Those electret microphone capsules are quite good but omnidirectional.
Is there any way to modify them to give a different pattern?
Modify the case, or some suitable shaped enclosure?

There are some digital recorders available with what looks,
though I haven't looked too closely, like two electret capsules
at right angles. If they are omnidirectional, they wouldn't give
much stereo effect. Anyone know what they are?

--
Eiron.

In article ,
Eiron wrote:
Those electret microphone capsules are quite good but omnidirectional.
Is there any way to modify them to give a different pattern?
Modify the case, or some suitable shaped enclosure?

I'd say not. Producing a cardiod capsule requires precision engineering.
So cheaper to simply buy one.

There are some digital recorders available with what looks,
though I haven't looked too closely, like two electret capsules
at right angles. If they are omnidirectional, they wouldn't give
much stereo effect. Anyone know what they are?

Omnis used for stereo are normally spaced some way apart. Near coincident
needs directional types.

--
*Never underestimate the power of stupid people in large groups.

Dave Plowman London SW
To e-mail, change noise into sound.

On 22/03/2013 19:03, Dave Plowman (News) wrote:
In article ,
Eiron wrote:
Those electret microphone capsules are quite good but omnidirectional.
Is there any way to modify them to give a different pattern?
Modify the case, or some suitable shaped enclosure?

I'd say not. Producing a cardiod capsule requires precision engineering.
So cheaper to simply buy one.

You're right. They seem to be 50p each at Farnell.
It looks like they just have a few precision drilled holes in the back.
I wonder if that's the only difference.

--
Eiron.

In article , Eiron
wrote:
On 22/03/2013 19:03, Dave Plowman (News) wrote:
In article , Eiron
wrote:
Those electret microphone capsules are quite good but
omnidirectional. Is there any way to modify them to give a different
pattern? Modify the case, or some suitable shaped enclosure?

I'd say not. Producing a cardiod capsule requires precision
engineering. So cheaper to simply buy one.

You're right. They seem to be 50p each at Farnell. It looks like they
just have a few precision drilled holes in the back. I wonder if that's
the only difference.

In principle you can get two pressure-sensing mics and place them slightly
apart. Then connect so that their outputs 'cancel'. This produced a setup
that outputs the 'differential' in pressure along the direction between
them. So gives a cardiod-ish shape. But although neat in theory you may
find it hard to get such a system working well. And it would need frequency
(wavelength) correction. So as Dave says, there is a lot of detail to sort
out. Simpler to buy the tool for the job unless you are interested in the
DIY experimentation involved and have the time.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"Jim Lesurf"

In principle you can get two pressure-sensing mics and place them slightly
apart. Then connect so that their outputs 'cancel'. This produced a setup
that outputs the 'differential' in pressure along the direction between
them. So gives a cardiod-ish shape.

** Read like a non sequitur to me.

A pair of OOP omnis simply has no output to sounds arriving from any
distance.

Nothing like a cardiod.

Jim can cite a contrary reference - any time he likes.

No thought experiments - PLLLEASE !




..... Phil

In article ,
Jim Lesurf wrote:
In principle you can get two pressure-sensing mics and place them
slightly apart. Then connect so that their outputs 'cancel'. This
produced a setup that outputs the 'differential' in pressure along the
direction between them. So gives a cardiod-ish shape

You've confused me. The easy way to make a cardiod pattern with two mics
is to use pressure and pressure gradient types.

--
*The best cure for sea sickness, is to sit under a tree.

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:
In principle you can get two pressure-sensing mics and place them
slightly apart. Then connect so that their outputs 'cancel'. This
produced a setup that outputs the 'differential' in pressure along the
direction between them. So gives a cardiod-ish shape

You've confused me. The easy way to make a cardiod pattern with two mics
is to use pressure and pressure gradient types.

Sorry, I should havbe given more detail. The above jumped over too much.

Two pressure sensors spaced apart will sense the pressures in those two
*different* places. A wave propagating between them takes time to do so.
Hence if you subtract their outputs you can output the spatial differential
of the pressure. However - as per your own comments - this isn't an easy
way to do it. :-)

In fact a 'velocity' sensor is also a type of sensor for the spatial
pressure differential. It works due to the pressures on either side of the
sensor being different. Its advantage is that one bit of material (e.g. a
ribbon) is used to sense both side-pressures so avoids the difficulty of
having to pressure sensors which may have different sensitivities, etc.

So a 1st order pressure pair will give something like a dipolar pattern.
More than three pressure elements can give more like a cardiod. And a
'velocity' sensor can take the place of two pressure elements in the array.
Hence the "pressure and pressure gradient" method.

If, like Phil, you're puzzled by this, have a look at:

Directional Microphones H. F. Olsen
JAES October 1967 (Also in the old 'Microphones' book of reprints by AES)

as an example. See his first figure where he explains 1st order gradient
mics before going on to look at end-fire arrays, etc.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Sat, 23 Mar 2013 09:26:44 +0000 (GMT), Jim Lesurf
wrote:

In article , Eiron
wrote:
On 22/03/2013 19:03, Dave Plowman (News) wrote:
In article , Eiron
wrote:
Those electret microphone capsules are quite good but
omnidirectional. Is there any way to modify them to give a different
pattern? Modify the case, or some suitable shaped enclosure?

I'd say not. Producing a cardiod capsule requires precision
engineering. So cheaper to simply buy one.

You're right. They seem to be 50p each at Farnell. It looks like they
just have a few precision drilled holes in the back. I wonder if that's
the only difference.

In principle you can get two pressure-sensing mics and place them slightly
apart. Then connect so that their outputs 'cancel'. This produced a setup
that outputs the 'differential' in pressure along the direction between
them. So gives a cardiod-ish shape. But although neat in theory you may
find it hard to get such a system working well. And it would need frequency
(wavelength) correction. So as Dave says, there is a lot of detail to sort
out. Simpler to buy the tool for the job unless you are interested in the
DIY experimentation involved and have the time.


No, the way you do it is to take an omni, but introduce a calibrated
leak into the back, so it is starting to tend towards a velocity
sensor. If you get that calibration dead right, you have equal outputs
of pressure and velocity, resulting in a cardioid. The heavy lifting
comes in getting that perfect match across a decently wide frequency
range. That involves a lot of work with ports, tuning tubes and
goodness only knows what else. With cardioids, you pay your big money
for a clean off-axis response.

d

"Erron"

Those electret microphone capsules are quite good but omnidirectional.
Is there any way to modify them to give a different pattern?
Modify the case, or some suitable shaped enclosure?

** No.


There are some digital recorders available with what looks,
though I haven't looked too closely, like two electret capsules
at right angles. If they are omnidirectional,

** Guess what ?

Wot a ****ing moron ...


..... Phil

On 23/03/2013 10:15, Phil Allison wrote:
"Erron"

Those electret microphone capsules are quite good but omnidirectional.
Is there any way to modify them to give a different pattern?
Modify the case, or some suitable shaped enclosure?

** No.


There are some digital recorders available with what looks,
though I haven't looked too closely, like two electret capsules
at right angles. If they are omnidirectional,

** Guess what ?

Wot a ****ing moron ...

Thanks Phil for your erudite and informative reply.
Any idea how noise-cancelling microphones work?

--
Eiron.