# The RTA thread (Use. Not how to build one)



## ErinH (Feb 14, 2007)

Been doing some reading on TrueRTA and RTA measurements in general this morning, just looking for tips here and there. Found some that were directly related to car audio I thought I’d share here. 


Google books. “The Master Handbook of Acoustics”. RTA stuff on page 501. EXCELLENT read for other information, though. EXCELLENT.
The master handbook of acoustics - Google Books




A post about trueRTA’s use in car:
TrueAudio's TrueRTA Software (take II)


above said:


> but the advantage of the slow sine wave sweep is that you can also quickly identify problem areas caused by distortion, either from the drivers or from the environment itself (e.g. vibrating panels, etc.). Apart from being audible in most instances, this distortion shows up on the RTA as any response above the fundamental frequency (during this test we quickly identified one source of distortion - loose protective covers over the 4" drivers on the dash).





Another…


avsforum said:


> When setting up the audio system in a car, you should EQ each side of the car separately (provided your EQ has separate adjustments for right and left and you are trying to get the car to sound good from both the driver and passenger side). After the initial setup of each channel, check both together (stereo). Do not boost any frequencies when adjusting both channels together, only cut frequencies. *Try using both correlated and uncorrelated pink noise when EQing each channel separately and together.* Set the EQ at an average between the 2. Do a lot of listening to well recorded audio tracks between EQing (like something from Sheffield Labs). And don't try to go for a flat (straight line) curve. Just get rid of peeks and dips. To do this properly, it will take a lot of time over the course of a week or two, depending on how flexible your processors are. ...






Beyond that, I’d like to talk a bit more about this. Setting up an RTA is easy… it’s using it and working with the results that can be tricky. I’ve used TrueRTA, SmaartLive, and aRTA so far. I’m going to get a copy of Room EQ Wizard when I get home.

What I typically do, for ease, is just use pink noise and set it to a reasonable listening volume. I play back the pink noise and then get my response. For cars that have L/R gain and EQ I’ll pan the pink noise to the left, take a measurement, then pan right and take measurements. 
For myself, I work live. Meaning I work the left side EQ to get a nominal response, then I save that response in the window. I then pan right and, while keeping the left side response up, I’ll work the right side EQ until I can get fairly matched to the left side. This helps me get things pretty level. Then I pan back to the center and take a reading with the summed response. I knock down peaks and call it a day. 

I’ve got a few questions/issues that some of you guys may be able to help me with (please leave your guesses out), especially you, Chad and Andy W.

#1. One of the above quotes/links says to use uncorrelated for L/R measuring. Then use correlated for overall measuring. I’m not 100% so I’m curious if me panning to the right or left is the same as playing uncorrelated and panning left or right to essentially shut off one of the sides. 
Or, in this case, would you want to play uncorrelated and then shut off one of the sides either via RCA into the processor, or some other means (ie: DSP control, manually disconnect speakers on that side at amp, etc).

#2. Do you ‘gate’ your responses depending on what speakers you’re allowing to play? I know I’ve read in the past, and then again today that the impulse response should be used to gate your FR response. What are the consequences of not doing this for our purpose? 
Personally, I’ve not really noticed huge differences when doing my own gating (I just throw darts and let the pink noise rip for a slight second for tweeters, and let it play a bit longer for the lower bandpass drivers). I know it’s not scientific, but doing my own gating and then just letting the pink noise play… I never really noticed a huge difference. I believe the gating is used primarily to narrow your window so that you’re not recording reflections. Thing I’m wondering is, wouldn’t you want to record reflections in our case of FR measuring? We’re (the car audio dude) isn’t measuring FR for the purpose of speaker measuring… we’re measuring acoustic response. So, is gating as important, still? I’m really unsure if I’m understanding all of that 100%.

*note, I’m leaving out the issue of mic placement for now on purpose*

That’s all for now…


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## matdotcom2000 (Aug 16, 2005)

good thread subscribed


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## ErinH (Feb 14, 2007)

The master handbook of acoustics - Google Books



Page 516 said:


> Figure 26-9 shows the frequency response for a measurement position that is roughly 3 meters from the loudspeaker. *This measurement has many reflections in it, and a longer gate time has been selected, which is similar to that of the integration time of the human ear-brain system.*
> 
> This measurement show the effect of multiple room reflections in the frequency response calculation. This would be a typical frequency response for far-field listening in an acoustically untreated room. The effects of comb filtering are obviously present, but much less idealized than they are in the preceding response graph. Multiple reflections causing these sharp dips and peaks can have a negative effect on stereo imagery. The addition of absorbers to surfaces causing reflections will tend to smooth this curve.
> 
> Compared to the other two measurements, the ‘in-room’ response graph shown in Fig. 26-9 is of little value in an environment with multiple reflections. A more meaningful response graph for this type of condition can be achieved in ETF by further post processing the results to yield a fractional octave response *(such as 1/3 octave) that more accurately reflects how we would subjectively perceive this frequency.*


Cliffs: In an environment with reflections, use 1/3 octave without gating as that’s what you hear. IOW, screw gating. At least, that's how I take it.


