Sound leak left to right speaker with teensy 3.2 + Audio shield

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seeyasia

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Hi All,

I'm relatively new to circuitry, but I have a Teensy 3.2 on top of an Audio shield, everything works fine other than the fact that when I connect a sine wave to the left speaker only, I get feedback/leak to the right speaker. I'm trying to output one frequency from one speaker and another frequency from the other and I want it to be pretty precise. When I turn one speaker off or don't play anything from it, I still hear the sound that's being outputted by the other speaker very faintly. Is it just because it's analog sound and there is no way around it? Or is there any way to fix this?

Here is my code:
PHP: 
// GUItool: begin automatically generated code
AudioSynthWaveformSine   sine1;          //xy=100,182
AudioSynthWaveformSine   sine2;          //xy=105,528
AudioOutputI2S           i2s1;           //xy=860,375
AudioConnection          patchCord1(sine1, 0, i2s1, 0);
AudioConnection          patchCord2(sine2, 0, i2s1, 1);
// GUItool: end automatically generated code

AudioControlSGTL5000     audioShield;     //xy=203,444
const int ledPin = 13;

void setup() {
  AudioMemory(20);
  audioShield.enable();
  audioShield.volume(1);
  delay(10); 

  sine1.frequency(100);
    //sine2.frequency(0);
}

I still get some frequency from the right speaker... Not sure where it's coming from. Removing the sine1 frequency will remove feedback on both speakers. (Same effect from line out or headphone jack)

I also had another unrelated question, does it really matter +/- on speakers? It seems like line out on audio shield doesn't identify between which L or R are -/+ (things seem to be working the way I have it wired, but this is unrelated to the issue above as headphones wouldn't be effected.)

Thanks!
 
I can't say for sure (I don't have a teensy audio shield available atm) but crosstalk between the two channels should be negligible.

When you say that you connected speakers to the shield you mean as in preamplified speakers? Because the line out of the Teensy Audio Shield is, well, a line out, not a speaker out, this means that it's made to drive high impedances , not low impedances like the 4/8/16 ohms ohms of a passive speaker. If that's the case, then the crosstalk could be very well due to the fact that you're pulling way too much current out of the chip.

Also, yes, the +/- on a speaker does matter because if you wire them the opposite way you get an inverted displacement of the cone; in case you wire one speaker in one way and one speaker the other way and try to put the same signal out of them, the signal will be 180° out of phase.
EDIT:In the case of speakers with a preamp, then it still makes sense because the "-" part of the jack will be connected to a ground while the "+" part will bring the signal; if you invert them, you'll end up shorting the output of the Teensy shield on the preamplifier's ground (that could also be a reason of crosstalk/noise/etc.).
 
Hi Paul/Mick,

Thanks for the quick response.

Paul: I have tried lowering the volume with no luck. But thanks for that input, I will keep the volume around the range you've recommended.

Mick: So, I have two outputs currently. 1) Headphones which is preamplified directly from Audio Shield. 2) Line out to an sound board which amplifies the sound and outputs to speakers. I'm getting this issue on both outputs, though a lot more noticeable on the headphone since the sound comes in much more clearly as I'm using bone conducting speakers for my speakers from the amp. I was in fact running into issues trying to connect directly to a speaker as you mentioned but ended up solving that by using an amplifier board.

Thanks for clarifying the +/- on speakers for me, that makes sense - I can't find any documentation however on which would be the + and which the - on the audio shield board...
 
Look at the schematic for the Audio Board:
https://www.pjrc.com/store/teensy3_audio.html

You’ll see that Line-Out-L and Line-Out-R outputs are single-ended from the IC, AC coupled, and are ground-referenced. If you’re amplifier’s input is also single-ended, then there’s no choice on how to connect it. If the amplifier’s input is differential, just connect the L & R outputs consistently.

Note, the Audio Board’s headphone outputs are NOT ground referenced.
 
Sorry I'm not good at understanding the terms. From what I understand, you're saying that the audio board couples the line out into 1 signal + ground? My amplifier's input are 'differentials' (I believe meaning there is a +/- on each speaker) At the moment, I'm connecting the ground-reference of each speaker to the - for line in on the amp and the wired line out to the +. Is that the right way of doing it?

Thanks!
 
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