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Old 2nd February 2011, 10:01 PM   #1
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Default MTTM advantages/disadvantages?

Hello,
I am looking to put some spare drivers to use--Hiquphon OW2's and Vifa P17's. Traditionally I have done high simple two-ways using 1st order xovers but am now looking to try out "something new" and possibly a MTTM design using said drivers above.

Plain and simple, I just can't find a lot of info, good or bad, about the MTTM configuration. I have read that long ago, that alignment was mandated initially for THX certified speakers. Nowadays, the only "high end" speaker I can find using MTTM are the large (and expensive) Dynaudio speakers which also use 1st order xovers.

Any comments, good or bad about using MTTM? Lobing better or worse then MTM? Wider/narrower sweet spot? I will be using 1st order, like the Dynaudios, however the tweeters will be set back into the cabinet to try and achieve better time alignment.

Any comments good, bad, or indifferent about MTTM's would be most appreciated....

Thanks in advance.
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Old 2nd February 2011, 10:33 PM   #2
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Look at your overall plan. First order x-overs are not easily done, and I believe not practical for a MTM or MTTM due to the lowish x-over point that you would need due to spacing of the P17s.
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Old 2nd February 2011, 10:39 PM   #3
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Default You should read D'Appolito's paper on MTMs.

Multiple tweeters, unless they are very and I mean VERY close together will have lobing issues and destructive interference/comb filtering at off angles.
If you crossover appropriately you should be just fine with only one tweeter, unless your mids are louder than the tweeters. One alternative might be to trim/crop the flanges of the OW2s so they fit closer together.
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Old 3rd February 2011, 01:26 AM   #4
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This is incorrect. Dynaudio runs one tweeter full range. You can learn more by reading here:

Dynaudio Confidence C4 loudspeaker | Stereophile.com


Using two tweeters can also provide valuable re enforcement at low frequencies where most tweeters suffer from excursion limits and distortion. Combining this with the reduction in high angle vertical off axis energy that would otherwise result in ceiling and floor reflections and you have significant improvements in SQ overall.

Center to center distance concerns are generally vastly overstated in DIY circles. Blanket rules of thumb cannot substitute for accurate phase difference calculations accounting for acoustic offsets, crossover phase, driver phase response, and time of flight differences. If you frequently listen from a ladder or while lying on the floor close to the speakers - you might have a problem. Otherwise, accurate calculations and measurements are necessary before one can rule out one approach over another.
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Old 3rd February 2011, 11:23 AM   #5
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Quote:
Look at your overall plan. First order x-overs are not easily done, and I believe not practical for a MTM or MTTM due to the lowish x-over point that you would need due to spacing of the P17s.
Well, I've done at least 2-dozen 1st order xover speakers, so *I* think they are easy. And there are a ew of examples of MTM's (and MTTM's like the Dynaudios) using them. The case in point however for MTM 1st order are the Dunlavy's and eventually the Duntech's which they later morphed into being. Both brands were/are known to be some of the finest transducers in the world and they are again 1st order, WMTMW.

I'm not worried at all about the drivers I have being able to handle 1st order. The P17's are the "darlings" of the 1st order community for those on a budget. Very smooth overall. The Hiq OW2 have real cajones. I've crossed as low as 2.4kHz 1st order with no audible stress, however 2.7kHz and up are where they shine 1st order.

My worry is that I've never done either an MTM or MTTM so I'm unfamiliar with what the best practices are and also why I can only find 1 manufacturer in the world (Dynaudio) doing a MTTM 1st order.
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Old 3rd February 2011, 11:27 AM   #6
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Originally Posted by fntn View Post
This is incorrect. Dynaudio runs one tweeter full range. You can learn more by reading here:

Dynaudio Confidence C4 loudspeaker | Stereophile.com


Using two tweeters can also provide valuable re enforcement at low frequencies where most tweeters suffer from excursion limits and distortion. Combining this with the reduction in high angle vertical off axis energy that would otherwise result in ceiling and floor reflections and you have significant improvements in SQ overall.

Center to center distance concerns are generally vastly overstated in DIY circles. Blanket rules of thumb cannot substitute for accurate phase difference calculations accounting for acoustic offsets, crossover phase, driver phase response, and time of flight differences. If you frequently listen from a ladder or while lying on the floor close to the speakers - you might have a problem. Otherwise, accurate calculations and measurements are necessary before one can rule out one approach over another.

Thanks a lot for that link, interesting read. So they "cap off" one tweeter at 8kHz to avoid top octave lobing. Hmmmm, would have to ponder that in the design.
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Old 3rd February 2011, 11:59 AM   #7
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Originally Posted by jjkozlow View Post

My worry is that I've never done either an MTM or MTTM so I'm unfamiliar with what the best practices are and also why I can only find 1 manufacturer in the world (Dynaudio) doing a MTTM 1st order.
No need to reinvent the wheel. Look carefully at the placement of the Dynaudio drivers and their crossover points and you should wind up with a similar result. The Hiquphons and Vifas are great - I've used them extensively myself. As for only finding 1 manufacturer using twin tweeters (aside from the myriad of line source designs out there) there are several manufacturers who have employed the technique successfully. This one is fairly well known and there's a "high end" design by a manufacturer other than Dynaudio that escapes me at the moment.

Floorstanding Speakers : Millennia M80 v3 - Axiom Audio
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Old 3rd February 2011, 12:49 PM   #8
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hello JJ...

First older filter is mostly a myth

The step provided in the stereophile review (joined below) is far from the first order type. They even add that the boomers are in reverse polarity !

So, don't start your job while taking Dynaudio as an honest example. .

Coincidentally, last year I have bee listening to the big Evidence model, and I can't say that the double tweeter formula produces some combing harshness. It's very clean (but the speaker itself is a little bit boring for my taste).
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Old 3rd February 2011, 01:47 PM   #9
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Originally Posted by Radugazon View Post
hello JJ...

First older filter is mostly a myth

The step provided in the stereophile review (joined below) is far from the first order type. They even add that the boomers are in reverse polarity !
.
Incorrect. Look closely at the blue trace in figure three of the measurements section. Clearly, the "boomers" possess a first order slope (down around 6db from 200 hz to 400 hz). From the graphed response, an asymmetric crossover is likely and the effective phase difference through much of the overlapping frequencies is likely to be less than 90 degrees despite the reversed polarity. You can't deduce the crossover topology from the fact that a particular driver's terminals are reversed.
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Old 3rd February 2011, 08:26 PM   #10
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Originally Posted by fntn View Post
No need to reinvent the wheel. Look carefully at the placement of the Dynaudio drivers and their crossover points and you should wind up with a similar result. The Hiquphons and Vifas are great - I've used them extensively myself. As for only finding 1 manufacturer using twin tweeters (aside from the myriad of line source designs out there) there are several manufacturers who have employed the technique successfully. This one is fairly well known and there's a "high end" design by a manufacturer other than Dynaudio that escapes me at the moment.


Floorstanding Speakers : Millennia M80 v3 - Axiom Audio
Thanks fntn! I also have used these drivers extensively too which is why I have spares! Matter of fact, this is one of my designs featured on Hiquphon's web site using OW/4:
Who sells Hiquphon dome tweeter. Where can I buy Hiquphon loudspeaker units

I have done so many 1st order 2-ways I am getting bored. Want to "broaden my horizons". MTTM will be the way I go then like the Dynaudio. Just need to start doing some planning on the xover and limit the one tweeters top end and such. Not sure if MTTM will be any better or worse then what I've done before, but how do I know if I don't try....
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