I spent a while looking at speaker drivers with no real guide to what I was looking for. I wanted something cheap, but good, with good bass and all those other things people like me think they want. I was getting nowhere, and taking a long time to get there. One day I was out walking and saw a discarded TV on the side of the road, and thought "well those speakers are free, and if they sound bad I've got an excuse!" So back home to grab a screwdriver, and I was the proud owner of a pair of ~5x2.5 inch 8 ohm speakers.

For those interested, the host TV was a:

Unfortunately, the generous TV donor didn't leave any spec sheets on the side of the road. (I know, right!?!) A bit of googling found me a similar pair that were once for sale in Brazil, with the useful added tidbit that they were 10 Watt speakers. I also went back and grabbed some of the TV's boards to harvest capacitors, and in the hope that I'd find a part number for the audio IC, but no luck there. So it looked like I would be measuring things myself.

I'll spare you the details of all the things I tried and failed at, and skip to the one that worked - Speaker workshop using Claudio Negro's cables - http://www.claudionegro.com/.

I won't repeat the process - you can read that on Claudio's site. Interestingly, though I followed all the steps, my passive component tester never worked - it just said everything was a 620 ohm resistor... But I pushed ahead and seemed to get ok looking results. (good enough for my needs, anyway)

The top curve is the smoothed out estimate, and the bottom one is the actual measurement. I've cut off the low frequencies on the measurement because they were just noise. The Thiele Small parameters are estimated at:

Ignore everything between Max excursion and Volume of Sealed Box in the right hand column - these are values you're meant to supply from the data sheet... I had to take a bit of a punt measuring piston area too, so it might be wrong. But close enough for a first speaker project...

Having done a course on basic speaker design, I was expecting to grab some numbers here, put them in a sub-woofer calculator and get a box volume. However, that process is for speaker drivers with a total Q well below 1, and here I find myself up around 1.4! So it's back to the drawing board I guess. Apparently open baffles are good for high Q drivers? And come to think of it, the TV was probably "open" backed with its ventilation holes. But does open baffle suit my requirements for portability?

Might be time to focus on the electronics while I mull over the design...