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## braves6117 (Feb 13, 2008)

Great Information! Can tell you how many things I've learned from you BP!

Thanks again, will have some reading to do tonight


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## M-Dub (Nov 29, 2006)

I do the whole left/right pink noise thing like everybody else, but one thing I started doing that I've never read about is:

- Sit in driver seat 
- play a known problem song, 
- hold mic in hand, move it around, switch hands
- eq to cut problem spikes in song

Begin the flames!


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## ErinH (Feb 14, 2007)

Keep in mind, I'm asking, too. Like I said, setting up an RTA is easy. It's learning how to use it properly.


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## ErinH (Feb 14, 2007)

Megalo said:


> I do the whole left/right pink noise thing like everybody else, but one thing I started doing that I've never read about is:
> 
> - Sit in driver seat
> - play a known problem song,
> ...


what flames? I do that myself. 

I play songs, listen for an issue, look at the RTA response and see if I can spot where the issue is. Then I go to work.


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## M-Dub (Nov 29, 2006)

bikinpunk said:


> what flames? I do that myself.
> I play songs, listen for an issue, look at the RTA response and see if I can spot where the issue is. Then I go to work.


Well from my reading, most use a mic stand and stay outside of the car. My personal experience showed this is not optimal. 

Some use pink noise and tune flat, some tune _"+9dB from 20-60Hz, smooth transition from 60 to 160. Flat from 160-about 3K, gentle slope downwards from there (adjust this slope and the amount of bass for personal preference)". _

In the end, there were always problem areas in certain songs. So I just started tuning to the worst problem song I know of "MGMT - Kids". I watch the frequency response jump up and down and I get everything to LOOK balanced. Things begin to also sound balanced at this point. 
Then I use pink noise to measure the left frequency response, then tune the right to match the left.

Oh yea, I leave my engine on and even crank my AC. I'm a freakin SQ rebel.


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## ErinH (Feb 14, 2007)

I tune outside the car. then I tune inside. pretty simple. 


the curve your describing is probably preference. I wouldn't be surprised to see it follow the equal loudness curve to some degree, either.


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## matdotcom2000 (Aug 16, 2005)

Well my truck sound pretty awsome so I am going to share my tuning ways. I start with the rta out side of the truck with the rta and use it for crossover settings 1st and to eq out peaks. When I do the crossover settings I do the 1 whole side and use different crossover point within drivers frequency range to get out out dips also trying slopes, I dont too much really worry about peaks yet unless it is at a crossover point and I let the driver that has the flattest frequency take it. Once I have finished with the crossover settings then I use the rta to get out the peaks per driver I dont eq everything flat because that can sound extremely boring depending on the drivers. So i keep the little peaks that are around i guess 3-5 db? and tune the extreme peaks down to those points depending on if those are close to that range also I try to get each side to look a like so one side does not have an advantage in a certain frequency range. So basically I still have peaks but they arent crazy. Then I put in my favorite cd and balance each set of drivers to the center mainly (songs with a center stage) I am maily leveling the left side because it can have a tendensy to be louder. Also when I rta I use the slow setting not the peak hold because sometime the peaks can becaused by panels rattling I can see it on the rta (no reason to eq those out).

What you think bp?


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## ibanzil (Jun 29, 2008)

I use a rendition of equal loudness. Anytime I need to tune I borrow an audio control RTA from my fave shop. They havnt used it in years but I might need to get my own b/c they are getting a new mic to hold SPL contests.

My most neutral sounding setup took the most time, its for competitions. That one is setup for the seat so far back I cant even reach the pedals. Using the A.control RTA, I looked at my graphs from back when I used the alpine Imprint and the imprint was pretty dead on with the plot.


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## matdotcom2000 (Aug 16, 2005)

I used the AC rta and I think it was pretty badass. I have not tried to rta with the computer since but i will attempt it again to see if there is a huge difference.


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## Catman (Mar 18, 2008)

I always tune while sitting in the drivers seat. You will be surprised how much you will absorb and block (especially me @ 275#) In a small car it is not unheard of for 2 occupants to reduce the internal volume of the passenger compartment by 20% or more.

