Parabolic Microphone Reflector

mrfeedback · 21st October 2002, 11:10 PM

Has anybody tried useing a Satellite Tv dish (60 or 80 cm) as a parabolic microphone reflector?, and results ?.

Eric.

pinkmouse · 22nd October 2002, 10:24 PM

Never used a satellite dish, but in school we once made reflectors using paper mache over half a large (18") balloon and they worked pretty well, we could pick up what the teacher was saying in the classroom across the quad

P.Lacombe · 22nd October 2002, 11:03 PM

I have used satellite TV dish to record bird songs at very high distance (100 m) Works very well, but unusable at low frequencies. Some equalization can be implemented in order to correct the increasing efficiency with the frequency. The position of the microphone must be carefully adjusted by extensive tests, because it's not possible to simply put the microphone instead of the LNA, which phase center is generally not well known.

Regards, Pierre Lacombe

mrfeedback · 22nd October 2002, 11:29 PM

Pierre, thanks for your reply.
"the increasing efficiency with the frequency" - is this a normal characteristic of parabolic reflectors at audio frequencies ?.

Eric.

Circlotron · 23rd October 2002, 02:37 AM

An umbrella with the inside surface coated with a more sound-reflective material e.g. varnish etc might be suitable. You also have a central pole to attach the microphone to, though it gets in the way a bit.

GP.

P.Lacombe · 23rd October 2002, 09:52 PM

Eric,

The increasing efficiency with frequency of parabolic reflector is normal at audio frequencies, as well as radio frequencies. But this is true only for a near strictly parabolic reflector (as SATV dish) not for umbrella or such approximate reflector, which exhibit a maximum efficiency for a particular wavelenght, depending of the actual incurvated form.

SATV dishes are computed for max efficiency at 4 or 5 GHz (in the USA) i.e. about 3 inches wavelenght. I suppose that the max efficiency occurs in the range 2...6 kHz for audio frequencies. European SATV dishes are computed for max efficiency at 12 GHz, requiring a more precise production, and the max efficiency occurs at about 6...15 kHz, giving a noticeable presence effect with a good electrostatic microphone (I use B&K 4133).

Regards, Pierre Lacombe.

mrfeedback · 23rd October 2002, 11:45 PM

Thanks Pierre,

I guess that the lifting response makes it better for eavesdropping on neighbours then.

I thought that a parabola is a parabola and effective at all frequencies, and the low frequency gain dependant on the area of the reflector.
I mostly posed the question for interest sake, but if I can get hold of a disused dish I am keen to try the experiment.

Eric.

Circlotron · 24th October 2002, 03:07 AM

You just want to listen in to me dreaming up nutty ideas over this side of the country. I know...

GP.

mrfeedback · 24th October 2002, 03:34 AM

Can you send me some of that water that you are drinking ?....

Eric.

21st October 2002, 11:10 PM	#1
mrfeedback diyAudio Member Join Date: Feb 2002 Location: Perth, Australia.	Parabolic Microphone Reflector Has anybody tried useing a Satellite Tv dish (60 or 80 cm) as a parabolic microphone reflector?, and results ?. Eric.

22nd October 2002, 10:24 PM	#2
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Never used a satellite dish, but in school we once made reflectors using paper mache over half a large (18") balloon and they worked pretty well, we could pick up what the teacher was saying in the classroom across the quad __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

23rd October 2002, 02:37 AM	#5
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Mary Poppins was really a spy, you know... An umbrella with the inside surface coated with a more sound-reflective material e.g. varnish etc might be suitable. You also have a central pole to attach the microphone to, though it gets in the way a bit. GP.

24th October 2002, 03:07 AM	#8
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	I'm on to you! You just want to listen in to me dreaming up nutty ideas over this side of the country. I know... GP.

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22nd October 2002, 11:03 PM	#3
P.Lacombe diyAudio Member Join Date: Jul 2001 Location: Orleans, France	I have used satellite TV dish to record bird songs at very high distance (100 m) Works very well, but unusable at low frequencies. Some equalization can be implemented in order to correct the increasing efficiency with the frequency. The position of the microphone must be carefully adjusted by extensive tests, because it's not possible to simply put the microphone instead of the LNA, which phase center is generally not well known. Regards, Pierre Lacombe

22nd October 2002, 11:29 PM	#4
mrfeedback diyAudio Member Join Date: Feb 2002 Location: Perth, Australia.	Pierre, thanks for your reply. "the increasing efficiency with the frequency" - is this a normal characteristic of parabolic reflectors at audio frequencies ?. Eric.

23rd October 2002, 09:52 PM	#6
P.Lacombe diyAudio Member Join Date: Jul 2001 Location: Orleans, France	Eric, The increasing efficiency with frequency of parabolic reflector is normal at audio frequencies, as well as radio frequencies. But this is true only for a near strictly parabolic reflector (as SATV dish) not for umbrella or such approximate reflector, which exhibit a maximum efficiency for a particular wavelenght, depending of the actual incurvated form. SATV dishes are computed for max efficiency at 4 or 5 GHz (in the USA) i.e. about 3 inches wavelenght. I suppose that the max efficiency occurs in the range 2...6 kHz for audio frequencies. European SATV dishes are computed for max efficiency at 12 GHz, requiring a more precise production, and the max efficiency occurs at about 6...15 kHz, giving a noticeable presence effect with a good electrostatic microphone (I use B&K 4133). Regards, Pierre Lacombe.

23rd October 2002, 11:45 PM	#7
mrfeedback diyAudio Member Join Date: Feb 2002 Location: Perth, Australia.	Thanks Pierre, I guess that the lifting response makes it better for eavesdropping on neighbours then. I thought that a parabola is a parabola and effective at all frequencies, and the low frequency gain dependant on the area of the reflector. I mostly posed the question for interest sake, but if I can get hold of a disused dish I am keen to try the experiment. Eric.

24th October 2002, 03:34 AM	#9
mrfeedback diyAudio Member Join Date: Feb 2002 Location: Perth, Australia.	Can you send me some of that water that you are drinking ?.... Eric.

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