones for Sale

pretty good deal

btw do you read pm's? i sent you a pm over a week ago but you didn't respond


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## Patrick Bateman (Sep 11, 2006)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*




gutz said:


> Patrick i need to read your last post again and again before it all sink in
> thanks for sharing your knowledge
> 
> i wanted to know why youre not using a calibrated ecm8000
> doesn't it throw off your all measurments?











Check out the curve - from 50hz to 5khz, it's +/- 3dB

The variations in frequency response in a car are on the order of +/- 10dB when you move the mic six inches in any direction.

So which is a bigger problem? A predictable reduction in SPL at low frequencies, or random peaks and dips that vary all over the cabin?

I'm not saying calibration is worthless, but the bigger problem is the cabin itself IMHO.

The poor resolution of the ECM 8000 from 20-40hz *is* a bit annoying, and I think I'll pick up a calibrated mic from PE because of that.

Anyways, I'll take the power response from an uncalibrated mic over the RTA result with a calibrated mic any day.




gutz said:


> here are the variations between different ecm8000 ( from hometheatershack )
> 
> 
> 
> ...


No I'm pretty bad about responding to emails. Since my primary goal in doing measurements is to encourage others to do so, it's a lot easier to get a response from me when posted in-forum.

Sometimes it can take an hour to post a proper response, and if I'm going to take the time, I would prefer to do it in a format where others can benefit also. For instance, when everyone was bashing the tapped horn that lordbaccus built, I spent three or four hours building and measuring a sealed box, plus two hours on simulations, just to make a point. I would never go to that much trouble for an email 

I used to track the "hits" on the images that I post, and some of these threads are being read by enthusiasts from all over the world. This stuff has a fairly large audience.


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## P_4SPL (Nov 7, 2009)

Using an RTA won't yeild the same response results?


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## gutz (Aug 8, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

You definatly encourage me 
ok so i have a couple more questions , some don't regard this thread so apologizes to the op 

1.Can you post a pic of your mic placement? do you set it on a tripod / mic stand? do you use the headrest and put it horizontal?

2.Do you use the ecm8000 wind sock? i saw someone here posted measurments using the wind sock , does it help to get a correct reading , make it worse? or do nothing?

3.How do you take polar measurments? i mean physically how do you move the mic if youre measuring from the listening position? move it towards the passenger's seat?

4.How do you determine the gate length? what is the calculation? 
lets say i have active 3 way in the front 
woofers at 70hz-500hz
mids at 500hz-3.5khz
tweeters at 3.5khz-20khz
the best thing is to measure each set in their appropriate gate , right?

5.After you measure each set , what gate do you use to measure the whole FR?
or do you also set number of gates and take number of measurements for different frequency sections?

6.What is the best way to level matching drivers using a measurment? gated ? pink noise with reflections?

7.Time alignment - do you prefer setting it by ear , measurment or both? if by measurment
what is the best way to do it correctly?

Thats it for now i guess , sorry if i ruined this thread 
you really need to open a thread with all the info from different threads 
there is a lot of info getting lost between the posts..

thanks again patrick


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## Oliver (Jun 25, 2007)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*



gutz said:


> lets say i have active 3 way in the front
> woofers at 70hz-500hz
> mids at 500hz-3.5khz
> tweeters at 3.5khz-20khz


U might want to try your mid-woofer from 70Hz to 200-250Hz.

run your subwoofer from 60Hz and down

Try your midranges from 200Hz or so and up to as high as they will play before you add in the tweeter to cover the rest of the frequencies


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## gutz (Aug 8, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*

my rs100's aren't in a good placement and appropriate enclosure atm so it doesn't sound as good down low
actually this is what i sent pm to patrick about ( ill copy some of my pm here )
i replaced yesterday my tweeters to tangband ceramic ,some of the pics including my old tweeters so just ignore them

midrange and tweeters ( ht25 ) sits like this :

























the dash pod is damped with ss damplifier pro :









i know the rs100 needs something like 1.4l to really get low but i prefer to avoid building kicks
i haven't done any t/a / eq yet and im using just gains and crossover points and im still messing with it ( i have a car-pc so there are alot of options here  )

distance from rs100's phase plug to windshield is ~3" 

atm the crossover settings are :
woofers - 70hz @ 12db / 500hz @ 12db
midrange - 500hz @ 12db / 3500 @ 12db 
tweeters - 3500 @ 12db and above

im planning on building a fibreglass enclosue on the dash for the mids and tweeters

here are some possibilites i tried :
1. tweeters and mids a little off-axis directed at the center of the vehicle 









2. mid off-axis directed at the windshield









*of course the tweeter is there just to support the angle of the mid , it wont be like that hehe

3. mid off-axis towards the windshield , tweeter off-axis towards the center of the vehicle









what do you think will be the best placement and will give me the best imaging / dynamics to one-seater configuration ? 
maybe something i didn't think about
currently im leaning towards number 3


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## Dryseals (Sep 7, 2008)

*Re: Measuring 2nd, 3rd, 4th, and 5th harmonic distortion...*



donkeypunch22 said:


> Do you use the SoundEasy in the car, and take your harmonic dist measurments there? Thanks for the reply!


