The MTM Project

This trio of speakers started out as a center channel only for a client in Michigan, but as I got further into the build I suggested that the design would make excellent mains as well and so the MTM trio was ordered. After searching through the available designs for a shielded project I decided to use the Usher UA721 configuration developed by Dr. Joseph D'Appolito. Dr. D'Appolito chose the Usher 9950C-15 tweeter and Usher 8836AC woofer because of their smooth response, linearity, and low distortion. The 9950C features a copper shorting ring on its polepiece, which reduces distortion and extends the high frequency response. The 8836AC's woven Kevlar cone contributes to the woofer's neutral reproduction and realistic dynamic range. Both drivers' motors incorporate magnetic shielding to prevent interference with adjacent equipment. The components were easily acquired from Parts Express, and I designed the enclosures using the calculated dimensions in Dr. D'Appolito's design notes.

The boxes started with .75 " MDF parts for all but the front baffle, which is made from 1" material. A very stiff interior brace is utilized with cutouts directly behind the two midbass drivers.

I chose to fillet the rebated midbass openings instead of templating the shape. This worked out fine as the client had requested a Walnut Burl veneer which would cover the inserts.

Here are some of the veneer flitches seamed up and ready to apply. This batch of veneer came from http://joewoodworker.com/ . Joe has a really fantastic selection of veneers and I am buying all of my veneer supplies from him now. Highly recommended!

These cabinets start to take on a life of their own when the veneer gets applied. The Burled Walnut has amazing patterns in the grains which seemed to produce the image of a tree when I placed them on the boxes.

I changed the crossover slightly to make the speakers more friendly for my clients amplifier. The addition of a transformer upped the resistance to 8 ohms from the as designed 4 ohms. This resulted in a 3 Db gain loss, but there is plenty of level here. Thanks to Dr. D'Appolito's efforts, the MTM provides smooth, controlled horizontal dispersion, even when the enclosure is positioned on its side for center channel duty. Destructive interference between the two woofer drivers is minimal, with some narrowing at 1 kHz that is not likely to intrude into a listener's perception of dialogue or similar program material. At the same time, "spill" onto the ceiling or floor is minimized by the MTM's trademark linear coverage in the plane that would be horizontal when the speaker is deployed "normally."

I was really surprised at how full the drivers sounded while testing the crossovers! Just lying on top of a receiver in the shop they were very pleasant and I listened to several cds this way while soldering. I was anxious to hear them in an enclosure!

Back at the woodshop the veneering was finished and the cabinets were ready to spray. I used a pre-cat satin lacquer for these enclosures.

These speakers sound very very nice indeed! The bass is very well defined and surprisingly deep. Several guests to the house have commented that they really like the MTM and consider them among the best I have built to date. For the price they stand up nicely to the much more expensive Accuton designs and are very much acceptable for home theater applications. I would love to do a five or seven one system using these cabinets with one of my 12" sub designs. I have listened to the speakers for about two weeks now and will be delivering them day after tomorrow. After I hear from the client I will update the write up here with her final word on the subject.

Update: Here is the owner's comments on these speakers after living with them a few months.

"Frank,

The speakers sound and look wonderful. I have not listened to the mains alone, only as a set with the center speaker. As a set of 3, I think they rival the sound that [  ] gets out of his speakers. I can close my eyes, and almost feel like I am in the same room as the musicians... there is that much depth to the aural experience. I am very pleased with them.
Thank you for all of your work, and for hand-delivering them!"