Comb Filtering Confusion - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 32 Old 11-27-06, 08:07 PM Thread Starter
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Re: Comb Filtering Confusion

Unfortunately I can't answer that yet. About two weeks prior to starting this thread, I had put in a contingent offer on another house. I had thought that by now I'd at least have some nibbles on this house. No such luck. The housing market in this area has all but crawled to a total stop. So depending on how long it takes to sell this house, will determine when I can start on the home theater in the new house. Fortunately for me, the owners of the other house haven't gotten any other offers. Even though the housing market is really slow, I don't understand why people aren't interested in this one. It's more than fairly priced, plus we just sunk about $20k worth of upgrades into it without raising the price to make it more attractive. Still nothing. Go figure. I just hope that the other house doesn't get sold out from underneath me. At this point, all I can do is wait and see what happens. I'd appreciate any volunteers for good luck finger crossing.
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post #22 of 32 Old 05-11-07, 09:53 PM Thread Starter
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Re: Comb Filtering Confusion

WELL IT'S ABOUT TIME !!!! GOOD GRIEF !! I was beginning to think we were never going to sell this place ! FINALLY !! And the house we wanted was still for sale so we bought it. Yea !

I deliberately started staying away from HT forums because it was getting to be depressing not being able to set-up my stuff. But now there's light at the end of the tunnel. There's a lot of good info in this thread and I plan on referring back to it when I start getting the theater set up. Thanks for the help. So don't be surprised if I start asking more questions. But that will be several months away yet.
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post #23 of 32 Old 05-13-07, 09:25 PM
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Re: Comb Filtering Confusion


You’re not gong to stay away until then, are you?

Regards,
Wayne



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post #24 of 32 Old 05-13-07, 09:43 PM Thread Starter
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Re: Comb Filtering Confusion

No. In fact I've started looking at the pics some of the members have posted of their own HTs to get some ideas as to how I want to do mine. I plan on using the brain-power within the "Home Theater Design and Construction" forum to help me with mine - particularly with the accoustics.
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post #25 of 32 Old 05-18-07, 05:39 AM
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Re: Comb Filtering Confusion

All this talk about comb filtering has got me wondering. Is the phenomenon ever used intentionally by speaker makers to achieve some particular design/sound goal. I'm thinking specifically of Definitive Technology bipolar speakers and Martin-Logan dipolar speakers. Both designs must suffer from extreme comb filtering if what I have read here applies to them. Must make situating them in a room very difficult.

Any thoughts on this?

Greg
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post #26 of 32 Old 05-18-07, 01:05 PM
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Re: Comb Filtering Confusion


How, or what about the design of those speakers, would make them suffer from comb filtering? Not trying to challenge you, just want to find out so maybe I can give a reasonably informed answer.

Regards,
Wayne



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post #27 of 32 Old 05-18-07, 02:52 PM
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Re: Comb Filtering Confusion

Well, let's see. The Def Tech's have the same signal coming from two sources at different locations, one on the front of the cabinet, the other on the back. I have to believe that there will be interference at some point. Dipolar speakers, such as Martin-Logans, Orions, Magnepans, et al, have an equal but out-of-phase signal coming from the same source but from the rear of the speaker. Again interference between the two wave fronts, one direct and one reflected, will most surely raise its ugly head at some point. Both types of speakers can, and often do, make beautiful noise. But I question their ability to be accurate except at certain frequencies and at certain location - both for the speaker and the listener. This is must reading.

http://www.legacyaudio.com/engineer/stereo-effect.pdf
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post #28 of 32 Old 05-18-07, 06:35 PM
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Re: Comb Filtering Confusion


Okay, I see what you mean. The bouncing-off-the-wall and out-of-phase thing have nothing to do with comb filtering. Comb filtering is generally recognized as a problem that arises when you have two transducers operating in close proximity of each other. This is why it’s typically recommended not to use two center channel speakers, for instance: Move yourself off center the slightest bit and what is essentially a mono signal is “split” and arriving at your ears at two different times. You can easily hear the effect.

Regarding Def Tech and Magnepan, I have to believe they design their speakers with the effects of the rear signal in mind, as Legacy says they design their speakers with each specific application in mind. The popularity of those brands should attest to the fact that they must be doing something right.

Regards,
Wayne



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post #29 of 32 Old 05-18-07, 09:16 PM
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Re: Comb Filtering Confusion

Wayne,

I appreciate your thoughts on the subject. I still believe, however, that comb filtering occurs in the examples I previously listed purely because of the way they are designed. Def Tech' bipolars are perfect examples of "two transducers operating in close proximity of each other". OTOH, comb filtering occurs all the time at every listening position in probably all but the most highly acoustically treated listening rooms. So I guess it's not always a bad, or even noticeable, effect. See:

http://www.harmankardon.com/technolo...b%20Filter

Always enjoy a good discussion. Thanks.

Greg
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post #30 of 32 Old 05-19-07, 05:14 PM
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Re: Comb Filtering Confusion


Actually, I think I gave a rather insufficient definition when I said “two transducers operating in close proximately.” In the case of the dual center channel speakers, you have the drivers on the same plane, right next to each other. That’s when you can easily get a comb filtering effect: the signal is essentially point-source, but not time-aligned if you’re not perfectly centered. The further you physically move the speakers apart, the less it becomes a problem, because then they can be localized separately.

True, the Def Tech drivers are operating in close proximity, but they aren’t on the same plane. They are opposed. And if I recall, the Magnepans naturally generate sound in both directions. By the time the rear soundwave bounces off the back wall and whatever else it might hit before it reaches your ears, its delay factor is much greater than you’d get with the same plane scenario. That’s why you won’t get that kind of comb filtering with the Defs and Mags.

Of course, that’s not to say there won’t be any comb filtering at all. But as you note, acousticians tell us that most rooms comb-filter, because of reflections. You can easily see it on a graph if you REW your speakers full-range. And as you note, it doesn’t appear to be particularly audible or destructive for the most part. However, if the room is already adding that much, I can’t really see how speakers like the Defs and Mags can make the problem worse. It’s probably a Catch 22: dampening the room more would reduce the comb filtering, but it would also reduce the ambience effect of the speakers.

Regards,
Wayne



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