Odd REW graph - any ideas? - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 2 Old 02-13-12, 03:43 AM Thread Starter
Shackster
 
Join Date: Feb 2011
Location: Sydney
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Odd REW graph - any ideas?

I think I've seen similar graphs over time to mine so I am not yet at panic stations.

First off, the equipment I am using:

Dayton EMM-6 calibrate mic (cal file loaded)
Behringer Xenyx 502
Mic stand
Yahama RX-V871 (I've run YPAO)

After calibrating the sound card, I calibrated (to the best of my knowledge) the REW SPL to match my SPL reading, using about 80dB (+/- 1dB) as a reference.

I then did 4x 512k log sweeps from 10hz to 20Khz for each LP (listening position) which are only 2 feet apart (at best). Only the mains are measured (two subs on the way), and I've set the speakers to large so there shouldn't be any CO issues.

The results for each is as follows:

Main LP
Odd REW graph - any ideas?-main-lp.jpg

Right LP
Odd REW graph - any ideas?-right-lp.jpg

Left LP
Odd REW graph - any ideas?-left-lp.jpg

LP Average
Odd REW graph - any ideas?-lp-average.jpg

The first thing that struck me was the huge null at the main LP which centers around ~80 to 105Hz, but is virtually gone a foot or two to the right of that position, and largely diminished a foot or two to the left of that position. I'm sure it's possible, of course, but still somewhat jarring to see such huge discrepancies between such small distances.

Now, obviously, that isn't my main concern. Needless to say the concern is the ~40dB difference in the highest bass peak vs the lowest measured frequencies on the high end (6kHz+).

However awful the graph my look, I will say though that the sound produced for both music and bass is very pleasing to my ears and seems well balanced (I hate 'bass-clouded' or bass-heavy sound) on both the high and low ends. Given that, I am confused by the measurement results. Has any body seen similar graphs, or is my system just that bad?

As a reference, I did a NF (near-field) measurement of both my right and left speakers with the mic about at the mid-point of the drivers and at 0 degree incidence at an inch or two away. I have no idea if it was done correctly, I just guessed that that is how it is done.

The results were interesting and consistent for both:

Left:
Odd REW graph - any ideas?-nf-left.jpg

Right:
Odd REW graph - any ideas?-nf-right.jpg

I am receiving my subs hopefully this week, so I want to get everything configured correctly within REW before they come. I am planning to level-match the subs, run them both through my FBQ2496 in stereo mode so the overall response is treated (and not done so individually) and only attenuate the peaks in the response. Luckily, there are very few nulls if any in the two designated spots I have for the subs in my room so that is a blessing.

Anyway, does anyone have any clues as to why my graph is so odd? I've seen the inverse happen with others (low bass SPL vs high SPL for the highs), but not so much like mine.

Any help would be most appreciated.

Cheers

PS- I'm curious about house curves. What determines the goals for the curve, personal preference, room behaviour, hearing sensitivity? I can't really see any information on that at, so I went with +10dB @ 20Hz and 0dB @ 80Hz.
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post #2 of 2 Old 02-13-12, 07:56 AM
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Re: Odd REW graph - any ideas?


Hey follz,

Yeah, the low end boost definitely looks peculiar. Make sure all tone and EQ controls on both the receiver AND the XENYX are set for flat. You can find a link with info on house curves in my signature.

Regards,
Wayne



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