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914 Speaker Mod
Wednesday, 16 May 2007

This is a mod from James - the 914pcbots.com Admin.

The speakers I had installed in my 914 were really not up to much, these are not the speakers you get as standard, but some quite similar ones. They worked ok, but the sound was not very loud when you are demonstrating the Bot in a room full of people, turning them right up caused distortion and wasn't generally very nice.

I decided to modify the speakers I had to make them a bit more beefy by fitting some larger speaker units and some better amplifiers inside. I salvaged some speakers units from an old pair of computer speakers - these are relatively substantial, but of course no longer fit inside a 5.25" drive bay device. This can been seen by measuring them up to a spare CD ROM drive:

Anyway, I had a cunning plan which you will see as I continue… I bought some 3.5 Watt amplifier modules from my local electronics store, there are two – one for each stereo channel. As I dismantled the existing speakers I realised just how very much smaller the original speakers were than the replacements:

I cut some speaker shaped holes in the lid of the existing drive bay mounted unit. I also sealed up any other holes with Polymorph/Shapelock as the top and bottom had various vents in them. The speakers will stick out of the top of the box, then be covered with two small plastic project boxes that just happened to be the right size for each speaker:

Here are some more pictures of the speakers mounted up, the internal wiring of the amplifier modules, and the boxes finally mounted and screwed on. I taped up all the seams to stop vibrations and to make sure the sound went in the right direction:

There was quite a lot of audible noise as the amplifiers are powered from the M2-ATX power supplies which are switched-mode. I got this noise suppressor from a car accessory shop which is intended to filter noise out of in-car entertainment systems. It’s basically a filter that goes on the power line:

Obviously the unit is now almost twice as high as a 5.25” bay device. However I noticed that the beak IR sensor array of the 914 does not fill a complete drive bay – only the very front part. So, the modified unit still fits in fine - with the speaker ‘lumps’ behind the IR unit above it. I found these wine-drip-catchers in an up market department store. You will see where I used them below:

Here are the finished pictures. I’m still looking for a more suitable volume knob but this one will do for now. The USB ports are still active and are cabled to the mini-itx board internally, but the other sockets on the front are no longer in use.

The overall outcome is that the speakers are much louder than before, you can turn them right up before they distort – probably too much to use in a my lounge with a few people who can no longer really hear themselves speaking to each other. This will be quite good for public appearances however…

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