MTM's

[Robh3606]

Just wondering how many of you have tried it out?? Since Project May was started I have always been curious about trying to build up an MTM using a compression driver and horns.

Well I finally settled on a set-up using 2118J's with 2435 on one of the PTH waveguides. The spacing works out to a crossover point of about 1.3K which is certainly workable with these drivers. I am using Ian's MTM layout which was part of the Project May documentation. I have my first test baffle and hope to get the other built up today so I can start messing around with them.

With the MTM's you have set-up what crossovers types are you using?? I am going to go active initially just to get an idea what it sounds like and if it shows promise I would eventually go passive for the MTM section.

Rob

[Titanium Dome]

Looks like you're moving into SVA territory there. I wonder if the network from an SVA1800 would serve as a starting place? It's very simple, crossing over at 1600Hz.

http://manuals.harman.com/JBL/HOM/Te...A1800%20ts.pdf

[Robh3606]

Looks like you're moving into SVA territory there.

Yes for the most part yes it's similar just the M's won't go fullrange. They will have a Le-14H under them. Thanks I will have a look see. Well here's the $64,000 question. How do they image?????

Rob

[yggdrasil]

That's great Rob. Keep us posted on the progress.

[Ian Mackenzie]

Just wondering how many of you have tried it out?? Since Project May was started I have always been curious about trying to build up an MTM using a compression driver and horns.

Well I finally settled on a set-up using 2118J's with 2435 on one of the PTH waveguides. The spacing works out to a crossover point of about 1.3K which is certainly workable with these drivers. I am using Ian's MTM layout which was part of the Project May documentation. I have my first test baffle and hope to get the other built up today so I can start messing around with them.

With the MTM's you have set-up what crossovers types are you using?? I am going to go active initially just to get an idea what it sounds like and if it shows promise I would eventually go passive for the MTM section.

Rob

Rob,

Nice idea.

It will be interesting to see what happens.

What are you going to use them for..... HT?

I have thought about it but finding the right horn is an issue.

The layout was scanned from a book.

Ian

[Robh3606]

I have thought about it but finding the right horn is an issue

Yes I know what you mean! I am using the same horns as in my HT set-up and figured they might work hear as well. They are on the wide side 100x100 but figure a 1" dome is actually much more than that until you hit above 10K or so. These will be going into the same set-up as the XPL's and 4344's. Well no matter what happens even if they suck it will be fun!

Rob

[Zilch]

From Alden, "Advanced Speaker Systems"

THE D'APPOLITO 3/2 SPEAKER GEOMETRY

In his 1983 paper, "A geometric Approach to Eliminating Lobing Errors in Multiway Loudspeakers," Dr. Joseph D'Appolito found a way to create a symmetric vertical radiation pattern from speakers. Reading the work of Linkwitz, it occurred to him that a symmetrical positioning of 3 drivers in a 2-way design, used with a 3rd-order crossover, would produce the quuasi-spherical vertical response illustrated by the solid curved line (A) in Figure 7-4.

He found that, in order for the 3/2 geometry to work properly, the distance between the centers of the adjacent drivers should be kept close to one wavelength of the crossover's frequency, Fc. If you wish to calculate this distance in inches, divide the speed of sournd (13,503.94 inches/second) by the crossover frequency Fc. The elegance of the 3/2 driver arrangement is that some type of symmetrical vertical radiation pattern is produced no matter what crossover type is used.

Figure 7-4 shows two other symmetrical radiation patterns that can be produced using the D'Appolito 3/2 dirver geometry. A 2nd-order All-Pass (Linqkwitz-Riley) produces the large symmetric lobe shown as the slotted curved line (B). This type of radiation pattern is useful if you want your speaker to produce very little sound pressue in the off-axis regions, so that reflections from nearby walls and floors are greatly reduced.

