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Title: Use of RTA
Post by: Garrett Trask on June 29, 2010, 02:46:58 PM
Hello everyone,

I recently installed a Driverack PX in a small church.  They meet in what is a more or less an acoustic nightmare of a room.  The room was never designed to support live audio.  I have been very interested in learning as much as I can about proper techniques in Equalizing the PA to the room.  The auto EQ function on the DBX unit really does not make any positive changes.  My best guess however is that my technique is bad, not the Auto EQ function.  I only placed the microphone in one location.  It was suggested to me that I place a measurement mic in several locations.  I would then average these measurements to get an overall curve of which to apply.  This does make sense to me.  Would you recommend this technique for stage monitors as well.  Our stage monitors are in the same location each week.  It would be nice to EQ my wedges so that they respond well with the stage. A concern that I am sure we all share is that a measurement microphone cannot necessarily tell the difference between the direct source of the audio and the reflections.  I want to minimize the amount of reflected energy that I measure...correct? Should I not place the microphone as close as possible to the speaker.  I do not have experienced enough ears to do it by ear and we do not have the  money to pay someone to come in and balance our PA to our room.  I would appreciate any input on this subject and resources that can help us.

Thanks everyone!
Title: Re: Use of RTA
Post by: Dick Rees on June 29, 2010, 03:29:24 PM
This is the latest, most definitive article on why RTA does not suffice for PA tuning:

http://campuspa.com/downloads/devil_with_rta.pdf

If the link does not work, "Google" this:

Bennett Prescott + RTA

After you have read the article, consider this:

1.  Everything starts with the proper speaker(s) properly deployed.  This means focusing the sound on the listeners and keeping the sound off the walls and ceiling to keep the ratio of direct sound to reflected sound as high as possible.

2.  Stage volume should be as low as practicable.  This includes any amplifiers and drums in addition to the monitors.  

3.  Proper equalization/DSP needs to be applied to the system to optimize things for your use.  This can be done by ear by an experienced sound person or can be done with sophisticated analyzation programs like SMAART and others.  You may be able to hire a professional to do this for you.  Properly done, it should be a one-time job/expense.

Best of luck.

DR
Title: Re: Use of RTA
Post by: Tom Young on June 29, 2010, 08:03:00 PM
Agree with all points including reading Bennett's article.

I forget whether he also discusses the futility of auto-EQ processes. Auto EQ does not work well. The process of measuring and analyzing sound (acoustics, electrocoustics, etc) is far more complex than we can achieve with a computer (alone) and there are elements of subjectivity (including experience and intuition) that play a role in this process. Among other things the computer cannot do is decide if the results it has applied sound good. We (pretty much all) can do this. It is not unheard of to spend much time optimizing a speaker system, listening to the results and then going back and starting from (or almost from) scratch. When this happens to me I usually know where I need to return to. The computer does not.

Another ingredient to all this is the acoustics. Along with speaker system design, measurement and anlysis and how the system is operated (including how folks play, etc) ..... much can be done to improve things with careful analysis of the acoustics (and the architectural elements that constitute this) and appropriate treatment.

There are just as many folks with 1/2 a clue throwing stuff on the walls and achieving changed, but still not very good, acoustic response as there folks "designing" speaker systems, hanging them, measuring them, etc.

It should come as no surprise that I am an advocate for hiring a qualified consultant who can do this sort of work effectively and as economically as possible.
Title: Re: Use of RTA
Post by: Dick Rees on June 29, 2010, 09:17:46 PM
Agreed.  

I jumped in with the link to the RTA article without really tying it in to the AutoEQ cited in the OP.  Auto EQ works off of the RTA function (as I understand it) and suffers from the inherent weaknesses thereof.

I'm all for optimizing what you have before spending money on the problem.  The first thing that would pry a dollar out of my pocket would be hiring a pro to look over the situation, adjust it as well as possible and make recommendations where to go from there.

Structural changes (re-hanging speakers, etc) and/or room treatments would be well down the line for me.  The better you set up the system, the less room treatment you'll need.  That said, some room treatment is usually desirable......after system optimization.

Again, best wishes for your endeavors.

