Stereo and Mono

Discussion in 'The Projects Forum' started by BWBW, Jan 8, 2015.

  1. BWBW

    Thread Starter New Member

    May 17, 2013
    For a small audio project, I'd want to maintain the stereo signal (from mp3/phone) and also sum to mono. The L and R would each go through their own bandpass to L and R amp for >200hz. The mono would be lowpass to amp <200hz. Could I use ~100 ohm from L and R to sum the mono, and would that maintain the stereo signal to those higher hz designated speakers?
  2. wayneh


    Sep 9, 2010
    No, you need more like 10kΩ. We're talking line out, right, not headphone signals?
  3. DickCappels


    Aug 21, 2008
    Yes and no. It will introduce a little bit of crosstalk between the channels, the amount depending upon the output impedance of the amp and the impedances of the speakers.

    It sounds like this is going to be used to drive a subwoofer. Since subwoofers can require a lot of power, you might find it works a little better if you use higher value resistors to sum the two channels and pass that through an amplifier if you're not planning to do that already.

    If you intend to do this at line level use even higher value resistors.
  4. BWBW

    Thread Starter New Member

    May 17, 2013
    Thank you. If it helps, a few more details...

    A 3.7 V battery to power a USB bluetooth adapter for audio source and two 2x3W amp boards. The amp boards, one for >200hz stereo L and R 2 3W speakers and the other board to power the <200hz 2 3W (listed as subs). For the "subs", Bluetooth -> mono sum -> passive low pass ->Class A common emitter (tested and working) -> L + R channels of 2x3W amp.

    I hadn't planned to run the L/R signals of upper band speakers through an emitter amp, I want to boost the bass power/response in the 2 subs. I assume the mid/upper speakers would be loud enough in relation to the sub setup for this little bluetooth speaker system, but that's based only on having assembled this project maintaining the stereo channel assignments through the passive filters into the amps.

    Does this change respones at all? Thank you!!