What I want to do, is build a center channel speaker for the home theater setup I am working on. For the mains I am using a pair of Bottlehead Straight 8’s. I have 4, 5" drivers, the MCM 55-1870, the same used in the 8’s. I plan to run 4 or maybe just 2, if it makes more sense, full range. The Fs= 54, Vas 10.04 L, & Qts= .401

The max box size I can use works out be about 1.95 cubic feet. (52.5 Lt.) , a bit smaller would be better but hey, we do what we gotta do…

So, My questions to O yee speaker gurus are.

Can you recommend a simple box program to use, I have not kept up.

How do I model an array as a single driver?

Do you think I should be modeling for a vented or sealed box, I bet if I knew the answer to 1 and 2 I could answer this myself

Thanks in advance…John

If you set the center channel to "small", what's the cut-off frequency?

A sealed box of .6 cubic feet will be -3 dB at about 100 Hz, with as stuffed-box Qtc of about .7.

A vented box of 1.2 cubic feet tuned to 60 Hz will be -3 dB at about 60 Hz. This is what I'd do, as I'd rather have the center channel's inherent rolloff well below the frequency where the processor cuts it off.

In my opinion, most center channels have a flawed driver layout. Horizontally spacing two midwoofers on the same baffle narrows, rather than broadens, their coverage pattern. The center channel should have a wide enough pattern to give uniform coverage throughout the seating area, and very few do.

You can make a better center channel by building a splayed array. Have two of the drivers firing about 22.5 degress to the left of the centerline, and the other two firing 22.5 degrees to the right of the centerline. Each pair is in a vertical rather than horizontal stack. This will give fairly uniform coverage across a 90 degree horizontal arc. The vertical coverage will be narrowed by stacking the drivers, but that's seldom a problem in home theater.

You can use either a convex or concave arrangement to get the splay. Both will work - and both have advantages and disadvantages.

Below is a link to a prosound speaker that uses a concave splayed array for the woofers. Looks to me like the splay is closer to 15 degrees. That 22.5 degrees isn't carved in stone - it can be more or less, but I wouldn't go over 30 degrees.

My $.02.

Duke

• http://www.reyaudio.com/index.html

Are you sure that phantom center is not working for you?

The splayed arrays look good. I will give that some testing with the speakers I had planed to use for the rears.

In the mean time my receiver has craped out. I have it on the bench but I am having a hard time finding the tubes.

One more question. How do I model 2 or more identical drivers? Do I plot for 1, then double the volume or do I somehow add the driver specs? Or? As you can see this is not my area…John

Or you can model one and then just double the box size. If it's a vented box, to keep the same tuning frequency double the port area but keep the same port length.

Duke

• SEAS Coxial driver

Thank you for your response, much good info there. I chose the MCM driver, well, because I have a few and they are the same driver as used in my mains. Your idea of a coax driver makes sense.

From you and others who have been kind enough to respond, I am getting the idea that smaller/vertical is better. I will work with that as far as the position I have will allow, I don’t think I want to mount a speaker over the TV, at least for now. I did find a box program that seem to work, it’s name escapes me for now. I used to build speakers some 20 years ago in a small way. I have forgotten most of that but with the help of the folks here, some of the little I knew is coming back.

I had a look at your photo site. Very impressive. I like the way you can lurk behind the wall of amps. Sort of like the ‘wizard of OZ’ …John