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Convert stereo Speaker Level to mono Speaker Level?

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  • Convert stereo Speaker Level to mono Speaker Level?

    I tried to Google this but all I found was line level information.
    I am working on a DIY project and need some info.
    Have a small digital amp board that outputs stereo signal speaker wires.
    And have a single full range driver.
    Should I expect trouble if I connect both speaker level power wires to the speaker at the same time?
    I'm guessing it'll be fine, will just change the impedance level and the single speaker will play both left & right signals.
    But I don't think I've ever done this before and am making things complicated in my head.

    I know most amps can take the (+) from one channel and the (-) from the second channel to a single speaker which will do a summed mono. But that's with a mono line level signal being fed to the amp.

    Why?
    For a single speaker DIY portable speaker project I'm considering.
    Dual speakers is looking tough to fit and a single speaker would really be interesting.

    NOTE: There are ways to do this if you have access to the input channel, but because this amp has Bluetooth built in and THAT is my source, I do not have access to manipulate the input channels.
    Posted at DIYaudio also but no help yet.
    I'm guessing I'm out of luck. :(
    http://www.diyaudio.com/forums/analo...ker-level.html

  • #2
    On most small digital amp chips each output channel is already bridged with itself inside the chip. This is done to get maximum watts per channel out of the power supply voltage. You can not bridge a second time between the L-R channels. (unlike some larger car amps that are not already bridged).

    Can you set the bluetooth source (e.x. phone) into mono mode?

    Picture of the board might provide an alternative.

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    • #3
      Running one speaker with two amp channels has to be in parallel, or bridged. Parallel to increase current capacity, and bridging doubles voltage. Both of these require the same signal in both amp channels. The output of an amp is very low impedance, a fraction of an ohm. Connected directly to another amp output it's effectively shorted out, so any difference in voltage will cause the amps to pump current into each other and cause damage. Theoretically, you could put 4 ohm resistors in series with each output, then tie them to the speaker. Any signal out of phase would just heat the resistors instead of damaging the amp. But it would be rather inefficient. If you try it, the resistors should be high power. If a straight out of phase signal is played the resistors get the full power of the amps and the speaker gets nothing.
      Electronics engineer, woofer enthusiast, and musician.
      Wogg Music
      Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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      • #4
        I would use a dual channel speaker and avoid problems: http://www.parts-express.com/dayton-...-each--300-409

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        • #5
          Originally posted by wogg View Post
          Running one speaker with two amp channels has to be in parallel, or bridged. Parallel to increase current capacity, and bridging doubles voltage. Both of these require the same signal in both amp channels. The output of an amp is very low impedance, a fraction of an ohm. Connected directly to another amp output it's effectively shorted out, so any difference in voltage will cause the amps to pump current into each other and cause damage. Theoretically, you could put 4 ohm resistors in series with each output, then tie them to the speaker. Any signal out of phase would just heat the resistors instead of damaging the amp. But it would be rather inefficient. If you try it, the resistors should be high power. If a straight out of phase signal is played the resistors get the full power of the amps and the speaker gets nothing.
          Yep, any level difference between the signals from passive component tolerances (in the mono summer or on the board) would make the signals uneven. The chip/board may be able to be modified into PBTL (parallel bridge tied load) if the chip supports that. You'd get a single mono channel but that may be beyond your capabilities. Since this is a single DC supply amp/chip, each channel is already bridged in the chip so PTBL is the only option. Simple bridging the L-R outputs will not work, will smoke the board.

          A picture of the board and/or marketing spec.'s would let us give you more definitive answers.

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          • #6
            I was going to suggest an Audioplex Monogizer, but I guess it's NLA.

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            • #7
              I had totally forgotten about this thread, sorry guys.
              Additional research suggests a 1k ohm resistor inline with each low level (+) output. Then tie them together to the single speaker (+) input.
              Anything from 1k to 47k has been suggested. I had a 47k so I tried it and it works. But I'm hoping sensitivity is directly affected because my output level isn't very good.
              I'm waiting on some 1k resistors to arrive in the mail to see if that works better.

              The dual channel speaker linked above is very cool but much too large for my project which is < a .05 cu.ft. sized enclosure.

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