# Measuring Car Frequency Response



## Sonnie (Apr 11, 2006)

Measuring home theater frequency response and correcting for it seems rather simple compared to the same for car. I generally place my home mic at my ear, nose, top of head, etc... and in most all cases the response is very similar within a foot of my head, varying only a db or two if any. I am not saying this is the exact case for all home theaters, but it has been for all of the ones I have been involved in measuring... from the main listening position. 

In a vehicle, from one ear to the next there are drastic differences... mainly because the left ear is next to the left window and the right ear is open to the remainder of the car. The left ear is getting more reflections from the window that the right ear does not get. Or should I say the left ear is getting the reflections much sooner... and varying reflections that the right ear may not get. Whatever the cause, it is drastically different between the two.

I see a lot of measurements taken from the center of the car, which to me seems to be fruitless, since that particular placement is vastly different in most cases than what we are hearing at our ears. You would be correcting for the center of the car... are you going to ride down the road with your head leaning over in center of the car? I see recommendations in manuals for the people to exit the car before the measurements are taken, which again seems useless since we listen in the car and our bodies effect the sound. It seems to reason that we would measure from where our ears are located... the mic tip at our ear opening. Of course I have no scientific proof of the accuracy level, but it seems logical that it would be more accurate than what I see otherwise. At least we should measure from where our head is located... and preferably while we are in the car.

Green = Left Ear
Red = Right Ear
Purple = Nose

Three averaged measurements for each mic placement:










Here is all nine measurements averaged:










I probably should have left the nose out. My initial thought was it would be the average of the two, but thinking on it, it would not be... and is not, as we can see.

Are we hearing the average between the two ears... is this how our brain processes varying levels of the same frequency? Assuming so... we would then correct for this average.


I know some might suggest this is overkill to try to be so precise... just measure one location and be done with it. If that is not going to be accurate, and I cannot see how it would be, why spend $300, $500... in some cases $1,000 for car equalizers/processors to do the equalization for us... and it not be right? What have we accomplished?

With car equalization being so expensive, we need to figure out a way to get a Behringer FD in the car. onder:


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## FLAudioGuy (Sep 21, 2011)

I think what you have seen are holdovers from the car audio competition circuits. dB Drag Racing and IASCA being probably the most popular in their heyday. Listening tests were done, obviously with someone in the vehicle whereas SPL tests were done with no one in the auto. In the early days of the competitions they would place a measurement mic (almost universally using an AudioSource 1/3 Octave RTA, later moving to LinearX PCRTA) in the center of the car. At that time, they were concerned with an average SQ for all listeners. As the years went on and rules changed, the mics were mounted on "official" mic stands, regardless of actual driver height. Now they concerned themselves primarily with the drivers seated position. As all autos were measured in the same fashion, it was deemed "fair to all". However they are all seriously flawed. Also keep in mind that car audio companies are in business to make money and the whole craze fueled an industry. So, of course, they loved selling $1k equalizers. SQ gave way to SPL wars as bass competitions drove industry sales.

From 20Hz-15kHz you have about a 25dB error range (±12dB response). There is some obvious phasing issues and cancellation nulls. Measure your vehicle interior. Side/side, front/back, floor/roof these should correspond pretty closely to null/peaks. Move the mic to a different position and you'll have a different response. I am not a big proponent of electrical EQ except for certain things. The best you can do, IMHO, is to try an equalize your path lengths as close as possible and use some EQ as fancy tone control. You will not be able to get rid of phasing nulls with EQ, since those are placement and time errors. Any EQ you do will be for one transfer function (path) only and may correct the response shape but only for that position. But, again, move the mic a few inches and it's all off. You have a myriad of reflections, far too many for any EQ to 'fix'. The best sounding cars had a sloping response of approximately 3dB/Oct with no more than 3dB difference in SPL from octave to octave. Once you have 'corrected' for whichever location you want, nothing more can be done. Don't waste your time. Cheers! :T


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## Sonnie (Apr 11, 2006)

You may be right about what I am seeing. I did not pay much attention to when it was actually written. The "Auto-EQ" instructions on my Pioneer head unit suggest placing the mic at the center of the head rest, assuming no one is in the car.

I think EQ can work well if it accomplishes the elimination of peaks that are effecting what you are hearing. That is my ultimate goal. So far... equalization has effected what I hear to a great extent. My process is to measure all around my ears (within a few inches in several directions)... and average those, then correct as needed.


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## GranteedEV (Aug 8, 2010)

Sonnie said:


> With car equalization being so expensive, we need to figure out a way to get a Behringer FD in the car. onder:


You can actually run a miniDSP in a car


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## Sonnie (Apr 11, 2006)

That might be a less expensive alternative for sure.


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## Andre (Feb 15, 2010)

The JBL MS-8. Little box filled with pixie dust, Merlins bones and magic.


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## Sonnie (Apr 11, 2006)

I did check out that unit, but it has some limitations that the Audio Control DQXS does not have... probably more of a preference thing for me. AC is also offered by one of my distributors, so the cost is a bit less. I can get a 3Sixty.2 at near cost as well... but would rather have the 3Sixty.3 when it is released. I may get one of those for my 528i.


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## Andre (Feb 15, 2010)

I thought BMWs were illegal in Alabama....


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## Sonnie (Apr 11, 2006)

They are... especially for hillbillies... I just haven't been caught. :bigsmile:


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## AndyInOC (Dec 15, 2010)

Sonnie said:


> I did check out that unit, but it has some limitations that the Audio Control DQXS does not have... probably more of a preference thing for me. AC is also offered by one of my distributors, so the cost is a bit less. I can get a 3Sixty.2 at near cost as well... but would rather have the 3Sixty.3 when it is released. I may get one of those for my 528i.


I have yet to hear one, but apparently the ms8 is nothing short of amazing in a BMW with the logic 7. I can say that in my humble lil XB that my car has absolutely never sounded better. It can be a real hassle sometimes, not being able to change crossovers on the fly, no amplitude adjustments on each channel etc etc but when its right, the only description is WOW. I know they pop up used a lot, and I've seen them as low as $429 shipped and factory authorized. 

