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Audio switch/mixer idea

alanb
Grafter
Posts: 459
Registered: ‎24-05-2007

Audio switch/mixer idea

I've got three computers under my desk at home. For years I've been trying to find a neat way of switching the audio outputs from my computers. I have a KVM switch, but allowing it to switch the audio source when I switch between PC's doesn't suit my needs. For a few years I've been using a cheapo stereo sound mixer to mix the line outputs from the PC's and send the mixed signal to my active speakers. It works, but that still is not quite what I want. However, while researching something else recently, I found this fantastic gizmo ...
http://www.behringer.com/MON800/?lang=ENG
It's a matrix mixer intended for use in a sound recording studio. Basically it has four stereo line inputs and four stereo line outputs. The four inputs are mixed together and fed to the four outputs (plus a built-in headphone amplifier). Every input has a mute button. Three of the outputs also have a mute button (the other it straight through).
With this I can send an audio signal mixed from any combination of inputs to any combination of outputs. I bought one last month and it works a treat with my old PC active-speaker set. I'm only using one stereo output channel, but when I get round to replacing my speakers, I'll be able to add an active woofer on another output channel.
Normally this type of equipment would be quite expensive. This one is from Behringer's budget range and only costs ~35 quid. It feels a bit cheap and plastic, but it's not too flimsy and should survive in a home environment unless you're in the habit of knocking your kit about.
The only downside that I can see is that the audio connectors are quarter-inch jacks or phonos, so there is additional expense to buy or make cables or adapters to connect to the PC kit. Oh, and you need to understand the difference between balanced signalling and unbalanced signalling to connect it up right.
Isn't it a nice feeling when you find the ideal solution to a problem that's been niggling you for a long time?  Smiley
9 REPLIES
geewizz
Grafter
Posts: 1,125
Registered: ‎01-08-2007

Re: Audio switch/mixer idea

Quote from: alanb
It's a matrix mixer intended for use in a sound recording studio.

It might come in handy for jamming a studio door open I suppose. Grin
Community Veteran
Posts: 1,850
Registered: ‎11-08-2007

Re: Audio switch/mixer idea

could you use this on several machines that were not connected with kvm?  for example, my main setup is against one wall and connected to my amp and thence the speakers.  i get the small desktop speakers and the larger kenwoods together.
at ninety degrees on another wall, i have my kvm two-computer setup, which needs speakers plugged into both computers for sound.  'cluttered' is understated.  if i could have my kvm setup and my main setup all using the same 4 speakers i'd be happy.
alanb
Grafter
Posts: 459
Registered: ‎24-05-2007

Re: Audio switch/mixer idea

Yes, the matrix mixer has abolutely nothing to do with the KVM.
I've connected the line outputs from the PC soundcards straight to the matrix mixer line inputs, so that I can use the input mute buttons on the matrix mixer to control which combination of PC's are sending sound to the speakers.
I only have one set of speakers connected to one of the outputs. If you wanted to use two sets of speakers you could connect your amp to one of the outputs and your desktop speakers to another. Then you could use the output mute buttons to choose to send the mixed audio to both or either of your speakers.
The mixed audio signal will also always be available via the matrix mixer's headphone output.
Bear in mind though, that the outputs of the MON800 are line signals, so your desktop speakers need to be the active type.
Community Veteran
Posts: 1,850
Registered: ‎11-08-2007

Re: Audio switch/mixer idea

i'm generally ignorant regarding audio technology.  would you clarify one or two points for me?
Quote
Oh, and you need to understand the difference between balanced signalling and unbalanced signalling to connect it up right.

and
Quote
Bear in mind though, that the outputs of the MON800 are line signals, so your desktop speakers need to be the active type.

i don't understand.
geewizz
Grafter
Posts: 1,125
Registered: ‎01-08-2007

Re: Audio switch/mixer idea

Balanced and unbalanced audio leads differ in the phasing. It's not a problem for most domestic situations but if you're running instruments and amps off different electrical circuits you want balanced leads to avoid loads of hum.
http://www.blitzfamily.eclipse.co.uk/tech_tips/techtip/art6.htm
Active speakers are powered speakers and do the amplification internally. Inactive speakers need to be fed with a signal that has already been amplified.
Community Veteran
Posts: 3,486
Registered: ‎02-10-2008

Re: Audio switch/mixer idea

I've turned the questions around.
Quote from: artificer
Quote
Bear in mind though, that the outputs of the MON800 are line signals, so your desktop speakers need to be the active type.

i don't understand.

