Freesound Forums

Does anybody know why the barrel of these mics is not a complete tube / cylinder ? They all have grilles incorporated into them, am I right in thinking that a complete cylinder with the cardioid or hypercardioid at one end would result in attenuation of some if not all frequencies due to standing wave phenomena or similar ? This question has intrigued me for some time now.

This cancels out sounds coming from the sides of the shotgun, therefor 'focussing' on what's directly in front of the mic.
Also if the openings wouldn't be there, your sounds would echo inside the barrel and you'd get audio sounding like it's recorded through a plumbing pipe.

Thank you nemoDaedalus.

your sounds would echo inside the barrel and you'd get audio sounding like it's recorded through a plumbing pipe

That I get

This cancels out sounds coming from the sides of the shotgun, therefor 'focussing' on what's directly in front of the mic.

Can you elaborate how ?

I found this definition at

http://www.testing1212.co.uk/default.htm

"Shotgun Microphone
A microphone with a long line filter (a tube that acoustically cancels sound arriving from the side) to make the microphone pick up much better in one direction than in any other direction. "

Fine, I believe it but how does it work ?. What physics are involved ?

I am even more curious now !

Benboncan

Fine, I believe it but how does it work ?. What physics are involved ?

Interference ... http://en.wikipedia.org/wiki/Interference#Constructive_and_destructive_interference

Yeah, the sounds coming in at an angle through the openings gets 'trapped' in the barrel. Because it comes in at an angle, the same sound is spaced a tiny bit apart, causing to interfere with itself and cancel out.
Iirc, it goes a little like this: (if it makes any sense)

\ \
\ \
\ \ <sound coming in at an angle
\ \ membrane of mic
+------------+--+
front | --=====| | back
+------------+--+
Sound enters barrel here, the = representing the same sound interfering with itself.

Thank you, yes it does make sense.