I'll measure the speaker first for a reference point. It depends on how critical you want to get for in car readings. Building a small enclosure that's tuned for the flatest response for the speaker and then stick it in the car at different locations.
Before hurricane Ike I had a small box that I used with a Tangband W5-704D for a mid woofer and a Seas 27TBFCG for the tweeter. Stick that in the car and get a reference point for how the car interior was going to respond, windows up and windows down.

Using the information from a reference test, you can see where the good and bad spots are going to be. Same goes for bass response, I used a Dayton RSS210HF-4 in a small box, you can see the cabin gain very clearly.

I'm 52 and been at this since I was around ten years old. I still have all my test equipment gathered form years past, it just collects dust now. SoundEasy does everything I need and then some. The hurricane wiped out alot of my test setup and I haven't had time to rebuild. But the key here is getting a reference point.

If you're shooting for loud, then all you need is a db meter, but that won't tell you how bad you're taxing the speaker. The vehicle cabin will introduce all kinds of effects on you measurements, you are going to have all kinds of dips and peaks.

I don't do this as a pro, just a hobby I really enjoy. The cost of the SoundEasy software is less than what most folks will spend for a set of speakers. It's a steep learning curve for some but there are a lot of folks willing to help out. If you want to see an example of what some folks do with it, check out Zaphaudio, tons of measurements and he does a great job of explaining the plus and minus of each. Just be aware, that he doesn't fall into the typical BS of the sales pitch, just good clean sound.


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## Patrick Bateman (Sep 11, 2006)

P_4SPL said:


> Using an RTA won't yeild the same response results?


Sound travels at 13.5 inches in a millisecond - which means that in a tenth of a second, there are hundreds of reflections "contaminating" the RTA curve. When the wavelength of sound exceeds the dimensions of what contains it, directivity no longer exists.







That's why you can put a big hunk of plastic in front of a tweeter, without screwing up the response. I know some people actually remove the phase plug but they shouldn't. As long as the gap between the diaphragm and the reflector is a fraction of a wavelength, you're fine. It's counter intuitive, because just looking at this picture, it *seems* like a bad idea.

It's the same thing in a car. As the distance between the speaker and reflective surfaces becomes a fraction of a wavelength, the sound waves lose directivity, and the problem with reflections is reduced.

You can do the math on your own car. My car's cabin is about 48" wide by 96" deep. (13500inches per second / 48") = 281hz.







This is the polar and the power response of an eight inch woofer in my car. See how the polar curves "tighten up" at 150hz, and also at 300hz? And see how they're all crazy between those two points? And see how they "tighten up" again at 80hz, and at every frequency below it?

That's the length, width, and height of the cabin at work. The response "tightens up" because the dimensions of the cabin are constraining directivity _but only in one dimension_. Once directivity is constrained in all three dimensions, the reflections decay away, and then the polar response and the power response are the same thing. (See 80hz and down.)

Above 2000hz, you'll also note that the polar and the power response are virtually identical. (That's A Good Thing.) That's because the woofer is beaming. In home audio a lot of people argue that wide response is a good thing. I think this curve demonstrates that in car audio, the last thing you want is wide directivity. That's why the best known cars in history use some form of directivity control. (Clark with horn loaded compression drivers, Biggs with waveguides and diffraction control on the midrange.)

Anyways, real time analyzers can't capture this amount of detail, because their measurement window is much longer. I use a window of 5-20ms, which is still longer than I'd like.


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## Dryseals (Sep 7, 2008)

Patrick Bateman said:


> It's the same thing in a car. As the distance between the speaker and reflective surfaces becomes a fraction of a wavelength, the sound waves lose directivity, and the problem with reflections is *reduced*.




Reduced or masked? take an 80hz sound, it takes 125ms to complete a cycle or 1687.5 of distance to complete one wave. So in your 98" cabin, it'll reflect back and forth 17 times before a cycle is complete. Very hard to pin point source. 2000hz on the other hand will complete in 6.5 inches. So sitting 5 feet away it gives it almost ten complete cycles before it reaches your ears, very easy to pin point.


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## Hernan (Jul 9, 2006)

Thanks Patrick for sharing all your efforts. Your posts helps many of us thinking outside the envelope.

One question. How usefull is doing far field measurements of individual speakers? 
I found that measuring the speaker on axis and at close (one feet aprox), usually ends with a very good FR. 
I think that lot of reflections are "masked?" this way.
If you think it could add some knowledge, please comment about this.
Thanks!