There is a TON of new processors on the horizon this year, mosconi, arc, alpine & RF all have new units coming at some point, so CES should be a lot of fun.

On a side note, I see you ran the auto eq on your pioneer, did you happen to do a factory reset first? Read somewhere (different forum, different thread, different pioneer) that it was essential to do a reset before doing an autotune even though the radio is brand new because pioneer runs the eq software before shipping to make sure it functions properly and there could be residuals left.


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## Sonnie (Apr 11, 2006)

My BMW does have the Logic 7, but I don't use it... stereo sounds so much better for music. I have not tried it for DVDs, but I don't watch movies in the car. I have however, such as on our recent trip to Gatlinburg, watched a few concert DVDs. Well... I did not watch them myself while driving, but the wife did.

I remember reading about a few different BMW owners using that JBL unit with success.

I did not run the Auto-EQ... and doubt I will. I did not wire up the parking brake on the unit, so Auto-EQ will not work... and I think I am going to be too lazy to tear the dash apart again and wire it up.


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## AndyInOC (Dec 15, 2010)

Sonnie said:


> My BMW does have the Logic 7, but I don't use it... stereo sounds so much better for music. I have not tried it for DVDs, but I don't watch movies in the car. I have however, such as on our recent trip to Gatlinburg, watched a few concert DVDs. Well... I did not watch them myself while driving, but the wife did.
> 
> I remember reading about a few different BMW owners using that JBL unit with success.
> 
> I did not run the Auto-EQ... and doubt I will. I did not wire up the parking brake on the unit, so Auto-EQ will not work... and I think I am going to be too lazy to tear the dash apart again and wire it up.



Obviously I read too quick and misunderstood, I thought you said you did run the autotune lol. I prefer my music in 2ch stereo as well and haven't yet heard the logic 7 personally. If my understanding of it is correct (on the ms8) it steers centered information to the center speaker, l & r information stays l & r and then any information that is out of phase is steered to the rear. Intriguing for sure, but I'm not doing all the work until I hear one in the real world.


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## jmsmith11 (Dec 11, 2011)

Did you use a calibrated mic and if so what angle did you use? My cross-spectrum mic came with 0, 45, and 90. I'm thinking 45 would make the most sense if I wedge the mic in between the headrest.


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## Erin H (Aug 26, 2009)

jmsmith11 said:


> Did you use a calibrated mic and if so what angle did you use? My cross-spectrum mic came with 0, 45, and 90. I'm thinking 45 would make the most sense if I wedge the mic in between the headrest.


The environment is terribly diffuse and so relatively nearfield that aiming isn't likely to yield extreme results. What is most important is taking multiple measurements and averaging them together to gain a more realistic example of the head area. Geddes wrote a paper on this back when he worked for Ford Automotive (or maybe he was contracted solely for a specific task). I've attached it to this post in PDF format. In a nutshell, what it prescribes is 6 measurements all taken within a head area window. Then you average these results together. This yields one curve to base your tune on.

The reason for doing this is simple: comb filtering. As the soundwaves from each speaker interact with the environment, a reflection is created. These reflections will often (how about, almost always) be out of phase to some degree (quite literally) with the direct sound. The results in either constructive or deconstructive correlation. The former shows up as a boost in response due to two+ soundwaves arriving at your ear/mic at the same time in phase. The latter shows up as a null (think of the 80hz null everyone loves to talk about). 

When you measure response in a car, an environment made up of mostly reflections, your results will vary from mic location to mic location. Especially the higher in frequency you go. There is some point, however, where the response changes very little from position to position; this is the transition point where the sound is transitioning from velocity based to pressure based. Below this band where you're more and more pressure based, there will be fewer differences in response. There will be some here and there due to the same issues but the scale is much less severe. Above the transition area where the sound is velocity based, even a small distance of mic movement will yield different results higher in frequency. I'm talking as little as ¼".

I've seen people tune for HOURS or DAYS based on a single-mic method; trying to resolve something they can't because everytime they put the mic back in the car to get a curve after making EQ adjustments, they put the mic a bit to the side of where it was. That means from about 1khz and above, the response is different simply due to mic placement. Talk about chasing your tail. :doh:

So, the takeaway from this is: ALWAYS take multiple measurements in the head area and average them together before you start tuning based on an in-car measured response curve. Otherwise, you're going to find (without a shadow of a doubt) the results to not be indicative of what you're hearing. 

- Erin


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## jmsmith11 (Dec 11, 2011)

Erin H said:


> The environment is terribly diffuse and so relatively nearfield that aiming isn't likely to yield extreme results. What is most important is taking multiple measurements and averaging them together to gain a more realistic example of the head area. Geddes wrote a paper on this back when he worked for Ford Automotive (or maybe he was contracted solely for a specific task). I've attached it to this post in PDF format. In a nutshell, what it prescribes is 6 measurements all taken within a head area window. Then you average these results together. This yields one curve to base your tune on.
> 
> The reason for doing this is simple: comb filtering. As the soundwaves from each speaker interact with the environment, a reflection is created. These reflections will often (how about, dang near always) be out of phase to some degree (quite literally) with the direct sound. The results in either constructive or deconstructive correlation. The former shows up as a boost in response due to two+ soundwaves arriving at your ear/mic at the same time in phase. The latter shows up as a null (think of the 80hz null everyone loves to talk about).
> 
> ...



Very interesting. How do I take an average using REW?


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## Sonnie (Apr 11, 2006)

You would have to setup REW the same way you have it setup at home to be able to run the sweep through all speakers... maybe connecting to your amp input if you have a single input coming from your headunit.

What I did was used a full range pink noise CD and took snapshots using the RTA in REW. I just put the tip of the mic (pointed up) right at the opening of my ears.

This is a very complicated process though. I am sure Erin can attest that tuning a car can be a daunting task, as there are soooo many factors involved.


I think JBL really figured it out with their MS-8. For most folks, it doesn't get any better than this for a fairly easy plug'n'play method of getting the sound right in your vehicle. And of all things (I had no idea at the time I wrote this thread)... their mic is a headphone mic that you actually sit in the drivers seat and wear it on your head... so the mics are right on your ears. You look straight forward for one measurement, look at the left side mirror for another and the right side mirror for another. The MS-8 does the rest... and it truly sounds incredibly good... much better than I could have ever made it sound.

