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-   -   MCM Driver Sealed Array (http://www.diyaudio.com/forums/multi-way/132462-mcm-driver-sealed-array.html)

wrenchone 3rd November 2008 05:21 AM

MCM Driver Sealed Array
 
Has anyone had experience with the MCM 55-1854 aluminum cone midbass? The specs look nice, but there seem to be no freq plots available. The price is certainly ok. I was thinking of using 18 pieces a side in a sealed hexagonal array, 8 ohm total impedance, with some tweeters to round out the high end.

sdclc126 3rd November 2008 10:30 PM

Here is a design with the 55-1853, 8 ohm:

http://www.zaphaudio.com/ZBM4.html

Definitely not the array type you have in mind, but at least you'll find the FR plots. The tweeter in this design might be considered for yours too.

sdclc126 4th November 2008 12:43 AM

2 Attachment(s)
P.S. - Guess I could have just posted the graph myself:

wrenchone 4th November 2008 02:48 AM

Rationale -
I have a pair of homebrew speakers that have been with me since 1978-1979 or so. They were inspired by an article in Audio Magazine on doppler distortion that made a lot of sense at the time (still does). Originally, I built some cabinets in a hexagonal prism shape out of particle board and loaded them with 16 pieces each of a Westwell 5 1/4" 8 ohm speaker available at McGee Radio (old hackers still miss their speaker deals) for about $5 apiece. These had cloth surrounds, which probably meant that maybe they were a bit too stiff for a lot of low end, but by the same token, these speakers are still around (sitting in my basement), as the cloth surrounds did not rot out like foam surrounds probably would have.... I also use 3 pieces each side of a Motorola piezo horn tweeter bought from Olson Electronics.

I ended up treating the cones of the Westwells with polyurethane varnish, which smoothed out the midrange quite a bit and no doubt lowered the resonant frequency somewhat. The piezo tweeters were replaced with Vifa textile dome tweeters (part number lost in the mists of time), which were a big improvement over the piezos.

Fast forward 20 years or so - Westwells replaced with 4.5" Vifa/JBL buyout speakers from Parts Express. Since these speakers were 4 ohm ,the cabinets went from 8 ohm to 4 ohm.

I set there speakers aside for a while, intending to cut a few more holes, and wire up two more midwoofs and one more tweeter so I could make the whole array 8 ohms - hasn't happened yet.

At any rate, I put one of them back in service, and was surprised by the bass extension I was getting with those 16 drivers. Midrange was alway pretty nice.

At any rate, I think I want to try an update of this speaker using smoe nice MDF or Baltic birch for the cabinets. I could re-use the JBLs, but The MCMs look nicer and don't have the 6-7kHz suxckout that the JBLs have, making crossover a little less critical. I have a bunch of nice little 1" dome buyout tweeters from PE I was thinking of using for the high end.

Rough description - hexagonal prisms with ~7.5" facets, 24" tall. Current config - front face gets 2 midwoofs plus 1 tweeter. Next two faces get 3 midwoofs plus 1 tweeter. Next two faces get 4 midwoofs each.. Back face has connection, no speakers. Current plans for mod (and what I might try wth the new speakers) are to put two midwoofs and one tweeter on the back face so all ca be wired up for a nice, sane 8 ohm cabinet.

I also want to try some experiments with damping. Currently these are sealed speakers stuffed with polyester fluff. I think I'm having some resosnnce problems along the long axis of the prism, so some damping/sound absorbtion material would be in order. One thing I'm going to try is pieces from a cocout fiber doormat (backed with vinyl). I'm thinking that the fiber structure would do a good job of drinking up resonances, and the mats are fairly inexpensive.


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