I thought the 800 Hz crossover seeemed high for this type of build. TLS, you don't happen to have any 3-way center channel builds in your drmarksays blog do you?
No I don't. However it is the old dilemma of three way speakers. This is particularly acute for the center channel. The center channel speaker is crucial, and has demands made on it, that other speakers don't.
Problem list.
Needs to be relatively small.
Has to produce high spl. effortlessly.
Has to have excellent speech clarity, at the same time produce natural speech, especially avoiding sibilance.
Needs limited vertical dispersion for optimal localization of voices and avoidance of muddling ceiling and floor reflections.
Needs to cover listening area, but no more, to minimize interference with mains, especially comb filtering.
Because of location and all manner of different adjacent boundaries, TV screens etc, optimizing step response for all installations is impossible with a completely passive crossover solution.
Therefore adjustment of the step response correction is highly desirable.
This is a very tall order.
To meet these criteria with a three way with no coaxial driver, avoidance of a crossover point in the speech discrimination band is highly desirable.
Therefore crossovers in at 350/400 Hz and 3.5 Khz/4KHz targets are desirable.
The number of units for use in the above frequency range is small. For most applications two mid range drivers will be required to meet THX specs. This will end up making a larger and tall enclosure.
The number of units available is very small. There is a Vifa unit that would likely have just about a high frequency enough reach.
The only satisfactory dome units that I now of that would be in any way adequate, are the Dynaudio D 76 and the ATC 3" dome. dome units are desirable, as no sub enclosure is required, which keeps the size of the speaker down.
The D76 is unfortunately no longer available OEM to the home constructor. Units show up on eBay but command high prices. I use this unit in the three way speakers in the first level, of my home.
This is a two channel, plus two sub system. Voice clarity is excellent, and you don't miss the center channel. Crossover points 400 Hz and 4KHz.
Because of the frequency characteristics of the ATC unit, a powered speaker with active crossover is pretty much mandatory. They also cost around $420 a piece. However they have VERY low distortion, high spl, and superb off axis response.
It is a real pity the B & W mid range driver used in their 800 series is not available to the home constructor. I think manufacturers denying their drivers to the home constructor is a short sighted business model and wrong headed on their part.
The above problems were the reason for the decisions I made.
I used a coaxial driver in a TL and used active step compensation so it can be precisely tailored to its location.
For a center channel a TL has huge advantages. Properly done there is no hint of chestiness in the tenor range of male speech. The coaxial driver has optimal dispersion characteristics.
I have had a lot of people hear this system now. And there is always very favorable comments on how natural spoken and sung voices are. At the same time there is good voice clarity in the rough and tumble of movies.
I have found a driver that comes close enough for diffraction compensation for use in a TL, but not a ported enclosure. TLs are much more tolerant of misalignments than ported enclosures.
If you really want a center that is better than any thing you can go out and buy, by far, and want to use it horizontal, then I suggest you build my TL center, and use
two of these either side of the coaxial unit.
I would recommend an active crossover and separate amp for the fill drivers. It is a very straightforward proposition and requires a first order low pass active filter at 250 Hz. This is a very simple circuit, with low part count, that can be built for less than the cost of a passive inductor and zobel.
The advantage of active step response correction, is the ability to tailor it to your circumstances. This is a huge advantage.
I' certain, that any one who builds this center will be delighted.
If you want me to work up a design round the Vifa driver I can, but I very much doubt it will be superior to the one I describe above.
