Jareticus
Posts: 7
Joined: Sat Jun 16, 2012 10:18 am

Old school drive-in movie theatre audio setup

Wed Apr 25, 2018 10:58 am

I'm putting together an outdoor movie setup for the garden for when there's the odd warm evening or two. I'm going to be using a Pi3B+ to play the movies, but it's the audio output options that are causing me to have to think.

I want to create 6 small "personal" speakers, one for each person watching. I don't want surround sound, at all. I want 6 mono audio outputs (combined L+R), from the Pi, so each listener hears the same mono audio, as the old US drive-in movie theatres used to do (or still do?). I want the audio to support any number of speakers up to 6 ( I don't see a need for more). Ideally, each speaker will have a volume control on it (a simple pot to reduce the volume as the listener prefers). I'd like to use guitar cables to connect each speaker to the Pi (5 meter cable length) for quick plug/unplug connections of the speakers.

My problem arises where I can't fathom which option to use for the audio output of the Pi. I'm not considering connecting all 6 speakers in parallel to one analog output, as I'm sure this will put un-necessary strain on the output and cause it to fail quite quickly.

Options
1. Transmit 6 lines of pre-amplified analog audio over the cables, passive speaker at the end.
Method: Connect 6 x Adafruit I2S 3W Class D Amplifier Mono Breakout (MAX98357A) boards to the Pi and somehow configure the Pi to output audio to all of them at the same time.

2. Transmit digital audio over the 5m cables, convert DAC to analog and amplify at the speaker.
Method: Connect an audio board (like a Pi-Digi+) to the Pi, split the digital audio output using a 6-way coax splitter, have some type of DAC to analog converter, small amp and battery in the speaker.

At the moment, I'm looking at option 1, due to cost, maintenance and low complexity (apart from the Pi configuration). I know there will be a drop in audio volume/power across the cable, but I don't need excessive volume, so I'm assuming this will be acceptable.

Option 2 is interesting, but adding unknown converters, batteries and charging boards to the speakers is an extra expense I'd rather not have, and I've no idea if there are standalone DAC to Mono analog converters available (can the adafrut I2S board be used here?).

Which option to go with, or is there somethign I'm completely missing?
Love the classics. Land Rovers and Minis, that is.

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