Hi Marco,=0D
=0D
The first sentence in the statement from the Macaulay Library is a general =
rule of thumb. The second sentence is inaccurate. From our article of parab=
olic accuracy, the gain equation is: "A Parabolic microphone gain is highly=
predictable, and when properly made, closely approaches the theoretical va=
lues given by the Gain Equation below: Where Dish Gain in dB =3D G, Diamete=
r in inches =3D D, Wavelength in inches =3DW, and E is the efficiency from =
0 to 1. The Gain equation is: G =3D 20Log(3.25DE/W). For a hypothetically p=
erfectly made system, E will equal 1." Practical microphones are very close=
to these figures. Efficiency can drop some at higher frequencies, but well=
above the frequencies we are discussing here. For example, using this equa=
tion, when diameter equals wavelength, gain is about 9dB. For 6dB of gain, =
the diameter can be about 0.66 of the wavelength. The equation was proven a=
ccurate with gain measurements on our Pro Mono Parabolic Microphone at an i=
ndependent test lab. I should add that our parabolic microphones absolutely=
responds down to 20Hz, like a normal microphone, unlike the idea the Macau=
lay Library eludes to some kind of fictitious hard filter the parabolic ref=
lector has.=0D
=0D
In our literature, you will also run into what is termed "Bass Dip". Bass d=
ip can often remove much of the gain below 1KHz, resulting in a dish respon=
se similar to what was stated by the Macaulay Library. Bass dip can be avoi=
ded, and our Pro Series greatly minimizes it. Most other parabolic systems =
will have a pronounced bass dip.=0D
=0D
As the gain equation predicts, substantial parabolic gain is available at l=
ower frequencies. Any parabolic system that does not realize this lower fre=
quency gain is most likely affected by bass dip due to many aspects of it's=
construction.=0D
=0D
I hope that helps explain parabolic gain.=0D
=0D
Bruce Rutkoski=0D
Owner=0D
www.wildtronics.com =0D
=0D
---In <> wrote :=0D
=0D
Bruce,=0D
you write at your website that =94Gain, for an ideal 22-inch dish with a p=
erfect parabolic shape and focus, is characterized by a curve starting at 0=
dB at 200Hz,=0D
=0D
The Macauly Library says that: =94The diameter of a parabola determines th=
e lowest frequency sound that a parabola can amplify. If the wavelength of =
a sound wave is greater than the diameter of the parabola, the sound wave w=
ill not be captured or amplified by the parabola.=94=0D
=0D
The wavelength of 200 Hz is 1,7 meters. Hence, a parabola capable of (star=
ting) amplifying at 200 Hz must have a diameter of 1,7 meters =3D 67 inches=
.=0D
=0D
The wavelength of 400Hz (where you claim that your 22" dish has 6 db ampli=
fication) - is 0,85 meters =3D 33 inches.=0D
=0D
Can you explain?=0D
=0D
Marco=0D
=0D
|