DR
Title: Re: Use of RTA
Post by: Brad Weber on June 29, 2010, 10:43:53 PM
I won't go into the general RTA issues as Tom and Dick (need to get Harry in on this to complete the set) have already covered that.

Garrett Trask wrote on Tue, 29 June 2010 14:46

I only placed the microphone in one location.  It was suggested to me that I place a measurement mic in several locations.  I would then average these measurements to get an overall curve of which to apply.  This does make sense to me.

Analyzing the system at multiple locations in the listener area is good, although I'm not sure that would be applicable to the AutoEQ function.  I personally do not like simple averaging, if I measure in six locations and five are right one but one is off I may decide to not negatively impact the five just to help the one, but then that may also depend on where the one that is off is located.  What it comes down to is that there should be some subjective consideration and it can be more than just a simple averaging.

Garrett Trask wrote on Tue, 29 June 2010 14:46


Would you recommend this technique for stage monitors as well.  Our stage monitors are in the same location each week.  It would be nice to EQ my wedges so that they respond well with the stage.

Not really.  For one thing, you are usually most concerned with the monitor response over a more limited area, perhaps even at one location.  Much of the equalization applied to a monitor may be for gain before feedback rather than just for subjective quality.  For monitors you normally want things as close as possible to actual use.

Garrett Trask wrote on Tue, 29 June 2010 14:46

A concern that I am sure we all share is that a measurement microphone cannot necessarily tell the difference between the direct source of the audio and the reflections.  I want to minimize the amount of reflected energy that I measure...correct? Should I not place the microphone as close as possible to the speaker.

You've actually touched on some of the very issues that can be addressed with more advanced analysis systems like Smaart, SysTune, Praxis, etc.  On the one hand, all you can really adjust with equalization is the response of the speaker (although you may also be adjusting phase without realizing it), you can't change what the room does or interactions between speakers with an equalizer.  On the other hand, the room and interaction among devices does affect what the listeners hear.  So to use an RTA effectively you have to learn to differentiate what you can and cannot 'fix' with EQ.  The dual channel FFT type analysis systems allow you to 'window' the measurement in time so that you can more effectively see the direct response as well as the response with varying elements of the room and other devices.
Title: Re: Use of RTA
Post by: Arnold B. Krueger on June 30, 2010, 08:47:34 AM
Garrett Trask wrote on Tue, 29 June 2010 19:46

Hello everyone,

I recently installed a Driverack PX in a small church.  They meet in what is a more or less an acoustic nightmare of a room.  The room was never designed to support live audio.  I have been very interested in learning as much as I can about proper techniques in Equalizing the PA to the room.  The auto EQ function on the DBX unit really does not make any positive changes.  My best guess however is that my technique is bad, not the Auto EQ function.  I only placed the microphone in one location.  It was suggested to me that I place a measurement mic in several locations.  I would then average these measurements to get an overall curve of which to apply.  This does make sense to me.



I agree with the other posts that question the autoamtic use of a RTA for setting up a room. Depending on the room, setting up eq can be either difficult or impossible. The learning curve can be long and frustrating. Classes like the Syn-Aud-Con class that has been being discussed here are good prerequisites for attempting to eq a room.

Quote:


Would you recommend this technique for stage monitors as well.  Our stage monitors are in the same location each week.  It would be nice to EQ my wedges so that they respond well with the stage.



I question the idea of setting up monitors for flat response. Smooth yes, flat not so much. Furthermore, most of my monitors have some narrow anti-feedback notches in them. No RTA I know of would put them in.

Quote:


A concern that I am sure we all share is that a measurement microphone cannot necessarily tell the difference between the direct source of the audio and the reflections.



No concern there, mics just can't make that decision, especially the omnis that are customarily used.

Quote:


I want to minimize the amount of reflected energy that I measure...correct?



Ideally, your monitor speakers should not be generating a lot of reflections. You might want to address that problem first.

Quote:


Should I not place the microphone as close as possible to the speaker.



Get that mic too close to the speaker and your measurements are being unbalanced by being close to one driver, and off-axis from another.

Quote:


 I do not have experienced enough ears to do it by ear and we do not have the  money to pay someone to come in and balance our PA to our room.



Plan C: get some formal education. And/or find a Christian sound guy in the area who will take you on as a ministry.

