naturerecordists
[Top] [All Lists]

Re: Minimics from Microphone Madness for field recording?

Subject: Re: Minimics from Microphone Madness for field recording?
From: Walter Knapp <>
Date: Thu, 03 Feb 2005 23:28:37 -0500
From: "John Hartog" <>

> I have a couple questions about this. What makes the Jecklin design 
> so inferior, and what sort of modifications would best improve the 
> commercial design?  What sort of barriers do you prefer?

I do not believe the Jecklin design is particularly inferior. Quite the 
contrary, it's a well accepted design that's been used by a lot of pro 
recordists with good results.

The recent commercial designs I've seen have been a bit lean on the foam 
layer. That layer is used to balance the frequency response of the 
system. Too lean will result in too much high frequency. Comments by the 
pro's seem to say that about them.

They are certainly overpriced. And that's the biggest flaw of commercial 
designs. For that money you could probably build several really good ones.

If there is a inferiority it is that the design is so simple looking 
that folks slap something together without thinking about the critical 
aspects of the design or it's use. It's a fairly easy design to find 
implemented poorly as a result. That's not a fault of the design, but of 
the people making and using them. They do not understand how it forms a 
stereo image, they do not do their homework.

> I have been experimenting with barriers with NT1-As and I83s.  For 
> the NT1-As I made a barrier sort of like a Jecklin disk, but its 
> oval instead of round and its thicker - about two inches thick made 
> from some dense fiberglass acoustic tile material I found at the 
> local recycled scrap store. It seems to work well for directional 
> stereo with both mics out a couple inches from the surface and faced 
> strait forward.
> 
> For the 183s I have been working on a barrier for use with a dish.  
> First I tried mounting the mics on a small disk of thin metal - 
> about two inches diameter. This had great stereo for the subject 
> sounds, but it flipped left and right for more distant sounds. My 
> guess is sounds from the right reflect off the left side of the dish 
> and into the left mic.  Today I am trying out a larger disk - it's 
> made from an old record, a standard LP what ever size that is.  My 
> hope is it will shield the left and right of the dish from sounds 
> from the opposite sides. The mics are mounted to the surface of the 
> record facing into the dish.  I suppose this may have some pzm 
> effect, though I don't know much about pzms.
> -John Hartog

A LP would be ok in diameter for a core, (except for being physically 
weak) but used alone it would reflect the high frequencies as you found. 
That's the purpose of the foam or sheepskin layers on a Jecklin disk. 
You actually don't want that reflection off the disk, the disk is there 
as a barrier to sound, not as a reflector.

The Jecklin disk is also one of the head spaced setups. Standard 
separation is 650 mm, though it sounds like you were close on that. 
Using that distance provides the best balance of phase differences.

PZM is a very different thing from Jecklin's disk. Though there are some 
hybrid designs that some think are variations of the Jecklin disk, 
introducing boundary mic characteristics changes the system quite a bit. 
PZM mounting is based on the mic diaphragm facing the barrier with a 
small gap. The gap spacing determines the frequency response, and can be 
calculated. By coupling the mic with the boundary effects at the 
surface, quite a few different design and use considerations are 
introduced. If you want to get into PZM, go to Crown's site and download 
the Boundary Mic Application Guide. The intro section of that will give 
you enough to get started.

Note it's been found that you can do away with the gap if the diaphragm 
is located in the plane of the boundary facing out. There should be 
little gap between the diaphragm and the boundary, and nothing solid 
between, but the gap must be sealed behind. This is the way it's done in 
the modified SASS/MKH-20 that Lang and I (and a number of others) use.

Walt




________________________________________________________________________
________________________________________________________________________

<Prev in Thread] Current Thread [Next in Thread>
Admin

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU