[JoshK]

I was thinking of trying it out on horns, so efficiency won't be the issue. 

[randytsuch]

Josh

For your "crossover", this may be an option
http://www.audiocircle.com/index.php?topic=131175.msg1396631#msg1396631

In future FPGA versions, he is going to implement a crossover, and some way to sync multiple DACs.  At least one guy bought two stereo DACs with the goal to implement a 2 way system.

Since the price for the DAC is pretty reasonable, might be a good approach.

Randy

[brj]

The average speaker system (driver) has large impedance swings and is too low efficiency.  The SPL curve looks like the impedance curve if driven with a transconductance amplifier source.  We can electronically equalize things pretty easily nowadays, but the efficiency issue still remains.

Current source amps are aimed at high-efficiency driver systems.  Horns, Fostex, Lowther, etc.

Davey, what efficiency do you consider "high"?  >100 dB/w/m?

I'm putting together an active system with a wave guide mounted compression tweeter (B&C DE250-8 @ 108.5 dB/w/m) and a fairly efficient woofer (B&C 12TBX100 95.0 dB/w/m).  The tweeter is protected by a series cap and the woofer has a (Music Creek) inductor on the positive leg to smooth out the impedance a bit and reduce the demand on the passive line level crossover.  (LP filter)

Certainly the tweeter seems efficient enough that a TC amp might be interesting, but I'm wondering how close even the woofer might be to the mark?

(Note that in my case, the passive line level crossover is just doing frequency splitting duty.  I'll have my Mac Mini doing driver EQ in the digital domain.)

[Davey]

I guess it depends upon how close you'll sit, how loud you want to listen, and what sort of power your amplifier is capable of.  You can (roughly) estimate SPL will drop about 6db for every doubling of distance, so a little arithmetic will yield some numbers.

Cheers,

Dave.

[brj]

Ah, ok - I thought that you were implying that TC amps were more sensitive to impedance (presumably combined with phase angle) swings and low efficiency than voltage source amps, and I was trying to understand your threshold.  I didn't realize that you were just referring to the usual power/distance/speaker count/boundary reinforcement math.

[Davey]

Well, actually I was implying that. 

With a transconductance amplifier any driver impedance swings would be translated directly to SPL variations.
Most of the "current" amplifiers I've seen.....like the Pass F1 are generally very low in power capability.....thus the requirement for fairly high-efficiency drivers.
The efficiency "threshold" would be yours, not mine.  That's what I was getting at with the power/distance/efficiency comment.

There are actually a few informative threads on this topic at DIYaudio.com  (Lot of different opinions on this topic.) 

http://www.diyaudio.com/forums/solid-state/250272-current-drive-loudspeakers.html
http://www.edn.com/design/consumer/4423155/Loudspeaker-operation--The-superiority-of-current-drive-over-voltage-drive

Cheers,

Dave.