Starting my new MTM project with 2118's + 2407 . . .

[pantaNS]

Finally my 2407J's arrived tonight
I already have 4x2118J's and 2x2342's. I'm considering MTM configuration, 2118's would play from 80-90Hz up to 1.2k or 2.1k in ported 28L cabinet tuned to 70-80Hz. Crossover would be 24dB Linkwitz-Riley.

I've searched through forum and JBL pro specs and founded that mainly 2407H versions are used as single drivers. Any input and suggestions regarding cabinet dimensions, eventually sealed enclosure and crossover frequencies and slopes would be helpful.

I've started with drawings already and soon I ill post some designs and images . . .


Cheers!

[Zilch]

2407 on 2342 is going to be a good combination, I believe.

I may have measured that and posted the data here, actually....

[JeffW]

Looks like Rob has tackled it. As long as you can cross them over low enough, it ought to be OK. My problem was I wanted to try it with a 3Khz or higher x-over and just didn't have room.

[pantaNS]

Since this pair of 2342's came from some pro box with integrated two ports ~68mm diameter and ~115mm in length I'm thinking about using them for a start. As both horns have cutouts 15mm deep (for 10" driver I assume) to achieve shorter centers distance. Would it be OK to to cutout the other side exactly so both 2118's would be equally distanced from center of 2342 at exactly 213mm each with 1.3k Fc? Or should I stick to "distance form TW to M should be EQUAL to ONE wavelength of crossover frequency?

For 213mm distance Fc would have to be 1.6kHz but I wanted to go with 1.2k or 1.3k max . . .

[pantaNS]

Here's a first tryout edges would be routed to 15mm radius . . .

[Robh3606]

Hello pantaNS

How flexible is your box?? Are you doing test baffles?? When I tried a similar set-up I just made simple baffles to try different driver combinations on. If you do that you could set-up a 3 baffle rail set-up where you mount the horn and then have the 2118's offset so to try out the other spacing all you have to do is flip the 2118 baffles over.

Rob

[pantaNS]

This is just first tryout. I just wanted to create box with minimized front panel to reduce diffraction as much as I can . . . I'll build this one to try out and maybe one for testing purposes with interchangeable front panel and adjustable back panel (for volume changing) . . . but I wanted to ask first about idea to place drivers close as much as it can be done - is it generally bad or good in MTM configuration . . .

[Robh3606]

Here is something I did a while back. It gives the spacing for 1.3K in inches. I used the same crossover point with a 24db active crossover. The Formula is one wavelength but I am not so sure if it is universal or not. I believe JBL trys to get them as close as possible with MTM's they have done as an example.

Rob

[Zilch]

1.2 kHz is a REAL stretch for 2407.

Fs = 1.75 kHz

http://www.audioheritage.org/vbullet...ad.php?t=21754

What's the lowest JBL uses it in product?

[pantaNS]

They say here 1.3k 24db LR crossover . . .

http://www.jblpro.com/catalog/suppor...=649&doctype=3

http://www.jblproservice.com/pdf/AE%...4215,95-WH.pdf


@Rob
I saw that MTM schematic too and that is what confused me . . . would it be ok to bring drivers closer with same crossover point or not? What could go wrong with shorter 'd' ?

[Robh3606]

I saw that MTM schematic too and that is what confused me . . . would it be ok to bring drivers closer with same crossover point or not? What could go wrong with shorter 'd' ?

That's a great question and I really cannot answer it. I don't think it would be a serious issue especially if it is only a small percentage of the wavelength but without doing simulations I don't understand the array well enough to predict what would happen. Sorry

I set mine up according to the formula and didn't experiment with changing the distances. There may be something is Project May where Tim did some distance simulations between the twin MTM 15" woofers.

Rob

[m8o]

Here is something I did a while back. It gives the spacing for 1.3K in inches. I used the same crossover point with a 24db active crossover. The Formula is one wavelength but I am not so sure if it is universal or not. I believe JBL trys to get them as close as possible with MTM's they have done as an example.

Rob

Rob, a question about your radiation pattern rendering. This may be a silly question, but I'm hoping to confirm... that is the radiation pattern only over the few octaves that the high and low drivers audibly overlap in the cross-over range?

pantaNS, Robh3606, Zilch, et al, I found this thread very helpful. Thanx. I'm planing a similar project, using two mid-bass drivers and a 2342 Horn with 2416H or Eminence 'equiv' drivers for side surrounds.

[Robh3606]

Rob, a question about your radiation pattern rendering. This may be a silly question, but I'm hoping to confirm... that is the radiation pattern only over the few octaves that the high and low drivers audibly overlap in the cross-over range?

Hello m8o

Yes I would say that is correct. The horn is going to determine the directivity above the crossover region. As long as the horn's directivity is similar through the crossover region to a direct radiator dome I would think the graph would be a good aproximation of what's happening through the crossover region as well.

Rob