Title: Re: Use of RTA
Post by: George S Dougherty on June 30, 2010, 12:47:37 PM
I tend to skip the AutoEQ and tune things by hand, using the RTA as a guide to make sure I'm not missing anything with my ears.  I don't have a fancy tool like SMAART to help me see the direct vs reflected response so I have to work by alternate methods.

The first thing I do is setup a speaker outdoors and do my baseline EQ there.  This only works of course if you can move a speaker outside in the first place.  Pre-hung speakers will be a challenge.  I've had 80ft from any buildings or large reflective surfaces recommended to me as a good guideline.  The RTA mic typically needs to be a minimum of 10ft from the speaker to allow for proper integration of the drivers as Arnold alluded to, and the volume of the pink noise needs to be at least 20db above any background noise, preferably 30db.

At that point, you're doing a pretty decent job of EQ'ing the speaker itself and not compensating for a room.  I target something closer to the equal loudness curves for my EQ rather than shooting for flat 20-20.  I've found flat gets near intolerable at loud volumes.  It tends to be overly bright and piercing because of where our ears are more sensitive.  In the Driverack I'd do all that in the parametric EQ's and store those as a preset.

Once you move the speakers into a room you could again use the RTA if you don't trust your ears and look at several points around your coverage area.  You're not trying to EQ the room at this point, just identify broader room nodes that may need to be pulled back to improve clarity in that space.  These adjustments can be done with the graphic EQ.

All that said, if the room is an acoustic nightmare, that's your first problem.  Getting a certified acoustician to help address those issues will have the biggest impact on problem spaces.  Outside of coverage patterns and placement, you can't solve acoustic problems with electronics.  The issue there is physical and modifying your signal won't correct that.
Title: Re: Use of RTA
Post by: Dick Rees on June 30, 2010, 03:12:55 PM
George.....

Personally, I would just deal with the speakers in place.  I would hope for the following:

1.  Proper placement for coverage.
2.  Proper speaker for coverage.
3.  A speaker of high enough quality that tweaks to the basic output would be unneeded.....or at least minimal.

If you happen to have speakers which require equalization to pass decent sound, I'd look at having them brought back up to specs or replaced with better speakers.  That said, most professional grade speakers will have information available regarding any DSP which should be applied.  You can simply open the PDF and look it up.

Best.

DR
Title: Re: Use of RTA
Post by: Brad Weber on June 30, 2010, 07:30:41 PM
George S Dougherty wrote on Wed, 30 June 2010 12:47

I don't have a fancy tool like SMAART to help me see the direct vs reflected response so I have to work by alternate methods.

What, SAC doesn't do this?  Smile

George S Dougherty wrote on Wed, 30 June 2010 12:47

At that point, you're doing a pretty decent job of EQ'ing the speaker itself and not compensating for a room.  I target something closer to the equal loudness curves for my EQ rather than shooting for flat 20-20.  I've found flat gets near intolerable at loud volumes.  It tends to be overly bright and piercing because of where our ears are more sensitive.  In the Driverack I'd do all that in the parametric EQ's and store those as a preset.

I tend to go for flat response for this type of speaker/array tuning and to then address any subjective tuning when addressing the room and system.  I want to be sure that without the effects of the room, the rest of the system, etc. the speakers can be as transparent as possible before putting them into the space.

George S Dougherty wrote on Wed, 30 June 2010 12:47

Once you move the speakers into a room you could again use the RTA if you don't trust your ears and look at several points around your coverage area.  You're not trying to EQ the room at this point, just identify broader room nodes that may need to be pulled back to improve clarity in that space.  These adjustments can be done with the graphic EQ.

Oops, the age old issue that you cannot "EQ the room" and you cannot fix room modes with EQ.  You may be able to adjust the speaker response to try to compensate for the acoustical environment but as you say later, you can't solve acoustical problems with electronics (except maybe some of the electronic reverberation enhancement systems).
Title: Re: Use of RTA
Post by: Darin Brunet on June 30, 2010, 11:27:43 PM
Agreed with the above statements. IMO, use the best CD (Constant Directivity or Controlled Directivity) loudspeakers you can find/afford and properly set them up to minimize reflections from side walls, floors and ceilings.

