Lomax
Posts: 189
Joined: Wed May 20, 2015 9:43 pm

Suggestions for multiple amplified audio outputs

Sat Mar 23, 2019 3:28 pm

I'm currently working on-site with an interactive exhibition, which makes extensive use of the Pi. Annoyingly, one exhibit includes three separate (mono) "earphones" where visitors can listen to different sounds. I would normally use something like the JustBoom Amp Zero for anything requiring <=2 channels of high quality audio, or the Adafruit i2s amp for monaural effects and game sounds, and sometimes I use the internals from Logitec's S-150 speakers (USB audio and power), which I bought about a dozen of last year. But now I have the need for three amplified audio outputs and I'm scratching my head wondering what the simplest/most elegant way to achieve this might be. Stacking Amp Zeros is of course not an option, nor is multiple S-150s (too much current draw for the Pi's USB). A separate multi-channel amp is complete overkill. So is using multiple Pis. Combining with the internal audio is not going to be good enough quality wise - and would still require another amp. Same for HDMI audio. Same for a 5.1 USB soundcard.

The more I think about it the most elegant solution seems to be to try and convince the exhibition designers to drop the third sound :D

Anyone have any clever suggestions?

epoch1970
Posts: 3804
Joined: Thu May 05, 2016 9:33 am
Location: Paris, France

Re: Suggestions for multiple amplified audio outputs

Sat Mar 23, 2019 4:05 pm

Lomax wrote:
Sat Mar 23, 2019 3:28 pm
Combining with the internal audio is not going to be good enough quality wise
Did you test it since audio_pwm_mode=2 was introduced?
analog + something stereo turned into dual mono would sum to 3.
"S'il n'y a pas de solution, c'est qu'il n'y a pas de problème." Les Shadoks, J. Rouxel

Lomax
Posts: 189
Joined: Wed May 20, 2015 9:43 pm

Re: Suggestions for multiple amplified audio outputs

Sat Mar 23, 2019 6:56 pm

epoch1970 wrote:
Sat Mar 23, 2019 4:05 pm
Did you test it since audio_pwm_mode=2 was introduced?
analog + something stereo turned into dual mono would sum to 3.
Ah yes, good point - I'd forgotten the internal audio had seen some quality improvement. Not sure if it can drive the loudspeakers directly (I think they're 8Ω, something like 2" paper cone), but worth a try! I had planned to use a Pi Zero, which lacks the headphone output, but I have plenty of 3As and 3Bs on hand too. As for the other two channels, the Amp Zero is total overkill power wise so I'm not sure what I'd use there.

drgeoff
Posts: 9901
Joined: Wed Jan 25, 2012 6:39 pm

Re: Suggestions for multiple amplified audio outputs

Sat Mar 23, 2019 8:16 pm

Lomax wrote:
Sat Mar 23, 2019 6:56 pm
Ah yes, good point - I'd forgotten the internal audio had seen some quality improvement. Not sure if it can drive the loudspeakers directly (I think they're 8Ω, something like 2" paper cone), but worth a try!
No RPi can drive a loudspeaker loud enough to be heard behind a wet newspaper. (I don't know where that expression originated but my Sunday school teacher used it often to the performers at rehearsals for the annual Christmas party where every child did a piece in front of the assembled children and their parents.)

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