ambulance siren.wav

This is one of two files that I recorded on the 18th Jan 2009 at around 8.00pm at the main road outside my house. The weather was cold and very windy. The geotag has been logged with the file. Recorded onto a domestic, hand-held mini disc recorder (Sharp MD MT80HS). The files have have not been post produced, they are exactly as recorded.

This is the first attempt I have made with my new, home-built, stereo imaging microphone, built for less than £20. For those of you who may be particularly interested in making one of these, the following description may help you to experiment with your own devices.

I bought a fairly cheap Sony, stereo 'lapel mic' which I mounted onto a 400mm length of doweling wood with insulation tape. This looked like an extended 'letter T'. Using the plastic lid off a tub of some tiling grout (a plastic paint lid would work just as well) also measuring about 400mm, I cut a hole in the centre and a slot at the bottom (for the mic to fit through in the middle and the doweling to slot through at the bottom. This was then nailed to the dowel. I then cut 2 circles of ordinary foam (about 25mm thick) and made a hole in the centre. This was then glued to the lid around the mic capsule. The reason for the foam was to provide stability for the next step. I used two (British) 'tea-strainers' (basicially a very small metal sieve with a wire handle) to cup the mic capsule and filled them with very sheer voile (a scrunched up handful of very fine gauze). This was duck-taped into position. I had a broken microphone clip which I glued with epoxy resin and duck-taped to the 'handle' at the base (for later stand mounting). Using some 'hairy fabric' I drew around the large circumference and stitched it into a circular 'bag'. It is important to use fabric which has long and short hairs for maximum effect. This can be bought from any good craft and fabric shop in the 'party costume' section (usually used for animal suits!). After fitting the bag to the lid, I lightly stuffed the remaining space around the two sieves with the wadding from an old cushion and stitched up the remaining length of the wind-screen. Finally, I used an old foam handle bar grip from a bicycle on the protruding length of dowel.

The final mic looks like a huge hairy lollypop, but the science behind it seems to work. For a 'correct' stereo effect, it is important to 'shield' the left field from the right field - just as on a human head. Advanced and professional stereo imaging microphones often employ a 'dummy head' for exactly this reason. Hence the plastic lid and wadding. The metal cage, voile, and hairy fabric is to reduce wind noise, which is done by creating a space of 'dead air' (breaking down the movement of air) around the mic head.

Finally, I had to be extra careful not to tip or tilt (or turn too much) as I was walking around, otherwise the final effect would be too dizzying!.