Re: [Phys-l] [tap-l] speakers

[John Denker <jsd@av8n.com>]

On 04/26/2011 07:52 AM, Brian Huang wrote:
> The impendance of the speakers has to do with matching the amplifier
> output.  If the impedance is different from that of the amp, you get
> reflections. 

Electrical reflections in this situation?  I very much 
doubt it.

Do the math:  The signal propagates down the wire at the
speed of light, within a factor of 2.  The length of the
wire is usually not more than 25 feet, i.e. 50 feet round
trip.  Therefore the timescale for reflections is on the
order of 100 nanoseconds, corresponding to 10 MHz.

It is very unlikely that the impedance of the speakers is
8 ohms at 10 MHz.  The impedance of the amplifier is also
open to question at 10 MHz.  The speaker wire itself is
not 8 ohms at any frequency;  not even close.  And last
but not least, you wouldn't be able to perceive anything
that happened to happen at 10 MHz.

If you want to talk about reflections at audio frequencies,
let's talk about the /acoustic/ reflections that happen 
after the sound has been emitted from the speaker, i.e. 
reflections from the walls, furniture, people, et cetera.  
These have a very large effect on the perceived sound 
(unless you set up your speakers in the middle of a very 
large open field, or anechoic chamber).

There are of course electrical reflections.  They are
significant at much higher frequencies and/or much larger
length-scales.