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Discussion Starter #1
Hi,

Can someone help me out with my measurement results? I am a newbie with REW, but I have 10+ years of experience calibrating my HT gear with AVIA and my RadioShack SPL meter.

I followed the "getting started" guide pretty closely including calibating the soundcard (external Behringer UCA202), following the "check levels" procedure (set levels to 75 db using my receiver's master volume set to -20db). Then I calibrated my SPL (radioshack analog) and got the following results:

(see next post for picture)

Room is in my basement and is L shaped with the main listening area measuring 21 x 13 x 7 (dropped celing).

My readings seem consistently higher than the 75db target. As I mentioned, I ran the check levels procedure at 75db on the SPL meter, and the 3-second check level test on the "measurement" function also showed 75db (although I had to adjust the spl level control up a couple of db's to get the pink noise to show 75 on the meter).

I am also curious about the calibration of my SPL meter. When I have it set to the 70db setting on the dial and match a test tone to the SPL (+5 on the 70 scale), the SPL reading in REW shows 75. However, when I change the dial on the SPL to 80db, the SPL reading in REW changes (goes down to 65db). Does changing the dial on the SPL change the input level gain on the microphone?

Thanks in advance for helping me out.
 

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I ran the check levels procedure at 75db on the SPL meter, and the 3-second check level test on the "measurement" function also showed 75db (although I had to adjust the spl level control up a couple of db's to get the pink noise to show 75 on the meter).
The last statement is your problem. The Check Levels toutine in the Measure popup panel is simply a sanity check that your End frequency matches with the levels you've set before testing. You don't readjust unless it tells you the levels are bad.

Either way, the plot placement is an overall average of 75dB taking into account the highs and lows, and overall your graph placement is fine. If you want to move you plot up and down, do so with the Trace Offset feature.


Does changing the dial on the SPL change the input level gain on the microphone?
Yes.

Please change your graph mode from LIN to LOG using the Freq Axis button icon in the upper right hand corner of REW .

brucek
 

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Discussion Starter #4
Thanks Bruce.

I re measured without fiddling with the levels in the measurement function, and here is what I came up with:

rew measurement 2.jpg

I have a rather nasty hump at 18.7db (this measurement was taken with Audyssey MultiQ engaged on my Denon). Any ideas how I could get rid of it? From what I understand about bass traps, they dont work well under 60Hz or so....

One other question about SPL meter calibration. The "getting started" guide suggests that the RS analog meter is calibrated at 80db. So I switch the manual dial to the "80" mark on the dial, adjust the volume on the receiver so that the RS meter registers 80db, then adjust the SPL calibration in REW to indicate 80db. All is good until I try to run sweep tests at 75db. I select the "70" mark on the RS SPL meter, do a levels check in REW settings, and REW tells me the levels are 66db when the RS meter is showing 75db. When I recalibrate the RS meter at the "70" mark instead of the "80" mark as suggested in the guide, everything works out fine. Any thoughts? SHould I just calibrate the SPL at 70 instead of 80? Thanks.
 

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Discussion Starter #5
If it helps, my sub is an HSU VTF HO. I am running it in MO mode - I have the "Turbo" attachment which enables it to extend down flat to 16Hz in ME mode, but I am running without it right now because the seal between the Turbo and the sub's ports was bad. Looking at the FR in my graph above, it doesn't look like I exactly need more output at 16Hz....

The HSU is my first "real" sub. It recently replaced a 10" DefTech ProSub100, which worked fine, but had literally no usable output past 27Hz. The HSU on the other hand is a real monster. It literally shakes my entire house from the foundation on up. I had no idea what I was missing out on in the low 20's.
 

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Discussion Starter #7
Yes, the RS meter rotary dial should be set to 80dB, and the levels are to be set to 75dB (not 80).
I actually was setting levels to 75, not 80, I was just setting the levels to 75db using the 70 setting on the dial of the SPL meter. So if I understand correctly, I need to set the dial on the SPL meter to 80, calibrate the SPL meter against the SPL reading on REW to 80db's, and then set levels to read 75 ( a reading of -5 on the 80db scale)? Actually now that I think about it, I shouldnt be looking at the actual SPL meter after it has been claibrated anyways, right?

Thanks for your help!
 

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So if I understand correctly, I need to set the dial on the SPL meter to 80, calibrate the SPL meter against the SPL reading on REW to 80db's, and then set levels to read 75 ( a reading of -5 on the 80db scale)?
You're making this more difficult than needed. :)
Simply set the RS meter rotary dial to 80dB, and the level at the listening position to 75dB. Everything is set to 75dB - not 80.

The reason you don't use the 70 setting on the meters rotary dial is because there wouldn't be enough headroom before you would clip the meter at full - a likely event as a result of peaks in the subs response. The 80 position for the dial allows for peaks that don't clip the meter.

brucek
 

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Discussion Starter #10
Move it around - specifically out of a corner.

I moved the sub from the corner to the middle of the front stage just beside my center speaker and no change in the bottom end spike. Any other ideas?

rew measurement 3.jpg


Is it possible that I have a room problem at 20Hz?
 

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Discussion Starter #11 (Edited)
Just for fun, I put the sub back in the corner and switched it to Max Extension mode (put the turbo attachment back on), rechecked levels to 75, and ran another sweep. All this did was move my spike back from 22 to 15...

16hz corner.jpg
 

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