11 October 2011

Wooden Dipole Cube Speakers

So as many will know, the DIY Audio quest never ends. Here is my latest edition, the cube speakers with optional dipole arrangement!

Inspired by the "golf ball" speakers sold by Sony, they have a tiny footprint of 44mm x 44mm x 44mm and have a frequency range of 900Hz to a whopping 28kHz!

Based on Vifa OC25SC65-04 1" dome tweeters (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-1018) they are intended to be used with an extended range sub woofer. These tiny tweeters placed around a room can provide the directional sounds while the sub woofer handles the less directional frequencies below 900Hz. This set-up can from a very compact home theatre/PC speaker system.

Having started life as birch blocks I found on eBay, the shop I bought them from where also able to drill me 6mm holes through the middle of each block. This aided in keeping my hole saw cutting straight as I don't own a drill press so could only reply on a small power drill.

The next step was to use a 38mm hole saw to bore a hole through the middle. I used a Bosch GSR10.8 li-po powered drill that required a fresh battery charge and a cool down for every block... If possible I would have used a mains powered drill but I didn't have one of these.

The block sides were protected with a tissue and clamped down. The drill may be small, but the torque it gives is still enough to do your wrist in.

Here I laid the speaker flat and traced around the bore so I could cut out the grooves that the speaker will sit in.

Next adding a few extra lines to show the depth I cut using a milling bit with a Dremel 300, ensuring to grind away just enough material to make the speaker fit nicely. (This step requires a lot of patients and EYE PROTECTION! Don't want blood on your work now do we?...)

Two out of the five speakers I made, I added secondary drivers facing the opposite direction wired out of phase in series creating a dipole arrangement. I have yet to take measurements but will update on the results.

For two of the speakers, I made these cut outs on both sides to accommodate for both tweeters.

This being one of the single driver speakers, you can only see the carved corners on the one side.

Now to create the hole for the speaker wire. I used some standard speaker wire that I cut to be long enough for the placement of each speaker.

I also used some 3mm LED holders to add a nice looking surround for the hole (not very good stress relief but that shouldn't be a problem).

Here a sideways hole creates the path for the wire to go through from the speaker to the back of the wood.

Now comes the sanding...

Using 320 grit wet dry paper, I sanded until all the saw marks had all disappeared from the wood. This required a lot of work and took several days to finish all the speakers. I only made a couple speakers, moving on to another couple once I'd completely finished the first set. That way you learn along the way and you can find ways of saving time and being more efficient in the next batch.

Here you can see there is still a small gouge on the edge of the block that was created when my Dremel decided to wonder. I rounded off the corners to hide these and prevent chipping the speakers in the future.

Once that's done, you can start sticking in the speakers. I used Super glue ultra gel because it holds well enough but can allow me to break the speaker out safely if I should need to without damaging anything. Epoxy would be good but the tweeters would have to be dug out if I wanted to take them out at a later date.

This would also be the time to solder in all the wires and if using a second rear facing tweeter, solder that too and then stick it down. It will be a tight fit.

Now to apply super glue to the outside of the block and stick on the speaker cloth.

Stretching over a bit of speaker cloth to prevent sag.

Trimming it off once it was dry, only 30 seconds or so.

Now to do the other side.

I cut a hole in the corner of the speaker cloth to allow the wire though. Once the cloth was stuck down, I fed the LED holder through and pressed it in place.

Make sure to do a test fit before encase the hole is too small, you'd have to undo a lot of work to make that hole bigger.

Then using some finger nail scissors I trimmed the cloth flush. These scissors have a nice angle to them and cut very smooth.

Here is the result. Not a bad little set of speakers, very cheap and easy to make. They sound great for their size.

Depending on how many speakers you require, you can make a set for stereo, 5.1 or 7.1. The single driver speakers can handle 25Wrms and the double driver ones can handle 50Wrms.

Look out for the sub woofer build that compliment these speakers. It will have an 8 inch woofer and six inbuilt class D amplifiers to power the entire thing as one unit.

Also look out for my testing and measurements of these speakers. It's starting to get cold outside so I'll have to find a quiet day I can measure the response without too much wind.

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