Wednesday, 4 January 2012

Notes on building underwater speakers

Here are some notes on what I have tried so far with building some underwater speakers.

Attempt #1:
This was an existing (and unfinished) subwoofer that I was using for my home theatre a few years ago. The speaker is a ported design with two large PVC pipe fittings as external ports. By rotating the ports and submerging them I was hoping that the pressure exerted on the water would cause displacement and sound under the water. It did not produce any sound and as it was mains powered had the potential to kill if it fell into the pool.

Attempt #2:
After some research on (overpriced) commercial underwater transducers I attempted to build one. I didn't take any photos of the process but it is pretty straight forward:
 - Sacrifice a reasonably sized woofer for its magnet and voice coil.
 - Glue magnet into waterproof housing (pvc drain pipe in this case)
 - Place voice coil in magnet for alignment and glue to front cap.
 - Route wires, assemble and seal with glue. I am using RTV silicone.

Here is the submerged speaker:

I chose a PVC drain inspection cap for the front of the transducer because I liked its size and shape. The voice coil is glued to the centre of the cap and the magnet is glued within the pipe section.
The electrical problems are solved by powering the driver from an inexpensive chip amplifier running from a 12v SLA battery. This removes the chance of any earth fault and I doubt that the voltage swings of the amp would be dangerous underwater - but this would still require the wires to come free from the speaker and be touched.

The sound from this single transducer is rather impressive and fills the whole pool. It has some very strong resonant frequencies that become annoying depending on the content played. I have read that this is a problem with all underwater sound systems unless some deadening is employed on the pool walls. 

Here are some other ideas I came across:

1 comment:

  1. This is really great! I stumbled upon this page while googling underwater speakers. Thanks for sharing your tips. Are you still using this setup? I'm thinking of building one as audio stimulus enrichment for some fish, and this seems to fit my budget! Did you have to do anything special for the wire to waterproof it?