TM vs MT vs MTM vs TMM vs MMT

[Bricolo]

I think the title is explicit enough


I'd like to know the advantages and disadvantages of all these configurations. I still haven't found an explanation that satisfied me yet.


And if someone could explain me lobing, tilts, polar response and such things, I'll know everything I want for a momment


Thanks
Alex

[ThorstenL]

Konnichiwa,

Originally posted by Bricolo
I think the title is explicit enough

Very explicit. X-Rated I'd think.

Originally posted by Bricolo
I'd like to know the advantages and disadvantages of all these configurations. I still haven't found an explanation that satisfied me yet.

Listen in order of personal preference and assuming identical M & T in all cases (except fullrange of course) and a crossover frequency that falls into a range where the "M" driver centerss are farther from the T driver Center than around 1/8 Wavelength of the crossover point....

Of course, in the end can make speakers that certain find to sound subjectively "good" in their personal settings using any of these arrangements and a few past that (line sources anyone?).

Fullrange
=========
Advantages - Point Source, Symmetrical Polar response without or with only minimal lobing, invariably fairly even off axis response.

Disadvantages - Non really

(except not easy to make a good one covering a wide bandwidth, possibly limited maximum SPL due to doppler modulation at very high SPL level with loads of bass, but again can be addressed by design and hence invariably expensive)

Coax
====
Advantages - Point Source, Symmetrical Polar response without or with only minimal lobing, invariably even off axis response.

Disadvantages - timealignment needs to be done by driver manufacturer or in the (active, digital or passive) X-Over

Semi-Coax
========
Advantages - Near Point Source, reasonably symmetrical polar response without or with only minimal lobing, fairly even off axis response.

Disadvantages - timealignment needs to be done in the (active, digital or passive) X-Over

TM - MT
========
Advantages - Non whatsoever apart from the possibility for mechanical timealignment, however the lobing structure is still comparably simple, compared to other options

Disadvantages - Asymetric Polar pattern (often strongly so) and problems integrating drivers.

Choices/Implications - with MT arrangement the first main lobe is reflected by the floor, which MAY be sound absorbing, with TM (tweeter on top) the first main lobe is beamed to thge ceiling where it will have a much longer arrival time to the listening position, which may or may not improve subjective Image hight and/or spatiality.

MTM
======

Advantages - Non whatsoever, except, the very ragged and messy vertical polar pattern is symmetrical which is VERY dubious as "advantage".

Disadvantages - Extremely messy Polar pattern, strong first main lobes pointing both towards the floor and ceiling can really mess up imaging etc., lobes created by both the two M Driver and each of these with the T Driver.

TMM - MMT
========
Advantages - Non whatsoever

Disadvantages - Extremely messy and asymetric Polar pattern and severe problems integrating and timealigning drivers.

Choices/Implications - with MMT arrangement the first several main lobes are reflected by the floor, which MAY be sound absorbing, with TM (tweeter on top) the first several main lobes are beamed to the ceiling where they will have a much longer arrival time to the listening position, which may or may not improve subjective Image hight and/or spatiality.

Best application would be using the second (M) as Woofer to help at lower end of the spectrum, so (T)(MW)(W) would be my best guess here using a dedicated woofer probably of slightly larger diameter.

Sayonara

[Bricolo]

Whao!

Thanks a lot, Thorsten! I wasn't exopecting such a precise answear.

You seem to be a fullrange addict

PS: where can I learn what exactly are polar response/pattern, lobing, etc

PPS: I remember having read in the loudspeaker design cookbook that the lobe "direction" is different for each crossover order. Is this true?

[Eul]

For different types of cross-over... yes, it is.

But what lobes are is perfectly described in the cookbook, so I suggest you take a look in the cookbook again, because I think it is hard to describe better than Vance has done in his book (not that I’m not willing to help, don’t get me wrong please…).

[Bricolo]

Originally posted by Eul
For different types of cross-over... yes, it is.

But what lobes are is perfectly described in the cookbook, so I suggest you take a look in the cookbook again, because I think it is hard to describe better than Vance has done in his book (not that I’m not willing to help, don’t get me wrong please…).

I rode this book some months ago, and I must admit that after all the good things I heard about, I was disapointed. I didn't find much usefull information in it, I don't understant why this book is condisered as a bible by some people.

A (not so) possible explanation could be that the french translation is less complete that the original one. I'll try to find the english version


I remember having read 2 or 3 pages in the loudspeaker design cookbook, about lobes, theyr orientation as a function of the XO's order, the accoustic centers alignment, the speaker configuration (TM, MTM...), but it was very basic

[ronc]

The best crossover is NO crossover.
ron

[GM]

Here's a good critique of D'Appolito's 3/2 MTM design that gives a good introduction into polar response issues: http://www.birotechnology.com/articles/VSTWLA.html

GM

[Eul]

I don't think the English version will be more detailed. It is seen as a bible for beginners, is describes every effect in the detail needed to understand what is is and what the effects are. To really understand al these affects you have to look further. THIS site is very good, it describes every effect very detailed. At first the it looks there is not much information but when you dig an read the articles you will see the is a huge amount of information on the site. From cross-over design to dipole speakers¡K. Good luck ƒº

[Bricolo]

Thorsten, when you said that a MT has it's main lobe beaming to the floor, and on a TM it's beaming to the ceiling


I was thinking about a solution to align the accoustic centers of the T and M
->using a sloped bafle (oriented to the floor for a TM, oriented to the ceiling for a MT)

When I want to have a horizontal main lobe, the solution is also to use a sloped bafle, but:
-oriented to the ceiling for a TM, and to the floor fot a MT



That's the problem! The 2 solutions are opposed


Is there a way to have a horizontal lobe, AND aligned accoustic cernters?

[jewilson]

I found most of your statements to void of technical proof and to be based on BS. Lobing is a function of the crossovers design and the location of the speakers on baffel.

For years MTM design have ruled: Example is John Dunlavy, Duntec Labs and his other designs.