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danmarx.org/blog

 

 

Dayton 7" Aluminum Woofers w/Morel MDT-20 Tweeters in an LCR MTM Design

This is my short write-up about a set of MTM speakers I designed for a good friend of mine who lives up in Utah.  I visited him this past week over the 4th of July and together we built these speakers in a day.  Well, it was half of one day, and the other half of another.  But essentially we started out with a sheet of MDF one day and was watching movies no less than 24 hours later.

But before get into all that, the project actually started months ago.  About 3 months ago to be exact.  My friend Jamin recently moved into a home with an unfinished basement.  And form the beginning he was designing up in his head what his new home theater would look like downstairs in that unfinished basement. 

Well it literally has been exactly 1 year later and the basement is about 1/2 complete, well 3/4 complete now that the home theater speakers are finally built and installed, but it's been months in the making.  Jamin built a false wall about 18" deep in which he wanted to house his front left/right and center speakers, the sub, as well as all the stereo gear.  In that wall he had cut out two holes 8" x 36" for the left and right speakers and so I basically had that to go from when designing the speakers.  I immediately thought of doing an MTM layout, with a small pair of 6-1/2" speakers or 7" speakers so they would fit within the space, but still be able to handle a lot of power and provide a lot of sound.  Nothing does that better than just doubling the amount of woofers you're using. 

While browsing PartsExpress.com, I tossed around a lot of different driver/tweeter combinations that varied with looks, performance and cost.  We wanted to keep the overall system fairly inexpensive, and we wanted to do all 3 front speakers exactly the same in the conventional MTM left/right with the center MTM on its side.  After going back and forth on a lot of drivers, and a lot of different price points, we finally settled on a pair of Dayton Loudspeaker Aluminum 7" Woofers and Morel's MDT-20 soft dome tweeter for each speaker.  Each of these speakers offers great performance at an exceptional cost.  Of course I'd never actually heard either of these speakers, but that's sometimes the case with picking out drivers - you buy them based on their specs, looks, and cost.  Or at least I do it that way.  Along with some experience with the drivers, such as the Morel tweeters, I've used the DMS-29 series tweeters before and just love the way they sound.  So I figured the 20's would be just about as good and they were a little cheaper.

With the drivers chosen, it was time to design the boxes and the crossover.  Without going into a ton of detail on this, let's just say I ended up with an 18dB/octave Butterworth crossover on both the woofer and tweeter and put the left and right speakers in a 1.52cu.ft. box tuned to 34Hz with the center channel housed in a 0.88 cu.ft. sealed boxed.  And that was the design we ended up with.  Again though, I went back and forth on numerous crossover options and box volume calculations.  In the end, we just built all three boxes as big as one full sheet of MDF would allow us.  The center channel was initially going to be ported along with the side speakers, but do to time constraints, the fact we would have needed to buy another sheet of MDF, and the fact that we thought the center channel would have looked funny if it had been as big as the side speakers, we opted to just make it smaller, and then keep it sealed.

So this is it, here's the whole design from beginning to end.  Here's a short 2 minute video clip I shot of us watching Star Wars and Independence Day for the first time.  Needless to say, we were both completely blown away.  (BTW, we also installed a pair of Dayton 6-1/2" two-way in-ceiling speakers for the rear surround as well and they sound great).  He hasn't got around to building the sub yet, so we were just watching in 5.0 surround sound, but man those little speakers kicked out some sound, and they sounded really good.  I'm not going to throw out a bunch of fancy words to describe them, I didn't get a chance to listen to them for more than 1/2 hour at most.  But they sounded really good, they played plenty loud, vocals from the center channel sounded natural and smooth.  They are probably a bit bright for music, but for movies they sound fine.  In the end all that matters is Jamin's happy, he said they sounded great to him, and his wife said the upstairs tables were rattling, so that's all good.  Actually his 3-year old daughter that same day we finished the speakers, while she was all alone downstairs, poked in the domes on all three tweeters.  Jamin about cried.  I went ahead and "sucked" them back out so they looked normal again, but he has to get cracking on those grills, and soon.  Kids and dust caps and tweeters, they're like a big red bull's-eye saying "Poke me in, poke me in!"  I should have got a picture of all three tweeter with the domes inverted in, it was truly sad to see.  But they all appear to fine now, so all is not lost.

Now all he needs is the drop-down perforated screen and the sub, and he's all set to rock to all his favorite movies day or night.  So there you go Jamin, hope you enjoy your new home theater, and next time when I visit, I definitely want to sit through an entire movie this time.

Morel MDT-20 Tweeter and Dayton 7" Aluminum Woofer

This was the design for the speakers on the front wall of the home theater with dimensions

The shopping cart of all the speakers and crossover parts from Part Express

The summed FR plot of the proposed crossover - 18dB with a Zobel on the woofers

Crossover Schematic - This was the simplest design I could come up with that yielded a decent FR plot

First pictures of all the new speakers and parts when the arrived

The almost-completed crossovers mounted to a piece of 1/8" bead board and hot glued down

Point-to-point soldering with 16 AWG wire on back ensures good electrical continuity and is easy to do

I did a few near-field response curves and measured the speakers with the new crossovers

Picture of the (3) cabinets that we built in only a few hours.

Crossovers screwed into place.  We didn't get a shot of the insulation, but the walls are lined in the two larger cabinets and the smaller center channel cabinet is filled 100%.

First shot of the drivers just sitting in the cabinets.  We spaced the drivers as close together as we could.

We screwed the cabinets into the studs in the walls before actually installing the drivers.

See the legs/arm in that picture above?  I had to get inside the wall to screw on the terminals cups since the speakers wouldn't fit into the walls with the terminal cups on the sides.  This is me climbing out of the wall.

Finished speakers mounted into the wall at the front of the home theater

Popped in Star Wars Episode II for the first listen.  Everyone is impressed.  They sounded great.

Jamin's projector is a Sharp and currently is projecting about a 75" image onto just a painted  wall


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This page last updated on January 31, 2017.

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