Horns and current drive

[mashaffer]

The question I have is related to how the enclosure type,specifically front loaded or tapped horns, might affect the suitability of a driver for current drive. As a starting point let me describe my understanding of the parameters appropriate for current drive (low DF).

As I understand it most modern drivers are designed with low mechanical damping and relatively high electrical damping (high Qms low Qes) and thus respond best to voltage drive where the Qe is not raised significantly and the amplifier can thus provide extra damping.

Now a driver intended for current drive would be designed with much greater mechanical damping (lower Qms). My assumption is that if it were possible to design a driver with otherwise appropriate parameters and a Qm of 0.5 to 0.7 then a pure current drive would be feasible.

Again my understanding is that the enclosure it self also affects the damping of the entire system (acoustical damping???). So the question is how would horn loading affect the overall damping and thus the suitability of high Z amplifier for a given driver?

Also is Qms primarily a results of the stiffness of the suspension? If so I can see one possible advantage of a horn in this situation in that the stiff suspension would tend to raise fs and the horn loading would allow lower f3 in relation to fs.

Would any enlightenment you can provide.

[chris661]

As far as I've seen/read, a current drive amplifier will seek to put equal current though the speaker at any frequency.

If you take a system (ie, a sealed cabinet) with an impedance peak, using voltage drive, the output would follow the simulations reasonably well. The peak in impedance will mean less current draw at resonance, but that's okay because little energy is needed to excite a system at resonance anyway.
Now, take the same system, and use a current drive source. Suddenly, there's equal current at resonance as elsewhere. Now, remembering that, with a voltage drive, the resonance only needed a fraction of the current as elsewhere in the frequency range, for similar output; there's going to be lots more output around resonance with your current drive amplifier, giving a very one-note-bass sound.

Now look at the impedance peaks in a horn loaded system.

Chris

[el`Ol]

The formula is Qms=2*Pi*Fs*Mms/Rms.
The most current-drive suitable bass driver I know about it the JA8008.