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
At 04:29 AM 5/25/2006, you wrote:
>Thanks for those who answered my query. The reason behind the question
>is that I'm building a reflector trying a variety of sizes and focal
>lengths. I'm targeting bird calls. One of my aims was trying to get a
>few more dB for my mics (Shure WL 183).
>There a several materials available ranging from metal, plastic (eg.
>umbrella), cardboard and fiberglass. Durability, ease of construction
>and weight are factors but is the difference in bD reflected of the
>surface going to be a major consideration?
>David
>
>Rich Peet wrote:
>
> > In my next version of the cube I will try very dense absorbtive foam
> > and not use wood. The gain of the boundary does not seem to be true
> > hemispherical. I have read reports on both sides of this. But I
> > figure if I keep using the very quiet mics types I really don't need
> > the boundary gain from what I am seeing in the field. I am just not
> > finding my mics with there high outputs can be driven to +60db on the
> > preamp. I would say the mics have too high of a noise but they are
> > out performing my ears so I can not complain.
> >
> > Rich
> >
> > --- In "John Hartog"
> > <> wrote:
> > >
> > > Hi David,
> > > It's important here to distinguish boundary from other barrier
> > techniques.
> > > For boundary mics the direct and reflected sounds that combine at the
> > > reflective surface give several dB of wanted free gain. For other
> > > barrier techniques, like a Jecklin Disk, an absorptive surface is
> > > ideal to reduce unwanted phase cancellation between direct to the mic
> > > and reflected off the barrier sounds.
> > >
> > > -John Hartog
> > >
> > >
> > >
> > > --- In Secomb's <secowlet@> wrote:
> > > >
> > > > Hi all
> > > > There have been a variety of DIY projects that have been floating
> > > > around. Which material that is used is essential component of any
> > such
> > > > project. I have been under the assumption that harder and smoother
> > the
> > > > material, the greater the sound would be reflected. To me Rich
> > making
> > > > a cube array with wood made sense but a softer material such as
> > high
> > > > density foam will result in less sound reflected towards the mic.
> > > The
> > > > concept of emphasising a particular range of frequency is
> > interesting.
> > > > A little while ago, a mouse pad was used as a Jenklin disk (I think=
).
> > > > Again a softer material with a slight texture will give less dB whe=
n
> > > > compared to wood for instance .
> > > > With those more experienced in sound recording is there a rule of
> > thump
> > > > what are the reflective properties of a variety of material that i=
s
> > > > used in DIY projects. It appears not only the degree of sound that =
is
> > > > reflected to consider, the tonal quality is also important.
> > > >
> > > > David
> > > >
> > > >
> > > >
> > > > --
> > > > No virus found in this outgoing message.
> > > > Checked by AVG Free Edition.
> > > > Version: 7.1.392 / Virus Database: 268.6.1/344 - Release Date:
> > 19/05/06
> > > >
> > >
> >
> >
> >
> >
> >
> >
> >
> > "Microphones are not ears,
> > Loudspeakers are not birds,
> > A listening room is not nature."
> > Klas Strandberg
> >
> >
> >
> > SPONSORED LINKS
> > Science kits
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science+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DLz9nlutNQy4QT0lkCYssxg>
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> > Science education
> >
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> > Science kit for kid
> >
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>
> >
> > Natural sound
> >
> <<http://groups.yahoo.com/gads?t=3Dms&k=3DNatural+sound&w1=3DScience+kits=
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ttp://groups.yahoo.com/gads?t=3Dms&k=3DNatural+sound&w1=3DScience+kits&w2=
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rst+science+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DQX11IJRDIZK15-qRl5t-Fw>
>
> > My first science kit
> >
> <<http://groups.yahoo.com/gads?t=3Dms&k=3DMy+first+science+kit&w1=3DScien=
ce+kits&w2=3DScience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&=
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rVRXSNw>
>
> > Sound
> >
> <<http://groups.yahoo.com/gads?t=3Dms&k=3DSound&w1=3DScience+kits&w2=3DSc=
ience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=3DMy+first+s=
cience+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DunzpqxF2mHIXi0JiJrzopQ>http://gr=
oups.yahoo.com/gads?t=3Dms&k=3DSound&w1=3DScience+kits&w2=3DScience+educati=
on&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=3DMy+first+science+kit&w6=
=3DSound&c=3D6&s=3D122&.sig=3DunzpqxF2mHIXi0JiJrzopQ>
>
> >
> >
> >
> > YAHOO! GROUPS LINKS
> >
> > * Visit your group "naturerecordists
> >
> <<http://groups.yahoo.com/group/naturerecordists>http://groups.yahoo.com/=
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> >------------------------------------------------------------------------
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> >No virus found in this incoming message.
> >Checked by AVG Free Edition.
> >Version: 7.1.392 / Virus Database: 268.6.1/344 - Release Date: 19/05/06
> >
> >
>
> ----------
>
>No virus found in this outgoing message.
>Checked by AVG Free Edition.
>Version: 7.1.394 / Virus Database: 268.7.1/347 - Release Date: 24/05/06
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>
>
>
>SPONSORED LINKS
><http://groups.yahoo.com/gads?t=3Dms&k=3DScience+kits&w1=3DScience+kits&w2=
=3DScience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=3DMy+fi=
rst+science+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DLz9nlutNQy4QT0lkCYssxg>Scie=
nce
>kits
><http://groups.yahoo.com/gads?t=3Dms&k=3DScience+education&w1=3DScience+ki=
ts&w2=3DScience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=3D=
My+first+science+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DzxdoipO7RHo6Ovyfekb5NA=
>Science
>education
><http://groups.yahoo.com/gads?t=3Dms&k=3DScience+kit+for+kid&w1=3DScience+=
kits&w2=3DScience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=
=3DMy+first+science+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DJdnZrWeIBv-vL8kM6Zy=
jqA>Science
>kit for kid
><http://groups.yahoo.com/gads?t=3Dms&k=3DNatural+sound&w1=3DScience+kits&w=
2=3DScience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=3DMy+f=
irst+science+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DQX11IJRDIZK15-qRl5t-Fw>Nat=
ural
>sound
><http://groups.yahoo.com/gads?t=3Dms&k=3DMy+first+science+kit&w1=3DScience=
+kits&w2=3DScience+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=
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>first science kit
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nce+education&w3=3DScience+kit+for+kid&w4=3DNatural+sound&w5=3DMy+first+sci=
ence+kit&w6=3DSound&c=3D6&s=3D122&.sig=3DunzpqxF2mHIXi0JiJrzopQ>Sound
>
>
>
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