Re: Apple IIe speaker

[pausch@saaf.se (Paul Schlyter)]

In article <20030529211138.15080.00000785@mb-m14.aol.com>,
Michael J. Mahon <mjmahon@aol.com> wrote:
 
> Dopefish asked:
> 
>> I have an Apple IIe without a speaker and I need to buy a new one. Does
>> anyone know the resistance that Apple II speakers had?
> 
> First, it's not the _resistance_ (DC) that matters, but the AC
> _impedance_.  Most speakers will have very low DC resistances.
 
I disagree with you here!  Maybe this is the case for _some_
loudspeakers, however all speakers where I've measured the DC
resistance had a DC resistance not much different from the specified
AC impedance.
 
Presumably most of the AC impedance is this DC resistance.  And this
could be a way to try to make the AC impedance fairly independent on
frequency.  If it was, as you claim, that the DC resistance is "very
low", then the AC impedance would be an almost pure inductive
impedance, and as such the impedance at 20,000 Hz would be some 1,000
times larger compared to the impedance at 20 Hz.  And this would pose
a significant problem to manufacturers of hi-fi amplifiers.
 
In real-world loudspeakers, the AC impedance is fairly constant up to
perhaps a few 1000 Hz, and above that it starts to rise significantly.
 
> The speaker in an Apple II is in the collector circuit of a transistor,
> so the higher the impedance, the better.  Stock speakers are
> mostly 8 ohm, but virtually anything will work fine.
 
:-) ...i.e. the impedance vale is quite uncritical in this case....
 
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