From: Kevin McMurtrie
Subject: Re: Cancel speaker resistance?
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Mon, 16 Sep 2002 04:10:13 GMT
NNTP-Posting-Date: Sun, 15 Sep 2002 21:10:13 PDT
In article ,
DPierce@TheWorld.com (Richard D Pierce) wrote:
>In article ,
>Kevin McMurtrie wrote:
>>Is there any advantage in using current to voltage positive feedback to
>>cancel the coil resistance of a single speaker driver? Would
>>eliminating the 5-something Ohms improve the sound or is it
>>insignificant compared to other factors?
>One can easily construct an amplifier that has a net negative
>output impedance, thus resulting in a net reduction in the
>total loop resistance of the amplifier/speaker circuit.
>Would it IMPROVE the sound? Yes, it would, if the electrical Q
>of the driver was too high, resulting in a total Q that was too
>high. If the electrical and total Q are what they are supposed
>to be, reducing the total loop resistance would result ina
>driver that is too OVERdamped and the resulting system would be
>less than optimum.
>More generally, if a speaker is competently designed to begin
>with, eliminating the DC resistance of the voice coil would NOT
>be a good thing. As a corellary, if you ARE going to go through
>the effort of reduing the effective resistance with something
>like a negative output impedance amplifier, it would most likely
>be for a specific design, i.e., a specific driver used with a
>Why would one want to do that? Well, getting the Q low enough in
>a driver can be expensive, because it means, generally, a bigger
>magnet, and the magnet is the most expensive component in a
>driver, for the most part. Now, if you were designing an
>integrated speaker/amplifier, and were constrained by budget or
>size, then such a scheme might make sense.
It now sounds like something I won't rush to try. The component count
to implement it is low so I was curious what it would do. I've heard of
it being done before but I couldn't find any links because it gets fancy
I got thinking about it because I'm trying to build an inexpensive sound
system for a small room that will play music from a computer jukebox.
It doesn't need to be loud but a broad and smooth frequency response is
important. I've looked at computer speakers but they've all had shrill
satellites with buzzy subs. It looks like a component amp plus
competent floor speakers will cost $300+ dollars.
My current idea is to build a little 40 WRMS Class AB amp and a speaker
set for it. I have spare time and tools so putting it all together is
not an problem.