Thanks everyone for their input.
I've been exploring the new DSP amplifier boards offered by parts express mentioned previously. These are really nifty products:
- There is a 2x50W module with DSP
- There is a 1x100W module with DSP
- There is a 1x100W module without DSP which can plug into the 2x50W module, allowing you to do a 3 way system 100x50x50W
- There is an outboard preamp/dsp module which can be combined with other amplifier modules, such as an IcePower 125x2 or 50x2, or whatever else is desired if higher quality amplification is needed.
I have asked a few people if they are willing to characterize these modules. I doubt they have state of the art audio quality, but if the power is reasonable, the addition of DSP should enable seriously high audio quality in a 2 or 3 way design.
I think the best application for these modules would be in a 3 way design. Why? A 3 way passive design has a lot of crossover components, which is a pain in the ass to build, measure and simulate. If you use quality passive components, the cost is not insignificant, especially if you're using a big woofer and midrange, requiring lots of inductance and capacitance. This is where an active implementation shines.
The cost of these DSP units? For a 3 way, stereo system, including 5A/24V power supplies, $221 USD. You can easily spend that much on crossover components for a relatively simple crossover. This is for a 50x50x100W system (
both speakers.) Connections would be 1 audio connection and one DC jack on the back of the speaker.
The use of DSP simplifies design of a 3 way immensely - matching driver sensitivity is no longer a driving concern, you can boost bass and use a smaller enclosure. Low order filters, which help blend directivity characteristics, are much easier to implement due to delay.
The great advantage of a good stand mount 3 way is a very dynamic sound coming from a big cone - 8 or 10". There is an 8" and a 10" driver I am looking at. With DSP in a sealed enclosure of around .6 cubic foot (17L), they can do around 92db/2M at 40hz, and 100db at 200hz+.
For the midrange and tweeter, costs can be significantly reduced. Finding a 3" midrange with low distortion from 400-3300hz is pretty easy, and finding a well behaved tweeter above 3300hz is child's play. If it were me, I'd use nice drivers I already have (sb26STC and Peerless ne123) which retail for a combined $90USD, but part of what you pay for with nice drivers is ease of use with simple passive filters. If you have unlimited EQ bands, you can do better with, for example, a Vifa TC9/Peerless BC25 (about 30 dollars combined.)
This puts driver and amp/dsp cost at around $240 for one speaker. This is pretty damn cheap. You could upgrad to SB acoustics drivers, for example:
SB23NBAC - $109
SB12MNRX - $51
SB21RDC - $46
Or about $316 for a speaker, but I'm not sure that with DSP, you get anything over the cheaper drivers in this case - perhaps a bit more SPL capability in the lower midrange.
What is the sound quality here? Well ASR has not measured many 3 way speakers, but a good 3 way with small (~3") midrange has very wide dispersion in the lower treble, with smooth directivity characteristics. This format of speaker has become somewhat uncommon due to size, but again DIY shines here - making a big speaker isn't that much more difficult or expensive than building a small one. In some ways it's easier.
Anyway - I'd be interested to read everyone's thoughts on this approach. I am going to give some more thought to cabinets next.