An "audio line" - by convention is a pair of wires - and are balanced - meaning neither is at earth potential with  a nominal impedance of 600 ohms
http://en.wikipedia.org/wiki/Nominal_impedance

Quote from: artificer
i'm generally ignorant regarding audio technology.  would you clarify one or two points for me?
Quote
Oh, and you need to understand the difference between balanced signalling and unbalanced signalling to connect it up right.

and

unbalanced means that one of the lines is at earth potential - balanced means neither is and at any point in time one wire can be + or - about earth.
The nominal power of a line circuit is about 1 milliwatt -- or you may see it refered to as 0dBm, hence the need of a power amplifier to drive loudspeakers

Community Veteran
Posts: 1,850
Registered: ‎11-08-2007

Re: Audio switch/mixer idea

thanks very much.  i'll go a-reading.
my kenwoods are omnitop, omni-7 at 8 ohm impedance and 60w max input.  the computer speakers have a power supply to cambridge soundworks sbs 35 from creative and another computer has altec acs 43.  they all give good sound and it would be nice to have all six connected.
the kenwoods currently come off a sansui au 2900 amp that i've had forever, almost.
would i still need to use the amplifier if i had this little gizmo?
alanb
Grafter
Posts: 459
Registered: ‎24-05-2007

Re: Audio switch/mixer idea

The MON800 is not an amplifier, so all your speakers will need to be amplified, or be "active" speakers that have a built in amplifier.
Also, you should understand that if you are doing 5.1 surround sound or similar, then the MON800 won't be any good for you as it only switches stereo signals.
As far as I can tell from a quick web search, your Altecs and Creative speakers have their own amplifiers, so they should work. It would be worth checking the manuals to be sure that they do indeed have their own amplifiers. Your Kenwoods would still need the Sansui amp to drive them.
alanb
Grafter
Posts: 459
Registered: ‎24-05-2007

Re: Audio switch/mixer idea

Unbalanced vs Balanced signalling ...
You don't need a detailed understanding, other than to be aware of the following ...
Consumer audio equipment (including most computers) uses unbalanced signalling (requiring a two wire connection per mono audio channel). A lot of professional audio equipment uses balanced signalling (requiring a three wire connection per mono audio channel).
On the MON800, the quarter-inch jack sockets support both types of signalling and automatically reconfigure depending on the type of jack plug that is plugged into the socket.
It sounds more complicated than it really is. First, you need to understand that each jack socket on the MON800 only carries a mono signal, so two jacks are needed to carry the left and the right side of a stereo signal.
To connect a PC to an input on the MON800 you need a 'Y' cable or adapter to split the left and right stereo channels. The stem of the 'Y' should be fitted a 3.5 mm stereo jack plug to fit the line output of the PC soundcard. The two arms of the 'Y' should be fitted with quarter-inch mono jack plugs (or more accurately TS jack plugs) to suit the left channel input and the right channel input sockets.
The above applies to input 1 and 2 on the MON800. Inputs 3 and 4 have RCA type phono plugs, which always do unbalanced signalling and are therefore always compatible with consumer devices. Inputs 3 and 4 still require a 'Y' cable but with phono plugs instead of quarter-inch jacks.
Similar 'Y' connectors are required for the outputs on the MON800.
I hope that's not too confusing.  Cheesy
By the way:
TS = "tip and sleeve", effectively a "two wire" jack plug connector. In the consumer environment its usually called a mono plug.
TRS = "tip, ring and sleeve", effectively a "three wire" jack plug connector. In the consumer environment its usually called a stereo plug.
Using a TS jack plug makes the MON800 use unbalanced signalling that is compatible with a PC. If a TRS jack plug is plugged into the MON800, it will assume balanced signalling and you won't get any audio because it will use the jack plug tip and ring for audio positive and negative - not stereo left and right as is the norm in the consumer world.
Alan.