Room EQ is of little use in most instances. For instance, you have "corrected" the response with the use of an RTA and EQ. Yet, the correction is only valid at that particular location where the mic was placed.

In other words, even if the central or other axis has been corrected to be perfectly flat, in no way, shape, or form is the response problem “corrected”. In fact, it might even be worse. It should be understood that electronic EQ can correct for any linear problem found in a loudspeaker prior to the acoustic domain, but it does not correct for problems within the acoustic domain itself, except along a single direction, i.e. a single point.

This is independent of whether or not this problem comes from the speaker or the room itself. The correction is valid only at that single point in space and nowhere else. Also, some very important aspects of a speakers sound quality is not at all apparent from an on-axis curve or any "single direction" curve.

Point is, once you have a well designed loudspeaker, there is no need for electrical EQ and in fact it is likely to make things worse. Acoustic problems can only be solved acoustically, and once that is done, nothing more is possible.
Title: Re: Use of RTA
Post by: George S Dougherty on July 01, 2010, 03:35:00 AM
Dick Rees wrote on Wed, 30 June 2010 13:12

George.....

Personally, I would just deal with the speakers in place.  I would hope for the following:

1.  Proper placement for coverage.
2.  Proper speaker for coverage.
3.  A speaker of high enough quality that tweaks to the basic output would be unneeded.....or at least minimal.

If you happen to have speakers which require equalization to pass decent sound, I'd look at having them brought back up to specs or replaced with better speakers.  That said, most professional grade speakers will have information available regarding any DSP which should be applied.  You can simply open the PDF and look it up.

Best.

DR


I'd hope for those too.  I've helped enough churches with GC grade speakers like the Yamaha club series though and those are often a different beast altogether.  If the speaker has suggested EQ in a manual that'd also be a great place to start.  Since I don't target flat anyway, I usually don't bother with suggested EQ settings.  

Replacing with better speakers would always be a great option, though as the OP mentioned they don't have the budget to even hire someone to set things up professionally.
Title: Re: Use of RTA
Post by: George S Dougherty on July 01, 2010, 03:54:00 AM
Brad Weber wrote on Wed, 30 June 2010 17:30

What, SAC doesn't do this?  Smile .

It will when they release a SMAART plugin Wink  I won't hold my breath, though there are some really sweet RTA plugins designed for studio use.

Brad Weber wrote on Wed, 30 June 2010 17:30


I tend to go for flat response for this type of speaker/array tuning and to then address any subjective tuning when addressing the room and system.  I want to be sure that without the effects of the room, the rest of the system, etc. the speakers can be as transparent as possible before putting them into the space.

I used to go for flat as well for much the same reason, but as I mentioned, flat gets a bit painful at high volumes to my ear.  Equal loudness curves are also what many headphones target in their designs so it makes it a bit easier to use headphones as comparison (obviously of little merit if you do have a set with flat response, though Dave Rat has found them to be few and far between in his testing)
I prefer to EQ to taste before since I'll often have a simpler EQ as a result if I do it all in one pass rather than go flat then tweak later.  As I understand it, more EQ means more tweaks to the phase of the signal and I'm assuming a simpler EQ with potentially less drastic adjustments where you might not boost or cut in the first place would yield beter results.  If you were to do something like I described outside the room it certainly wouldn't hurt to create two presets for both scenarios.

Brad Weber wrote on Wed, 30 June 2010 17:30


Oops, the age old issue that you cannot "EQ the room" and you cannot fix room modes with EQ.  You may be able to adjust the speaker response to try to compensate for the acoustical environment but as you say later, you can't solve acoustical problems with electronics (except maybe some of the electronic reverberation enhancement systems).


