AusOcean Underwater Speaker Guide

Note this version is deprecated for AusOcean use. See updated guide for current version.

Created: 10th February 2019

Revised: 22nd June 2020

Author(s):

The information contained herein is licensed under a Creative Commons Attribution 3.0 Australia License.

Notice

AusOcean is not liable for any losses, damages, costs and/or other consequences resulting directly or indirectly from using or relying on the information in this document.

Table of contents

1.0 Introduction 3

2.0 General materials and equipment 3

2.1 Adhesives 3

2.2 Tools 3

3.0 Speaker Housing 3

3.1 Materials 3

3.2 Process 4

4.0 Electronics Assembly 8

4.1 Materials 8

4.2 Process 10

5.0 Software Setup 12

6.0 Complete Assembly 15

7.0 Final Remarks 15

1.0 Introduction

AusOcean speakers are utilised for audio playback underwater for reef sound treatment applications, typically at areas directly below the supporting rig. The speakers are considered a peripheral therefore, are powered and controlled by the on board controller. The rig acts as a base to provide sufficient power for indefinite operation or until the end of a data collection period.

2.0 General materials and equipment

The processes demonstrated in this guide were all executed while using appropriate safety equipment and measures. These are, but not limited to, gloves and safety glasses. Other essential equipment is listed below.

2.1 Adhesives

PVC cement - Type N
JB Weld - Two part epoxy
Sikaflex - 291 Marine Adhesive Sealant
Duct tape
Electrical tape

2.2 Tools

Soldering iron + solder
Cable strippers
Drill
10mm drill bit
Hacksaw
Multiple grits of sandpaper (eg. P80, P120, P400, P1200)
Ruler / Measuring tape
2 x G clamps or F clamps

3.0 Speaker Housing

The housing, the main structure that encapsulates the surface transducer (speaker) and the terminals of the corresponding audio cable.

3.1 Materials

Item	Image
1 x 60mm cut of 90mm diameter PVC pipe
2 x 90mm diameter PVC end cap
1 x 32-25mm conduit reducer

3.2 Process

Step	Description	Image
Body
1	Use the hacksaw to cut a length of 60mm from the 90mm PVC pipe.
2	Use the drill with a 10mm bit to drill a hole in the centre of one PVC cap.
3	Sand any rough burs on the pipe and caps from the cutting and drilling process until you have smooth edges.
4	Lightly sand the surfaces on the inside lip of the caps, the outside rim of the pipe, and the rim of the conduit reducer to ensure good bonding surfaces for gluing.
5	Fully remove any logos or stamps off the cap with the hole drilled into it. The surface area around the hole must be smooth to ensure a strong bond when gluing. Also, sand any logos or stamps off the other cap so the front of the speaker is smooth too.
Front
1	Use JB Weld to glue the vibrating face of the speaker to the inside center of the front cap (without a hole).
2	Ensuring not to move the speaker, use PVC cement to glue the pipe into the cap. This join needs to be watertight so use a generous amount of cement around the inside of the cap and the outside rim of the pipe.
Back
1	Use PVC cement to glue the conduit reducer to the center of the cap with a hole in it.
2	Take one end of the two-core cable and strip the outer plastic jacke to expose 40mm of the two inner cables (strip outer black cover back 40mm). Further strip the plastic jackets off the smaller inner cables to expose 8mm of bare wire.This will be the speaker end of the wire.
3	Once the PVC cement on the reducer has been left for 15 minutes to harden, cut a square of duct tape and block the 10mm hole on the inside of the cap. Using a sharp tool to puncture a hole through the centre of the tape. Thread the exposed speaker end cable until 80mm has been fed through. This connection is called a C5 connection and a detailed guide can be found here.
4	Tip: use a roll of duct tape as a support for the cap to keep it horizontal while gluing. The center hole of the roll allows the cable to hang below without tilting the cap. Secure the cable vertically so that it won’t move, then fill the reducer with 10mm of JB Weld. Tip: wrap some tape above the 10mm mark so that once the glue has cured, it can be removed, leaving a clean cable. Tip: mix the JB Weld on the inside corner of a ziplock bag. When mixed, cut a tiny hole in the corner and use it as a nozzle for higher accuracy.
5	Once the JB Weld has been left for 4 hours to harden, fill the remainder of the reducer with Sikaflex and taper it up the side of the cable. This will improve the cable’s flexibility. Tip: Once the Sikaflex has been left to harden for at least an hour, wrap the connection in tape to tidy it up.

4.0 Electronics Assembly

The amplifier and other electronics responsible for audio playback are located at the opposite end of the audio cable. The electronics are grouped together into a speaker module, which is typically positioned up the mast of a rig. A basic schematic is illustrated below.

4.1 Materials

The following table provides component names, suggested supplier and image for reference. These components, however, are only suggestions, other variations of these could be used instead.

