Please help with RTA analysis

Hello, everyone.

I've got the following stereo setup (integrated with a HT, but only focusing on stereo at this point):

Bluesound Node > Schiit Gungnir > Odyssey Candela Pre > Odyssey Mono Extremes > ML Ascent i's. I also have a Velodyne sub which I can turn on and off.

My room is approximately 20'9" long x 13'9" wide x 8'8" high. The rear wall is a bit irregular with a large opening into an adjacent room. I have no room treatments.

Here is a pic...although I now have a couple of chairs on the right side.



So I've been considering some DIY absorption panels. Not really because I hear a problem, but simply because I believe that every room will benefit from some treatment. So I purchased a Dayton iMM-6 microphone and downloaded Audio Tools RTA to my iPhone and ran some signals to "see" how my room behaves today, with no treatments. Sitting in my sweet spot I ran the RTA using 1/3 octave pink noise. Here is the plot.



OK, so to my untrained eyes I notice a +/- 4 to 5 DB between 250 up to 5 before it starts to drop. For my calibration, should I consider this to be "pretty flat" through the mids and upper mids? I also am a bit surprised to see such a dramatic roll off on the ends - 200 hz down and 5k hz up. I can turn on my sub to bring up the low end to a point. Not sure what to do about the highs rolling off.


OK, so now what? I guess I was expecting some sort of peak that needed to be absorbed. I was going to try diy absorption panels in corners and 1st reflection points, then remeasure to see the differences.

What kind of treatments should I be thinking of?

Any advice is appreciated.

Thanks, Bob

My advice is to ditch the iPhone mic and RTA software. Buy a calibrated USB mic (Dayton UMM-6 or miniDSP UMIK-1) and learn Room EQ Wizard (REW). You'll need the impulse response and RT60 measurements for seeing the impact of room treatments. Tuning via pink noise and RTA is how they did things like 20 years ago, there's better methods like REW now.

|Tch0rT| said:

. Buy a calibrated USB mic (Dayton UMM-6 or miniDSP UMIK-1) and learn Room EQ Wizard (REW).

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+1

Fully support this post.

Look on eBay for some cheap measurement microphones and use REW Wizard. Home Theatre Shack has a stack of information on the application. If a measurement mic is too much bother, they also have correction tables for the cheap Radio Shack SPL meters.

Alternatively, for a simpler "all-in-one" measuring system, check out the Parts Express OmniMic V2, or XTZ Room Analyzer Pro II packages.

Bob, the rolloff from 250 hz down looks very much like the shape of the high-pass filter that Apple programmed into the iPhone before iOS6. With iOS6, that filter was removed and the frequency response of the iPhone became quite flat.

Need to update iOS anyhow :ROFL:

OK, so I took the advice offered.....and returned the iPhone mic. I bought a Dayton Audio UMM-6 USB mic and ran it into REW.

Following mic calibration (I didn't calibrate the sound card because my LT doesn't have a line in) I ran the test signal. Here are the graphs.




Perhaps someone can explain the black line below the SPL curve? Also, I don't understand the degree axis to the right.

In general things look pretty choppy.

Also, here is the waterfall.



Please educate me. It looks like most frequencies above 100 hz decay in < 240ms. Is this good?

I'd appreciate any treatment suggestions as I plan my room. I'm thinking DIY absorption panels at the usual spots, but I can build diffusion as well.

Thanks, Bob

Crawdaddy said:

Perhaps someone can explain the black line below the SPL curve? Also, I don't understand the degree axis to the right.

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That's calibration data for your mic. The degree is the phase but it doesn't look like that data is showing.

Crawdaddy said:

In general things look pretty choppy.

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Play with placement more especially with your sub. Measure each speaker individually, even the sub.

Crawdaddy said:

Also, here is the waterfall.

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Waterfalls are good for around 200-250Hz and under. Take the ms to about 350. You want to see where the "mountains" stop.

Crawdaddy said:

Please educate me.

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This is a good thread to consult:
http://www.avsforum.com/forum/91-au...surement-techniques-how-interpret-graphs.html

It's always good idea to read the REW help file, at least once
Best forum related to REW is of course: http://www.hometheatershack.com/forums/rew-forum/

So here is what I'm thinking of building. DIY 4" OC 703 panels behind the speakers and at 1st and 2nd reflection points. Some sort of DIY bass tubes in the front corners. I've got a cabinet with glass doors and a treadmill in the back corners. I cant really put base tubes back there, but could hang a few panels at the treadmill as it gets "boomy" back there while running.

What do you all think? Should I consider angled panels in the front corners instead of tubes? Should I consider panels hung from the ceiling at 1st reflection point? What about diffusion?

Of course, I still need to convince my wife on all of this!