[Jonathan DA]

A pair of center channels would not be good, you'll end up with comb filtering effects that will create a very lumpy freq response and interfere with dialog intelligibility. If you use a center speaker that has the tweeter offset to one side, then you can push that side up against the beam such that your tweeter is likely to only be about 4-5" off center. With the speaker behind the screen, the brain is going to localize the sound to the visual image on the screen rather than the visual image of the speaker cabinet. Chances are no one would ever realize the speaker was off center.

Alternatively, you could tear out the beam and replace it with a beam on each side of a perfectly centered speaker.

[pmeyer]

So no dual speakers then.

I guess my thinking is colored by my current horizontal center (woofer-tweeter-woofer). If I mounted it (or my new center) vertically, the offset wouldn't be too bad.

As for the beam, my only hesitation is that I would be into structural work (structural engineer or architect: $$). I'll hold off on that until the current round is done.

[Henry Gale]

Found what I think is a real bargain today.
There's a new consignment shop over at the Galleria, near Hwy. 71 & Bee Caves Rd. Behind the Backyard.
So, I'm in the back of this big cluttered store and I spot a Bell'Ogetti component rack, with a matching TV stand.
They were asking $199.99 but when I hesitated they immediately went to $175.00.

Uh, I didn't buy it, it's still there (I guess, possibly, perhaps).

It was tempting as hell but the fact is I've got a real nice 6 shelf Bell'Ogetti rack and I'm not planning to build a new little HT upstairs anytime soon
It's a 4 shelf adjustable rack, the TV stand has 2 glass shelves.

Go get it! Somebody!

[pmeyer]

Weird, I live about two blocks from there. I'm tempted to run over, but I'm resisting. From what I can see of Bello racks, they are attractive furniture designed to be out in the room. I'm looking for more along the lines of bolt on rack mount equipment closet stuff that will not be visible.

By the way, for anybody looking for that store, I think it is called 'World Market' and it's to the left of the Petsmart and across the way from Best Buy in Bee Cave.

[pmeyer]

Actually, the one I was thinking of is called the "Home Consignment Center" in Bee Cave. (World Market is a few stores to the right). I stopped by just for the heck of it to take a pic in case anybody wants it, but they are open 10-8 on weekdays. I can stop by there tomorrow night on the way home if anybody wants a better description.

[pmeyer]

Quote:

Originally Posted by Jonathan DA

A pair of center channels would not be good, you'll end up with comb filtering effects that will create a very lumpy freq response and interfere with dialog intelligibility.

Jonathan, total noob question here:

My current horizontal center has a single tweeter and a matched pair of mid-range drivers, one on each side, with a crossover around 2KHz. I would estimate the two mids are about a foot apart. How do they avoid comb filtering issues? Is it more of an issue above 2 KHz (hence the single tweeter)?

I'm not really proposing anything, just trying to learn, but if I had three separate drivers: a tweeter just to the right of the beam and a pair of mid-ranges a foot to the left and right of the tweeter, what would be the issue? Both mid-ranges connected to a single amp off the same (or matched) wires.

Specifically, is it a case of:
1) It would not work because...
2) In theory, one could build such a weird custom speaker, but in practice it would be difficult to avoid problems, or
3) It would work, it's just a lot easier to move the beam and put in a single center.

Just curious. If I decide to go center behind the screen, I'll likely build a false wall, center the screen slightly to one side or the other, or move the beam.

By the way, new pictures are up. The old room is out. I have some more ceiling destruction to do, then it's time to start rebuilding. http://www.meyerzone.net/meyerht/

[Jonathan DA]

Paul,

The answer is...the speaker doesn't avoid comb filtering! In order for two drivers whose centers are 12" apart to minimize comb filtering (aka lobing), the drivers would have to operate below the frequency of a 12" wavelength. A 12" wavelength is roughly 1000Hz. You will rarely find a two-way speaker with a 1000Hz crossover. The only ones I can think of are the Linkwitz Pluto, and a few pro-sound speakers that use large horns.

So you might be wondering, "if a horizontal MTM with a 2kHz crossover causes a loss of dialogue intelligibility, why do they sell them like that?" The answer--Marketing! The vast majority of speakers are sold on wow factor, and one of the biggest elements to wow factor is visual appeal. Most people think symmetrical horizontal speakers are much more visually appealing than odd designs that manage to vertically squeeze a tweeter and midwoofer into a horizontal form factor. So even though the engineers know its a compromised design, they create them so that marketing can actually sell them to a buying public that's more interested in looks that actual performance.

If you go with the acoustically transparent screen, I'd suggest using a traditional upright speaker design rather than something that's marketed as a "center channel" speaker. There are exceptions, but in general this will yield the best sound.

[pmeyer]

Very cool. Thanks for the useful information.

Assuming the two woofers are matched and in phase, I assume that the center-line wouldn't have this problem. The primary listening spot (assuming it's centered on the speaker) wouldn't see any effect. Sketching it out, 5" off the center 10' away would see the first null at ~13KHz, out of the woofer range (the woofer spacing is actually 10"). At 4' off center, the first null is at 1.8 KHz. Cool, I actually get it! With a 2KHz crossover, this center channel has a bit more then a 6ft wide spot with no comb filtering at 10'. Beyond that, I'll start to get peaks and nulls down to about 1KHz (all the way around at the front wall).

I take it this applies to all speakers with multiple drivers in the same frequency range? I see lots of highly rated tall vertical speakers that appear to have multiple vertical woofers. They would have a vertical comb filter problem. However, looking at them, they tend to be three way speakers. I suppose the woofer->mid crossover must be low enough to eliminate the issue.

--------------------------

I was thinking about audio the other day. The conclusion I came to:

With the theater construction, I have enough to think about without digging into the intricacies of speaker shopping right now. I'm going to start with my Marantz SR8000 and my 5.1 paradigm setup (non-ideal, but works for me).

Once I have the theater in and have a baseline performance expectation, I'll start listening/measuring my sound, and auditioning alternatives. I'll see where to go from there.

In the meantime, I'll keep reading and learning (and listening if I get the chance)

Paul

[Jonathan DA]

Sticking with your current speakers will work fine for now. The Paradigms are nice little speakers. For an easy center channel fix, just take your existing speaker and turn it vertical, centering the tweeter at your ear level behind the screen. Then you're pointing the nulls at the ceiling and floor. It still monkeys with your power response, but that's a secondary concern at this point.

[pmeyer]

I need advice:

As you can see in this picture, I have three cabinet cavities across the screen wall and one on the front of the right wall. The right front corner (where the TV hole is now) is going to be squared off.



Options:

a) remove the cabinets completely and drywall the wall.

b) remove the cabinet fronts and leave them flush to the wall. Fill them with cotton or 703. They'll be covered by GOM or equivalent when I treat my front wall. Essentially free bass traps in non-ideal positions. No implication that they would be the only bass traps (I'm still looking at soffit and corner possibilities).

Thoughts?