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Optimizing 16 m² room Equalisers (HW)
Old 3 weeks ago
  #31
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Quote:
Originally Posted by akebrake View Post
I noticed high distortion (20%) and some times high background noise. (pic)

Are you sweeping loud? Or too much mic gain? Too much send level? (REW O/P)
No, not very loud. I think I'm at -8 dBFS in REW and the output is at around 50 % volume. The microphone gain is pretty high and I'm shooting for -20 dBFS to -24 dBFS in REW.

Quote:
Originally Posted by akebrake View Post
Check the Oscilloscope Tab after a measurement (for headroom) if critical. e.g. very strong modes.
Can you show me how to do that?

Last edited by johannburkard; 1 week ago at 06:01 PM.. Reason: Microphone gain, not volume
Old 3 weeks ago
  #32
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Quote:
Originally Posted by johannburkard View Post
...Can you show me how to do that?
Imedately after a sweep is performed go in the Scope tab. There y can see the outgoing log sweep voltage amplitude on the timeline, 100% (nearly) if I remember correctly, overlayed is the received signal.
Which varies a lot in a room. You have to zoom in and tweeak a little
Strong modes in the low end can easily distort the measurement.
Note 50% voltage is only 6 dB down.

8350 analog input is rather sensitive. Try to optimize the gain staging from REW generator out to spkr in.

Good luck
Old 3 weeks ago
  #33
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Quote:
Originally Posted by akebrake View Post
Imedately after a sweep is performed go in the Scope tab.
I did two quick experiments today but forgot to do that.

Next time.

Quote:
Originally Posted by akebrake View Post
8350 analog input is rather sensitive. Try to optimize the gain staging from REW generator out to spkr in.
Well, I have reduced the microphone gain and increased the output. What's weird is that I get these peaks in the measurements.


Random REW measurement 1 by Johann, on Flickr


Random REW measurement 1 by Johann, on Flickr

Strangely, this box also has problems with playing back music (probably due to futex'es timing out in the Linux kernel ) so that could also be the reason.
Old 3 weeks ago
  #34
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Quote:
Originally Posted by johannburkard View Post
Well, I have reduced the microphone gain and increased the output. What's weird is that I get these peaks in the measurements.
Quote:
Strangely, this box also has problems with playing back music (probably due to futex'es timing out in the Linux kernel ) so that could also be the reason.
Hi johann,

I'm not a computer guy so I cannot help here. ( I'm on Mac btw)
Maybe John Mulcahy (REW author) can advise if you post on AV Nirvana Forum.

Cheers

PS Its quite possible that this dist figure don't affect the results in significant ways, but it feels a bit "unsafe" to spend hours scrutinizing measurement and then find out they are not valid...
Old 2 weeks ago
  #35
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In many SPL graphs I've seen on gearslutz, there is an area of 100 Hz to maybe 500 Hz where you'll see wild swings before things start to settle down. In my screenshot

Quote:
Originally Posted by johannburkard View Post
and in this one by @che_guitarra:

Quote:
Originally Posted by che_guitarra View Post
Is there a reason why things seem to get smoother at around 500 Hz and is there anything specific that is causing these peaks and dips between 100 to 500 Hz?

Last edited by johannburkard; 2 weeks ago at 03:52 PM.. Reason: Spölling
Old 1 week ago
  #36
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I've bought two more Monster Bass Traps, one with Range Limiter, one without.

With the two new Monster Bass Traps, I've rearranged the panels on the rear wall. I now have (left to right) a Monster Bass Trap, two 244 Bass Traps and a Monster Bass Trap in a 45 ° angle in the rear right corner.

I have also rearranged the Spot Panels on the right side to cover a first reflection point.

Overall, the results are pretty good:
  • The 83 Hz room mode from the left speaker was reduced by maybe 40-50 %.
  • The suckouts between 75 and 109 Hz from the left speaker are either gone or much reduced.
  • The 84 Hz room mode from the right speaker is pretty much gone completely.

I still have one more Monster Bass Trap that I will probably place that on the ceiling or maybe the right side wall.

The .mdat is here but it's all without SAM so the frequency response with SAM is of course better.

Overall, the effect of the new panels on Genelec SAM has been that fewer filters are used. Here are the parameters, before and after (filter Q omitted):

Code:
before			after

  42.1   -9.5		  42.3	 -9.8
  43.0	 -0.1		
  44.3	 -9.8		  44.4	 -9.0
 139.0	-10.1		  60.9	 -0.7
 160.1	 -4.7		 141.6	-10.4
 211.5	 -3.8		 211.2	 -3.2
 345.2	 -0.3		 323.5	 -0.5
 992.7	 -1.0		1000.0	 -1.3
One thing regarding Genelec SAM that I didn't know: Genelec SAM uses the same filter parameters for left and right speakers. I had expected them to optimize both speakers individually which is implied by the software somehow but they don't.

@akebrake I checked the scope tabs this time but there was no obvious sign of overload. I guess the distortion numbers are BS in my measurements.
Old 1 week ago
  #37
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Last edited by johannburkard; 6 days ago at 09:28 PM.. Reason: Making things clearer.
Old 1 week ago
  #38
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Quote:
Originally Posted by johannburkard View Post
One thing regarding Genelec SAM that I didn't know: Genelec SAM uses the same filter parameters for left and right speakers. I had expected them to optimize both speakers individually which is implied by the software somehow but they don't.
You can select if you want to use individual filters or not by enabling or disabling "use symmetric eq" in the calibration screen.
Old 1 week ago
  #39
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Quote:
Originally Posted by Ilkka View Post
You can select if you want to use individual filters or not by enabling or disabling "use symmetric eq" in the calibration screen.
Thanks for the tip, I'll try that out next time.
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