We just need to get someone to build that headphone mic for the home. Audyssey should take note.

It would probably be need to send these headphones to Herb at Cross-Spectrum and let him create a calibration file for them, then they could be use with REW at home.


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## Erin H (Aug 26, 2009)

JBL uses binaural Mic's as well. That's how they achieve their spatial averaging. If you've seen the MS-8's target curve and know what was shadowing is, it makes sense. 

As for using REW for spatial averaging, I'm not sure. There are different ways to skin this cat. Let me look at the software again and get back to you.


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## Erin H (Aug 26, 2009)

Here's a link to where you can purchase binaural mics.
http://www.soundprofessionals.com/cgi-bin/gold/category/110/mics

I highly suggest reading their FAQ before trying to use them. Truth be told, I don't even recommend going that route anymore. I'm working on a tutorial for my site (shameless plug alert!), medleysmusings.com, that breaks down an efficient way to tune manually, assuming you have an outboard DSP. While most of the folks here probably aren't as gung-ho on car audio as those of us on the car-audio-centric forums, there may be a few folks here interested in it. But I have no idea when that will actually be finished. I'm still in the planning phase. :/


As far as REW and averaging, it looks stupid easy. There's an "average" button on the bottom left. Looks like you just check all your measurements and click "average". Done. :wave:

The other method is to measure in real time (RTA) and set the "averages" high while you sweep the mic in a head area.


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## Sonnie (Apr 11, 2006)

Yeah... averaging is very easy with REW. I do that often with my home system when measuring my subwoofers response. I will measure all around my head where I sit. Not a lot of difference in the home, but as you said earlier, in a car, it can be drastic within a few inches.

Those binaural mics probably need calibrating as well... although it shows 20-20,000Hz as the frequency response, it does not say it is flat... and I suspect it ain't.


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## jmsmith11 (Dec 11, 2011)

Erin H said:


> Here's a link to where you can purchase binaural mics.
> http://www.soundprofessionals.com/cgi-bin/gold/category/110/mics
> 
> I highly suggest reading their FAQ before trying to use them. Truth be told, I don't even recommend going that route anymore. I'm working on a tutorial for my site (shameless plug alert!), medleysmusings.com, that breaks down an efficient way to tune manually, assuming you have an outboard DSP. While most of the folks here probably aren't as gung-ho on car audio as those of us on the car-audio-centric forums, there may be a few folks here interested in it. But I have no idea when that will actually be finished. I'm still in the planning phase. :/
> ...


Very cool. Why don't you recommend them? Seems like a good way to tune. I'd be very interested in your recommended tuning method. Some people would say that I'm obssesed, but I might refer to them as "acoustic heathens." :bigsmile:

So, performing a "sweep" would be like it sounds? Waving the mic around in the general head area?

I was considering just tuning for the driver location and having a setting for that. I will try tuning each speaker separately in the future, but if I perform a linked tuned (left and right fronts with the same settings) the passenger should get very similar results. That, and I doubt they will be as persnickety as I am. Tuning for the driver alone is enough work, but if you add a passengers and/or the ability to tune each speaker the project grows exponentially. :gulp:


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## Sonnie (Apr 11, 2006)

The mic would be stationary during each sweep that REW produces.


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## jmsmith11 (Dec 11, 2011)

Sonnie said:


> The mic would be stationary during each sweep that REW produces.


Oh, so using sine wave sweeps? Shows how much I know. :bigsmile:


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## Sonnie (Apr 11, 2006)

Correct... lol... that is what we are here for. :T

You would probably be better off to experiment with REW in your home first... then move to the car. Remember we have the REW Forum that can really help you tremendously in working with REW.


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## Erin H (Aug 26, 2009)

Sonnie said:


> The mic would be stationary during each sweep that REW produces.


yep.

BUT, if you are using the RTA portion you just physically sweep the mic. You have to make sure to set long averages. Otherwise the changes will occur too quickly and you'll wind up getting a measurement of the last mic location rather than a measurement averaging the head area.


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## Erin H (Aug 26, 2009)

jmsmith11 said:


> Very cool. Why don't you recommend them? Seems like a good way to tune. I'd be very interested in your recommended tuning method. Some people would say that I'm obssesed, but I might refer to them as "acoustic heathens." :bigsmile:
> 
> So, performing a "sweep" would be like it sounds? Waving the mic around in the general head area?
> 
> I was considering just tuning for the driver location and having a setting for that. I will try tuning each speaker separately in the future, but if I perform a linked tuned (left and right fronts with the same settings) the passenger should get very similar results. That, and I doubt they will be as persnickety as I am. Tuning for the driver alone is enough work, but if you add a passengers and/or the ability to tune each speaker the project grows exponentially. :gulp:


there are different aspects here.

I recommend you measure left side and right side separately. you can do this by simply adjusting the balance on your headunit. as stated above, you can get by without doing sweeps; just use the RTA and set averages to a high value.

as far as tuning for each seat, the results will not carry over. Consider the topic of spatial averaging. if the response varies at the driver's seat within ¼ inch, imagine how varied it will be when it's 3 _feet _over at the passenger's seat. This is especially true when you start reaching ILD domain where what you hear is dominated by intensity rather than time *and* you factor in the pressure region of response starting around the 500-700hz mark (car dependent). this is all relative to your ear geometry vs wavelength. ITD is the time function. ILD is the level function of hearing and location awareness. Around 1-2khz is where the two are somewhat intertwined and below that ITD is prominent and above that is where ILD is prominent. 

That boils down to this: the system response curve you set at the driver's seat will not at all correlate to the response heard at the passenger's seat above this range, and actually a bit below this where the response is still not quite pressure based. Just one more reason why mic placement and averaging is important.


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## jmsmith11 (Dec 11, 2011)

Erin H said:


> there are different aspects here.
> 
> I recommend you measure left side and right side separately. you can do this by simply adjusting the balance on your headunit. as stated above, you can get by without doing sweeps; just use the RTA and set averages to a high value.
> 
> ...


