Room Modes Measurements - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 4 Old 09-28-10, 12:04 AM Thread Starter
Shackster
 
Join Date: Sep 2010
Posts: 10
Question Room Modes Measurements

Hi,

I am completely new to everything so if I may be asking things that have been answered. If that is the case please direct me to the appropriate post.

I have the following components in my home theater:

2 x Klipsch RF-7 II (LR)
1 x Klipsch RC-64 II (C)
4 x Klipsch RB-81 II (SL, SBL, SBR, SR)
2 x TweakCityAudio CS18.2 (Subs)
1 x Anti-Mode 8033
1 x Pioneer Elite SC-37 (AVR)
1 x Pioneer Elite Pro-111FD (TV)
1 x Oppo DV-983H (DVD Player)
1 x DishNetwork ViP 722 (DVR)

I would like to measure my Subs SPL as well as find out any Sub placements that give me best results with Anti-Mode 8033. Also need to know which house curve (Anti-Mode Lift) option I should be using and whether using any of the Parameteric EQ on the Dayton SA-1000 amp for the sub gives me any better results than the default Anti-Mode calibration with its supplied mic.

Also I would like to run a full freq sweep so that I can adjust the Pioneer MCACC setup to get better results compared to the defaults set by MCACC using the suplied mic.

I would like to use TrueRTA to do all the measurements. I already have the 1/24 Octave license for the latest 3.5 version. I will be using a DELL Precision M4300 laptop with Windows XP SP3 for my measurements.

Please let me know what all heardware do I need.

I am thinking I will need the following (please correct me if I am wrong):
1 x Behringer ECM8000 Calibrated Mic from Cross-Spectrum
1 x M-Audio Fast Track http://www.m-audio.com/products/en_us/FastTrack.html - Provides 48V Phantom power over XLR.
1 x 15' or 25' long XLR cable
1 x 1/4" to 1/4" cable. Can someone tell me if this needs to be a stereo pins on both ends or what? Please direct me to a link of the cable that I need. Thanks.
1 x Digital Voltmeter DVM850BL http://www.parts-express.com/pe/show...number=390-550

Do I need anything else or will the above be sufficient to take SPL readings along with generating Freq. graphs using TrueRTA?

Like do I need to buy Rives Audio Test CD #2 http://www.rivesaudio.com/software/TestCD.html or something similar to generate test tones for SPL measurements etc. Also do I need any cable to connect the laptop with the AVR for measurements? If yes, what kind of cables?

Thanks for taking the time to answer the above questions.
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post #2 of 4 Old 09-28-10, 01:03 PM Thread Starter
Shackster
 
Join Date: Sep 2010
Posts: 10
Question Re: Room Modes Measurements

Since I already have Anti-Mode 8033, I asked Anti-Mode support if I can use the mic supplied with Anti-Mode for measurement of Room Modes. Here's what they replied back. Hope this information is of some value to others too.

Quote:
The microphone needs biasing voltage. Easiest and safest way to use the microphone in precision measurements is with our MicAmp http://www.dspeaker.com/en/products/...ment-kit.shtml which is very inexpensive too.

The correction file given for the microphone applies to the microphone assuming the microphone amplifier has ultra-flat response (like our MicAmp).

We use the same capsule as ECM8000 but our microphone construction has smaller deviation between the units than ECM8000. So with a generic calibration file as the one provided on our website, our 8033 microphone delivers slightly more accurate response compared to Behringer ECM8000. our microphone is also more accurate out-of-box, uncalibrated.

But if you have individually measured and calibrated ECM8000 (with comparison to a reference mic like B&K) then that is of course more accurate.
Quote:
Our microphone should not be used with 48V phantom voltage, as it could damage it. The bias voltage or "line powering" is much lower, about 3V. Remember the ECM8000 has different electronics inside it, so it works with a different voltage.

See other microphone powering techniques for reference.
So does anyone knows how DSPeaker MicAmp kit can be used with TrueRTA for measurements? Also what other equipment do I need like an SPL meter etc?

Thanks.
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post #3 of 4 Old 12-09-10, 07:09 AM
Ile
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Join Date: Nov 2010
Location: Finland
Posts: 77
Re: Room Modes Measurements

Quote:
achugh wrote: View Post
So does anyone knows how DSPeaker MicAmp kit can be used with TrueRTA for measurements? Also what other equipment do I need like an SPL meter etc?
I just build Linkwitz mic amp for my Antimode mic, seem to work nice with REW.

I used Radioshack SPL meter for setting level to program, but you can also estimate 75db spl level and set that to program. Estimation is good enough for checking room modes, absolutely correct SPL level is not needed.

I used DSPeaker calibration file for mic.

There comes 3.5 mm plug cable with MicAmp kit, so you can use that cable for sound card calibration.

Last edited by Ile; 12-09-10 at 07:21 AM.
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post #4 of 4 Old 12-09-10, 08:33 AM
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Kal
 
Join Date: Aug 2006
Location: NYC + CT
Posts: 1,839
Re: Room Modes Measurements

Quote:
achugh wrote: View Post
I would like to use TrueRTA to do all the measurements. I already have the 1/24 Octave license for the latest 3.5 version. I will be using a DELL Precision M4300 laptop with Windows XP SP3 for my measurements.
The limitation of TrueRTA is that it will not tell you about modal decay or anything in the time domain. Consider supplementing it with RooomEQ Wizard.

Kal Rubinson
__________________________________
"Music in the Round"
Senior Contributing Editor, Stereophile
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