Two centers? Bad idea? - Page 2  

I've heard 'em and stand by my stated position.

Concomittant. Nice one Kal. (Scrambles for mom's moth-eaten OED.)

Sanjay

Thanks. Forgot the spell-check.

An important question to ask is whether more than 3 center channels are utilized in SDDS encodes. To my knowledge, filims that also had an SDDS sountrack on them still stuck with 5.1, despite SDDS's capability for 5 onscreen channels instead of 3. I am not aware of any films that actually had mixes that used more than 3 on-screen channels, but I would be curious to know if they exist.

That of course, ia a significantly different question than dual speakers though.

You are correct for what you want to achieve, Kal -- a precise FR/phase/time "image" at your seating position.

I'm trying to use affordable parts to provide an immersive sound field, including good dialog intelligibility, over a wide area.

I discovered that multiple centers sounded better to me by accident, and I continue to simply recommend that people try it with speakers they already have before spending money on it.

Back to the original posters situation: I'd like to get some clarification on the dimensions of his theater. 12 to 15 feet between mains and 900 square feet would result in a room only 6 to 8 feet deep! That's darn close to a 102" screen!

My nickels worth:

Although personally, I can't stand horizontally oriented MTM centers (I'm by no means an expert, but I have tried a few, and myself, my wife and others all through a movie often say "what did he say?" "I didn't understand what he said", etc). I ditched my speaker setup in favor of 5 identical matching bookshelves and have no more off axis intelligibility problems.

Anyway, to the point: Its well known about the issues of horizontal MTM centers (no offense, I know some like them fine, and actually ALL MTMs are fine when ON AXIS), so you would think dual centers would be a bad idea. But maybe not necessarily.

I do not know the math behind it, but the problem with MTMs is the interaction between the midbass drivers, that usually cause problems near the vocal range. However, adjusting the distance between the midbass and/or tweaking of the crossover can reduce the problem.

I seem to recall reading somewhere that at some point (a certain fraction of wavelength? 1 full wavelengths?) that the interaction becomes a non-issue. That must be true, because afterall, all our stereo TVs we own when fed a mono signal would experience the same issues off axis, and I have never noticed it to be a problem.

Point is, spread far enough apart, it *might* work. I'm just saying from a mathematical standpoint, it should work. Now in the real world, it may not fly.

Food for thought.

-Alan

Right but that is only a part of the issue. It is the distance between ANY 2 drivers that are reproducing the same sound and that means it applies to the woofer and mid or the mid and tweeter at crossover. You should have any 2 drivers (that are producing the same signal) less than 1/2 wavelength apart or you will get constructive and destructive interference in the plane of their displacement.

Note that there are few (if any) high quality domestic loudspeakers for any application in which drivers are horizontally arrayed. That is to avoid this interference in the horizontal plane.

I say you skip the second speaker and jump right ahead to having a third. :cool:

More is alway better, isn't it? :eek:

Not if they're reproducing the same mono information.

Sanjay

It is good to remind folks who may not have done any speaker design why one usually does not mount drivers reproducing the same fequency side-by-side, but instead mount them above one another --- and that is the fact that our ears are located on the sides of our head, making us much more sensitive to variations in the horizontal plane.

So an ideal center channel would be something like a Walsh driver with something like double the power handling of the mains, putting out a nice cylindrical wavefront.

Lacking that kind of solution, I continue to offer that for many of the 'common' affordable theater brands, that have center speakers that sound great on axis but not so much even 10 degrees off axis AND instead of being twice the size of the mains as the relative power distribution woiuld suggest, are half the size -- you might find multiple centers an improvement.

I.E., even if imperfect, a comb over is better than a bald spot :)

In my experience, only those who comb over believe this.

True, but even 2/3 of a wavelength to a full wavelength isn't too bad if seated not too far off-axis (less than 45 deg or so). The higher ratio of separation to wavelength you go, the tigher the banding becomes.

no.

I used a M&K S100 center speaker for 10 yrs. When i upgraded to Revel Performas for the fronts i still used the S100. After 2 weeks i decided to add the matching Revel C30 center. I didn't like the sound from the C30, a bit hollow, so i went back to the S100. However, now the S100 no longer sounded right. Using a Radio Shack speaker selector, i did an A/B test of these 2 center speakers- to my suprise, i discovered that i could play both at the same time and that i liked them together.
My problem now is that i'm upgrading to Nordost Heimdale speaker cables and i don't know how to connect the Heimdale to the Radio Schack as its imput is a small holed spring loaded clip barely big enough to take 14 guage bare wire.

Yeah. there are degrees of corruption, some of which may be tolerable.

Funny!
(Or nice troll)

Well, at least there are no nulls if seated within 45 deg in either direction of center-axis.

How did we go from "isn't too bad" to no nulls?

That's what I was using as a quick "isn't too bad" index. The null banding you see on the image I posted earlier in the thread doesn't occur at all at 1/2 wavelength (as you suggested), but still doesn't occur within 45 deg of the center axis at a full wavelength.

There's surely some addition and cancellation anyway, but that's true even at 1/2 wavelength.

OK. It is a matter of degree (no pun) and tolerances may vary.

This is just theory on my part. I haven't tried to listen to these effects at these speaker separations. I just plotted out what the phase addition and cancellations would look like when changing the spacing between the two sources.

Have a good night!

my hearing isn't what it once was and i was haveing some trouble hearing the dialog from my center.so i had a pair of old bookshelves laying around so i layed them on their sides on top of my tv,hooked them up and wow it made a BIG difference to ME and my wife.i'm no expert but WE enjoy it and thats all that matters.so to the orignial poster try it and see what you think.

Irrelevant to this issue since there are many other variables in your operation. I suspect that the higher efficiency and/or peaky midrange of those old speakers might be more relevant to your results.