Understanding sub phase/group delay for placement

jtalden

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May 22, 2017
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247
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Arizona, USA
My AV System  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
Rotel RMB-1066 6 chnl P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
I'd be grateful if you have any observations or ideas.
SW to mains XO timing looks ideal.

Misc thoughts:
  • This SPL result is actually more in line with what I would expect based on the FDW measurements. SPL charts I had seen posted by others previously were perfectly flat SPL results. I had wondered how any EQ method can impact strong room effects like both you and I have. That shouldn't be possible. Those with flat SPL results apparently have very favorable room setups.
  • Your RT60 is near the low end of the recommended range and that suggests you have significant room treatments so they must not be a solve-all solution either.
  • Your room curve doesn't rolloff at higher frequencies. That is a bit unusual for most tunings at the LP.
 

FargateOne

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Jun 5, 2017
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My AV System  
Preamp, Processor or Receiver
Rotel 1562
Additional Amp
Bryston 3B3 for fronts mains
Universal / Blu-ray / CD Player
Cambridge CXU
Front Speakers
B&W 804 D2
Center Channel Speaker
B&W HTM4D2
Surround Speakers
B&W 705
Subwoofers
SVS PC-2000
Other Speakers or Equipment
10 PEQ filters/channel in receiver with REW
Video Display Device
Samsung UN55ES8000
May I ask a question about Group delay. I read the REW help about it and some others sources. The goal is to get the most flat line possible; this is possible , among other things, by choosing the right place for the sub. If I see a big spike or an abyssal dip those FR area can't be EQ because, very often they are at the same FR than a dip in FR response which can't be EQ. In the capture here, from the mdat at post #37, I see a flat GD graph between 100Hz and 200Hz for the L,R which tell me that I can set a filter Q and a gain of 2 or 3 db without messing with phase, ... isn't it?:hide: For the CC the dip at 164Hz says not to EQ higher? Or Is it the alpha male for all mains and it forbid to EQ those 3 channels higher than 164Hz? Or should have generated excess groupdelay response?
 

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JStewart

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SW to mains XO timing looks ideal.
Credit Dirac for that.

Those with flat SPL results apparently have very favorable room setups.
This was my assumption. What I did notice one time looking at some measurements Sonnie had posted (good room) was the range (peak to peak) of the HF comb filtering on his response was about 1/2 or less of what mine is using the same smoothing.

Your RT60 is near the low end of the recommended range and that suggests you have significant room treatments.
Yes it is. A little overdone for 2 channel but good for multichannel is my listening impression.

Your room curve doesn't rolloff at higher frequencies. That is a bit unusual for most tunings at the LP.
Also correct and the speakers are not toed in either which makes it more surprising. About 8ft from MLP to the speaker plane and the speakers about 8ft apart to be on either side of the sceen. I believe it to be the speakers. Other speakers I've had in the room have shown more roll off. With 62 year old ears it doesn't sound bright at all to me. So far the one benefit of aging I can point to. :)

Amazing what you are able to deduce from a set of measurements!
 

jtalden

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Joined
May 22, 2017
Messages
247
Location
Arizona, USA
My AV System  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
Rotel RMB-1066 6 chnl P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
I don't use GD or excess GD to decide any EQ adjustments. Maybe there are others that do and will chime in. I am more comfortable using the other charts. [In my room and many other marginal rooms the unwindowed GD is basically meaningless for me. When windowed, the GD chart makes more sense, but still is difficult to interpret as the GD spike size and frequency location changes greatly as the FDW width is changed. The SPL, Wavelet Spectrogram, and waterfall charts are easier for me to interpret.]

PEQ between 100 and 200:
The sharp notch in the FL and CC SPL at 109 Hz cannot be removed using EQ. The sharp notch in the CC SPL at 164 Hz also cannot be removed. Any EQ those areas can effect the surrounding frequencies however. Changes to the speaker and LP positions can effect these notches, but often it just changes the frequency location of them. For a clearer understanding we can open the EQ panel and manually place a peak filter at a strong notch and view the SPL impact with various gain and Q changes to the filter.
 

FargateOne

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Thread Starter
Joined
Jun 5, 2017
Messages
65
My AV System  
Preamp, Processor or Receiver
Rotel 1562
Additional Amp
Bryston 3B3 for fronts mains
Universal / Blu-ray / CD Player
Cambridge CXU
Front Speakers
B&W 804 D2
Center Channel Speaker
B&W HTM4D2
Surround Speakers
B&W 705
Subwoofers
SVS PC-2000
Other Speakers or Equipment
10 PEQ filters/channel in receiver with REW
Video Display Device
Samsung UN55ES8000
With 62 year old ears it doesn't sound bright at all to me. So far the one benefit of aging I can point to. :)
You bet! I am 62 too and are my ears too!
 
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