Help understand REW measurement - Home Theater Forum and Systems -

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post #1 of 8 Old 06-13-08, 12:48 AM Thread Starter
Join Date: Jun 2008
Location: Coudersport, PA
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Help understand REW measurement

Well I've been trying for the past 2 days to figure out how to use REW.

It's a really nice program, and I appreciate the work that was put into it. Thank you.

This picture is my best attempt at getting a reading for my eD A3-250. I found out the hard way that I could only take a measurement from about 25Hz (actually that's all I dared) as the really low frequencies clipped my subwoofer. The Elemental Design subs don't include a governor (limiter) so as to maintain dynamic range and power.

Did I do it seemingly correctly? I don't understand why my subwoofer is dropping off at 80Hz.

That would be fine except that my receiver only goes down to a 100Hz crossover. So it seems I'm losing all the information between 80 and 100Hz

Any help in understanding what I'm looking at would be appreciated.

Also want to add that my speakers are set to "small" and my subwoofer is connected to the "LFE In" and not the "Line Level In". I have the crossover set to 100Hz (as I've said, that's the lowest I can go).

I came up with my current placement of my subwoofer by placing it in a corner and about 6 inches from the wall with the port facing the wall and the amp facing outwards by that being about my only option as I have such a high crossover and I wanted the sub to be near the mains to prevent localization as much as possible.

I then used my AVIA disk and RadioShack SPL meter and ran a 100Hz to 22Hz sweep of just the subwoofer and moved around the room until I got the flatest response I could see.

I then rearranged my entire room so that I could be sitting there.

Here's a shot of my room after the movements, I have my sub in the upper left corner of the room in the pic.

Thank you for your time,


Last edited by kamui5785; 06-13-08 at 01:01 AM. Reason: I hijacked someone else's Thread Title :p
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post #2 of 8 Old 06-13-08, 12:55 AM Thread Starter
Join Date: Jun 2008
Location: Coudersport, PA
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Re: First attempt at REW (help understand)

I was just thinking while re-reading my post.

Is it possible I'm sitting in a null at that frequency?

Or maybe the phase adjustment on the sub?

Thanks again for any help you might offer,

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post #3 of 8 Old 06-13-08, 03:43 AM
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Re: Help understand REW measurement

I would suggest playing a 80Hz sine wave then moving around the room to see if any places on the wall seem to vibrate more intensely than in other areas. A good indication might be a wall that will vibrate some in an area where the sound is less easily heard. My guess is that it would be a room mode between two opposing surfaces such as your left and right wall probably nearest to the floor. You might try folding some blankets about 5 times and placing them on each side of the room if this is the case to see if there are any improvements in the 90Hz area . If it helps then perhaps the area could use some bass trapping.
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post #4 of 8 Old 06-13-08, 05:16 AM Thread Starter
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Location: Coudersport, PA
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Re: Help understand REW measurement

Okay, here is my best attempt at REW.

And here is the same graph, but in the format you all ask for:

I found out some weird things too.

In order to get this frequency response, I had to adjust the distance setting on the receiver from 7.5 to 15.5 feet (delay).

I also found out that my phase control on my A3-250 is useless (which might be because of how many times I clipped the sub ). It turns out that I can either have 0 degrees or 180 degrees with NO in between. Also, it makes a clicking sound when you go all the way to 0 degrees (which is the only position to set the dial in that it will come out of 180 degrees [I'm probably not making any sense, but it's really not important anyways]) and then causes the sub amp to clip!

Unfortunately my GF is slepping and I'm waiting for my sub to come out of it's clipped stage again, so I can't yet give any listening evaluations.

I've come a long way with this and have learned a LOT about how my system works and interacts with the enviroment.

I just hope it sounds as good as the graph looks


P.S. Thanks for the suggestions, that just sounds like more work than I want to do after all I've been through already!
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post #5 of 8 Old 06-14-08, 02:37 PM
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Mike Bentz
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Re: Help understand REW measurement

8ft is about 7ms of delay, which would correspond to about 180 degrees at 80Hz - so that totally explains why adjusting your distance settings got rid of that dip.

Real quick...are your distance settings coming out within 1 wavelength of being correct? In other words, is 0 ft or 15 ft closer to the actual distance from the sub? What distance do you have the mains set to?

Btw, did you ever measure the sub just by itself? Acoustical interference like you were probably experiencing doesn't happen if your mains are turned off... (or unplugged)

-Mike Bentz
~It's all about compromise~

"It's territorial with the soundboard. So you're mixing and some dude comes by spewing opinions and trying to turn knobs. It's akin to going up to an artist and painting over his unfinished masterpiece. You just want to shove your paint brush up his nose and throw the soundboard out the window!"
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post #6 of 8 Old 06-17-08, 06:26 PM Thread Starter
Join Date: Jun 2008
Location: Coudersport, PA
Posts: 14
Re: Help understand REW measurement

I've been messing around like crazy with REW and my room and subwoofer placement.

Any more and I'll probably throw my back out!

I just can't seem to figure this stuff out.

I have tried moving my sub near-field, in the corner, along all the boundries, even directly in front of me.

I've moved my listening position in every spot in my room as well. I'm going crazy!

This is the best I've been able to get my subwoofer to sound, but it just seems since I'm not limited on placement, that I could do better. So please me, I just don't know what else to try.

I do realize that bass traps, a better sub, better room, an eq and all that would help, and I'm not asking for perfection, it just seems to me I could do better with room placement alone than what I have gotten.

Anyways, here's my subwoofer:

Here's my mains:

and with some funky phase and delay settings, here's my mains + sub:

What I'm hoping to hear is that it's really not that bad, I just hate to think how much I'm missing out on


Also want to add that when I hold the radioshack meter close to the speakers or port of the sub, I get an almost perfectly flat response, so it seems to me it's gotta be the room.

Please help, and thanks in advance,

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post #7 of 8 Old 06-17-08, 06:52 PM
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Re: Help understand REW measurement

What I'm hoping to hear is that it's really not that bad,
You can relax....most people would love to have a response like that..

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post #8 of 8 Old 06-17-08, 07:12 PM Thread Starter
Join Date: Jun 2008
Location: Coudersport, PA
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Re: Help understand REW measurement

I thought for sure that when I saw "brucek" as the one who responded that I would have to open REW again and take different screenshots of my measurements

If you mean that honestly though, then I am VERY pleased indeed!

I also thought about my mains, in that I had the RS meter pointed up towards the ceiling when I took those measurements, and I know that when I aimed it at the speakers from the LP it was tremendously improved, wheras the sub didn't make much difference at all.

Also, I have my sub calibrated a little hot in those images (I forgot to turn it down for measurment).

I have seriously been going nuts over this and my GF hates hearing BOOOOOMM-Beeooooop-beeeeeepppppp at 4 in the morning (Can't imagine why ).

Anyways, thank you brucek for taking the time to read my post and reassure me



BTW, it sound AMAZING! (I'm just being greedy )
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