TMT, or MTMTM....???

Yoda

Member
2001-07-30 1:35 am
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

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
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]
 
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

Member
2001-07-30 1:35 am
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.
 
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
 
Comb filtering for one thing. The output from the tweeters in a TMT will interfere destructively and constructively so you'll get areas where the sound is diminished and amplified. Though you'll get good pizza, but will also have to deal with Ninja attacks.

It's why pretty much the only time you'll see multiple tweeters is in a line array, where you are essentially trying to make one huge tweeter and why they are typically so tightly packed.

Also it's a lot easier to be efficient in a tweeter, where the primary limitation is how fast you can vibrate, not how much air can you move, like with a mid or woofer. So usually it's a question of tamping down the tweeter's efficiency to match the other drivers and not the other way around. So gaining efficiency wt multiple drivers, is usually not desirable with tweeters.

The comb filtering is less of an issue the lower you get in frequency, but is still the reason why it is recommended that you not put the Mids further apart than some fraction of the crossover point wavelength. You don't want to use a RAAL 140-15D in a MTM for example because it's too long for that distance with most Mids.
 
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lilun

Banned
2013-10-08 8:25 pm
Also it's a lot easier to be efficient in a tweeter, where the primary limitation is how fast you can vibrate, not how much air can you move, like with a mid or woofer. So usually it's a question of tamping down the tweeter's efficiency to match the other drivers and not the other way around. So gaining efficiency wt multiple drivers, is usually not desirable with tweeters.

The comb filtering is less of an issue the lower you get in frequency, but is still the reason why it is recommended that you not put the Mids further apart than some fraction of the crossover point wavelength. You don't want to use a RAAL 140-15D in a MTM for example because it's too long for that distance with most Mids.

but with gedes horn loaded tweeters, this is done to increase tweeter efficiency so youre wrong
 
but with gedes horn loaded tweeters, this is done to increase tweeter efficiency so youre wrong

Try reading all of the words first.

I'm talking about your typical speaker. Thus the use of words like "usually" in my statement.

If I make an absolute statement feel, free to poke holes in it, but try to pay attention to the details. I do try to be specific as to exactly what my statements are intended to cover.

If you bother to read all the words, you'll notice that I do tend to liberally sprinkle words like "usually", "often", "typically", etc... Specifically because there are almost always exceptions and situations where a statement is incorrect.

Geddes's speakers and the other similar speakers like the SEOS are a very different kettle of fish from your typical speaker.

Nor are they MTM arrangements, at least none of the ones I'm familiar with. Most of them don't even have a mid range.

Obviously there are mid and woofers which are more efficient than many tweeters, but they aren't commonly used.

The wave guides are used for for more than one reason, not just to increase efficiency. They typically permit a lower crossover point, help control directivity and often help to smooth out the response of the tweeter.

aren't you going to explain to me why?

It has to do with the length of the wave at a frequency. It's why subwoofers are much less sensitive to location than regular speakers and you can use multiple subwoofers in a room. When the length of the waves are longer than the area you're placing them in, location becomes much less important.

Before you start getting all semantic police again, these are broad generalizations and not absolute statements.

For an MTM arrangement, I believe the reason you want to keep them within some distance of each other, is that as long as you do so, they tend to behave as a source as described above in kelticwizard post. But MTMs do suffer from certain amount of comb filtering, regardless.
 
well comb filter can happen even with Bass tweeter. If you have a 1st order crossover, you have comb

Did I say it didn't happen in other types of speakers? It's just more of an issue with an MTM design than it is with most others, an MTM is still used because the advantages are considered sufficient to outweigh the disadvantages in a good MTM.

This is one of the reasons that some people like/prefer coaxial speakers after all. A coaxial speaker can help minimize this sort of effect.

Speakers are inherently and inescapably flawed devices.

There is no such thing as a perfect speaker. There are always trade offs and disadvantages to any method of reproducing sounds.

The art of speaker design revolves around minimizing those trade offs and maximizing the strengths of an approach. It's why there's a nigh infinite number of ways to build a bad speaker and a much more limited number of ways to build a good one.
 
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Is anyone else thinking what I'm thinking? ;)
 

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I try to give people the benefit of the doubt.

He's clearly not a native english speaker, so some of the subtleties of the language are almost certainly lost on him.

One of my favorite quotes is "Never attribute to malice, that which can be explained by incompetence."

Though he does seem to have drunk heavily from the cup of "audiophile" myths.