A Center Channel Speaker












Under Construction!

I got a new tv set, so I guess the home theater bug got to me. I bought a Pioneer
receiver and was looking for speakers. I already had left and right channels made up
with the 8 inch Onkyo drivers designed by Keith Johnson and the matching tweeters, built
up into medium sized towers, similar to the the setup of the speaker shown on my Audio Stuff page.
The problem I have is a large picture window on the wall with the tv. I didn't want to obstruct the
view too much. I looked all over for a suitable speaker of decent quality. Many were poor quality
or unobtainable, such as the slim Polk center speaker, only available with systems. Bose has about
the smallest center channel speaker, but is fairly expensive, and it's BOSE!

So on with the construction project! First some words on the performance. The only tests done were
octave band analysis and listening tests. My first objectives were to create a speaker with a broad horizontal
dispersion, and response starting about 100 Hz. Free of any over emphasis of bass, or lobbing problems
with midrange frequencies. The tweeter I selected has a rising response in the treble. I put in a cut back
circuit to help control it. It still has some rise, but at typical listening distances the rising response
is not noticed. I would not use it as a near field monitor. The overall results impressed me, I even made one
for my sisters system. Set up with pink noise, you can rotate the speaker around horizontally without hearing
any noticeable artifacts. Even at 45 degrees, the high frequencies just start to reduce in an orderly manner.
I think this is a good speaker. The small drivers have a little to be desired in efficiency, but should handle
a 100 watt program source. Notice the 8 ohm drivers are in series, giving a 16 ohm net nominal impedance.

I needed a slim design, so I used 1/8 or 3/16 inch Luan and 3/4 inch plywood inserts. With the added supports, and
mostly filled foam material, the box doesn't exhibit any noticeable resonance's. I probably should have tried
matching box size a little better with this closed box, but my guess is its pretty good, at least from listening
tests. This isn't a detailed speaker construction project. I've given the basics, so just follow with your own
judgments. The hardest part was coming up with the crossover. A little bit of my own knowledge and allot of
listening and substitution produced the final crossover circuit. The woofers are placed close to the tweeter
to keep lobbing problems to a minimum. I put some felt like material near the tweeter to help control radiation
hitting the grill, and top and bottom Luan sheets. The thin grill material was glued to some small strips made to
fit the box, with some Velcro attachments.

The box is made crude with overlapping edges. I use a large rotary sander to square off and finish the edges.
I have this style of painting boxes to give an overall effect, and cover imperfections. Using simi gloss black
latex paint, I use a rough roller to add a texture. This involves first brush painting a primer, then applying thick
coats, along with the help of a hair dryer to set the texture before it runs. takes a little practice. The primer should
dry first. It should only need one large coat for the finish. A second one when the coat is set, but not dry,
will add to the texture.

Oh yes, the drivers. The drivers I got from MCM Electronics. The paper cone 3 inch rubber surround woofers are
54-605, and the Dynovox tweeter is 53-571. Both 8 ohm. Probably just over $50 with shipping. Resistors were sandstone types
about 2-5 watt should be good. The 4.7 ohm types should be at least 5 watt. I came up with a combination to get 12 ohms
and 33 ohms. On the first model I used a 1.5mh woofer inductor, but I used 2mh on the second edition which seemed better.
On the woofers, I applied two coats of Airflex 400. Regulars white Elmers could be used with less success. White
surround glue can also be used. I think this makes it sound better, and also reduces the high frequency response
of the woofers which we don't want. Cut foam blocks to fit into most of the enclosure, and provide snugness with top and
bottom panels. The back panel is hel on with wood or drywall screws. Add some Mortite or foam to seal it.
Lastly, but you have to do this first, cut off some of the top and bottom of the tweeter plastic frame. This must
be done to fit the woofers size. I used the same sander to do this. It could be cut off with a hack saw.
*** The 54-605 has bee replaced with a 54-606. I don't know the specs on this driver. The other two drivers
54-600, 54-610, can also be tried in the project using polyproplyne and aluminum cones.