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Discussion Starter · #1 ·
I am getting some awesome help in the NHT speaker thread regarding some sound quality issues I am dealing with on my system (you rock cavchameleon!), but as a result came across something interested which appears to be more related to the my receiver (Denon 4311) that I am hopeful someone here could perhaps shed some more light on.


The image below is the frequency response of my center channel, as measured by my SPL meter approximately 6-7'' away from the front grill. For additional context, I had the mic propped up to be basically on axis with the middle of the speaker with a small but stable diameter object (don't have a tripod that goes that low) so I wasn't sitting in front of it or anything. Audyssey was turned off, and I played a test tones CD in multi-channel stereo mode with all other speakers unplugged from the AVR (minus the subwoofer - mainly cause I forgot about it lol) and recorded the results. As a final note, the crossover setting for all of my speakers is 80hz.


I think it is safe to ignore the roll off on the end at 7500hz, as that is probably a function of the RS meter. What is interesting is the 15+ db slow rise from 80-750hz! I did the same experiment again but this time using one of my main towers and the response was almost perfectly flat across the entire lower range with a slight 4-5 db boost on the upper end (which might have been an off axis artifact since I had the mic in the middle of the tower and only 8" away - not sure what an appropriate distance is for drivers spread out like that). Anyways, this control experiment verified that the measurement technique and equipment used was not causing the observed response on the center which I guess is good news...


I then thought, what if it is the actual signal being fed to the speaker from the AVR that is causing this? What I found was when plugging the center speaker into the "L" port on my AVR and running the same test I get a drastically different response! The second plot series shows this FR in parallel. While there is still a 5db swing across the range (I might have been two close to catch the C channel woofers) but it does look to have the a similar response to what I saw on the tower so this output variation does appear to be related to the information being sent TO the speaker and not the speaker itself.


What I am looking for guidance on is the following: Is this expected behavior for multi-channel stereo output on the center channel, or does this mean the AVR isn't feeding the center speaker correctly? Maybe multi-channel stereo doesn't work as I assumed - where it would play the same content at the same level across all frequencies for each speaker.


Thanks in advance!









P.S. I originally posted this in the specific Denon 4311 forum but thought it is best served as its own general topic
 

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In a multichannel stereo setup I think the front left and right are in stereo and the surround left and right are in stereo. It may send a combination of L/R content to the center speaker.


I'm not sure how the center is mixed.
 

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Discussion Starter · #3 ·

Quote:
Originally Posted by afrogt  /t/1522590/multi-channel-stereo-frequency-response#post_24484339


In a multichannel stereo setup I think the front left and right are in stereo and the surround left and right are in stereo. It may send a combination of L/R content to the center speaker.


I'm not sure how the center is mixed.

Thanks for the response - I figured something like that is going on.


Do different AVRs mix this sound mode differently?
 

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Discussion Starter · #4 ·

Quote:
Originally Posted by afrogt  /t/1522590/multi-channel-stereo-frequency-response#post_24484339


In a multichannel stereo setup I think the front left and right are in stereo and the surround left and right are in stereo. It may send a combination of L/R content to the center speaker.


I'm not sure how the center is mixed.

From what I've been able to find it appears that it is supposed to send a combination of the L/R to the center speaker. However, according to my plots this is not in fact being done.


Can someone else chime in if this is expected behavior or a sign my amp is misbehaving?
 

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It looks like it is using the center for the primarily voice band, which is what I would expect.
 

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Discussion Starter · #6 ·

Quote:
Originally Posted by DonH50  /t/1522590/multi-channel-stereo-frequency-response#post_24492716


It looks like it is using the center for the primarily voice band, which is what I would expect.

Hey Don,


Thanks for the response back. I figured that as well, but doesn't the fundamental voice frequency go down to 100hz or so?
 

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Not sure, and all my references are at home whilst I am, well, not at home.
I think I recall 100 Hz or so may be the lower end; the usual telephony voice band is 300 Hz to 3 kHz but that is for intelligibility not fidelity. My suspicion is that the processor is sending a narrow frequency range to the center channel to focus just on the fundamental'ish vocal range. It'd be interesting to see if the response changes with different processing modes. When I measured my system I did it in Pure Direct to get rid of most all processing.


It's all guesswork from me at this point, but I doubt the AVR is misbehaving; I think most likely it is designed to limit lower frequency content to the center. Helps prevent bass cancellations and such, and most centers are not designed for full-range signals (at least on the lower end).
 

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I think that perhaps you are looking for / at something that doesn't really exist ... as in "this is how it is". What the heck is "multichannel stereo" .... sure that exists for "R" and "L" channels and is probably obvious. But what does it mean for a "common channel", probably what ever the manufacturer wants it to be within "reason" of their designers.
 
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