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  1. #1

    Default Multiple audio outputs, one audio input.

    Hi, I work at a school district, in the classrooms I have a VCR and DVD connected to a switch with RCA outputs for video and audio L/R, and a PC with the standard 1/8 audio output, and I need them to all go to one pair of speakers, and output without no user intervention involved. If it helps the video signals are kept separate and run to a ceiling mounted projector. I appreciate any suggestions. Thanks!

  2. #2
    Join Date
    Jul 2006
    Location
    Davis, CA
    Posts
    2,155

    Default Re: Multiple audio outputs, one audio input.

    First, you will need an amplifier to power the speakers. I assume you have one or know how to get one that fits your needs.

    If I get what you are saying correct, you want all the audio inputs to feed in to the amplifier so that, without any switching, you can just play one of the devices and have the sound come out of the speakers? If that is indeed what you are after, you can just connect all the audio inputs together using various "Y" adapters (e.g. 2RCA female -> RCA male, one per L or R channel; 1/8 Stereo jack -> 2 RCA male; etc.). Then connect this to the amplifier inputs.

    It should not "hurt" one component to have signal applied from another device to it's output. As long as you do not have multiple audio output "on" at the same time, you should only hear the one you are "playing" through the speakers.

    Does that help answer your question?

    -Charlie
    Charlie's Audio Pages: http://audio.claub.net

  3. #3
    Join Date
    Sep 2005
    Location
    Costa Mesa, Calif.
    Posts
    233

    Default Re: Multiple audio outputs, one audio input.

    Quote Originally Posted by charlielaub View Post
    If that is indeed what you are after, you can just connect all the audio inputs together using various "Y" adapters (e.g. 2RCA female -> RCA male, one per L or R channel; 1/8 Stereo jack -> 2 RCA male; etc.).
    No, he has multiple outputs, not multiple inputs.

    You can use Y cables to fan an output into multiple inputs, but multiple outputs into a single input requires summing, or combining.

    The lossy way to do it is with passive resistor summing, in which you put each output through a series resistor (a value that all the inputs can drive; 1 kΩ is common) and then join them all together, and the junction point goes to the input. It's simple and cheap, but the downside is that you lose a lot of signal level.

    A more satisfactory way would be to use an active mixer to sum the signals together.
    Bob Lee
    Applications engineer, QSC Audio
    Secretary, Audio Engineering Society

    "If it sounds good, it is good."
    -Duke Ellington

  4. #4
    Join Date
    Aug 2007
    Location
    Howell NJ
    Posts
    7,125

    Default Re: Multiple audio outputs, one audio input.


  5. #5

    Default Re: Multiple audio outputs, one audio input.

    Quote Originally Posted by bobleeqsc View Post
    No, he has multiple outputs, not multiple inputs.
    I'm pretty sure the original poster wanted to use each device one at a time. There's no need for mixing, and also note the original post - 'and I need them to all go to one pair of speakers, and output without no user intervention involved.'
    A mixer definitely would require user intervention.

    That said, I'm +1'ing charlie's suggestion.

  6. #6
    Join Date
    Aug 2007
    Location
    Howell NJ
    Posts
    7,125

    Default Re: Multiple audio outputs, one audio input.

    a passive mixer set at half volume does not need any intervention. It can be set and forget. Charlie's idea can also work but if someone runs all the gear at the same time watch out. The passive would help protect against someone running 2 or 3 of the pieces of gear at the same time.

    remember Charlie also said running one 1 piece of gear at a time would be safe. knowing schools and classrooms I can see or hear all 3 pieces of gear turned on.

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