Field Workshop Notes, Part 3: Parabolics
Posted: July 9th, 2010 | Author: Nathan | Filed under: field recording, gear, nature recording
Lookit that man out there. He's quite a dish.
One of the best reasons to spend a weekend with other sound recordists is a chance to try out new gear. A classic nature recording technique is the use of a microphone set in a parabolic dish.
The general public knows of parabolics mostly from seeing people use them on the sidelines of sporting events. In nature recording, they’re for capturing species-specific sounds rather than ambiences. This is because the microphones in parabolic dishes are mono, and have sound pushed into them by the dish itself. This creates a very narrow “beam” of listening. Perceptually, parabolics seem like they “zoom in” on sounds, but this is simply due to such microphones just attenuating all the sounds outside that narrow cone.
Parabolics are also interesting because the frequency response is directly tied to the size of the dish. For most song birds, this is fine. Besides, making and transporting a 17-meter-wide dish just to get a 20Hz-20kHz frequency response just seems silly. At that point, you’re practically into SETI territory! :-)
I got the chance to use one at the Nature Sounds Society Field Workshop. The unit you see in the photo above was the one used by the founder of the NSS, Paul Matzner, so I was holding a bit of history: Hand-made of fiberglass and aluminum, the NSS archives have lots of photos with Matzner holding this thing. Had I looked at the archives before heading into the field, I’d have gotten a way better handling technique. Holding it by its edges introduced horrendous amounts of handling noise.
Today’s sound is from this unit, recorded at 5:01am at Yuba Pass, off California Route 49. As far as I can tell, this is a chestnut-backed chickadee. You can tell, even in this recording, he’s got a lot of pals around (woodpeckers and sparrows at least).
[soundcloud url=”http://soundcloud.com/noisejockey/chestnut-backed-chickadee-yuba-pass-ca” params=”show_comments=true&auto_play=false&color=dd0000″ width=”100%” height=”81″ ]
[DPA 4006 omni microphone in custom 1m parabolic dish into Sound Devices 702 recorder]
How directional was it?
It was SO directional that it made a compass look inaccurate!
No, actually, it was directional enough that what’s considered “on axis” is really a cone only inches across. This gets tricky if, like in the recording in this post, the subject is 50′ up in a tree…fractions of an inch can make a huge difference in aiming these things at long distances.
I was impressed by the off-axis response; it was a lot quieter but not strongly colored other than some subtle high-frequency rolloff.
Hi,
A friend om mine thought that perhaps he could record sound with a microphone in a parabolic reflector from a car headlight.
Do you know if sound and light moves in the same way so the sound would be collected to a microphone placed where the lamp would sit in a headlight reflector?
Any answer is interesting for us, thanks in advance,
Karl, Sweden
Karl: While it depends a lot on what you want to record, I don’t think that will work very well. If you re-read the article, it mentions that the frequency response is directly tied to the reflector size. A car headlight will create a very tinny, frequency-limited recording. The larger the reflector, the better. The 1m dish you see me using in the image above did great for birdsong, but it’s designed for that range.