Do you have a target curve in mind when you tune? I know some people go for a flat response (which I find to sound bad), some do it by ear, I've seen someone just trim or boost frequencies that were out of step from neighboring frequencies, and also read about tuning with pink noise and an a-weighting (which is heresy too most people, but I tried it and it sounded great).


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## Erin H (Aug 26, 2009)

I don't shoot for any curve, per se. I just look for problem areas and try to knock them down. I don't worry about nulls as much as I do peaks. And I also try to level match the tweeter band to the midrange band.


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## mojozoom (Sep 25, 2012)

Hi Erin,

Nice to see you on HTS. I'm on DIYMA as well and have really enjoyed your posts and site.

I've been tuning my car system with REW for a while and really enjoy it. I'm using an Audyssey mic believe it or not, and have had great results with it. 

I'm a firm believer in HRTF and always measure one channel (and one ear) at a time. I use sweeps for quick measurements, then switch to 8 sample averaged RTA for final level balancing. At this point I get really nice imaging from this method alone, and haven't bothered with trying to tune with both channels live at the same time. The reflection off the drivers side window makes a real mess of things.

Really my biggest issue is determining a target curve, as without it you're just shooting in the dark. I had tons of trouble getting Tori Amos correct, and it was all in the slope of my lower end (100-1000 hz). If we could get a bunch of target curves together for people to try it would really help. Once you have a target, REW can get you there quickly and easily.


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## jmsmith11 (Dec 11, 2011)

Target curve you say? I just found this thread on DIYMA

http://www.diymobileaudio.com/forum...iscussion/131029-target-curve-comparison.html

Once I get my minidsp I'm going to try each one.


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## jmsmith11 (Dec 11, 2011)

Are you "bikinpunk?" I've been reading so much of your stuff on DIYMA hahaha. I'm reading your a-weighted tune thread right now =)


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## Erin H (Aug 26, 2009)

jmsmith11 said:


> Are you "bikinpunk?" I've been reading so much of your stuff on DIYMA hahaha. I'm reading your a-weighted tune thread right now =)


yea.

caution when reading that thread: it's not terribly accurate. that was when i was still learning (not that I'm not still) and I posted a lot of things that I wouldn't necessarily advise now. the one thing it has going for it is in some ways, it mitigates cabin gain; which was the goal. the problem is that cabin gain starts lower in frequency than the weighting of the A-weighting. the real goal, in my current opinion, should be to know how the car drives the response from flat. ie: what does cabin gain in your car do (where does it start and what slope does it ascend). Then, simply aim to follow that curve. All you'd really wind up doing here is attenuating peaks and getting rid of resonance via a parametric EQ with narrow bandwidth. from about 300hz and up, you can focus on trying to get a 'flat' curve as a baseline. then tune from here. 


it's incredibly difficult to explain the best way to tune; not one size fits all and everyone has their own take on what the suggestion is. if you tune with a single mic location your tune will sound horrible if you're shooting for flat or any respective target curve. if you do an average, it'll be better. you're still not addressing the left/right side balance, and this needs to be done as well. so, i'd recommend doing a good spatial average on the left side only, then the ride side only and compare those two when you're trying to level match.


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## jmsmith11 (Dec 11, 2011)

Did you use an a-weighted SPL meter or and RTA that has an A-weighting? I haven't found an RTA that does that directly on the graph.

Is there a measurement type or method to measure cabin gain? If so, could I just adjust the EQ to compensate for this gain?


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## Erin H (Aug 26, 2009)

Think I used smaartLive back then. 


Cabin gain: measure a subwoofer outside of the car, far away from any reflective boundaries such as a house or walls in a room. In other words, take it outside. Measure the FR using the ground plane method about 1-2 meters away. Save the measurement. 

Now put the sub in the car. Measure the response of the sub only from the drivers seat and passenger seat. Compare the two. Look at how the response compared of those two measurements compare with the measurement outside of the car. That should tell you what your car is doing. You'll measure the effect of modes but the two seat measurements should make it where you can get an idea of cabin gain.


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## mojozoom (Sep 25, 2012)

I'm just starting to experiment with tuning to equal loudness curves, as nothing else has sounded even close to correct to me.

I've worked up ISO 80 phon and 60 phon house curves, and they seem to be a pretty good starting point. I'll be trying F-M curves as well just for fun. They don't have the bump at 1.5k that the ISO curves do, so they may be a nicer sounding baseline for some people.

I already tried straight up A-weighting and it seemed really lifeless and dull.

My goal is to have a simple target curve I can shoot for as a starting point to get a system to have nice tonal balance, so I can then follow with left/right frequency balancing to get the imaging centered.

I've asked John if he could add a 1/3 octave GEQ to REW. Erin, I don't know if you've tried it yet, but REW has an auto filter routine that would be sweet for car audio if it could set up typical 31 band GEQ gains for us. Couple that with a little routine to blend the results into the text file for the 3sixty.2 and we pretty much have auto tuning to whatever curve we want. Nice.


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> I'm just starting to experiment with tuning to equal loudness curves, as nothing else has sounded even close to correct to me.
> 
> I've worked up ISO 80 phon and 60 phon house curves, and they seem to be a pretty good starting point. I'll be trying F-M curves as well just for fun. They don't have the bump at 1.5k that the ISO curves do, so they may be a nicer sounding baseline for some people.
> 
> ...


When you tuned for A-weighting how did you do it? 1/3 Octave pink noise? There are a few ways I tried to do it and not all worked out so well.

After reading into A-W and similar methods I came across ITU-R 468. I'm going to try that tune out of curiosity since I had such good results with A-W before. ISO226:2003 was another setting that came up a lot during my research, but I couldn't find a table of responses like I did for A-W and ITU-R 468. Same goes for F-M curves. 

One method for tuning I'm about to try is to modify my 1/3 octave mic calibration file to reflect target curves (A-W, Audio Control curve, etc.). If I get the RTA flat with the modified file that means it is actually the target curve.

I'm getting a MiniDSP which I believe integrates with REW for the AutoEQ feature. I'm hoping that I can load a target curve and it will figure everything out for me, but I haven't had a chance to play with it yet. If it works this will make life much simpler/faster. 

