M-T-M centre speaker question

Yeah it probably would. However they add the second woofer for a few reasons: some ppl like the more uniformed symmetrical look, and it also adds more bass extension.

There have been attempts to correct this as in a cascade tapered array in which one of the Ms of the MTM is a mid/woofer and the other M is a woofer only so its a 2.5 way speaker. I may be wrong but I think Klipsch and Polk both use that method.

In response to your above, Klipsch's RC-64 II has four 6.5" woofers coupled with one compression driver tweeter. The rest of their center channel speakers use two, same size IMG woofers. The G-28 flat panel speaker uses four additional passive IMG woofers. FWIW, the top three tier Klipsch center channel speakers all have similar bass extension of 56-59Hz.

The reason for a second woofer in an MTM is to be able to use two smaller woofers rather than one larger woofer, allowing a higher crossover point to the tweeter, eliminating the complexity of a 3 way system with the same dispersion. It also gives better vertical pattern control. The key word is 'vertical'; for an MTM to work per the design intent the speaker must be vertically aligned. When horizontally aligned as is done in most center speakers there are no advantages and many disadvantages, including lobed response and narrowed dispersion. So why do manufactures do it anyway? Because consumers aren't aware of these facts, and where there's a buyer willing to spend money on a product there will be at least two sellers ready to take his money.

Because not everyone can use a vertical speaker as their center channel. I have matching MTM LCRs across the front but I have no way of using a 26" high center channel. Much easier to fit a center thats only 5-8" high.

Manufactures don't create demand, the consumers demanded a product to fit their needs so, manufactures created the supply.

Oh sure, now it's PT Barnum's fault.

"A fool and his money....."

I was going with the reason for horizontal placement being, that's how most entertainment credenzas are set up. Viewing gets more and more difficult, the higher a television screen is positioned and at base height, setting a bookshelf size speaker in front of a television's center-line creates it's own set of vertical viewing troubles; not to mention the WAFF; wife approval factor frown.

My understanding, in truth, the best measured numbers come out of a two speaker, vertically standing bookshelf with tweeter on top. In a real world environment, the, horizontal, b-stock, Klipsch RC-64 II is the best darn center channel I've heard.

From an engineering standpoint there's no justification for horizontal placement, it's purely a visual thing, and as is often the case what looks pretty sounds bad. For instance, the Klipsch you referenced could only work reasonably well if the two outer woofers were low-passed at their 1 wavelength center to center distance, about 500Hz. Nothing in the Klipsch literature suggests that to be the case, making it an inherently flawed design. To put it simply, consumers assume that sound waves work the same way that light waves do, so a horizontal speaker will give wide horizontal dispersion. The exact opposite is true, but show me one manufacturer/seller of horizontal centers that points out this acoustical engineering fact to prospective buyers.
This way to the Great Egress.

What's a poor married speaker buyer to do? We both know that in most homes, right or wrong, aesthetics wins out over practicality whether trimming unneeded landscaping or one's buying choice in a car purchase so yes, aesthetics are rationally in play. We also know that for the most part, societal conventions, coupled with traditional credenza styles available to audio-heads, convention wins out over objective reasoning. But I will admit, as to looking and sounding good, female Italian supermodels do both equally well.

FWIW, I LPF the RC-64 II at 60Hz. We're you the forum member who posted the graphs regarding the evils of horizontally placed M-T-M speakers vs vertically place two-way bookshelf speakers? Very eye opening article. As to the "Great Egress," I was hoping to make that the last attraction as I'm still enjoying all these other attractions.

