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Comb Filtering Effect. What do we know about it?


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#1 of 9 OFFLINE   Panayotis Melas

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Posted February 05 2011 - 10:42 PM

Good day to all


Not long ago, I had a very informative discussion with Audyssey guy Chris Kyriakakis, asking him if I can use a pair of dipole speakers as Back (Rear) Surrounds.


In the same discussion (link = http://ask.audyssey....rround-speakers), I gave him a brief description of my system, explaining that I intend to use two center speakers instead of one, placing them side-by-side on the rack, in front of the front seaters and under the center of the screen.


Mr. Kyriakakis returned to me by NOT recommending the use of two center speakers, claiming that this would create a "comb filtering effect".


Although I explained that the main purpose to use two centers instead of one is to close the "gap" between the two front main L-R speakers, ude to their difference in size and therefore in SPL and soundstage, he insisted not to do it.


Briefly, my system consists of the following:


- A pair of Mirage M3-si front L-R (floor standing-bipolar)

- A pair of Mirage M5-si Surround L-R (floor standing-bipolar), placed behind the seaters, at an angle of about 30-40 degrees from the "sweet spot"

- Two Mirage MC-si speakers (normal bookself-bipolar) as front center ones, driven by separate power amplifier channels, which shall be fed by the same porcessor signal from the AV pre-pro (Onkyo PR-SC5507).

- Two Mirage OM-C2 speakers (larger bookself-omnipolar), hung from the ceiling on specially made stands, above the the front main L-R speakers, as front height L-R ones.

- A pair of Paradigm ADP-190 dipoles (small bookself), also hung from the ceiling on a special stand, located at the center of the space, behind the seaters and at about the same height as the front height ones.

- Separate power amplifiers for all speakers.


However, as I said above, Mr. Kyriakakis told me to abandon the idea of the two front centers, due to the possibility of the "comb filtering effect" creation.


What is your opinion on this?


Thanks in advance.



#2 of 9 OFFLINE   Leo Kerr

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Posted February 06 2011 - 02:28 AM

the problem with what is, in essence, a monaural signal (the center channel,) is that when you have two speakers producing the exact same signal, there will be areas where you have different frequencies combining and canceling throughout the space.  I remember seeing a fairly good description of this concept, with a couple of nice charts and graphs in the TAB book, The Master Handbook of Acoustics, 3rd Edition, by F. Alton Everest.  Chapter 17 is entirely about comb filtering. In short, though, there would be a "line" projecting out directly between the speakers that would be relatively "clean," and the further off to the sides you got, the worse this speaker-pairing would sound.

(I'm referring to this particular imprint, 'cause that's the copy I have on my shelf.  But in addition to this, it has a whole lot of good stuff in it..)


Leo



#3 of 9 OFFLINE   Panayotis Melas

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Posted February 06 2011 - 06:47 AM



Originally Posted by Leo Kerr 

the problem with what is, in essence, a monaural signal (the center channel,) is that when you have two speakers producing the exact same signal, there will be areas where you have different frequencies combining and canceling throughout the space.  I remember seeing a fairly good description of this concept, with a couple of nice charts and graphs in the TAB book, The Master Handbook of Acoustics, 3rd Edition, by F. Alton Everest.  Chapter 17 is entirely about comb filtering. In short, though, there would be a "line" projecting out directly between the speakers that would be relatively "clean," and the further off to the sides you got, the worse this speaker-pairing would sound.

(I'm referring to this particular imprint, 'cause that's the copy I have on my shelf.  But in addition to this, it has a whole lot of good stuff in it..)


Leo



Thanks, Leo, I have this book. I bought it long time ago, so I am not sure what edition it is. I am going to read that chapter carefully and I will be back.


Be well.



#4 of 9 OFFLINE   Leo Kerr

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Posted February 07 2011 - 01:33 PM

the scary thing is I remembered that, and knew exactly where to find my copy of said book.  I expect that I shant be able to remember anything useful for the next week or so!


Leo



#5 of 9 OFFLINE   Panayotis Melas

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Posted February 08 2011 - 05:09 AM

OK, Leo, hope you do. During these days, I've gone through the ch.17 - again - and this time I discovered really interesting things written there. From what I read, my case may not fall in that effect. But, I need more reading....



#6 of 9 OFFLINE   chuckg

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Posted February 08 2011 - 06:26 AM

Wow, it's a good thing they don't make MTM speakers, then, because they'd have horrendous comb filtering problems.


--ignore the man behind the curtain

#7 of 9 OFFLINE   smithb

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Posted February 08 2011 - 11:54 AM


Originally Posted by chuckg 
Wow, it's a good thing they don't make MTM speakers, then, because they'd have horrendous comb filtering problems.


From what I recall, the MTM design was never about best sound quality, but instead a compromise to fit the needs of placement issues that many have with a vertically aligned center speaker. From what I have read a matching (to the right and left speakers) vertically aligned center is still best.



#8 of 9 OFFLINE   David Willow

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Posted February 09 2011 - 02:04 PM

Chris Kyriakakis is a member here.  Maybe PM him and he may join in....



#9 of 9 OFFLINE   Stuart Booth

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Posted December 27 2011 - 05:27 AM

One is Enough: I have a Yamaha processor in the midst of my Quad pre and power amps. My front speakers are a pair of massive Cambridge R50 Tramsmission Lines (Kef B139; Kef B110; Kef T27; Coles Super-tweeter). For my centre I use a single Kef 103.2 (Kef B200G and Kef T15 tweeter).. I've tried two 103's both in series and parallel and it is just too loud with too much bass. I also have a £50 "top of the range" Celestion Centre Speaker, which is totally outclassed. To use only one of the Kef 103.2 is beautifull, though still a bit too Bass efficient. I would like to create a custom built 3-way using a matching Kef B110 (in the top?) if I could decide on the right crossover. - Anyone like to offer any advice please? Stu.