>^..^<


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## KP (Nov 13, 2005)

#1 The mic must be moving at all times. 

#2 Look at the RTA, make a few notes of what MIGHT need adjustment. 

#3 Remove the RTA and sit in the car. 

#4 Make said adjustment while actually listening to the music. Is it better? Worse?

#5 Repeat as needed.

The key is learning how to understand what an RTA can and cannot tell you. What the RTA and your ear hear is two different things. You must have the correct equipment to make the changes. Todays processors are not very suited to truely dial a system in. This includes my 'beloved' DSP6, Bit-one, F1, H701, etc. They are great storage devices though. 

Unless you have sat in a car with some old school 31 band SLIDER EQ's in your lap you would not understand.

Kirk


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## donkeypunch22 (Nov 5, 2008)

AcuraTLSQ said:


> #1 The mic must be moving at all times.
> 
> #2 Look at the RTA, make a few notes of what MIGHT need adjustment.
> 
> ...


When measuring with an RTA, why do you feel "the mic must be moving at all times"? Just curious.


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## less (Nov 30, 2006)

Bikin said it so well with his comment: assembling an RTA system is easy - interpretting and applying the results is the tricky part! I'm in my first two days of actual testing - so as a complete newb. The first changes I made using the initial RTA results did improve things somewhat - but its obviously both an art and a science to translate these findings into processor settings to yield good results in the car environment!

In poking around the web today, I found yet another software program, but this one has a page offering fairly simple instructions on how to use it to achieve various types of test results. Looks like it could apply to other software too - so here it is: YMEC info It may even be decent software too and has a decent array of features for a price of around $25.

Hope someone finds this useful. Oh - an I too am curious why the mic should be moving at all times... very counter-intuitive since my head isn't moving at all times when listening.


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## goodstuff (Jan 9, 2008)

Ok. I'd like to reask the question, why does the mic need to be moving all the time?
Seems like it would add wind noise, and as stated by less, our heads are not moving at all times.


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## ErinH (Feb 14, 2007)

you can ask Andy W on his advice as I beleive he's touched on it occassionally.

The one real problem with taking measurements from one spot is the fact that you may have peaks/dips from the placement of the mic itself and therefore be getting invalid data (ie: headrest may absorb things you would hear, but the proximity of the mic to the headrest may give you data that you may use falsely). 

IMO, one location is enough. The only time I move the mic is when I want to see if a peak or dip is attributed only to that specific mic location. When I move the mic, it's typically only a couple of inches. If the results look the same or very similar, I move the mic back and continue. If it looks different then I take a few to think of what the issue is. Then I either move the mic to another location or back to the original and continue.

The ultimate point is that the RTA is a tool, but not a replacement. I tell people all the time, one of the biggest uses of the RTA setup is to use it in CONJUCTION with your ears. Sit in the car, listen. When you hear a problem spot but are not sure what it's fundamental or harmonics are, use the RTA to help you. Sometimes this is tough, sometimes it's easy. 
I sat in the car with another guy who came to my GTG last weekend and we heard a pitchy spot that shouldn't have been there. A few minutes with the RTA and we narrowed the trouble spot down to 1.6k-2khz. Did some EQ work and remedied the problem. 

In place of your ears, the rta is a good way to level match and (obviously) find trouble spots. 
It can also be used to find when things are in/out of phase. If the flipping of phase of a driver results in a summed response (particular crossover points have a higher response level), whereas out of phase drivers result in a suckout (drop) in the response at that area. Very good for this.

Just keep in mind, again, the RTA is not your ears. It's easy for me to forget to sit in the car intermittently while using the RTA. It's amazing how many ways you can totally wreck progress when focusing too much on graphs. My advice is to run RTA for a bit to help you get some issues more well defined, tune by ear, listen, RTA again (either while listening to problems or just trying to fix problems you see on the screen).

I also suggest looking at the equal loudness curve and getting a general curve of that instead of trying to RTA 'flat'. This has worked best for me, and when I RTA'd about 5 cars this weekend, I found that all of them have a curve that is similar. Funny how we tune to what is considered how we humans hear. 
Yes, you've seen me talk about this before. You'll continue to as well. This is what I call 'beating it in your head'. At least give it a shot.

One final thing: I can get any curve I want any number of ways. They may not all sound good. In fact, they may all sound like complete butt. Use your ears. Don't forget... USE YOUR FRIGGIN' EARS!