Ok I looked it was Polk who uses this Cascade Tapered Array for solving lobing and comb filtering issues.

http://www.polkaudio.com/polk-university/technology/cascade-tapered-array-crossover

Klipsch used to do it too. The RC-7 used a "tapered array" crossover:
CROSSOVER FREQUENCY: HF: 1950Hz, MF: 550Hz

http://www.klipsch.com/rc-7-center-speaker

Audioholics did some articles and measurements on this subject a little while ago:

http://www.audioholics.com/education/loudspeaker-basics/vertical-vs-horizontal-speaker-designs/250-mtm-horizontally-oriented-measurements.html

The conclusion I drew from their charts is that when choosing a center channel, one must take their room and seating positions into consideration. My room is long and narrow, and the front left and right listening positions are about 15 degrees off axis. By looking at the charts they did, it looks like about 20-25 degrees off axis is where things really start to deteriorate. So as long as you don't have listening positions in this area, you should be fine. Alternatively, if you don't care about the "cheap seats", again, you'll be fine. Just be sure to always sit in "your" spot.

Of course, the ideal situation is an acoustically transparant screen with three identical speakers behind it. But that isn't feasible for a lot of people. Also, you'll get arguments from people who say the screen isn't truly acoustically transparant. So instead of having the "vertical center" people yelling at you, you'll have the "grill off" people yelling at you.

Bottom line is do what works best for your situation in your room. No matter what you do, there will be some audiophile or videophile trying to crucify you for not doing it the "right" way (their way).

I would have a question regarding changing MKT capacitors for MKP once in an old loudspeaker crossover.The box is 20 years old and I red that MKP capacitors better open midrange and highs.So I took out old MKT capacitors from midrange and tweeter part of the crossover and put new ones from ClarityCap and Mundorf.Now the sound is much more open and clear but the box is more loud then before and some part of midrange is emphasised so it is somewhat unpleasant for the ears...The question is - Can I change only capacitors as I did or I should corect other parts of crossover?

Tweaking a crossover involves a lot more than swapping out caps. The best crossovers take literally weeks, if not months, to get right, and it requires good measurement gear.

What You mean by " they take weeks" - you mean they take time to become smooth (capacitors)...now it sounds a little bit hard

My take, it takes time to bake a cake and it takes time to make changes, test and then make more changes until you get the crossover just right.

There's ready made cakes (crossovers in a speaker) and then there's do-it-yourself cakes. Not being baker nor EE, I buy both, ready made.

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To get more power from the tiny woofers.  

Edited by Kal Rubinson - 8/15/12 at 8:44am

I may have missed something here, but are the quoted posts relating to multiple subs or why a typical center channel is an MTM rather than a horizontal design with a single "woofer" (really a mid in most cases)?

Yup.  Will correct post.

What if the T in the middle is able to rotate?? then wouldn't it be the same if u were able to place it vertical like these that i might be buying?? http://www.adam-audio.com/en/installation/products/gtc77/series..

It takes weeks to tweak , measure, re-tweak, ad infinitum until right. But as for caps breaking in, they don't, and most of the differences 'heard' are placebo effect. After all, if they're more expensive they must sound better, right? DBT has found no more differences between caps than between cables, ie., slight, and not cost related. Lobed response on the horizontal plane if the drivers are too far apart.

You do know that with your above, you're dangerously close to messing with the whole space-time continuum thingy and that can't be good.

1 wavelength on-center. If the crossover is at 2.5kHz that's 5 1/2 inches, so you can't have no lobing with a 61/2 inch woofer and a tweeter with a 3 inch frame.. True, because then the lobing occurs on the vertical plane, so no matter where you are on the horizontal plane it's not a factor. The same applies to the MTM. Originally Joe D'Appolito, who invented it, specified a 1 wavelength center to center of the midbasses at the crossover to the tweeter, but even he no longer recommends that.

The same as for the MTM since the M and T will be producing the same signals in the crossover region.  That is why you rarely ever see a modern full-range system with drivers not vertically arrayed.

I had always thought that the "safe" separation is no more than 1/2 crossover frequency wavelength since both drivers are usually no more than 6-12dB down an octave on either side.  

1/2 wavelength is unachievable with most driver/crossover scenarios. For instance, In an MTM loaded with 6.5s and a 2.5kHz crossover that would be 2.7 inches. Even 1 wavelength, 5.4 inches, can't be done, even if there's no tweeter between the midbasses.