One thing I noticed is that when I had my best tune the tweeters were attenuated -2dB. Now that they are set back to normal, regardless of the DSP I used I can't out tune the tweeters. After reading a lot of Erin's stuff I came to realize how important level setting is. You mentioned you are going to do L/R balancing afterwards, but I'm thinking it should be done first. I'm going to go -2dB on the tweeters again (their in the sails so that's probably why they need to be cut), then bi-amp so I can even out mids w/ tweets, and L w/ R. This should make any EQing more successful. 

There are so many opinions out there, many of them polarized. I'm beginning to think that those of use who opt for A-W tunes or right, but for the wrong reasons. The other camp says go for flat, but this doesn't pan out on the RTA (I'm guessing because of reflections, cabin gain, etc.). It might just be a accident that A-W worked so well for me. This line of thinking alone makes me want to toss the RTA, but then I remember other speakers I've tested. After feeling dissatisfied with my Rockford T3s I compared the RTA response to my mom's stock Rav4 speakers and my S4 earbuds. Both sound great imo. In comparison, the T3s were very jagged in response, particularly beyond 1/3 octave. The shape of the Rav4 and S4 was a smooth transition from frequency to frequency on 1/3 octave and much less jagged on other settings such as 1/48. So rather than completely tune by ear I think I will do the above, EQ the 7 band PEQ to taste, and then use the 31 band GEQ to smooth the transition between frequencies. The only problem I see now is how to arrive at an overall RTA response by tuning each speaker individually. onder:


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## mojozoom (Sep 25, 2012)

I did some Google searching and found data for A-weighting and made up a house curve. It’s a very smooth, roughly parabolic curve shape with a lower top end and exaggerated low end, and sounded good but not as good as some of my other eq sets. Definitely on the right track though.

As that went so well, I dug up info on the ISO curves, and eq’d to ISO 80 phon and ISO 60 phon curves. I really like the ISO 60 curve, and prefer it over my previous favorite eq set after back to back listening. It’s sounds absolutely great on Michael Ruff’s “Wishing Well”. It is stretching my little Hertz mids quite a bit though, especially on messy, bass-heavy stuff like The Prodigy. I found that Tori’s “Scarlet’s Walk” CD sounds best when I drop the bass -1 and increase the treble +2 at the head unit, so there’s still room for improvement (although it is a notably bass heavy recording). I’m going to work up an ISO 70 curve and eq to that next.

In case you want them, I have REW housecurves made up for:
A-Weighting
Audiocontrol (RTA)
IASCA (RTA)
MECA (RTA)
JBL Andy (RTA)
JBL MS-8 (RTA)
ISO 80 phon
ISO 60 phon









I tried a bunch of things before I started tuning each ear independently, and so far it’s worked the best for me. I’m using REW and an Audyssey microphone for testing, and my system is a passive two-way front with a sub in the rear, run off the factory head unit and a RF 3sixty.2, so all I have is the 31 band GEQ.

My logic was (whether or not it’s correct is another question):
1) your brain can tell the difference in as little as 2” of time alignment
2) HRTF impacts the amount of reflected and primary sound received by each ear

Back when I used to try to measure without being in the car, I found huge cancellations in certain frequencies due to reflections coming off the drivers side window. Once I stuck my head in there, the reflections were blocked, and the cancellation went away.

Some people advise to run all channels at the same time to take into account the contribution of the reflections, and I can understand that logic. But, if my brain can distinguish the reflections from the primary signal (as there’s more than 2” of difference), then why add them in to the mix. For my brain work out the imaging in a track, it needs to have a full range signal to the left ear coming from the left channel (and same for the right ear), not some signal that has been artificially reduced because of equalizer settings that compensate for the crosstalk info from the right channel that has bumbled over to the left side. My brain knows that the crosstalk isn’t part of the primary signal due to the delay and level, etc. It’s a smart brain.

So, I eq each ear independently to a target house curve, then compare the final curves for each ear and balance the levels between them to solidify the imaging. If the levels aren’t balanced when you’re finished the image will wander.


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> I did some Google searching and found data for A-weighting and made up a house curve. It’s a very smooth, roughly parabolic curve shape with a lower top end and exaggerated low end, and sounded good but not as good as some of my other eq sets. Definitely on the right track though.
> 
> As that went so well, I dug up info on the ISO curves, and eq’d to ISO 80 phon and ISO 60 phon curves. I really like the ISO 60 curve, and prefer it over my previous favorite eq set after back to back listening. It’s sounds absolutely great on Michael Ruff’s “Wishing Well”. It is stretching my little Hertz mids quite a bit though, especially on messy, bass-heavy stuff like The Prodigy. I found that Tori’s “Scarlet’s Walk” CD sounds best when I drop the bass -1 and increase the treble +2 at the head unit, so there’s still room for improvement (although it is a notably bass heavy recording). I’m going to work up an ISO 70 curve and eq to that next.
> 
> ...


Did you try the other target curves on the link I posted? I see you have tried some of them, but there were a few others there.

Also, what is your method to EQ for the target curve? The image you posted implies you are going about it a different way than I am. I was looking at the combined responses of all speakers and cutting frequencies to get them to match the target curve I was trying to accomplish. Not very easy/effective so far so I'm guessing there is a better way.


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## mojozoom (Sep 25, 2012)

I've tried all of those curves and then some. Most have been developed for use with RTA methods, so they aren't as applicable when using sine sweeps as the pink noise is already weighted.

To eq to a new curve, I grab a file that should be close, record sweeps of each side, and then use the eq section of REW. I've saved a set of 20 empty PK filters that cover the top end of the 31 bands of my eq, using a Q of 4.31 on each. Then I let REW set the target curve level, and compare it to the level it selects for the other channel as well. Usually I have to adjust one side's target up or down so they match. Often I have to refence back to what cuts have already been made so I don't run out of room on a given band.

Then its just a matter of sliding gains up and down on the filter set in REWs eq window until I get the curve where it needs to be. Once that's done, I add or subtract the gains I came up with in REW for each band from what is already set up in the 3sixty as the starting point.

After that I sweep again or do RTA averaging to check the finished curves for each ear and balance levels from band to band. The whole thing takes about 20 minutes.

I've asked John if he could add a 31 band 1/3rd octave eq set for us so we can auto eq, as that would be really nice.