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## gutz (Aug 8, 2008)

Patrick ive just noticed the admins have merged donkeypunch22's thread with this
i don't know if you saw them but ive asked some questions 
can you please respond to them?


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## Dryseals (Sep 7, 2008)

Hernan said:


> Thanks Patrick for sharing all your efforts. Your posts helps many of us thinking outside the envelope.
> 
> One question. How usefull is doing far field measurements of individual speakers?
> I found that measuring the speaker on axis and at close (one feet aprox), usually ends with a very good FR.
> ...


If you have some spare time, this is a very good article. It'll give you a better feel for why the industry sticks to near field, far field tends to toss in a lot of curves.


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## Nero (May 3, 2009)

Thank you for the the article.


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## Hernan (Jul 9, 2006)

Nero said:


> Thank you for the the article.


+1. Thanks!


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## donkeypunch22 (Nov 5, 2008)

Thanks Patrick


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## tigwelder (Nov 30, 2009)

thank you for your very informative post Patrick


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## SNIPR (Dec 4, 2009)

THX..!


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## gutz (Aug 8, 2008)

patrick , any response to my questions? :\


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## cobraa (Dec 4, 2009)

Wow this forum has so much information.


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## DaPhenom07 (Dec 12, 2009)

im not too familiar with the technologies there are out there that are accessable to me, but it really does seem like you know your stuff patrick baetman. i'd like to hear more about what you were saying about the arta program on a PC. im really into car audio, but im 17 and dont really have much to start out with. please send your feedback. i'd like some input from you on some projects i have for my 1999 Honda civic.


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## namboy27 (Oct 16, 2009)

seems easy enough. =/ lol man i need to learn more vocabulary


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## vactor (Oct 27, 2005)

i got $80, looking for more PB goodness here ...


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## yischrax (Nov 22, 2009)

I just wanted to say thank you I just bought a Rockford fosgate threesixty.2 and I know to have a chance of using it to half it's ability I needed to do something of this form. My problem is I didn't have a clue on what program to use only thing I knew of was truerta and didn't know what one to buy. I am going to fallow you and use the same program. I am just guessing I will have some time getting to know the program before I feel comfortable but I feel I can atleast in my best way to explain it drive a car with the blind fold off my eyes now. With reading this thread it was like taking drivers training. There is a lot of trial and error I am sure but atleast I am using one sense to suport the other being able to see what I am hearing now. I was unsure and still unsure on what mic and preamplifier to get if you could choose anything to work best setting the 360.2 what would you get for 150.00 for preamplifier and mic seeing as software is free I know you made a sugestion bit giving a higher price ability if it will make it any easier or more acurate for me.I need to tune the up to 31 band eq and do time alignment "I assume this program will tune time alignemnt also" thanks and I would like to give you props and shake your hand for helping me make my system 10x what I knew it could be. I too curently feel like you use to knowing what your hearing that you don't like but not knowing how to fix it with just my ear and with me being so impatient doesn't help.


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## Patrick Bateman (Sep 11, 2006)

yischrax said:


> I just wanted to say thank you I just bought a Rockford fosgate threesixty.2 and I know to have a chance of using it to half it's ability I needed to do something of this form. My problem is I didn't have a clue on what program to use only thing I knew of was truerta and didn't know what one to buy. I am going to fallow you and use the same program. I am just guessing I will have some time getting to know the program before I feel comfortable but I feel I can atleast in my best way to explain it drive a car with the blind fold off my eyes now. With reading this thread it was like taking drivers training. There is a lot of trial and error I am sure but atleast I am using one sense to suport the other being able to see what I am hearing now. I was unsure and still unsure on what mic and preamplifier to get if you could choose anything to work best setting the 360.2 what would you get for 150.00 for preamplifier and mic seeing as software is free I know you made a sugestion bit giving a higher price ability if it will make it any easier or more acurate for me.I need to tune the up to 31 band eq and do time alignment "I assume this program will tune time alignemnt also" thanks and I would like to give you props and shake your hand for helping me make my system 10x what I knew it could be. I too curently feel like you use to knowing what your hearing that you don't like but not knowing how to fix it with just my ear and with me being so impatient doesn't help.


You can get an audio buddy preamp off Ebay for about $50, and the Behringer or Dayton mics are about $50. Buy some cables and you're set for under $150.

As for the 360.2, I don't know the first thing about it


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## kulic (Sep 27, 2008)

AUr6 said:


> excellent thoughts here. I've got to agree that i think the biggest goal here with this type of testing as it seems he stated is to determine whether the driver or the environment is causing any distortion in the tuning of the desired sound stage.
> 
> As far as anechoic chambers go, i've been in one of the big ones where they can fit whole aircraft, and the only way you can talk to someone even close to you is to look directly at them when you speak. all reflections you're used to hearing are completely absorbed/dispersed by the walls/floor/ceiling. It's definitely unlike anything in nature... almost TOO quiet!