Suppose I should have been more clear in my meaning.  I wouldn't then re-eq to get everything back to where I'd had it outdoors.  I'd find the more consistent summation issues due to room dimensions.  Notches are less audible but resonances will often exacerbate feedback issues and mask other frequencies.  You can't "solve" them, but with some judicious cuts you can make them less of a problem.  Trying to fix suckouts with radical EQ boosts is of course a fools game.
Title: Re: Use of RTA
Post by: Brad Weber on July 01, 2010, 08:40:37 AM
George S Dougherty wrote on Thu, 01 July 2010 03:54

I used to go for flat as well for much the same reason, but as I mentioned, flat gets a bit painful at high volumes to my ear.  Equal loudness curves are also what many headphones target in their designs so it makes it a bit easier to use headphones as comparison (obviously of little merit if you do have a set with flat response, though Dave Rat has found them to be few and far between in his testing)
I prefer to EQ to taste before since I'll often have a simpler EQ as a result if I do it all in one pass rather than go flat then tweak later.  As I understand it, more EQ means more tweaks to the phase of the signal and I'm assuming a simpler EQ with potentially less drastic adjustments where you might not boost or cut in the first place would yield beter results.  If you were to do something like I described outside the room it certainly wouldn't hurt to create two presets for both scenarios.

You can't know what a speaker or array will sound like in the final installation as a result of free field testing, so you're going to end up tweaking it in place anyways.  And whether you adjust for a desired response before or after installation you are still going to be looking for the same end result.  It is personal preference and I prefer to start with a speaker or array that is by itself neutral, that way when addressing the room, installation and subjective aspects I know I am looking just at those and not at the speaker itself.
Title: Re: Use of RTA
Post by: Dick Rees on July 01, 2010, 10:56:39 AM
The following quote always amuses me:

"they don't have the budget to even hire someone to set things up professionally"

I have spent my professional life listening to this excuse.  While it may be true in a few cases, the reality is that people have money for what they WANT more often than they have money for what they NEED.

It's (unfortunately) human nature......
Title: Re: Use of RTA
Post by: Tom Young on July 01, 2010, 11:51:43 AM
Well said and a true "truism".

Title: Re: Use of RTA
Post by: George S Dougherty on July 01, 2010, 12:17:36 PM
Dick Rees wrote on Thu, 01 July 2010 08:56

The following quote always amuses me:

"they don't have the budget to even hire someone to set things up professionally"

I have spent my professional life listening to this excuse.  While it may be true in a few cases, the reality is that people have money for what they WANT more often than they have money for what they NEED.

It's (unfortunately) human nature......


True enough, though there are a lot of churches these days that don't even have the budget for what they need and better sound would be something they want yet doesn't get on the list either.
Title: Re: Use of RTA
Post by: George S Dougherty on July 01, 2010, 12:21:54 PM
Brad Weber wrote on Thu, 01 July 2010 06:40

George S Dougherty wrote on Thu, 01 July 2010 03:54

I used to go for flat as well for much the same reason, but as I mentioned, flat gets a bit painful at high volumes to my ear.  Equal loudness curves are also what many headphones target in their designs so it makes it a bit easier to use headphones as comparison (obviously of little merit if you do have a set with flat response, though Dave Rat has found them to be few and far between in his testing)
I prefer to EQ to taste before since I'll often have a simpler EQ as a result if I do it all in one pass rather than go flat then tweak later.  As I understand it, more EQ means more tweaks to the phase of the signal and I'm assuming a simpler EQ with potentially less drastic adjustments where you might not boost or cut in the first place would yield beter results.  If you were to do something like I described outside the room it certainly wouldn't hurt to create two presets for both scenarios.

You can't know what a speaker or array will sound like in the final installation as a result of free field testing, so you're going to end up tweaking it in place anyways.  And whether you adjust for a desired response before or after installation you are still going to be looking for the same end result.  It is personal preference and I prefer to start with a speaker or array that is by itself neutral, that way when addressing the room, installation and subjective aspects I know I am looking just at those and not at the speaker itself.


True enough on all counts.  So would you tackle the room and subjective adjustments on a separate EQ or are they additive such as additional bands of parametric on the same processor?  Probably depends on the installation?
Title: Re: Use of RTA-AC
Post by: Ivan Beaver on July 03, 2010, 06:42:36 PM
Dick Rees wrote on Thu, 01 July 2010 10:56

The following quote always amuses me:

"they don't have the budget to even hire someone to set things up professionally"

I have spent my professional life listening to this excuse.  While it may be true in a few cases, the reality is that people have money for what they WANT more often than they have money for what they NEED.

It's (unfortunately) human nature......

