Tuning speaker / room response?

I have a similar question to Njonker's. I have plotted a graph using the test tones from Stereophile test cd 3. I used a Radio Shack spl from the listening position. My results are much flatter than Njonker's, staying within +-4 db of 80db at 1 kHz, with the exception of a 10 db spike at 6000-8000 kHz. What room characteristic would cause this? how does this compare to others who have tried this? Njonkers, I think you may have started something with your graphs. You have inspired me to get up to speed with my computer skills.

The methods described so far really only give rough approximations to the actual response at the sweet spot. This is because of the multitude of reinforcements and nulls that are caused by the multiple reflections. Your actual response is actually much worse than the curves shown. Impluse methods, such as MLSSA or those used by Sigtech, or specialized sweep tones should be used for room tuning. The asc tube trap site has an extensive explaination on their MATT test page (http://www.tubetrap.com/. I use both ASC tubtraps and a Sigtech DSP to tune my room. They make a huge difference and my room is good to begin with.

I think I may have missed the thrust of this discussion, and I'm a month late to boot, but here's some related info:

It looks as though the analog RS SPL meter is capable of providing data sufficiently accurate to be useful in addressing speaker/room frequency response. By applying the published correction values you are "calibrating" your $35 test instrument! The overall response of the meter is far from flat, but apparently pretty consistent from unit to unit, so the corrections should apply to your meter as well as mine. The analog version is preferred over the digital version for its superior high frequency response, and it is the one the corrections were established with and for. If you are so inclined, you can modify the meter with some capacitor changes and a better electret mic capsule (cheap and obtainable from Digi-Key) and improve the meter's response so that the corrections are no longer needed. Running repeated tests and charting the results is mighty tedious, and I'd recommend wearing earplugs to protect your hearing and preserve your sanity. Considering the HUGE frequency response deviations exhibited by virtually all speakers/rooms, the testing is worth the effort if you are able to make constructive changes based on the measurements. But, if there's nothing you can do about a mountain-range response, you might be happier not having it staring you in the face! Personally, I think that correcting (or at least minimizing) these gross frequency response errors caused by speaker-to-room interactions yields a more significant improvement to a system than most of the stuff we spend our time and money on.

Here are some sites/pages to check out:

(Sorry, but I don't even know how to make these active links, much less generate and post beautiful graphics! I guess you'll have to cut and paste...)

1) http://216.150.71.139/audioinnovation/rsmeter.html

2) http://www.hometheaterforum.com/uub/Archives/Archive-000001/HTML/19990806-17-000048.html

3) http://www.audiophilia.com/hardware/spl.htm

4) http://www.smr-archive.com/forum_3/messages/1220.shtml

5) http://www.gti.net/wallin/audio/audio.html

Jaycee, thanks for the response.

I ended up buying a different instrument to test with, after some people had pointed out the flaws in the methodology I was using here, and using different test methods. Some of the things seen in the graphs above were artifacts from the RS meter used, but not all.

Using my Terrasonde The Audio Toolbox 2, a handheld, calibrated SPL meter, tone generater, and real time spectrum analyser, I did the tests again with pink noise and slow C weighting. I found that I had a high-frequency and a bass problem. The high frequency problem was mainly caused by reflections from the walls it seems; hanging a rug about 2.5" from my back wall solved most of that. Right now, my in-room response abve about 400Hz is within +/- .5dB! The difference is amazing... Imaging improved incredibly, and the system sounds 'calm' now.

As for the bass problems, I tried building some traps using the mthods found in an article on headphone.com, but I made some calculation mistakes, so they did more harm than good. Then I found the ASC website, they sell accoustical products to deal with room acoustics, and offer a free consulting service. I have provided them with room and frequency response information, and they are working up a solution for the bass problem. We shall see what comes out of it...

Niels.

Njonker, is it possible for you to show the graph of your room before treatment with the toolbox. I've been intrigued by this product, and was wondering just how different the results were.