Comb Filtering Problem From Dual Center Speakers

Comb filtering, an imbalance in a tonal balance or "frequency response", is clearly audible when two speakers reproducing the same signal differ in distance, sometimes by as little as 1 inch. Therefore pros and commercial cinemas use only ONE center ch. speaker even though using two can potentially place the center phantom image in the middle of a non-AT [acoustically transparent] screen. Instead the principle called the" image proximity illusion", aka "the ventriloquism effect", should cover most situations when mounting one speaker below or above the screen: listeners usually perceptually fuse the acoustic image to the visual image their eyes see even if they are separated by up to about 10-15 degrees, or so. [It can vary by listener and of course the smaller the better.]

[@andrasora]

I think this test is great. Thank you. I think it would be great with human voice coming from the speaker as well.

[@Enemji]

Excellent procedure. Thanks 🙏🏼. I now keep my center channel vertical. I am actually thinking of getting a single bookshelf speaker from the same speaker set and use that as a center channel.

[@MeZillch]

In Dolby Labs where they invent this stuff their center speaker (only one of course, because two cause comb filtering) is EXACTLY the same speaker as the L and R for the best sound stage. This is also true of recording studios and commercial cinemas. There the center hides behind the acoustically transparent screen.

[@bigdaddymex2003]

Wow right on great demo.

[@danedewaard8215]

Nice demo!!!!

[@jsizzle2k6]

ive been considering running dual centers. i currently have a klipsch rp500c and just bought a rp504c which is the same thing just twice the length and 4 drivers vs 2. so if i was to run the center preout to a 2 channel amp and place dual 500c centers directly beside each other essentially being a 504c but with dual tweeters vs 1. would the same issues persist. the 504c is roughly twice the length as the 500c anyways

[@adam3402]

This was very enlightening. I’ve always been a bit bothered by having a center channel below the TV, wishing it could somehow sound like it was coming directly from the center (using a normal tv, not a projector) and always thought that it may be a good idea to have dual center channels with one above and one below to create the centered image directly in the middle.. But your video shows why that wouldn’t be a good idea, haha. Any further thoughts on that? Basically just have to put it below or go with projector and speaker behind the screen?

[@m.zillch3841]

In a real commercial cinema there are three identical speakers in a straight line behind the acoustically transparent projection screen. That's the ideal but if you can't swing that you have a few choices: just above the screen, or instead just below, both hugging as close to the edge as possible, or no center at all (aka "phantom center"). Zillions of people use that option; they call it "stereo". It too has a phantom center image.

[@flex-cx9bi]

No, you should NOT aim for single driver for a certain register because of the "out-of-phase" cancellation shown here. Even if the shown effect also creates a comb filter I would say that it is of no importance here since it mainly effect the midrange and tweeter and not the bass as shown here.
What this demonstration shows is the importance of having your drivers time aligned to the listening position to prevent phase cancellation in the crossover region (about an octave).
There is another fenomen that's not discussed here and that is the out-of-phase cancellation because of room reflections, and the most significant reflection is the floor reflection that create a -6 to -12dB dip in the bass at approx. 80-300 Hz depending on the distance to the floor and the reflection coefficient.
By using several bass drivers at different distances from the floor you can even out this problem.
So using several bass drivers is beneficial to the sound and frequency response. It makes it much easier to find a good sounding position for your loudspeaker in the room.
As long as the drivers are basically time aligned you should not be afraid of using several bass drivers.
In practice you should aim at getting several bass drivers to be time aligned to your listening position within 0 to 1/5th of the distance between the top driver and the floor.
So this video is disinformative.
In practice one single driver is more effected by room reflection than two drivers are as long as they have different distances to the floor and still time aligned to the listening position to 1/5th of the distance between the top driver and the floor. Three or more drivers is even better as long as they are time aligned.

[@onderbecerik]

🙀🙀🙏🙏🙏🙏🙏👍