Re: USB sound cards

[James Johnston <audioskeptic@xxxxxxxxx>]

It's a bit more complex than that. The response is damped by the speaker motor working against the  2nd order loudspeaker (not 1st, 2nd) impedance.

The speaker impedance's resistive parts is in series with the source impedance AND the crossover inductor resistance.  This total sets the Qts of the speaker. The box design is a very critical function of Qts for any good design (those of you using sealed enclosures can argue with me in another thread) and must combine with the box's acoustic impedance to provide a good low frequency response that does not either just be missing OR alternatively peak terribly.  Vented boxes and passive radiator boxes are especially sensitive to this problem.

Source impedance does matter. It also can matter in headphones, and most expect a voltage driven system.

jj

On Tue, Dec 16, 2014 at 9:28 AM, Richard F. Lyon <dicklyon@xxxxxxx> wrote:

I understand that at the low end of the frequency range, the resonance you guys are talking about is inductive and is damped best by a lower source impedance.  But at higher frequencies, esp if there are crossovers and such, there may be other resonances, and impedances that look more capacitive in the relevant region.  Source impedance will affect these in different ways, and with higher-order systems the damping factor is perhaps too simple a concept.  Nevertheless, my point remains that the source impedance will affect the spectrum of the sound, in possibly complicated ways, and the traditional use of low driving impedance only optimizes one aspect of that, which may not correlate with the benefit that some say they get with added resistance.

It's worth looking at more closely.

Dick

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James D. (jj) Johnston

Independent Audio and Electroacoustics Consultant