Hi all
Tom
I have used the site that you mentioned and found it very
useful,especially the spreadsheet which one change to get the desired
size and focal length. I have tried using cardboard but found achieving
a reasonable shape challenging. How did you go getting the shape using
plastic and are at the stage of testing it yet?
David
tk7859 wrote:
> 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=
.00
>
> 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
>
>
>
>
>
>
>
> "Microphones are not ears,
> Loudspeakers are not birds,
> A listening room is not nature."
> Klas Strandberg
>
>
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