To MTM or not to MTM?

[Colin]

I'm plotting a new pair of two-ways. I'll be using two 5" drivers and a treble (actually a Jordan JXR6 so crossing around 700 - 1000Hz).

I've read the original Joseph D"Appolito articles in Speaker Builder and see the logic behind the MTM arrangement.I note that it used to be more popular in speakers available commercially (early Meridians, for instance). Looking around now, it seems to be used less.

Do any of you have a preference for using either MTM or MMT (the two mid/bass units below the tweeter)? Is there some subsequent research which has caused it to fall out of favour?

The only thread I've found which addresses this is

MTM vs. two-way.........


I should add that the two mid/bass drivers will be run in parallel on the same baffle - I'm not intending to roll them off at different frequencies.

All input appreciated.

[tinitus]

seems you have dealt with some issues of the MTM principle, by your choise of drivers, enabling a low xo 'point'
MMT have its own issues as well, by using double woofers, crossed high
probably a matter of picking what kind of poison you can deal with
but since you ask, I guess you know that

height of box will be different
MTM needs to have tweeter exactly at listening height
with MMT, tweeter only needs to be slightly above

[Richard Ellis]

The MMT arrangement 'fouls up' the polar response, keep the tweeter in the middle, do you calculations for the driver spacing. Radius off the baffle edge & keep it narrow.....imaging is spectacular, but keep it up high on-axis best possible to your listening position. You could further apply some absorbent material on the front of the baffle....with all this, group delay will be virtually non-existent.
Will you be able to use a subwoofer with this arrangement?

__________________________________________________ _____Rick.........

[TICUL38]

If you can move the handoff frequency beyond 3kHz you will surely avoid "fouling up" the most sensitive frequency region in which the ear-brain combo will sub-conciously tell you that is enough for today! Listening to music should not involve extraneous brain activity such as caused when it needs to interpret noise... yes XO's introduce signal deformations that are simply noise in the music signatures.
MTM is good way to go, and is in fact my next and final build project...coming right up!
I have tried many, and none are perfect... just pick one and become happy with the result if well planned (informed).
Louis

[AllenB]

Originally Posted by Colin

Is there some subsequent research which has caused it to fall out of favour?

It's a matter of opinion, but if you see the goal of an MTM as controlling lobing around the crossover to balance the tone of room reflections, then reducing those reflections using waveguides might be the current trend.

If you see the (quasi) point source as the benefit then the unity horn might respresent an advance. Naturally they are more difficult to build and so the MTM still has its place.

[tinitus]

Originally Posted by TICUL38

If you can move the handoff frequency beyond 3kHz you will surely avoid "fouling up"
Louis

ehh, what ? with double woofers MMT ?

actually, I think Focal/JaqueMahul was first with the 2.5way
and we all thought, dodgy and strange
but it tested good, so..
wonder if they were fully aware of why it worked

but we have been asked not to.., sorry

[tinitus]

btw, how 'efficient' is the Jordan driver, compared to your two 5" (mid)woofers ?

[sreten]

Hi,

MTM guarantees a symmetrical vertical polar response on the tweeter axis,
irrespective of how well or poorly the crossover is designed, by default.

MMT is usually 0.5 way for the MM, and has less vertical lobing due
to there only being two sources at the c/o point, MTM has three.

As stated by others MMT is physically shorter in height, can be a factor.

MTM's with fairly high c/o points can and do create a power response
that is relatively unpleasant for a flat axial response compared to a MT.
(This is basically due to line type effects around the c/o point.)

As a final note MTM is a staple of AV systems, as the centre can appear
to match the the Left and Right, but not really, and consequently " real
hifi" speakers tend to go for MT or MMT out of anti AV MTM snobbery.

Not completely unfounded IMHO technically, but FWIW there are MMT
that are pure two ways, not 2.5 ways or variations thereof, and with
a low c/o point and two 5" bass drivers its certainly doable, the two
drivers being equivalent to a 10"x5" racetrack, and 1kHz is OK for 10".

rgds, sreten.

[TICUL38]

Originally Posted by tinitus

ehh, what ? with double woofers MMT ?

I dont follow you here??
Firstly, I would go MTM and not your MMT preference .... for me, vertical box placement is pedestal dependent. My suggestion in first posting is to remind the often overlooked need to avoid "fouling" the most important portion of the frequency range when crossing over "too low" in the 300-3000 Hz region.

Originally Posted by tinitus

but we have been asked not to.., sorry

What are we alluding to here?
Maybe I need to read completed sentences to get the intent?

Louis

[tinitus]

not sure a 2.5 way makes much sense with such low xo point

but I see one possible issue in a design like this, with low xo point
its the bigger xo components

funny, a few years back I had some ideas about a 3way, with a top section exactly like what you suggest here
two small woofers, with a small 'widerange'
and I had the exact same 'question'