# Measuring and interpreting impulse response and ETC



## vinculum (Feb 13, 2007)

I thought I'd start a thread on measuring and interpreting REW impulse response and ETC charts for my room for the purpose of planing and executing a room treatment strategy. I recently became aware of this function and find it a fascinating tool to look at energy reflections. I do not yet have any acoustical treatments except behind my AT screen. Those treatments include OC703 36"x24"x24" superchunk traps in left and right corners. Covering the entire front wall and superchunks is 2" of black fiberglass duct liner. I've always felt that the audio can seem harsh and fatiguing at higher volume levels. My walls are paneled and suspended ceiling tiles are not even the acoustical type. After some discussions on other forums I'm convinced I should be using the impulse response and ETC measurements to identify my anomalies first. Then with surgical precision apply appropriate treatments instead of blindly throwing up absorption or diffusion. I also wish to confirm my measurement techniques and done properly. I'll post some graphs and more information when I get a chance to at home. I just wanted to get a thread established and topic introduced while I had a moment with my iPhone!


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## vinculum (Feb 13, 2007)

My measurement rig consists of a Dell 700m laptop, an EMU 0404 external sound card and a Nady CM100 mic (ECM8000 equiv). It does not have a calibration file, so I'm just using the generic ECM cal file floating around the internet. I've done the usual REW calibration for measurements.

Here is an initial chart I ran last night. The microphone is at the primary seating position. I measured the RIGHT channel only, No Subwoofer, no processing, Audyssey off, ect. Immediately what stood out to me are the evenly spaced spikes, which happen to come out to my room width exactly. 12.1ft

Is this what I believe to be some kind of flutter echo?
Is its down in level too far from the "big bang" to make any noticeable difference?
Should not have ETC clicked on in this image?


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## glaufman (Nov 25, 2007)

Some excellent questions there. I'm admittedly not the most knowledgable at reading the impulse/ETC graphs, but...
I'd say most definitely the repetitive spikes you see are a concern. Whether they represent flutter echo, or slap echo, or something else I'm not sure I can say. Can you get a friend to stand where your speakers are and clap their hands while you listen from your mic position? since the fist and largest of these appears to be less than 20dB down from your impulse peak, I would think taming these would make an audible improvement in your experience.
do you have hard floors (hardwood, ceramic...)? If so, you might try an area rug with some thick padding underneath, if not, yo might try placing some pillows at your first reflections points just as an experiment (FRPs are wherever on the walls/ceiling/floor you can see your speakers in a mirror while sitting in your listening position).


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## vinculum (Feb 13, 2007)

Thanx for your reply. Experimentation with absorption will be my next step to see how it effects the graphs. I have a few pieces of 703 left and some decent 1" studio foam that was given to me. Being a "home cinema" so to speak, there are multiple seating positions to tend to, and multiple speakers, so i foresee lots of legwork. I'd just like to see if there is an intelligent way to look at these graphs and concentrate my efforts. Hopefully someone with more knowledge will give some advice.

My floor is berber carpet. Someday I'd like to change that! I also have a slate coffee table, which can probably go. I'm sure its not helping the situation, but it does make a nice place to put drinks and remotes. I'll see if i can get more pictures up a little later.


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## glaufman (Nov 25, 2007)

One thing to note, as I just re-read your first post...
When you say it sounds harsh, especially at high volume levels... that can sometimes be caused by driving your amp into clipping, which is bad for your speakers as well as the sound...


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## vinculum (Feb 13, 2007)

Greg,

I'm using active studio monitors which have several layers of protection against clipping. They have an LED on the front which starts to blink when transients get near clipping. I can see the LED through my AT screen. I'm pretty certain my room is to blame, as I've had them in a much different room before and they sounded much better. Your concern is a valid one. I might not always have active monitors, so I need to keep things like that in mind for the future.


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## vinculum (Feb 13, 2007)

Just an update. What I'm reading on other forums seems to be that I should start with a general room treatment first, THEN start measuring and looking for odd problems. I figure I should start by putting up some general absorption on the side walls and ceiling first and revisit these charts. The front wall and front corners are already well taken care of with absorption. This was my original plan anyhow and doesn't cost much to try. Then I'll focus on the first 20ms and -20dB window to try and create a RFZ for the listening positions. I'll report back here with my results.


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