But let the HVAC unit break and see how fast they can come up with some money to get it fixed.

But finding money to hear the Pastor clearly and have the sound system work better-Now that is really asking a lot.

I don't mean to be sarcastic-but that is true more often than not.

It is all about priorities
Title: Re: Use of RTA-AC
Post by: Arnold B. Krueger on July 05, 2010, 11:26:05 AM
Ivan Beaver wrote on Sat, 03 July 2010 23:42

Dick Rees wrote on Thu, 01 July 2010 10:56

The following quote always amuses me:

"they don't have the budget to even hire someone to set things up professionally"

I have spent my professional life listening to this excuse.  While it may be true in a few cases, the reality is that people have money for what they WANT more often than they have money for what they NEED.

It's (unfortunately) human nature......

But let the HVAC unit break and see how fast they can come up with some money to get it fixed.

But finding money to hear the Pastor clearly and have the sound system work better-Now that is really asking a lot.

I don't mean to be sarcastic-but that is true more often than not.

It is all about priorities



I still remember meeting with our trustees over 25 years ago when we were trying to get approval for the first PA we bought that actually worked. Several of the trustees asserted that we didn't need to make this investment since they could hear the pastor just fine. It was well known to may of us  that in fact many of them routinely frequenctly "rested their eyes" through sermons.

We didn't get the system installed until several years later because the bequest that would have bought the new sound system was *redirected* in order to add a Trumpette En Chemade array to our pipe organ. I think those particular pipes have been played about a dozen times in the more than 25 years since then. Maybe fewer times than that, unless you count rehearsals.

Yes, for most churches it is all about perceptions about priorities. Keeping needed technical changes on hold can be like "marking behavior" for some in the church. Being able to stall useful upgrades is a demonstration of personal power and influence for some.
Title: Re: Use of RTA
Post by: Don Sneed on September 12, 2010, 08:06:59 PM
I am a sound contractor/installer for churches & movie theaters, I use a 2 or 4 microphone setup using a USL microphone 4-plexer, & an Ivie IE-35 RTA/Scope, I use averaging Equalization. I EQ for a flat response to 4K than drop 3db step down to 16K. It always sound great, now the RTA is a tool, you still have use yours ears to fine tune to control feedback, but I usually have very little to adjust using the average technique & 4-mics. I perfer a 1/3 octave graphic Equalizers over a PEQ... (to each his own)....This 4-mic averaging is also a Movie Theater (Cinema) THX requirement or the theater will not pass the test & get the THX certflication, I am a THX re-certify technicians for movie theaters, we use a THX "R2" or the new "D2" RTA unit that must be purchase from THX & use only for their techs & certify sound compacies. I can get in the ball park with an GEQ, but perfer to use a RTA to do it correctly....
Title: Re: Use of RTA
Post by: Brad Weber on September 13, 2010, 07:43:03 AM
Don Sneed wrote on Sun, 12 September 2010 20:06

I am a sound contractor/installer for churches & movie theaters, I use a 2 or 4 microphone setup using a USL microphone 4-plexer, & an Ivie IE-35 RTA/Scope, I use averaging Equalization.
Don Sneed wrote on Sun, 12 September 2010 20:06

I can get in the ball park with an GEQ, but perfer to use a RTA to do it correctly....

As noted back at the beginning of the thread, an RTA can be very useful but does have several limitations.

Having multiple measurement points is a great idea, but direct averaging may not always be desirable.  For example, say your goal is a value of 90 and you have four measurements of 90, 90, 90 and 80.  The average is 87.5, but do you really want to add 2.5 to all of them when three of the measurements are right on and that still leaves the fourth 7.5 away from the target goal?  That may depend on where the individual measurements were taken or any of a number of subjective considerations.  Many people find, and research supports, that determining how to address variations between multiple measurements is often a much more complex issue with both objective and subjective components and is not best addressed by than simple averaging.

