ht design opinions

I've got a peculiar design problem. The room that I have my ht setup is constructed in such a way that i have space and prewiring to the ceiling for the front L/R speakers. Given the actual construction of the room, I have about 8-10" of vertical height and relatively unlimited horizontal width in which to place speakers. The center can be horizontal or vertical in it's orientation. the rears will have to be similar to the fronts.

What are your thoughts on driver number and alignment?

p.s. i realize this isn't ideal, nonetheless it's what is most aesthetically pleasing given my room and WAF is a very important consideration.
the front satellites will be on the ceiling, which is ten feet high.
there is a sub-it's a sealed tempest, which can be crossed over at anywhere from 50-100.

i suppose i'm limited to 5"-6.5" drivers, my question is, what's the best arrangement. i wonder if i could get away with a vertically aligned mtm as center and horizontally aligned mtm's as R and L, with the midbass drivers angled back 20-30 degrees on the cabinet to minimize the dips in the frequency response. the units would be fairly close to the ceiling wall boundary (~1 foot from the corner of a 2 wall boundary). to align the listening couch with the driver axis, the units will have to be angled downward approximately 45 degrees.
i would love to have vertically aligned mtms as front L and R, but the only way to do this is in my room would lead to an angle of 15 degrees between the left, right, and seating position. i'm shooting for 30-45 degrees.

the problem with a horizontal mtm is that there is up to a 25 db frequency dip roughly in the crossover frequency from woofer and tweeter cancellation and woofer-woofer interference, occurring off axis at 30 degrees. not so bad for my wife and i sitting on axis, but pity our guests sitting on the couch off to our side. angling the woofers backwards decreases the frequency dip.

most horizontal mtms are designed that way for aesthetic reasons-it seems that buyers prefer a speaker aspect ratio similar to their tv/projector.


diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
I have not located the specific driver for this-I think one exists- but how does this sound?

A 6.5" co-axial vented to 75 Hz or so.

The action of the port lasts for only 1 octave above the tuning frequency. If you port to 75 Hz, ("classic" alignment, there are others of course), there is no port action above 150 Hz-which is right where the human voice range starts. Yes, I know bass voices go lower, but how many of them do you listen to?

Even a 5 inch co-axial might work, if it has sufficient power handling.

Angle the front of the speaker board down at whatever angle you find reasonable. Don't forget to correct for the angle in your volume measurements.

Incidentally, if you do angle the speaker board down, you increase it's size. A speakerboard angled downward at 25 degrees can fit an 8.9" face into an 8" slot.
hadn't thought too much about coaxial, but it' actually not a bad idea and far as the location is concerned. i know at one time KEF made coaxial ones that were more for home use as opposed to autosound. i'm not sure if they still sell to diy-will have to look around.

Incidentally, if you do angle the speaker board down, you increase it's size. A speakerboard angled downward at 25 degrees can fit an 8.9" face into an 8" slot

Now i hadn't thought of that-funny how such an obvious concept eluded me. this gives me a bit more room.


diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State

Seas has a line of coaxial speakers that seem to be precisely what you are looking for. A tad pricey, (around $80), but they include the tweeter and they seem to solve a lot of your problems all at once.

A) High power handling: 80-100 Watts for the 6.5" models.
B) Excellent alignments: low Qts, high Vas/Vb ratio that yields superior transient response for vented enclosures. Transient response approaching sealed systems, but with excursion saving ported enclosures.

In another thread, Thomas W. said that a coaxial system has to be aligned at the factory to within .05 inch or some similar number. Nothing for the home builder to mess with, if he wants correct time alignment.

Available at . Click on "catalog", scroll down to "Seas" and click on "html". You can also view a pdf. file for graphs.

I normally prefer Peerless drivers which are a bit cheaper than Seas. But they don't make coaxial units. These are not THAT much more expensive, and considering what you are up against with this project, I would strongly recommend them.

In fact, I am glad I found them. Where a coaxial from a high quality manufacturer seems just the ticket, these look really good.

Looking at the response charts, I notice they put them in closed boxes with extremely low Q's. The speakers will have much flatter responses in the vented box I would recommend. Also, I think they raised the response of the tweeter to visually separate it from the woofer.