[opendtv] Re: Microphone for Parabolid Reflector
- From: "Hunold, Ken" <KRH@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 12 Jan 2012 09:57:22 -0500
You need a mic pattern that can "see" the entire surface of the
reflector. Just like a satellite dish feedhorn, the mic needs to
"illuminate" as much of the reflector as possible. Note that any
overspill will result in pickup from the unintended direction.
Theoretically, a cardioid mic would be an ideal match to a parabola, but
in the real world, sounds from the sides often creep into the intended
signal. Also, the best shapes for sound pickup may be too large or
awkward to be held or supported.
A smaller mic would be better, because more of the sound is being
collected at the focal point. This sometimes works against having a
directional microphone, as they can be bigger. Unless, of course, if
this larger area is properly concentrating the energy it gets to the
transducer element.
Are you using a true parabolic shape, or spherical? Most of the
"parabs" out there are really spherical, and that's not necessarily a
bad thing. A true parabolic reflector only has one focal point, located
on axis and at a distance determined by the f/d ratio. You will get the
most gain out of the mic-reflector combination only if you put the
"phase center" of mic at the that focal point. Any other position
results in lower gain and sound coloration. When people talk about
"tuning a parab" they are just talking about adjusting the mic position
for the sound they like, not what gives the most gain. As with any
other source, feel free to use any console filtering and effects to get
the sound you want/like.
As I mentioned, most of the "parabs" in use in sports are really
spherical reflectors. When you put a mic in the "center," the beam can
point in a slightly different direction, depending on where the mic is
really placed. This can be used an advantage if the person pointing the
contraption can monitor what the mic is picking up. In the classic
football use, an attentive/skillied operator can fine-tune the direction
of the reflector to maximize the intended sound.
There is some science associated with these mic arrays, but most of the
time you just have to deal with what you get.
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
On Behalf Of dan.grimes@xxxxxxxx
Sent: Tuesday, January 10, 2012 12:08 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Microphone for Parabolid Reflector
Anyone have good reference material for parabolic mics? I have a
parabolic mic/reflector and am going to replace the mic element on it. I
am thinking that a wide pickup (surface area of the pickup, not angle of
pickup) is best to get a good surface area to capture all those waves. I
am also thinking about using a mild cardioid with low off-axis rejection
until it gets outside of the reflected area. But I am not sure if this
is wise or not. Also, I only have full frequency elements available so I
probably will need to roll off the low end to keep directionality. I am
hoping that doing this at the console is okay versus using a narrow band
transducer.
So if you know of some good discussion on which transducer is best for a
parabolic reflector, let me know.
Dan
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