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Discussion Starter #1
Hi guys,
After building an IB about a year ago, I'm finally getting around to taking REW measurements. I have a tenuous grip on all the setup procedures, but I followed the help file and think I got it right.

I'd appreciate any feedback on how response looks and whether I should be EQing further (I do have a BFD in the chain, but no filters are set up).

Setup for measurements is: Sub only, 80Hz lowpass enabled on Denon 1909 receiver, sub amp is a Behringer EP2500.

Measurements were taken in the primary seating position, 15 feet from the sub. The room is about 25x35, and is a combined TV room and kitchen, with lots of open areas and glass and tile.

For some reason I can calibrate everything just fine at 75db, but when it's time to measure I have to increase volume to avoid a "level is too low" warning.

My goal is to try the "hard knee house curve" outlined by Wayne P, so that's what I have loaded on these screens.

Thanks for any advice!

No smoothing:



1/6octave smoothing:
 

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For some reason I can calibrate everything just fine at 75db, but when it's time to measure I have to increase volume to avoid a "level is too low" warning.
There is a reason for that. The Check Levels routine in the Measurement screen and the Check Levels routine in the Settings screen use different values to generate the pink noise test signal.

The Check Levels routine in the the Settings screen uses the fact that you have the Check/Set levels with Subwoofer pull-down selected to generate its test noise (this a band limited signal with a low and high cut of 30Hz - 80Hz).

REW wants to double check and verify that the end frequency of the sweep that you have selected in the Measurement panel roughly matches the test signal setting for sanity, and so its Check Level routine uses the end frequency as the test pink noise hi-limit cutoff. So, if you had (for example) 20KHz as the end frequency to measure for your sweep, and you were measuring your subwoofer, you can see how the pink noise would be different (between the two Check Levels) and as such the low level signal you're experiencing.
To measure a subwoofer you should have the limits of the sweep in the Measurement routine set to 0-200Hz.

Often, even if you have the levels and sweep frequency set correctly, a peak or dip in the response of the speaker being tested will have energy at a frequency that trips the sanity check and announces that levels are too low or high.

Simply return to the Settings screen and adjust the input level of the soundcard a bit lower and then run Calibrate SPL and carry on.

how response looks and whether I should be EQing further (I do have a BFD in the chain, but no filters are set up).
Your response looks quite good and I don't see much there that a BFD would correct. Your only trouble is between 30-40Hz and since you can't move an IB around, you're basically stuck with the problem, other than moving your seating position (and that may not help). This is (as I'm sure your aware) the biggest problem with IB's.
Anyway, the dip at 40 is sharp and wouldn't be too audible. The one at 32 is a bit worse.
BTW, smoothing is not usually used on sub plots.

brucek
 

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Discussion Starter #4
brucek and robbo266317,

Thanks very much for the replies! Having nothing to compare with the IB, I'm glad my curve is reasonably good.

Bruce, your explanation of REW levels makes perfect sense - I had missed the frequency differences in the settings.

The IB has been a mixed bag for me. It's technically fascinating, and my wife loves its invisibility, but it's a very subtle, smooth sound that you don't really notice right away. It's great for movies, but when you've been raised on lots of muddy mid-bass thump in your music, it's tough to think of a flat response as "better". I've also discovered that I occasionally I get annoyed by 15-20Hz frequencies, no matter how well-balanced. :yikes:

I'm going to experiment with some house curves now that I'm finally up and running with REW.

Thanks again,
cokeefe
 

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Discussion Starter #6
Thanks for the reply Wayne. And also for your house curve manifesto, which I'm still studying.
 
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