TMT, or MTMTM....???

[Yoda]

we've all heard of the MTM arragnement of drivers, but what are the other posibilities? I have 4 Hi-Vi RT2 ribbon tweeters, what are your comments of an MTMTM config, or TMT, or TTM... what do you think? I'm using the Hi-Vi RT2 and F6 , both drivers i highly reccomend, check them out @ http://www.dulcet.com
P.S.
I have used these ribbons in a horizontal and vertical orientation, which is better?

[kelticwizard]

I am no expert on the subject, but I do know this: when you have two identical drivers arranged one on top of the other, the ear hears as if the sound came from the center. I have read that in audio magazines many times. So the other arrangements you mention should be alright.

Ribbons should be used vertically-both positioned with the ribbon vertically and one atop the other if using more than one.

The smaller the speaker, the better the high frequncy dispersion. Generally, we want speakers with wide horizontal dispersion, but low vertical dispersion. This is because floor and ceiling reflections are a bigger problem than reflections from the walls in the room. We want less sound hitting the floor and ceiling, therefore we want a speaker that is large in the vertical plane.

There isn't much you can do about a round dome tweeter-it has equal dispersion in the horizontal and vertical plane. But ribbons are unique-large in the vertical plane, slim in the horizontal plane. There will be better horizontal dispersion than vertical dispersion when the ribbon is mounted vertically, and when multiple ribbons are arranged above and below each other. Since we want more horizontal dispersion than vertical dispersion, that is the way to go-in fact, it is one of the advantages of the ribbon design.

I do not mean to say that the ribbons had to be located directly above the other-only that they had to be in a vertical line. If you want the MTMTM arrangement, I see no reason you cannot use ribbons as the T. I have not tried the arrangement, but I have read nothing that indicates against it. Both the T's and the M's will be perceived as coming from the center of that line.


[Edited by kelticwizard on 10-15-2001 at 08:55 PM]

[Super]

There are only a few problems I could see with a TMT arrangement. Firstly, I hate overly bright speakers. It seems to me that if you have 2 tweeters, that it may overpower your midrange, unless you do an excellent job with the crossover. Also, by adding a second tweeter, you're taking power away from the midrange and bass drivers, which require more power than tweeters to be driven efficiently. This is generally why you don't see tweeters with power ratings as high as other midrange and bass drivers. Other than that, I don't see any problems with it either. Only way to know for sure is to experiment.

[Yoda]

I am going to be bi-amping these, so effeciency isnt an issue. Here is an interesting follow up, if i have 1 amp for the 3 M's in an MTMTM, what if i wired the two outer M's (MtmtM) in series with the middle M (mtMtm) in parallel, i should get 1/2 the power into the middle speaker, and 1/4 to each top and bottom. I think that would make it sound more centered... what do you think?
sure, this will present a 5.33 ohm load, but my amp can handle it.

[GRollins]

Bear in mind that part of the strategy behind the MTM configuration is a kind of time alignment by creating a balanced wavefront. If you start spacing the tweeters out: MTMTM, or some such, you'll lose that aspect of the MTM system. Which is not to say that music won't come out...just something to keep in mind.
For my two cents worth, I'd try to align the ribbons as closely as possible vertically, treating them as one driver (adjust levels as necessary to achieve flat response, of course), then array your midrange drivers in a manner that suits you, whether MTTM, MMTT, or whatever.
I would always use ribbons in vertical orientation, so as to get as precise an image as possible. For that matter, I'd use the MMTT only vertically:
T
T
M
M
but the MTTM could be used either way (for example, as a 5.1 front center, or floor standing). It would be trivial to mount the tweeters in a square board that could be bolted in one way for vertical or turned 90 degrees and remounted for horizontal. Use Allen bolts and T-nuts or something of that nature so that it looks clean.
I wouldn't advise trying to play games with dividing the power unevenly among the drivers, not for the amp but for the drivers. They should share the load so as to keep distortion as low as possible; if you've got the driver, let it earn its keep.

Grey