Try a wet rainforest on an extremely foggy day. The moss clinging to the trees behaves similarly to anechoic material, and there are similar issues with sound transference. Two points: first point is I don't quite believe that no one can hear you in an anechoic chamber unless directionally related to the speaker. This would rule out transverse conduction of sound, which happens. It may be very faint, which would seem weird (as foggy rainforest seems spooky) but it's there for you to hear. The second point is that the anechoic experience is not 'unnatural', in the sense of not happening in nature. It does happen in nature. You've just been in the city too long, like all of us. As for ideal listening environment, that of course depends on the desired effect. Different environments have different effects; it's like asking for the ideal musical instrument, crunchy guitar or Gregorian chant vocalist? It's a good discussion though.

One favorite is when the echoic properties are few and simple and not muddled: for example, an empty and humid basement room with a concrete floor. Ideal listening environment (my subjective experience and opinion) for string quartet late Beethoven. Why? I don't know. The echo/delay adds a corpus aura to each note, and interacts nicely with all the natural/composed induced (note relations) beats. The key was having pretty much a uniform echoic surface (the clean smooth concrete floor) that reflected high frequencies transparently along with the low.

I've had great auditions in relatively anechoic environments also (the aforementioned rain-forests, acoustic guitars, and psils. The guitar is much quieter of course, but then everything is quieter, and the point is that precisely, any slight ambient sounds can become part of the (remins Cage) performance. 

How this relates to auto audio I have no idea, but I've heard that it's a challenging environment to work with.


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## kulic (Sep 27, 2008)

Edit: later started to question my own statements about transverse propagation in atmosphere. Wrong. 

The other point though, I still think is right. There are anechoic materials in nature, and there are anechoic environments. An even better candidate is mountaintop peak with lichen or moss ground cover. Very spooky/anechoic. And yes, I believe one can't hear someone who is talking in an oblique direction to the listener now. I retract that.


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## terranova (Apr 11, 2010)

good read thank you


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## 94VG30DE (Nov 28, 2007)

Instead of a mic preamp, I have a couple Mackie 1202-VLZs sitting around. That would accomplish essentially the same thing correct? Provides phantom power, outputs to TS/TRS/RCA/whatever I want to put into my sound card. Would that create any issues for me?


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## schmiddr2 (Aug 10, 2009)

If I can get the equipment together I would love to try Polar measurements.

It seems this would be wise to use, during the building stage, to determine speaker placement/direction. For direction, using different mounting ring angles, then retest for reflections. With all the information we can gather using mics and computers, it seems that we should be more worried about location/angle of the speaker rather than the DSP and RTA of a fixed place speaker. Any more info on this?


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## Patrick Bateman (Sep 11, 2006)

94VG30DE said:


> Instead of a mic preamp, I have a couple Mackie 1202-VLZs sitting around. That would accomplish essentially the same thing correct? Provides phantom power, outputs to TS/TRS/RCA/whatever I want to put into my sound card. Would that create any issues for me?


Yep! Just be sure there's no processing in the device. For instance, it took me months to figure out why a bunch of my subwoofer measurements were misbehaving. Turned out there was a high-pass filter in the Arta software, to protect users from blowing out speakers under measurement.


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## Patrick Bateman (Sep 11, 2006)

Does anyone know if running my microphone cables for fifty feet would cause a problem?

At the moment I have my measurement rig in the garage, and I'm thinking about moving it to my living room so that I can measure my subs indoors.

Ideally I should use a laptop, but I don't want to blow $400 on something I only use a couple of times a month.

According to what I've read, you can run mic cables as far as 200ft, but it seems to be dependent on the preamp.


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## ST7677 (Jun 20, 2009)

1. Can you describe where and how do your position your mic? I am putting it between the backrest and the head rest, pointing, in front, 30 deg right and 30 deg left and then averaging.

2. How do you determine the Sampling frequency, sequence length and the gate duration? Please provide a simple calculation? 
I have 2 way passive components in front and a subwoofer

3. After measure each set (front Right, front left, and Sub), how to measure the whole FR together to see overall response – what settings?

4. In ARTA I am using single gated for measuring components and double gated measurement for subwoofer, is this correct? With window gate is set at 10ms – 100ms.

5. What type of noise to use for Component and subwoofer measurement – Sweep / Periodic noise / MLS?

I notice that once I EQ everything flat, and am satisfied, later after few hours when I remeasure it, I find peaks and dips appear from no where (with all the settings remaining same)! Any idea why?

Many thanks in advance for your guidance.


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## backwoods (Feb 22, 2006)

don't know if this site has been mentioned, but tons if free software is available.


Steve Ekblad's Free Audio Software and On-Line Enclosure Design


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