Specialized mic need

[Innovations]

Here is an unusual mic selection problem.

My son the wildlife biologist wants to record bird songs using a DIY dish microphone (like those things you see on the sidelines of NFL games to hear the QB.

The dish part is pretty simple. And it is the dish that does all the sound focusing. In other words the microphone in the center of the dish should be picking up sound reflected to it from the entire dish surface. So I am thinking either a cardiod or omni pickup pattern.

The other main characteristics should be:

1. Very flat frequency response since it is being used for scientific measurements.

2. Very detailed response, also because it is being used for scientific meansurements.

3. Durability, as this will be used outdoors with a windscreen. Low cost is also desired.

I can think of several mics that meet one or two of these criteria but not all three. For example a sm57 would certainly be highly druable but not detailed and flat. A ECM8000 would have the flat response but I am concerned about all the descriptions of its high self-noise interfering with recording. So I am currently looking at inexpensive small or medium diameter condensers. Which one(s) would have flat responses and reasonable durability?

 

[Harvey Gerst]

Since the noise on the ECM8000 is constant, it should be easy to filter it out later. A lower noise source woud be the MXL 604 or the Studio Projects C4 (both come with omni and cardioid capsules). I suspect a parabolic reflector would work best with a cardioid capsule, but the omni would give you the highest quality, down to where the dish diameter is smaller than 1/2 wavelength. At that point, the frequency response will drop off 12dB per octave, no matter which capsule you use.

 

[scrubs]

I'm not sure what their response curves typically look like, but I believe shotgun type condenser mics are often used for directional distance recording like you are describing.

 

[Innovations]

Thanks for the very good response, I have a couple of follow-ons:

1. Is the higher quality of the omni because of the lack of proximity effect or some other reason?

2. What does the 1/2 the wavelength mean as a practical standpoint? In other words with a 12 or an 18 inch dish where would the dropoff occur? Would it be safe to compensate for the loss with EQ?

3. Not having worked with an ECM8000 before what is the noise like on it? Is is a single frequency or set of frequencies or is it broad spectrum like white noise or pink noise?

 

[Innovations]

I'm not sure what their response curves typically look like, but I believe shotgun type condenser mics are often used for directional distance recording like you are describing.

True, but a parabolic dish is even more 'focused' than a shotgun. One site used an analogy to photography. A typical cardiod patter is like photographing with a 28mm fisheye lens in terms of where you are seeing the sound from. A typical long shotgun would be about a 78mm lens and a medium size parabolic dish would be about a 200mm lens. Once you are using the disk you are no longer listening toward the subject buy you are listening to the dish surface. So you want a pickup pattern that sees the whole dish.

 

[amra]

This is an interesting thread.
I have been thinking about a shotgun mic to use on my camcorder to improve the sound quality. I had never thought about the dish thing - recording the surface of the dish as opposed to the object. I always figured you would want a shotgun mike for that application. Makes sense though, if you think about it. This page has a good selection if you choose to go the shotgun mic direction.

http://www.bhphotovideo.com/bnh/controller/home?O=breadCrumb&A=search&Q=&ci=8533

 

[Harvey Gerst]

Thanks for the very good response, I have a couple of follow-ons:

1. Is the higher quality of the omni because of the lack of proximity effect or some other reason?

Omnidirectional mics respond to pressure, not velocity, so the diaphragm material and design becomes less important to the final frequency response.

2. What does the 1/2 the wavelength mean as a practical standpoint? In other words with a 12 or an 18 inch dish where would the dropoff occur? Would it be safe to compensate for the loss with EQ?

A 12" disc should get you down to around 600 Hz, good enough for most bird calls.

3. Not having worked with an ECM8000 before what is the noise like on it? Is is a single frequency or set of frequencies or is it broad spectrum like white noise or pink noise?

It's broad spectrum.

 

[amra]

A cool article about recording the sounds of nature. It has some useful and relevant info:
http://emusician.com/daw/emusic_going_wild/


And this one goes in depth into the differences between shotgun mics and parabolic dish setups:
http://www.telinga.com/attach.htm