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> I've tried all of those curves and then some. Most have been developed for use with RTA methods, so they aren't as applicable when using sine sweeps as the pink noise is already weighted.
> 
> To eq to a new curve, I grab a file that should be close, record sweeps of each side, and then use the eq section of REW. I've saved a set of 20 empty PK filters that cover the top end of the 31 bands of my eq, using a Q of 4.31 on each. Then I let REW set the target curve level, and compare it to the level it selects for the other channel as well. Usually I have to adjust one side's target up or down so they match. Often I have to refence back to what cuts have already been made so I don't run out of room on a given band.
> 
> ...


I'd like to give that a shot. Can you send me those housecurve files?


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## mojozoom (Sep 25, 2012)

Sure - not sure how best to do that though on this forum. Maybe pm me with you email address. I'll also try to log on with my laptop and see if I can post them here as a link.

I forgot to mention earlier that I shut off the sub when setting up a new curve, and mess with sub integration later. When doing the eq work in REW, I select "Bass Limited" as the speaker type, and enter in the crossover point and slope I'm using on the mids (80 hz and 24 bd/octave in my case). REW will then revise your target housecurve to reflect the high pass filter you'll have in place at the low end of the mids, which makes it alot easier to set up the low frequencies.


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> Sure - not sure how best to do that though on this forum. Maybe pm me with you email address. I'll also try to log on with my laptop and see if I can post them here as a link.
> 
> I forgot to mention earlier that I shut off the sub when setting up a new curve, and mess with sub integration later. When doing the eq work in REW, I select "Bass Limited" as the speaker type, and enter in the crossover point and slope I'm using on the mids (80 hz and 24 bd/octave in my case). REW will then revise your target housecurve to reflect the high pass filter you'll have in place at the low end of the mids, which makes it alot easier to set up the low frequencies.


Wow, this sounds like a really efficient way to try multiple curves in a short time. 

This is probably a really basic question, but how do you conduct sweeps?


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## mojozoom (Sep 25, 2012)

OK, here are the three housecurves (if this works):

View attachment housecurve_iso60.txt


View attachment housecurve_iso80.txt


View attachment housecurve_a weight.txt


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> OK, here are the three housecurves (if this works):
> 
> View attachment 38824
> 
> ...


Got it! Thx =)


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## Erin H (Aug 26, 2009)

mojozoom said:


> OK, here are the three housecurves (if this works):
> 
> View attachment 38824
> 
> ...


Thanks for posting those.

What I'd propose (for the sake of system linearity) is to try to average the 90 and 70phon curves. That way you can get a good, well rounded response at nearly all volumes. I did this a couple years back (think I had to extrapolate the <100hz portion myself) but don't have the file since it was on my old laptop.


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## mojozoom (Sep 25, 2012)

Here's the ISO 70 phon housecurve:
View attachment housecurve_iso70.txt


I really think the ISO curves make great starting points. The sound is well balanced across the frequencies, and by picking the ISO 60, 70 or 80 you can alter how much bottom end boost you roll in to the system to compensate for road noise and such (of which I have a lot).

The next hurdle is finding a way to isolate things that still don’t sound right to us. Once we know where they are it’ll be pretty possible to address them, but when you are running separate EQs for each channel (or even each speaker) all you can do is adjust one band on one speaker at a time so it’s hard to spot the changes, and you don’t want to loose track of your original settings. If you link the EQ channels in the 3sixty eq they become the same level, and that’s not what we want, as the relative levels have to be maintained for imaging.

What I think we need is the ability to listen to source music and apply a parametric EQ to both channels at the same time. That way we can set a narrow filter (probably a cut) and sweep it back and forth until we find the offending frequency, reduce the filter until it sounds right, and then apply that amount of cut to the EQ setting in our actual DSP settings on each channel.

It really seems like the best way to do this would be to play the source CD through the laptop, and use the laptop to apply the PEQ. Currently I’m leaning toward VLC Media Player to handle this, as it is supposed to have PEQ built in, although I sure can't seem to find it.


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> Here's the ISO 70 phon housecurve:
> View attachment 38864
> 
> 
> ...



That's the problem I think I'm going to run into - adjusting each speaker individually trying to reach an overall curve. I'm hoping once I get the levels set and each speaker response smooth (not necessarily flat) that I can reach a net effect by adjusting each speaker the same amount. For example - if I need to boost 6.3k by 1dB I can adjust both tweeters by the same amount and then remeasure system response. 

I can't speak for the .2, but in the .3 I can adjust the levels, EQ, and x-over individually for each speaker or pair them. So if you want to pair EQ, but not levels maybe you need the .3.

Also, the .3 is parametric, not graphic. I found this to be a pain at first, but I wasn't by bi-amping or level setting before, so hopefully that solves my issues in my next install. Most people love PEQ and hate GEQ for reasons I don't yet understand. With the MS-8 cutting frequencies was so much easier with a GEQ.



> What I think we need is the ability to listen to source music and apply a parametric EQ to both channels at the same time. That way we can set a narrow filter (probably a cut) and sweep it back and forth until we find the offending frequency, reduce the filter until it sounds right, and then apply that amount of cut to the EQ setting in our actual DSP settings on each channel.
> 
> It really seems like the best way to do this would be to play the source CD through the laptop, and use the laptop to apply the PEQ. Currently I’m leaning toward VLC Media Player to handle this, as it is supposed to have PEQ built in, although I sure can't seem to find it.


This I don't quite understand. Are you using pink noise for this step? Why would you play through the laptop?


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## mojozoom (Sep 25, 2012)

It sounds like you're trying to set up both channels at the same time - correct? I've been testing with only one channel at a time. I run just the right side, no sub, and sweep with the mic at the right ear. Then mute the right side, turn on the left and sweep with the mic at your left ear position. Then you eq each side separately to meet the target curve, with the target curve offset the same amount for each channel. The tweak to match levels.

I want to run my source music (Tori Amos for example) on my laptop, and feed that in to the head unit via the aux input. That way I can apply a PEQ at the source on the laptop to find the problem areas. Once I identify the offending freq, I can make cuts on the 3sixty.

