What are the disadvantages of an MTM array...

[454Casull]

... besides narrower vertical dispersion and lobing, if the crossover frequency is too high?

 

[gary f]

Well, there might be another small problem sometimes is that if the 2 woofers are wired in parallel, the impedance can be low (like 3 Ohm or maybe less if you have 6 Ohm woofers). But that is not always a problem.

Also, lobbing is not so bad if you keep drivers close together.

F

 

[SY]

The narrowed vertical dispersion is only a disadvantage if you don't want it. For many applications, it's an advantage. Call it a "characteristic" of the MTM, if you want to be neutral.

The disadvantages are larger cabinet volumes and higher driver costs.

 

[audiosteve]

The talk I read above re narrow dispersion and lobing in an MTM is simply not correct. Minimal lobing on the vertical axis is precisely what an MTM does best (when the crossover is properly designed). The comment re low impedance is spot on though. You have to watch that.

 

[jesper]

About lobing of MTM.
Below is Matlab plots of lobing of a MTM, 2500hz x-over, third order, drivers spaced one wavelegth appart.

 

[jesper]

How do I add multiple pictures?

/Jesper

 

[jesper]

I'll put them in seperate posts.

 

[jesper]

1500hz..

 

[jesper]

2000hz..

 

[jesper]

2500hz..

 

[jesper]

3000hz..

 

[jesper]

The plots shows the vertical disperision whith the drivers simmulated as monopoles.
It's lobing allrigth, evenly though. If if the x-over is changed to 4:th order (or any other even order with the drivers in-phase) it looks allot worse.

/Jesper

 

[audiosteve]

Looks like I could be wrong. I read an article in Speaker builder some years back that extolled the virtues of MTM because the polar response was +0/-3 db. Could this have been been only at the crossover frequency and lobing will occur at other frequencies due to the displacment between the LF drivers?? Is this the issue with MTM?
I'm trying to understand it better as I obviously have an incomplete grasp of the topic.

 

[jesper]

The plots are purely mathematical. No drivers are true pointsources so in reality the dispersion will be somewhat smeared. Real world measurements may show as good as 0/-3db at x-over frequency.
The major lobing are, as you say, at lower frequencies due to the spacing between the M's.
However, with even order x-over, the lobing is not nearly as evenly spread. If you are interested I can post same plots with a 4:th order x-over.

/Jesper

 

[Bricolo]

Looks like I could be wrong. I read an article in Speaker builder some years back that extolled the virtues of MTM because the polar response was +0/-3 db. Could this have been been only at the crossover frequency and lobing will occur at other frequencies due to the displacment between the LF drivers?? Is this the issue with MTM?
I'm trying to understand it better as I obviously have an incomplete grasp of the topic.

was the article about vertical or horizontal polar response?

 

[audiosteve]

[QOUTE]..was the article about vertical or horizontal polar response?
That article was about vertical polar response with MTM in a vertical array