The point/slotted curved line (C) shows a symmetric radiation pattern that is produced when a 3rd-order high-pass section of a crossover is combined with a 2nd-order low-pass section. This shows that the 3/2 geometry produces a symmetric radiation pattern even when used with a mixed-order crossover. It is of great benefit to speaker builders that the 3/2 geometry works with odd-order crossovers, even-order crossovers, or mixed-order crossovers.

I designed Hamilton's horizontal MTM center channel speaker according to these guidelines. In that instance, it was the horizontal radiation pattern controlled. That was two 2118s with a 2342 in the center:

http://audioheritage.org/vbulletin/s...ead.php?t=7004

[Titanium Dome]

Well here's the $64,000 question. How do they image?????

Rob

As I've hinted elsewhere, like lasers. Spread them wide or narrow and everything hits you with almost pinpoint accuracy. Of course, the SVAs use soft domes, not compression drivers, though there's a Ti dome you can swap into them if you're adventurous. (The SVA1800s have a 1 inch opening while the SVA2100s have a 1.5 inch.)

[duaneage]

I've made a few M-T-M designs and they do image well regardless of the driver. But the horn is little deep so you might have some propagation delay compared to the 8s. I would try and cross them low to minimize the effect.

[Robh3606]

But the horn is little deep so you might have some propagation delay compared to the 8s.

Yes there is about a 3/4-1" offset using the pole pieces to line things up. I want to try them flush first and then with a spacer to see how it goes. I may switch out to 2344's to get things going as I already have networks built and they are very much a known to begin with. The 2344's are a good bit deeper so a spacer will not work with them.

I have subs from Allen. Nice guy and it was a pleasure meeting him. They sound good. Ran them as 4344 bottoms. That was fun!!

Went with the 2344's to get the project going hope to have them powered before the end of the week if all goes well. I need to get the sub boxes up off the floor so I need to build a pair of short dollies to get the horn height right as well. Probably turn the sub boxes to loose a little height.

Rob

[Robh3606]

I got them up and running. They are up on stands, same one's I use for the XPL's gets the horn at the right height. I ended up triamping them with the DX-1 doing the lower crossover point and an M552 doing the upper split. They sound pretty good right out of the "box". They look good on the RTA as well. I already tried a measurement of the dual mids and brother what a mess!!! I will try a measurent on the system with CLIO with the crossovers in place.

Those sealed subs provide a very nice anchor. Really punchy with great definition. I get more 20-40Hz grunt out of the 2235's but you really don't miss it with these.

Rob

[Zilch]

Hello, Rob.

I'm having a disconnect about Allen and the subs. Can you link to that, please? What are they?

And do you mean you don't really miss the grunt with these?

Also, if you measured the dual mids and they were a "mess," what have you changed to make that different now?

I'm not being critical, rather, just trying to follow the project exposition....

[Robh3606]

Morning Zilch

The subs are 121A drivers, the ones from the L212 subwoofer.

T/S

http://www.audioheritage.org/vbullet...highlight=121h

And do you mean you don't really miss the grunt with these?

Yes they don't put out as much below 40Hz. They are sealed and come up almost flat with room gain so that's where you hear the most difference asside from the punch and clarity these things have.

Also, if you measured the dual mids and they were a "mess," what have you changed to make that different now?

I just kinda charged ahead. The dual drivers with that seperation had all kinds of problems up top. I tried a ground plane and that looked 'eh' and free field measure from where the tweeter would go was plain awful

Looked OK on an RTA though. So I just threw it all together to see what it sounded and looked like with a crossover up top.

Rob

[Ian Mackenzie]

Hey Rob,

They look great!

Ian

[Robh3606]

Hello Ian

Thanks! Well you will be hearing them soon enough. Here's a stab at how they measure. Broke every rule in book getting these. They are measured in different spots 1 meter out from the Left and Right speaker. They are very smooth with the transition between the Mids and the Horn on the RTA and these look OK through the 1.5K crossover region. Below 400Hz it's all over the place but they sound smooth and pretty well balanced.

Rob