On the 3sixty.2 the eq link is stupid. If i have the left 1k set at -2 and the right set at -4, then move the left to -1 it'll make the right side -1 as well (instead of -3). It doesn't maintain the relative levels, but simplay makes them both the same as the one you change.

So I want to leave my nice ISO 60 eq curve alone, and use a separate PEQ upstream of the 3sixty to figure out where to make changes.


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> It sounds like you're trying to set up both channels at the same time - correct? I've been testing with only one channel at a time. I run just the right side, no sub, and sweep with the mic at the right ear. Then mute the right side, turn on the left and sweep with the mic at your left ear position. Then you eq each side separately to meet the target curve, with the target curve offset the same amount for each channel. The tweak to match levels.
> 
> I want to run my source music (Tori Amos for example) on my laptop, and feed that in to the head unit via the aux input. That way I can apply a PEQ at the source on the laptop to find the problem areas. Once I identify the offending freq, I can make cuts on the 3sixty.
> 
> ...


Do you sweep with sine waves or pink noise?

Erin gave me the idea to use averages. I took a 32 period average of noise angled straight, left 45 degrees (similar to how the MS-8 makes you turn toward the mirror), and right 45. When I combined them the curve made more sense, although the difference wasn't dramatic. I see you just face it left when tuning the left speaker. Another variable for me to try. 

I was eqing both speakers before and tried and un-linked tune. It was impossible to get a good tune either way though because I wasn't bi-amping. When I get my new amp I will try a linked and an un-linked tune to see which works better. I suspect a linked tune will work well for a front or all setting.

With the .3 you can adjust either side without affecting the other if unlinked. When you link you have to copy one side's settings to the other. This is annoying because I think it would be smart to tune each speaker, link them, then adjust then make further adjustments at the same time.

My idea right now is to set the levels equal on the front mids and tweets on both sides for a driver based tuned. I will try Z and A to see which works better. Another variable is pink noise or a test tone. I think noise makes more sense. Not sure if I should set the rears at the same level, a percentage of the fronts, or off completely. I noticed that having the rears higher sounds off, around equal or lower you don't really notice them except if you sit in the rear. I've heard on SQ cars they don't even use rears.

After levels are set I will EQ for a smooth response. I'm guessing this might upset the levels though and lead me back to step one. I've read that you should level set first, but perhaps smoothing out the response is best done first and then you can level set. This might be minutia, but I will try both and figure out which works best. I guess at this point I will start working towards target curves.

One cool feature with the .3 is that I can save 4 different curves and cycle through them with a press of the knob. Makes A/B comparisons a snap.


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## mojozoom (Sep 25, 2012)

I use the sine sweeps in REW mostly. For mic position, I just set my Audyssey mic on my shoulder ner my ear, so it actually points up.

As a sanity check I tried EQing to the ISO 60 curve with both channels running. There's alot of comb filtering going on, as the results aren't nearly as repeatable as when you only run one channel. Here's what i ended up with:









The sound wasn't bad, but the imaging was not good at all. I ran separate channel sweeps (left channel measured at left ear, right channel measured at right ear), here's what I got:









You can see why the image was moving around - there were huge level differences between ears throughout the frequency range.

I suppose you could go through each band and move the right up and left down to get them to match, which would for the most part preserve the tonal results. I really think the tonality that came from working each channel separately is a little better anyway.

The .3 seems like quite a step up. For me to listen to a different EQ set I have to load it up which takes about 2 minutes.


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## jmsmith11 (Dec 11, 2011)

Is there a sweep function in REW or do you plan a sweep track? I only know how to play pink noise and save the image when it settles.

I read somewhere on here, I think the calibrated mic thread, that you should point towards the ceiling. The calibrated mic guy, Herb I believe, said angled slightly forward was the best. This sounds similar to what you said with the mic pointing slightly up. more variable to try =) =(

I have found that with speaker testing and other obsessions of mine that monitoring two variables before proceeding is sufficient. For example, a year or two ago I went through this whole process with coffee. If you combine every variable (brand, grind, grinder, brewing method, temperature, time, etc., etc.) you end up with a gazillion tests. I found that finding a preferred variable, brewing method for example, was preferred across the board and not just for that set of variables. If this wasn't the case I might still be searching for optimal coffee, lol. This gives me some hope for these audio tests.

I think testing with the mic on your should is good for another reason. It factors in your body. Gotta try that as well. So many good ideas here lol.

Do you think if you averaged both speaker responses and adjusted them the same amount according to the deviation from the target curve that it would sound good? For example, your idea was to adjust each speaker individually, based on it's own response.


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## mojozoom (Sep 25, 2012)

The sweep tone generation is built in to the main measurement portion of REW. In the upper right corner there's a box called Measure that you click, then don't worry about the SPL calibration, then you set the freq range you want to sweep and click start measurement. It's really easy. After that do the typical ctrl-shift-3 to get to 1/3 octave smoothing and you're done.

Alot of people tune their system by ear or whatever, and then go back and cut from one side and boost the other side until the levels match. There at a few popular threads on that on DIYMA, "My soundstage ate my windshield" or something like that is one of them that is hard to forget.


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## jmsmith11 (Dec 11, 2011)

If the tone is coming from REW do I need to connect my laptop to the .3? 

Do I need to worry about the "check levels" feature at any point? That is another thing I never messed with.


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## mojozoom (Sep 25, 2012)

You'd need to get the signal from the laptop somehow. I hook it up to head unit the same way i hook up my mp3 player. If you go straight to the 3 you'd miss any effect of the head unit.


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## jmsmith11 (Dec 11, 2011)

I only have ipod adapter access to the head unit. Not really good at tearing apart the dash.

A big point of the .3 is to eliminate the head unit as a factor. Basically being able to hook it up to an OEM head unit and have amazing SQ. Maybe there is still some HU influence, but I'm thinking (hoping) it's insignificant. 

I can intercept the Male RCA wires near the .3 itself. Don't know if I could unplug them from the .3 and go through my USB mixer, then back to the .3.


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## mojozoom (Sep 25, 2012)

Maybe you can burn a sine sweep to a cd and run that during the measurement instead of playing through the laptop. I think you need to use the whole signal path including the head unit to get the best picture of whats going on.

