Re: USB sound cards

["James W. Beauchamp" <jwbeauch@xxxxxxxxxxxxxxxxxxxxxx>]

I agree with Bob. Most loudspeakers are designed to be driven by
an ideal voltage source. Under this criterion they attempt to get 
the flattest possible response overall. This is not necessarily 
the most efficient response. In fact, some loudspeaker designs, 
like the Small-Thiele closed-box non-vented design, are very 
inefficient.

Jim

Bob Masta wrote:
>From: Bob Masta <audio@xxxxxxxxxxx>
>Date: Sun, 14 Dec 2014 09:15:19 -0500
>To: AUDITORY@xxxxxxxxxxxxxxx
>Subject: Re: USB sound cards
>
>On 13 Dec 2014 at 21:59, Richard F. Lyon wrote:
>> On Sat, Dec 13, 2014 at 5:52 AM, Bob Masta <audio@xxxxxxxxxxx> wrote:
>> 
>> > It's the other way around:  Adding resistance in the
>> > driving circuit gives poorer damping.  "Damping Factor" for
>> > a power amplifier is the reciprocal of output impedance.
>> >
>> 
>> Bob, I wasn't aware of that definition.
>> I was thinking of http://en.wikipedia.org/wiki/Damping_ratio
>> rather than http://en.wikipedia.org/wiki/Damping_factor
>
>Oops, you are correct... I should have said it is 
>*proportional* to the reciprocal.
> 
>> Is there an understanding of why high "damping factor" would be good?
>> Jont's findings suggest otherwise (I believe he's saying the current is
>> typically more relevant than the volage).
>
>The second reference you cited covers it under 
>"Explanation".  Basically, a conventional electrodynamic 
>speaker is both a motor and a generator.  Imagine that the 
>speaker receives a momentary voltage pulse, after which is 
>is instantly disconnected from the source.  The speaker 
>would ring at its resonant frequency, damped only by 
>friction.  The generator would be creating a voltage, but 
>no current, so no load to add damping.
>
>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.  
>
>Conventional loudspeakers are designed to be driven by 
>voltage sources, not current sources. The current may be 
>more "relevant" (in the sense of force generation), but not 
>for getting a flat frequency response from a conventional 
>speaker design.  (Although there have been occasional 
>attempts at current drive, the ones I recall required 
>special dedicated amplifiers.)
>
>Best regards,
>
>Bob Masta
> 
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