[Gllug] Good quality audio cards - going OT

Ken Smith kens at kensnet.org
Sun Jun 20 10:17:12 UTC 2004


I have heard all kinds of nonsense about audio cables, but a little
application of ohms and watts laws can bring some sense to the discussions.
Most speakers are fairly low impedance (8 ohms or less) which means that to
send, say 100 watts, to a speaker a current of around 3.5 Amps is flowing.
So whatever cable is used needs to carry that without undue volt drop. 20
metres of 1.5 mm cable will have a resistance of 0.6 ohm and in carrying 100
W to an 8 ohm speaker 7 watts will disappear in the cable. This becomes
really significant if you have long speaker cables to PA speakers that are
sometimes 4 or even 2 ohms.

I have heard people waffling on about skin effect where the current tends to
flow near the surface of the cable - but skin effect is only really
significant at GHz frequencies and no music recordings I have heard of go
anywhere near that high!

Another factor to consider is that the amplifier / speaker combiination is a
machine for accurately shaking air. The amplifier needs to be able to
control the movement of the speaker and the lower the impedance of the wire
between the output transistors(or FETs or whatever) and the coil in the
speaker the better so the amplifier has the best chance of making the
speaker cone move exactly how it is intended. If the impedance of the
connecting cable is significant compared to the impedance of the speaker
then the cable acts like a kind of spring and the amplifier is moving the
speaker cone on the end of the spring and the result is that the speaker
cone can flap about outside of the amplifiers control. Therefore not
producing the intended sound. Hence the availability of imtegrated
amplifiers in speakers such as the Genelecs and many others. I have found
that placing the amplifiers behind my speaker cabs (an amp per speaker
cabinet)  linked by less than a foot of thick cable was what made the
biggest difference to my audio system.

Gold plated connectors do help too make good connections but I have seen
some stupid prices for 'special' cables that musicians buy thinking that it
will improve their sound. Why not spend the money on music lessons?

But back to the original discussion - transfering vinyl to a PC. If you can
possibly get an pre-amp for the record deck that has a digital SPDIF or
TOSLINK output and plug that into your sound card (obviously with a similar
digital input) you will keep the precious analog sound signals from the
vinyl away from the interference caused by the buzzy digital world inside
your PC. You'll just be left with the clicks and pops from the vinyl.

my 2p's worth

Ken

----- Original Message -----
From: "Chris Bell" <chrisbell at overview.demon.co.uk>
To: "Greater London Linux Users Group" <gllug at gllug.org.uk>
Sent: Sunday, June 20, 2004 10:32 AM
Subject: Re: [Gllug] Good quality audio cards


> On Sun 20 Jun, Dylan wrote:
> >
> > On Sunday 20 Jun 2004 09:53 am, Chris Bell wrote:
> > <SNIP>
> > >    Many people would think that the sound from their TV speaker is
> > > good until they are able to switch between that and their hi-fi
> > > system.
> >
> > Yes, but this is down to the abysmal quality of TV speakers and amps in
> > general.
> >
> > Dylan
> >
>    I totally agree, but the quality of audio equipment does not increase
> linearly with cost, and if you are attempting to reach the ultimate then
you
> must consider every part of the system, and then you discover some
> unexpected complications.
>    I was lucky enough to be able to purchase a pair of second hand BBC
> speakers after a failed research project. They are by no means the BBC
best,
> they do not reproduce extremely low frequencies, but what they do
reproduce
> is very clean and can show up problems caused elsewhere.
>
> --
> Chris Bell
>
> --
> Gllug mailing list  -  Gllug at gllug.org.uk
> http://lists.gllug.org.uk/mailman/listinfo/gllug
>


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