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Discussion Starter · #1 ·
Anyone actually use a real time spectrum analyzer on their room to tune it? I'm holding off on some of the wall treatments just in case I need to tweak further, but was wondering what others have done for serious acoustic tweaking.


I suppose if it's really necessary, my Integra 9.1 receiver would let me put a graphic equalizer in between the front three channels and the amp, but the surrounds don't allow for inserting an equalizer.


I also have the Avia DVD and a radio shack SPL meter for starters.


Eric.
 

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You can purchase a calibrated mic and software for use on a pc or laptop that will let you take measurements of your own room. Your looking at an investment of at least a few hundred bucks. Check out TrueRTA Spectrum Analyzer or Efta Acoustics. A google search should lead you to their sites.

TrueRTA has a free download you can try out.
 

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Discussion Starter · #3 ·
That's exactly what I was thinking/planning. I downloaded the freeware version of TrueRTA. It is a very neat tool and I'd probably spring for an upgrade for finer granularity. Although I have a Korg digital mixer, I was thinking of laying down the $80 for a behringer mike and mixer/preamp specifically for tuning.


Seeing as I spent the money for Smart III calibrating tools for my projector and Avia, I figure another $150-200 for proper audio calibration tools would be well worth it.


Then I can decide if I need an equalizer, or more tweaking of my room treatments.


By the way, I'm returning the digital Radio Shack SPL meter I got for the analog version. It's amazing that the cheaper analog version actually works out better since you can get a more accurate reading! The digital one only reports results in integers, whereas the analog meter will at least let you estimate non-integer values!


Eric.
 

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The final tuning, or tweaking of the room/speaker interface requires the use of an RTA with (at least) 1/12 octave resolution. Parametric equalization can be used for peaks but will not be successful for nulls.
 

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Discussion Starter · #7 ·
First off, I'm very pleased to have both Ethan and Dennis's input on this!


TrueRTA (the $99 version at least) will let me get down into the 1/24 octave range. I'm certainly not going to try attacking this only with equalization. I have wall treatments, am willing to build bass traps, etc. etc. I'm just trying to form the most accurate assessment that I can.


Right now, I've treated the side walls (a little more than the lower half) with insulshield/fabric, and the screen and alcove wall up to the ceiling, as many prescribe. I've got plenty of corner space available for bass trapping if I need it, as well as the entire back wall.


Incidentally, my wall panels are removable, so that in a pinch I could swap out a pure insulshield one for something a little more akin to one of Ethan's bass/mid traps if I need to.


Just trying to not leave any stones unturned!


Eric.
 

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Quote:
Originally posted by Ethan Winer
Buph,


> Is there any reason why doing the analysis in this fashion would not be able to adequately characterize room modes?
 

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Discussion Starter · #12 ·
Hmmnn... The PAS product seems to only have a granularity of 1/3 octave...
 

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Discussion Starter · #14 ·
OK, let me phrase this another way... I have avia, DVE, a radio shack spl meter, TrueRTA pro (1/24 octave version) and the means to fabricate traps, acoustic panels etc. I've already done most of the simpler room treatments.


If you were me, what would you concentrate on next? Is it a waste to try to use TrueRTA, or is it just overkill? Seems a heck of a lot more accurate than the typical SPL meter approach.


How do you measure a rooms response?
 

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Discussion Starter · #16 ·
Um, how do I measure the reverb time?
 

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Discussion Starter · #17 ·
BTW, my room has a ton of extra corners. Any predictions on how that impacts the bass and where I should place traps? The screen is actually in an "alcove", and there's a smaller alcove in the back. let me try a crude text representation:



front

_|----------|_

|XXXXXXXX|

|XXXXXXXX|

|XXXXXXXX|

|__XXXX__|

XX|___|

back


I added the X's to just take up the spacing.
 

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Quote:
Originally posted by Ethan Winer


Sorry, I get easily carried away... :D
No worries. As far as the sine wave generation, that was the purpose of the second link, which is for a test CD. The frequencies on that CD sub 200Hz are quite close. Take a look at it.
 

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The reason an RTA must be used to properly "splice" in the subwoofer is because without the RTA you cannot see the behavior of the frequencies within the crossover range. For example, it is very easy to get rid of any crossover notches when you can watch the RTA as you adjust phase. While with an SPL meter you can measure the SPL of the sub, or the spl of the mains, or the sub and the mains, you cannot see any dips or rises as the 'shared' frequencies add in the crossover range...thus uneven response.

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Doing RTA measurements one or two orders of magnitude finer than human hearing resolution is horse-by-product if room correction is what you're attempting. Further to this nonsense is why one would measure more than an order of magnitude or finer than the device or mechanism you're going to use to address the problem can resolve to in any event.

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Reducing a peak will not deepen a null elsewhere.

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If you want to determine what peaks/nulls are a result of modal resonance (as opposed to some other issue such as SBIR or phase/path difference), then place your RTA's microphone in the corner by the floor of the room. The peaks on the RTA are modal frequencies.

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Fiberglass at the boundary is not useful for modal correction unless it is very thick. Modal frequencies are at high pressure/low velocity at the boundary making fiberglass ineffective (or certainly much less effective). Further, the addition of considerable amounts of fiberglass will lead to the addition of wattage, too dead a room and other problems with the room's acoustics.
 

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Discussion Starter · #20 ·
I'm also amenable to platforms, stages, etc... If my measurements warrant it. Right now I just want to figure out where the real issues and troublespots are first.


My reason for first bringing this up was to figure out if many out there had gone to the trouble to really measure room performance, or if we're all just following "best practices".


There are certainly a lot of people going the extra mile and using smart to calibrate their projectors. I'm sort of suprised that most folks stop at SPL meters, rather than going all the way to RTA measurements for audio tuning/tweaking. Especially given that a good PC based system, with a mic and pre-amp is less than $200.
 
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