Comb Filtering, Acoustical Interference, & Power Response in Loudspeakers

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admin

Audioholics Robot
Staff member
Comb Filtering and Acoustical Interference are two audio terms that relate to the manner in which two or more sound sources (such as two separate speakers or two drivers within a single speaker system) interact and affect each other. The importance and audibility of these phenomena are the subject of this article, and they are a source of a continuing difference of opinion among well-respected equipment designers and acoustic theorists/researchers. Dealing with potential acoustical interference issues of multiple drivers in the same loudspeaker cabinet is something any serious designer should be concerned about and not just brushed off as a measurement artifact that doesn't have real world implications.


Discuss "Comb Filtering, Acoustical Interference, & Power Response in Loudspeakers" here. Read the article.
 
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shadyJ

Speaker of the House
I'll admit to not understanding all of the article, but it was interesting nonetheless. I would assume line arrays work by having so much cancellation and reinforcement that it becomes a relatively flat frequency response and the combing effect is smeared out by averaging all the signals produced by all the drivers. Do line arrays have the acoustic interference in the vertical plane? If so, why couldn't that also be remedied by using a grid of drivers instead of just a line? I never see that- 'grid arrays'.
 
gene

gene

Audioholics Master Chief
Administrator
I'll admit to not understanding all of the article, but it was interesting nonetheless. I would assume line arrays work by having so much cancellation and reinforcement that it becomes a relatively flat frequency response and the combing effect is smeared out by averaging all the signals produced by all the drivers. Do line arrays have the acoustic interference in the vertical plane? If so, why couldn't that also be remedied by using a grid of drivers instead of just a line? I never see that- 'grid arrays'.
Yes you pretty much got it. Line Arrays have interference in the vertical plane which designers try to minimize by narrowing the beam width vertically.
 
Gordonj

Gordonj

Full Audioholic
Yes you pretty much got it. Line Arrays have interference in the vertical plane which designers try to minimize by narrowing the beam width vertically.
The interpretation of Line Array speaker clusters is a different topic then the comb filtering article. The effect of using line array design approaches by 1/4 and 1/2 wave formulas allows for the reduction of the inverse square law. With traditional speaker approaches the Inverse Square Law is that every doubling of distance reduce the level by 6dB. With the use of Line Array design approaches that doubling of distance is now only a 3dB of reduction in volume. Further, 1/4 and 1/2 wave combining, that occurs at the cluster location, allows for directional control down to much lower freqs. then "traditional speaker clusters" due to the "creation" of one line source driver (the longer the cluster in boxes/height the lower the overall frequency control.)

Gordon
 
agarwalro

agarwalro

Audioholic Ninja
Gene said:
on the topic of comb filtering. Some engineers use this term interchangeably with acoustical interference implying the audible effects of comb filtering between a pair of speakers playing in a room is similar to multiple high frequency drivers spaced further apart than their common wavelengths of operation in the same cabinet.
Must be the same "engineers" who use speaker sensitivity/ efficiency or phase/time aligned as interchangeable terms.

Acoustic interference is a physical phenomenon resulting from interaction of sound waves moving in air, whereas comb filtering is an electrical phenomenon resulting from summing a signal with a delayed version of itself. Acoustical interference of single frequencies under controlled conditions can be made to graphically look similar to a comb filters' response. To be fair, in an ABX test the physical and electrical outcomes may be audibly indistinguishable.

In a real life listening scenario, the acoustic interference, like room modes and floor/ceiling/wall bounce will swamp out all but the most egregious electrical errors, like incorrect polarity between drivers and amp clipping.
 
MinusTheBear

MinusTheBear

Audioholic Ninja
Is it a far assumption that the difference between acoustical interference occurring within the driver layout of a loudspeaker will ALWAYS share the same signal and amplitude while listening to a pair of speakers in stereo, the Left/Right speaker might not always share the same signal and/or amplitude. You talked about two sound sources sharing the same signal, say you change the amplitude of the one sound source, what implications does this have on comb filtering and/or acoustical interference?
 
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Beatmatcher247

Full Audioholic
A while back, I asked about adding another set of Synchrony One towers to the front would be and was advised against it because of comb filtering. I don't understand that much about it, but would the following setup sound like a disjointed mess because of comb filtering?

 
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Beatmatcher247

Full Audioholic
Sorry it didn't link in the post above.

 
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gotchaforce

Junior Audioholic
Heh, no attention given to this article because it flies over most peoples heads.

It was explained VERY well most people just dont have the patience to take it in.

They rather talk about how pretty speaker with horrible headroom and power response measurements compares to the other pretty speaker with horrible headroom and power response measurements.
 

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