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