The 2 plots the oem head unit freq response. In my case it was dead flat, but lots of factory head units aren't. Maybe you can see the initial freq response curve on the 3 as well.


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## jmsmith11 (Dec 11, 2011)

When doing OEM it shows a before and after freq response on initial setup. With an aftermarket HU it does not. I believe that the .3 makes it flat based on the before/after OEM screenshots I've seen.

I have some sine sweeps I can put on my iPod and play through the HU. Just waiting for my 2-ch amp and then it's party time.


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## mojozoom (Sep 25, 2012)

If the 3 shows the "before" response as flat, then there'd be no need to feed the signal thru the head unit. You could feed the signal out of the laptop right into the 3.

I forgot to mention, I gave up on rear speakers a while back. All they seem to do is muddy the sound. I may try some wierd processing later on with the rears to simulate an echo and gain a deeper stage. For now they stay off and everything is simpler and cleaner.

I'm going to try a tune based on comparison listening between a given song played through the head unit and the same through my headphones. To me the tune I have on my headphones is almost perfect, so if I can clone that I know I'll be happy.


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## jmsmith11 (Dec 11, 2011)

What is the difference between correlated and uncorrelated pink noise? I'm assuming uncor is completely random and correlated would affect time alignment and phase, but I'm not sure which to use and when.


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## mojozoom (Sep 25, 2012)

I believe uncorrelated is used for frequency tuning and correlated for time alignment. Correlated is essentially mono.
I'm not sure what periodic pink noise is though.

I don't know if REW uses the typcial math for its RTA. It seems like my RTA results using pink noise on REW don't look anything like other RTA packages results. If it's really using FFT we may be better of testing using white noise.

I finally got my iso70 tune done. I trimmed down the hump on the high frequencies quite a bit and it sounds really nice.


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## jmsmith11 (Dec 11, 2011)

I believe periodic pink noise works with one of the REW settings to provide instant feedback on changes. It's been awhile since I used it, so I'm not sure exactly how it worked. If I recall correctly, using the right periodic noise type with the right setting type was like having long averages, but without waiting for it to update.

Can you tune with white noise? I did this once, but only out of curiosity. All I ever here about is pink noise. I actually intended to try every noise type (blue, brown, etc.) just to make sure I tried everything. Eventually I figured out other noise types weren't going to work and the concept behind having equal energy per octave. I wonder how tuning with white noise differs from tuning with tones.


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## jmsmith11 (Dec 11, 2011)

Strange thing happened. I tuned each individual speaker to flat (or the best I was able to). When I played all the speakers with pink noise it was anything but flat (even after setting the levels), which I found surprising. Even more surprising was that it sounded amazing. Switching back and forth from untuned to flat was night and day. Next step I suppose is finding my ideal curve. 

Perhaps the people that say tuning to flat will sound bad are tuning the entire system at once. When I tried this in the past I was tuning 6.1 speakers all at the same time. This makes me think that each speaker ended up playing some bizarre response.


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## AudiocRaver (Jun 6, 2012)

jmsmith11 said:


> What is the difference between correlated and uncorrelated pink noise? I'm assuming uncor is completely random and correlated would affect time alignment and phase, but I'm not sure which to use and when.


Correlated versus uncorrelated applies to signals coming from multiple speakers at the same time while measuring. If correlated, then the same measurement signal is coming from the speakers in phase. This is not good for determining EQ settings, you will end up with phase cancellation at some frequencies, phase reinforcements at other frequencies, and will get a totally crazy frequency response curve. Move the measurement mic a few inches, and you get a totally different crazy frequency response curve.

By using uncorrelated pink noise, the measurement signal coming out of each speaker is random and completely unrelated to all the others, so there will be no phase cancellations or reinforcements, and you get a sane looking frequency response curve.

Which one to use when? Always use uncorrelated. The only use for correlated pink noise for taking measurements would be when you want to play a trick on someone who doesn't know any better and have them waste a bunch of time. That would not be nice.

Of course, you only run one speaker at a time while equalizing, so none of this applies to the normal measurement/equalization process. It can be useful/interesting to do it after equalization is complete, to get a curve showing how all the speakers are working together.


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## AudiocRaver (Jun 6, 2012)

jmsmith11 said:


> Can you tune with white noise?


Pink is the only noise color that is useful for all practical purposes. White noise gets stronger and stronger at higher frequencies, after EQ you would end up with a curve that was all bass.


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## AudiocRaver (Jun 6, 2012)

jmsmith11 said:


> Strange thing happened. I tuned each individual speaker to flat (or the best I was able to). When I played all the speakers with pink noise it was anything but flat (even after setting the levels), which I found surprising. Even more surprising was that it sounded amazing.


Strange indeed, perhaps that final test was done with correlated pink noise, which would give a meaningless measured frequency response curve, as explained in post number 62.


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## jmsmith11 (Dec 11, 2011)

AudiocRaver said:


> Strange indeed, perhaps that final test was done with correlated pink noise, which would give a meaningless measured frequency response curve, as explained in post number 62.


I didn't update my findings, but I didn't stay with the flat tune. It did sound much improved over my untuned response, which I found interesting enough to post. 

Since I was tuning each speaker individually, it wouldn't have mattered if it was correlated. Correlated and uncorrelated pink noise have the same response unless you are measuring with a pair of speakers.


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## AudiocRaver (Jun 6, 2012)

Ditto, I now realize that we were talking about different uses of correlate pink noise. Didn't mean to cause confusion.:sn:


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## jmsmith11 (Dec 11, 2011)

mojozoom said:


> Here's the ISO 70 phon housecurve:
> View attachment 38864
> 
> 
> ...


Where did you get the data on ISO curves? I can only find pictorial representations and not the data points. 

I've had such good success with A-weighting that lead me to similar curves. This image I'm attaching shows A-W compared to ITU-R 468 and ISO 226. Both are newer and supposedly more accurate weightings. ITU-R I did find the data points for and made a tune, but A-W was far superior. ISO 226 sounds similar to your ISO curves, which I will attempt next.











Another idea is getting a professional hearing test and finding which frequencies are weighted higher/low specifically for you. Then using that data to create a curve. It might be the best of tuning by ear + RTA tuning.


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