Hi All
I am in the middle of making a 24 inch diam. reflector out of "Corrux"
a corrugated plastic much used for lightweight signs.
My material is quarter of an inch (6.5mm) thick and the finished dish
without handles or mics weighs in at 1.5 lbs. It seems to be very robust.
I used the info at
http://graffiti.virgin.net/ljmayes.mal/var/parabola.htm
I think I misread/misused the spreadsheet attached to that site. I
was hoping to make a 500mm diam dish with a focal length of 12.5mm.
However I have ended up with a dish of 600mm diam. Hopefully the
focal length will still be 12.5mm.
Some preliminary photos of its construction are shown in the
"Parabolic Reflector" album at
m("btinternet.com/my_photos","//uk.pg.photos.yahoo.com/ph/g0sbw");">http:
Normally I don't post info on DIY projects until I can also post some
proof of how they are working (an MP3 file of a nature recording made
with the equipment). Clearly I'm not able to do that at this point in
time but I'm so impressed with the constructional attractiveness of
"Corrux" I thought it sensible to post this now.
Some of you might note the album "Jecklin Disc" in the above photos
URL. This shows photos of a work in progress but not yet reported on.
It is, however, somewhat topical. Preliminary results are very
promising (apart from one major faux pas). I will report on this
project shortly including comparison of the DIY project with my NT4.
BTW both the parabolic and the Jecklin Disc will initially use my very
cheap (=A30.35) capsules sourced locally.
Talking of money, the cost of the parabolic dish on its own is about =A34.0=
0
Complete, ready to go in stereo mode, it will be less than =A36.00
Cheers
Tom Robinson
--- In Greg Clark <> wrote:
>
> David,
>
> Parabolic reflectors that have a hard surface absorb less sound than
> materials like cloth. You can make a reflector out of an umbrella
and it
> will provide some gain, but cloth is not as good as polycarbonate
plastic.
> Aluminum microwave dishes are a good place to start before you try to
> create your first scratch-built reflector. If you do decide to build
your
> own, fiberglass is the easiest way to make the actual dish. The
trick is to
> make the mold master, something that I have done several times, and no
> accurate parabola mold master is easy to build. If you can come up
with an
> aluminum microwave dish you can use that as a master and make a
fiberglass
> copy of it. That will reduce the weight you have to carry around. I
think
> the gold standard is polycarbonate, but you need to have an oven and
a mold
> master (and usually a vacuum pump) in order to make an accurate dish.
> Remember that more gain is not the only goal. As the dish size
increases
> you also improve the frequency response of the dish. That is another
reason
> to try a microwave aluminium dish first. Making large accurate
parabolas
> (bigger than 24 inches) with the focus at the plane of the rim of
the dish,
> is difficult.
>
> Greg Clark
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