I'd like to try recording birdsong using a microphone at the focus of parabolic reflector. Currently, I'm having difficulty thinking of domestic items which I could cannibalise for their parabolic shape. Any ideas would be welcome. Best I've thought of so far is an old radiant heater with the cylindrical heating element at the centre of a spun reflector.
Thanks (I am aware of the professionally priced reflectors from Sweden.)
Old (solid) satellite dish.
For 7Khz song, you need surface accuracy of 1/4 * 340m/s /7000Hz = 1.25cm. One way of cheating is to take a strip of plywood. Now, form it into a curve. Yes, it's flat, but as long as it's only a small strip, it can fairly well approximate a strip of a parabola.
I had ideas about this years ago and considered taking a papier mache mould of the round end of a spacehopper.
What I would do is glue chunks of blue foam together, then make a parabilic shaped template, and use a wire brush and maybe spinnin the lot and sand a parabola on that.
You can then lay upo a fibergallss one obver teh top, nd when set, rip the foam away and use acetone to clen it all off.
Voila! a parbolic reflctor.
Or just nick someones sky dish instead.
Blow up a balloon. Coat it with wax polish and then cover a suitable end in glass fibre to the shape you require.
They are better if you also have a tube on the front to prevent side noise.
How about printing yourself a parabola on a graph (using excel or something), use that to cut some templates from ply which you then assemble into a star pattern. Finally lay it up with firbreglass tissue and resin....
"Malcolm Stewart" wrote in message news:d1iecl$6fq$ snipped-for-privacy@news8.svr.pol.co.uk...
Be aware that most satellite dishes are offset and the dish axis doesn't point directly at the satellite. Given a dish (eg Sky) which is nominally vertical and the satellite is at approx 36 deg. elevation or so (from London) the offset is 36 deg and the LNB is 36 deg below the dish parabolic axis. Dishes which are true parabolic have the LNB on the central axis usually on a tripod arrangement and the dish is pointed up directly at the satellite.
john
Not a domestic item but ...
How about a Wok
How about a big torch, the sort that takes a lantern battery?
Enough room in there also to do a small battery powered preamplifier.
Mine's more a section of a sphere (must be a name for that) raher than a parabola. The particular property of a parabola he needs to exploit is that there's a point of focus.
There are some plastic lightweight transparent dishes around., Have a Google for them....
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on the wild side?
mike
Don't think metal is a good idea - too much 'ring' to it. Glass fibre would be my choice.
As others have said, an old satellite dish of the large type you plonked in the garden?
IMHO, you'll need something larger than a metre or so for decent results.
Some good suggestions have been made in this thread.
However, have you thought about putting the microphone close to where the birdies are tweeting? You could run an extension cable for the microphone etc. Or maybe set up a tiny radio microphone like this one:
Andrew
If you just wanted general bird song, then any mic would do. But if trying for one specific bird - and not getting close enough to scare it off - parabola is a very good way of doing it. You listen to the output of the mic and point it to get best results.
The beauty of a parabola is it adds gain and directionality to the chosen mic 'for free'. Rifle type mics work by rejecting unwanted sounds so sort of lose gain.
Of course a rifle mic is easy to carry and handle - not so a large parabola.
Last time I actually used a parabola was on a cup final at Wembley (mutter) years ago. The idea was to get close up sound of the ball being kicked - from the top of the grandstand.;-) Worked much better than rifle mics on the touchline.
Must have been about the most boring job ever - panning it around after that ball.
Thanks guys for all your suggestions.
A bit of background:- I'm using either a camcorder or a MiniDisc recorder.
1 So far I've tried placing a pair of small omnis around the top of a fence post spiked with bird food. Very successful for capturing the wing-beats as birds came down to feed, and also caught some calls very well indeed. Mikes also captured the distant noise of road repair work.2 Have captured some excellent soundscapes, including birdsong, via dummy head stereo - using a pair of omnis on the sides of my baseball cap. But traffic noise was a problem.
Hence I'm now thinking about making a reflector system. I'll lose the stereo effects but hopefully the traffic noise will also be reduced. (Location wise, I'm close to the M1, and traffic noise is apparent more or less everywhere in and around Milton Keynes, and in Salcey Forest (a few miles north) which is cut by the M1.)
Anybody want to buy a 1.8m centre lnb dish on a tripod mount?
Depends how much MF and LF response he wants... there is a relationship between dish diameter and the lowest frequency that it will focus effectively. They do have a lot of "suck" and directivity though at the expense of frequency response. Do a UK google search on "sound mirrors" for real parabs...
Last time I rigged a parab was at Headingly on a test match to get the whack of leather on willow, there where also mics buried in the pitch and cabled back, these had to be delayed.
Steep high pass filtering (bass cut) will help a great deal with traffic noise with minimal effect on most bird song. However, such steep filters aren't easily available outside pro recording equipement, but you might find a suitable prog to do this in your PC. Can't help there as I don't have one. ;-)
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