This also touches on the differences between a typical cinema application and a typical church application.  A cinema tends to be a much more controlled acoustical environment and the room is usually not as much of a factor in terms of reflections, echoes, etc.  Cinemas also typically have a single speaker per channel for the main channels and you are typically not dealing with speaker arrays, delay speakers, fills and so on.  And perhaps most importantly, cinemas do not usually have open microphones in the main space, much less multiple open microphones, along with stage monitors, amps on stage and so on to address.  A good example of where the application can strongly impact the most effective approach and tools to apply.
Title: Re: Use of RTA
Post by: Dick Rees on September 13, 2010, 12:46:59 PM
Brad Weber wrote on Mon, 13 September 2010 07:43

Don Sneed wrote on Sun, 12 September 2010 20:06

I am a sound contractor/installer for churches & movie theaters, I use a 2 or 4 microphone setup using a USL microphone 4-plexer, & an Ivie IE-35 RTA/Scope, I use averaging Equalization.
Don Sneed wrote on Sun, 12 September 2010 20:06

I can get in the ball park with an GEQ, but perfer to use a RTA to do it correctly....

As noted back at the beginning of the thread, an RTA can be very useful but does have several limitations.

Having multiple measurement points is a great idea, but direct averaging may not always be desirable.  For example, say your goal is a value of 90 and you have four measurements of 90, 90, 90 and 80.  The average is 87.5, but do you really want to add 2.5 to all of them when three of the measurements are right on and that still leaves the fourth 7.5 away from the target goal?  That may depend on where the individual measurements were taken or any of a number of subjective considerations.  Many people find, and research supports, that determining how to address variations between multiple measurements is often a much more complex issue with both objective and subjective components and is not best addressed by than simple averaging.

This also touches on the differences between a typical cinema application and a typical church application.  A cinema tends to be a much more controlled acoustical environment and the room is usually not as much of a factor in terms of reflections, echoes, etc.  Cinemas also typically have a single speaker per channel for the main channels and you are typically not dealing with speaker arrays, delay speakers, fills and so on.  And perhaps most importantly, cinemas do not usually have open microphones in the main space, much less multiple open microphones, along with stage monitors, amps on stage and so on to address.  A good example of where the application can strongly impact the most effective approach and tools to apply.


Excellent, Brad.  Getting right to the heart of it, the difference between live sound and playback is apples/oranges, night/day.  What may work for one does not mean it will work for the other.
Title: Re: Use of RTA
Post by: Richard Carter on November 17, 2010, 09:32:18 AM
I agree RTAs and AutoEQ are generally not good for what you are doing.  I would suggest a program called ARTA (http://www.fesb.hr/~mateljan/arta/) which has a lot of the functionality of SMAART but can be used for free with some limitations.

With something like the Driverack, I would try to use the parametric EQ first for overall sound and then use the 1/3 octave for specific areas.  You can get an idea of where these are by hooking up a mic and then turning it up until you get feedback.  Then either measure it with a frequency meter or adjust the board EQ until you find it and transfer to the Driverack.
Title: Re: Use of RTA
Post by: Brad Weber on November 17, 2010, 12:36:01 PM
Richard Carter wrote on Wed, 17 November 2010 09:32

I agree RTAs and AutoEQ are generally not good for what you are doing.  I would suggest a program called ARTA (http://www.fesb.hr/~mateljan/arta/) which has a lot of the functionality of SMAART but can be used for free with some limitations.

Smaart, SysTune, Praxis, WinMLS, etc. also have free working demo downloads with some restrictions but that may be fine for some limited use.  I found ARTA not as user friendly or well supported as some of the other options but a pretty amazing program for just over $100 for a personal use license and just over $200 for a commercial/multi-user license.
Title: Re: Use of RTA
Post by: Tom Young on November 17, 2010, 06:05:27 PM
Quote:

With something like the Driverack, I would try to use the parametric EQ first for overall sound and then use the 1/3 octave for specific areas. You can get an idea of where these are by hooking up a mic and then turning it up until you get feedback. Then either measure it with a frequency meter or adjust the board EQ until you find it and transfer to the Driverack.


This is NOT how you should equalize a speaker system.

What you describe may be OK for finding feedback frequencies and addressing them with channel EQ for the specific mic. But if you grab a mic and adjust the speaker system (with its DSP) based on where this mic feeds back this will result in a speaker system that is sort of "tuned" for that microphone and where it is placed. This is not good for all of the other mic's and their response (individually and collectively).