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Multiple inputs, single output

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Anonymous
February 1, 2005 4:11:20 PM

Archived from groups: rec.audio.tech (More info?)

I have two computers with a pair of speakers each. The speakers are
standard MM speakers, powered with a sub that serves as amp. I want to
use the speakers on one computer as the rear set of surround sound
speakers on the other computer, and still have the computers be able to
send to their respective speakers.
What I have designed is a switch box that allows me to select which
computer signal goes to which speaker set, with diode protection on the
inputs from the computers to prevent backfeed.

My question is twofold - First, are the speakers going to be able to
handle the dual signal from both computers? I can't decide if the amp
will handle it or not.
Second, do the grounds or cable sheilds need to be diode protected as
well, and if so, which direction? Toward or reverse from the input
signal direction?

Thanks.
Anonymous
February 2, 2005 12:47:35 AM

Archived from groups: rec.audio.tech (More info?)

AudioGeek wrote:


> What I have designed is a switch box that allows me to select which
> computer signal goes to which speaker set, with diode protection on the
> inputs from the computers to prevent backfeed.

Have you heard of alternating current, aka AC?
A switch box with a DPDT switch will do the trick
but you don't need the diodes.

--
Eiron.
Anonymous
February 2, 2005 3:43:51 AM

Archived from groups: rec.audio.tech (More info?)

"AudioGeek" <bh325@yahoo.com> wrote in message
news:1107292280.598808.132730@z14g2000cwz.googlegroups.com...
>I have two computers with a pair of speakers each. The speakers are
> standard MM speakers, powered with a sub that serves as amp. I want to
> use the speakers on one computer as the rear set of surround sound
> speakers on the other computer, and still have the computers be able
> to
> send to their respective speakers.
> What I have designed is a switch box that allows me to select which
> computer signal goes to which speaker set,

That will work. A passive resistor matrix would work also
(assmuing you can make up the level loss.)

> with diode protection on the inputs from the computers to prevent
> backfeed.

No, no, no. You don't use diodes for audio. At best, a
diode will produce horrendous and unlistenable distortion,
and at worse, they won't pass any audio at all.

Second, "backfeed" is not necessarily something to be
concerned about (depending on eactly which sound card
and speakers you have).

> My question is twofold - First, are the speakers going to be able to
> handle the dual signal from both computers? I can't decide if the amp
> will handle it or not.

Are we dealing with line level or speaker level here? At line
level (which most comptuers & speakers use), there should be
no issue of whether the amp handles it, as the amps will still
be driving only their own speakers.

> Second, do the grounds or cable sheilds need to be diode protected as
> well, and if so, which direction? Toward or reverse from the input
> signal direction?
>
> Thanks.
>
Related resources
Anonymous
February 2, 2005 10:03:37 AM

Archived from groups: rec.audio.tech (More info?)

Eiron,
Indeed I have heard of AC current, but I do belive that audio signals
are in fact a low level DC current. In all my work with Audio, I have
never heard of an AC audio signal. Please let me know if I am wrong in
this point.

Eiron wrote:
> AudioGeek wrote:
>
>
> > What I have designed is a switch box that allows me to select which
> > computer signal goes to which speaker set, with diode protection on
the
> > inputs from the computers to prevent backfeed.
>
> Have you heard of alternating current, aka AC?
> A switch box with a DPDT switch will do the trick
> but you don't need the diodes.
>
> --
> Eiron.
Anonymous
February 2, 2005 10:12:02 AM

Archived from groups: rec.audio.tech (More info?)

Thanks for your help so far, I had a couple more questions.

You stated that backfeed would not be a problem. What about the signal
from one input, say from computer one, traveling into the output jack
of computer two? This is what I meant be backfeed, and what the diodes
were for. I did find some very low noise audio diodes, but they are
rather expensive.

I thought that line level would not be a problem with the inputs to the
speakers, but a freind of mine said otherwise, so I wanted to get a
second opinion before I built the thing. Since both signals are liine
leve, they should be ok to just hook them together into a single
speaker set? Like using one speaker set for two computers?

Thanks!

Richard Crowley wrote:
> "AudioGeek" <bh325@yahoo.com> wrote in message
> news:1107292280.598808.132730@z14g2000cwz.googlegroups.com...
> >I have two computers with a pair of speakers each. The speakers are
> > standard MM speakers, powered with a sub that serves as amp. I want
to
> > use the speakers on one computer as the rear set of surround sound
> > speakers on the other computer, and still have the computers be
able
> > to
> > send to their respective speakers.
> > What I have designed is a switch box that allows me to select which
> > computer signal goes to which speaker set,
>
> That will work. A passive resistor matrix would work also
> (assmuing you can make up the level loss.)
>
> > with diode protection on the inputs from the computers to prevent
> > backfeed.
>
> No, no, no. You don't use diodes for audio. At best, a
> diode will produce horrendous and unlistenable distortion,
> and at worse, they won't pass any audio at all.
>
> Second, "backfeed" is not necessarily something to be
> concerned about (depending on eactly which sound card
> and speakers you have).
>
> > My question is twofold - First, are the speakers going to be able
to
> > handle the dual signal from both computers? I can't decide if the
amp
> > will handle it or not.
>
> Are we dealing with line level or speaker level here? At line
> level (which most comptuers & speakers use), there should be
> no issue of whether the amp handles it, as the amps will still
> be driving only their own speakers.
>
> > Second, do the grounds or cable sheilds need to be diode protected
as
> > well, and if so, which direction? Toward or reverse from the input
> > signal direction?
> >
> > Thanks.
> >
Anonymous
February 2, 2005 11:48:30 AM

Archived from groups: rec.audio.tech (More info?)

AudioGeek wrote:
> Indeed I have heard of AC current, but I do belive that audio signals
> are in fact a low level DC current. In all my work with Audio, I have
> never heard of an AC audio signal. Please let me know if I am wrong
in
> this point.

You must not have worked very much with audio in all your work
with audio. Try hooking an oscilloscope to the output of one of
your soundcards, or across a set of speaker terminals and observe
the waveform. Note how the voltage changes rapidly and, indeed,
the "current" "alternates" between positive and negative on a
pretty frequent basis, often thousands of times per second.

Now try reading the audio signal from these devices with a DC
voltmeter. Try it instead with an AC voltmeter. Observe the
rather radical difference in the readings you get. Which is
more accurate, do you suspect? (hint: it ain't the DC voltmeter,
not by a long shot).

Next, take any audio electronic device you have laying around,
play music through it and listen. Now, build a filter which
eliminates all AC and passes only DC current (this would be
called a low-pass filter with a very low cutoff frequency).
What what you expect you'd hear? (hint: nothing at all: since
audio IS AC, and you eliminate the AC, you eliminate the audio).
Anonymous
February 2, 2005 6:31:05 PM

Archived from groups: rec.audio.tech (More info?)

AudioGeek wrote:

> Indeed I have heard of AC current, but I do belive that audio signals
> are in fact a low level DC current. In all my work with Audio, I have
> never heard of an AC audio signal. Please let me know if I am wrong in
> this point.

You are wrong on this point.
!