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## jsun_g (Jun 12, 2008)

I had a shop manager tune a system of mine for flat RTA with a 30-band Alesis EQ a few years ago. Absolutely hated the sound...all treble and no bass. I was dead-set against using an RTA ever again, until a year ago. With some advice from a couple guys on here, i got TrueRTA and a set of earbud mics. I can say that the earbud mics really showed me via my laptop the difference in response my right/left ears were hearing as I sat in the driver's seat. So the approach is helpful in separate L/R EQ, if your system has that capability. Unfortunately with RTA software, it is easy to over-tweak and end up with a result that just doesn't sound right, when all you really needed to do is pinpoint what your ears were telling you is wrong and fix that.


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## goodstuff (Jan 9, 2008)

bikinpunk said:


> you can ask Andy W on his advice as I beleive he's touched on it occassionally.
> 
> The one real problem with taking measurements from one spot is the fact that you may have peaks/dips from the placement of the mic itself and therefore be getting invalid data (ie: headrest may absorb things you would hear, but the proximity of the mic to the headrest may give you data that you may use falsely).
> 
> ...


Yeah I'm not really looking for flat, Hell I just got the thing going so I don't even have an opinion on what I want. I just wanted to be able to see problem areas easier and fix any big peaks or dips then listen and see if it will improve things. 



jsun_g said:


> I had a shop manager tune a system of mine for flat RTA with a 30-band Alesis EQ a few years ago. Absolutely hated the sound...all treble and no bass. I was dead-set against using an RTA ever again, until a year ago. With some advice from a couple guys on here, i got TrueRTA and a set of earbud mics. I can say that the earbud mics really showed me via my laptop the difference in response my right/left ears were hearing as I sat in the driver's seat. So the approach is helpful in separate L/R EQ, if your system has that capability. Unfortunately with RTA software, it is easy to over-tweak and end up with a result that just doesn't sound right, *when all you really needed to do is pinpoint what your ears were telling you is wrong and fix that*.


This is what I am trying to do.


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## goodstuff (Jan 9, 2008)

Sooo. Last night I almost commited myself. I've been trying to get the rta going for years now...I had it working fine upstairs. I carefully moved the computer and everything out to the garage, and got all set to take a measurement. ****ING CPU WOULD NOT LOAD FUXING WINDOWS AT ALL!!!! Here's a shot of me reloading windows after I violently removed the hard drive, smashed the **** out of it with a hammer and slammed another drive in there. **** X100000000!


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## T3mpest (Dec 25, 2005)

donkeypunch22 said:


> When measuring with an RTA, why do you feel "the mic must be moving at all times"? Just curious.


An omnidirectional mic is very different than your head with two ears attached to it. Play tones and move your head from side to side. On certain tones you'll find you'll get large differences by just moving your head slightly. If you dont' keep moving the mic you don't get a spacial average of where your ears actually are when your sittign down nor the spots they can and will occupy as your driving. Just a inch or two move of the mic can make difference of several decibels at some frequencies, if you don't average it out, your basically eqing in the dark as you can't be quite as sure if what your measuring is valid or not.

Whether or not you need an equal loudness curve depends alot on your listening level. For more polite volumes you need some extra top and bottom end to get things to sound right. If you car can reach realistic volume levels and you tend to listen closer to that point, you'll probably find a fairly flat curve will sound better.

Also as others have said, dont' try and shoot for a super flat curve anyway. IMO, the most important thing for good sound is getting your left and right to be similar in frequency response. It's alot easier to hear things pull to the left or right than it is to hear a +2db boost at 400-440hz lol. Slightly colored sound isnt' bad as long as both sides are similar. If one side is way up and the other is equally way down, the sum will be flat, but it would sound like poo.


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## ErinH (Feb 14, 2007)

T3mpest said:


> Whether or not you need an equal loudness curve depends alot on your listening level. For more polite volumes you need some extra top and bottom end to get things to sound right.


Did you look at what the equal loudness curve actually is? 
You just defined it.


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## otis857 (Feb 12, 2008)

Im in (for future reference)


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## ANT (Oct 15, 2005)

Old thread but worth the bump.

ANT


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## ErinH (Feb 14, 2007)

yea... but I don't suggest tuning to the ELC any longer. 

old thread. my ideas and methods have changed a bit.


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## bongbut (May 15, 2012)

bikinpunk said:


> yea... but I don't suggest tuning to the ELC any longer.
> 
> old thread. my ideas and methods have changed a bit.


could you share a little bit for us ?  what changed past year.


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## Wy2quiet (Jun 29, 2010)

Yeah wow I have been RTA'ing for the first time ever with a 64 band parametric per speaker (Car PC). 

I have been trying to achieve a somewhat flat and identical curve for 1/3 octaves (I tried using 1/12 or 1/24 octaves but its a complete mess in a car) and it just doesn't sound right even though it is flatter.


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