Re: PC speaker driver (fwd)

From: Ian Carr-de Avelon (
Date: Wed May 10 2000 - 09:33:10 EST

David wrote:
> said:
>> Most computers that I saw have a small nice speaker (the sort you
>> could see in radios couple decades ago). The problem however is not
>> with speaker but with the way it is driven (on and off if I remember
>> correctly). That is the speaker can either be told to emit a square
>> wave at a certain frequency (which is used for beeps) or you can drive
>> that square wave with cpu. Hence unlike sound cards that have from 256
>> to 65536 gradations (or more) pc speaker has 2.
>True. The speaker is attached to a single digital output line from a
>one-shot timer, IIRC.
>However, we're not quite as limited as you suggest. As you can expect a
>small amount of capacitance, you can divide your time into small units,
>and for each time unit, you allow the line to be set high for a percentage
>of that time proportional to the desired analogue signal level at that
I think it depends on the inertia of the speaker rather than elecrical
capacitance. My point is that as the inertia of the speaker becomes
lower there is less filtering of the 18k component. Ie the speaker
cone starts to follow the square wave. I can hear a high piched whine
on new PCs which I don't notice on older PCs.

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