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## Re: Making a parabola

 Subject: Re: Making a parabola "freitojos" freitojos Fri Sep 21, 2012 4:33 am ((PDT))
 ```Michael, This pdf said the efficiency of a parabola in the formula of the gain: 10*log10 ((efficiency 0,45-0,7*(4phy/wave lenght^2)*Area of the parabola))= is between 45% and 70% . My question is a fiber glass parabola 3mm tich, what woud I chose to coefic= ient 0,45 or 0,7? One aluminium parabola inside and with fiberglass in the rear? http://www.coe.montana.edu%2Fee%2Frmaher%2Fpublications%2Fmaher_aac_0805.pd= f&ei=3DK0tcUNPcHcTKhAfJl4HoCQ&usg=3DAFQjCNE5XycXqQBeTLUvCCZNMPQH6qnYnA I have made one exel with the formula and parabolas with 40cm, 60cm 80 cm = and 86,8cm diameter, here is the results: Areas 40cm 60cm 80cm 88.6 cm Hz wave le^2 0.1246 0.2826 0.5024 0.6162 300 1,330177778 -2,33 1,24 3,75 4,64 400 0,748225 0,17 3,74 6,25 7,14 500 0,478864 2,11 5,68 8,18 9,07 1000 0,119716 8,13 11,70 14,21 15,09 2000 0,029929 14,15 17,72 20,23 21,11 3000 0,013301778 17,67 21,24 23,75 24,64 4000 0,00748225 20,17 23,74 26,25 27,14 5000 0,00478864 22,11 25,68 28,18 29,07 6000 0,003325444 23,70 27,26 29,77 30,66 7000 0,002443184 25,03 28,60 31,11 32,00 8000 0,001870563 26,19 29,76 32,27 33,16 efici=EAncia 0,50=09=09=09 My next parabola (88,6 cm diameter and 20cm focal distance)is one in alumin= ium foil 0,8mm tich with fiberglass in the rear, now I know it is not nece= ssary to made one clay mold the aluminium is the parabola and the mold for = the fiberglass. This formula is a general formula for waves, light, radio or sound in a = parabola, is it a fiable formula to calculate the gains? I know from posts = here (Klas,Telinga or Avocet, David)that in the sub 1kz it is not so intere= sting to have a parabola. But in a tripod a big parabola would be a good op= tion. Regards, Jos=E9 --- In m("yahoogroups.com,","naturerecordists"); Klas Strandberg wrot= e: > > when you have side wind hitting the dish, which you always have when > pointing up into the sky, there will be strong turbulence in the dish. > A base filter must be used before the first input transistor, > otherwise it will cause severe distortion, OR a piece of cloth > working as a wind shield, covering the entire opening of the dish. > > Klas > > > At 21:05 2012-09-20, you wrote: > > > Hi all =AD interesting discussion =AD I=B9ve used friends=B9 parabola= s > > and have been > > > considering trying to rig up a home-made version as well. > > > > > > a few questions...avocet wrote: > > > > > > =B3Always use a maximum bass roll-off - you can put the bass back lat= er > > > if necessary.=B2 > > > > > > I=B9m wondering how you=B9d do this ? Why wouldn=B9t you roll off the= bass > > > post-recording instead? I really don=B9t see how you could simply =8C= put back=B9 > > > bass that was never recorded...not meant as a criticism, necessarily = =AD it=B9s > > > more that I=B9m intrigued by this statement, particularly as your (av= ocet=B9s) > > > posts seem to indicate an incredible depth of recording-related knowl= edge. > > > > > > also =AD it seems to me that the material used to construct the > > parabola would > > > have an impact on the sound =AD would the plastic or nylon surface of= an > > > umbrella dampen/muffle the sound at all ? I was trying to figure > > out a way to > > > coat the surface with something more reflective, but wonder if it=B9s= that > > > necessary ? > > > > > >Cheers... > > > >Michael > >.................................... > > > >http://michaeltrommer.blogspot.com/ > >http://soundcloud.com/sans-soleil/ > >http://michaeltrommer.bandcamp.com/ > >http://www.mixcloud.com/sans_soleil/ > > > > > > > > > > > > > >------------------------------------ > > > >"While a picture is worth a thousand words, a > >sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause= . > > > >Yahoo! Groups Links > > > > > > > Telinga Microphones, Botarbo, > S-748 96 Tobo, Sweden. > Phone & fax int + 295 310 01 > email: m("...","telinga"); > website: www.telinga.com > > > ```
 Current Thread Re: Making a parabola, Avocet Re: Making a parabola, MARTIN Re: Making a parabola, NordicNature Re: Making a parabola, Avocet Re: Making a parabola, Klas Strandberg Re: Making a parabola, MARTIN Re: Making a parabola, michael trommer Re: Making a parabola, Klas Strandberg Re: Making a parabola, Avocet Re: Making a parabola, michael trommer Re: Making a parabola, freitojos <= Re: Making a parabola, Klas Strandberg Re: Making a parabola, Avocet Re: Making a parabola, freitojos Re: Making a parabola, Scott Fraser Re: Making a parabola, Klas Strandberg Re: Making a parabola, Scott Fraser Re: Making a parabola, Klas Strandberg Re: Making a parabola, vickipowys Re: Making a parabola, Klas Strandberg Re: Making a parabola, vickipowys