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Re: USB sound cards

It is not lossless, there is the voice coil resistance, which absorbs the energy. It does not matter whether the resistance is internal or external. It is true that almost all audio amplifiers are voltage amplifiers with practically zero output impedance, but ironically lot of problems would disappear in loudspeakers, if driven with current amplifiers. The main reason for using voltage amplifiers is just the electromechanical damping it offers at the low frequency resonance. The same would be achieved with acoustical resistance elements behind the diaphragm - just like in many headphone drivers - but this is not currently done.  Loudspeaker drivers from 30’s and 40’s often have basket openings covered with a mesh serving just this purpose. At mid and high frequencies the driving source impedance does not matter as the diaphragm does not vibrate as a piston but bending waves are propagating along it. What matters there is the diaphragm internal damping, i.e. mechanical losses. 


On 16 Dec 2014, at 07:30, Richard F. Lyon <dicklyon@xxxxxxx> wrote:

On Sun, Dec 14, 2014 at 6:15 AM, Bob Masta <audio@xxxxxxxxxxx> wrote:
However, if instead of disconnection the leads were
*shorted* after the pulse, the generator would be driving
all its current into the zero-ohm load, giving a maximum
damping effect.

I'm not buying that.  A zero-ohm load is lossless, just like an open circuit.  Damping requires loss.  Whether higher or lower resistance makes more damping depends on the nature of the resonance.