Item	Image
1 x desired length of twisted 2 conductor speaker cable
1 x 20 watt 8 ohm speaker
1 x 3.5mm audio plug (optional, depends on amplifier / playback device)
Raspberry Pi 3 or 4
Stereo 20W class D audio amplifier
DC Voltage Regulator
Hook-up wire
7.5A Power Cable

4.2 Process

Step	Description	Image
1	Solder the red wire from the speaker to the red wire on the speaker end of the cable, and the black wire from the speaker to the black wire on the speaker end of the cable. Use electrical tape or heat shrink to ensure that the bare wires can not touch each other. Tip: if you don’t have a soldering iron, crimp connectors can be used to splice the wires instead.
2	(Optional, depending on what amplifier / playback device you are connecting the speaker to). Strip the plastic jackets off of the plug end of the cable exposing 5mm of bare wire. Unscrew the cover of the 3.5mm plug and slide it onto the cable. Solder the black wire to the long ground conductor of the 3.5mm plug. Solder the red wire to the short signal conductor of the 3.5mm plug. Slide electrical tape between the soldered connections to ensure that the black wire and ground conductor cannot touch the red wire and signal conductor. Tip: if you have a stereo plug, orient the long ground conductor so that it is on the bottom with the plug facing away, solder the red wire to the left short conductor. Mono audio should travel through the left channel. Screw the plug’s cover back on.
3	This is a good point to test the speaker before gluing the front and back together. Connect it to an amplifier or playback device and play a sound through it. The sound should come from the front assembly. If the sound is too quiet and the device’s volume can’t go higher, that indicates the need for an amplifier which can be used between the device and the speaker. If you don’t hear any sound, it’s possible that some wires are shorting or there is a faulty connection. Check all the soldered connections and make sure the red and black wires are not touching. Stick electrical tape between the wires or contacts if necessary.
4	Use a generous amount of PVC cement to glue the front assembly to the back assembly. Apply a significant amount of pressure for 5 minutes. The air inside will want to push the cap outward. The easiest way to do this is with a couple of G clamps or F clamps on opposite sides of the speaker. Be careful not to over tighten. Wait 24 hours for the PVC cement to fully cure before testing the speaker underwater.

5.0 Software Setup

Download the Raspberry Pi Imager for your OS. Insert the SD into your computer and use the Raspberry Pi Imager to flash Raspbian lite onto the SD card.
Connect keyboard, monitor and power to pi and log in with username: pi and pass: raspberry.
Use the following command to enter the raspi configuration UI:

$ sudo raspi-config

Go to “localisation options”->”keyboard layout” and select your keyboard type. If your keyboard is not there, select a generic model. You will then need to select region. Select English (US).
Now select “Change User Password”. Set username and password to something of your choosing. NOTE THIS DOWN!
Again go to “interfacing options”->”SSH” and follow prompts to enable SSH. SSH is useful for debugging the Pi in future, or to do remaining steps.
Now we’ll perform some steps to install golang. Firstly perform the following:

$ cd

$ sudo apt-get update

$ sudo apt-get -y upgrade

Now get the golang zip:

$ wget https://dl.google.com/go/go1.13.5.linux-armv6l.tar.gz.

Unzip the package using:

$ tar -xvf go1.13.5.linux-armv6l.tar.gz

Move to the right location:

$ sudo mv go /usr/local

Open .profile file using:

$ sudo nano ~/.profile

And add the following lines to the end of the file:

export GOROOT=/usr/local/go

export GOPATH=$HOME/go

export PATH=$GOPATH/bin:$GOROOT/bin:$PATH

Update session using:

$ source ~/.profile

Check go installed using:

$ go version

Install git:

$ sudo apt install git

Verify that it is installed by typing:

$ git --version

Create directory structure:

$ cd ~

$ mkdir -p go/src/bitbucket.org/ausocean

Enter the create directory:

$ cd go/src/bitbucket.org/ausocean

Clone the AusOcean av repository:

$ git clone http://bitbucket.org/ausocean/av

Install ffmpeg:

$ sudo apt install ffmpeg

Verify the install using:

$ ffmpeg -version

Install omxplayer:

$ sudo apt install omxplayer

Navigate to the looper directory:

$ cd ~/go/src/bitbucket.org/ausocean/av/cmd/looper

Build looper, the software that will repeatedly play our audio file:

$ sudo make install_hard

We’ll now need to copy over our audio file to the raspberry pi. This will require that we plug an ethernet cable into the pi, and connect it to our network.
We’ll need to use nmap to find the IP of the pi on the network. Instructions on how to do this.
Use scp to copy the files over to the pi. Instructions on how to do this.
Now we can either SSH into the pi from our computer, or connect the pi to the monitor and keyboard again. We’ll need to modify the audio file flag in ./looper command in /etc/rc.local to the path of the file we’d like to play. Use the following command to modify open rc.local:

$ sudo nano /etc/rc.local

Now modify the highlighted section of this line in rc.local to the location of the file we’d like to play.

sudo ./looper -path=/home/pi/example.mp3 &

Enable rc.local:

$ sudo systemctl enable rc-local

Start service:

$ sudo systemctl start rc-local.service

To check that the install was successful, plug headphones into the audio output jack and reboot the device:

$ sudo reboot

Sound should eventually play once the device has booted again!

6.0 Complete Assembly

7.0 Final Remarks

Your speaker is now finished and ready to record some sounds under water!

The Australian Ocean Laboratory Limited (AusOcean)