In article jBh4d.90618$D%.43447@attbi_s51 writes:

Now you have my attention. Why won't small omnis work in a Decca
tree? I really need to know. Thanks,

The Decca Tree mic arrangement doesn't follow any particular rules but
just happens to work because of the pattern characteristics of the
Neumann M50 that makes three mics a few feet apart in a triangle a
"Decca Tree." Anything else is just three mics a few feet apart with
the associated phase problems. Nothing special.

You may be able to rig something with partially absorbent baffles to
approximiate the high frequency directivity of the M50. If it works
for you, name it the Norm Tree. (or something)

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

normanstrong wrote:

Why won't small omnis work in a Decca
tree? I really need to know.

Because small omnis have truly omni polar patterns, even at high frequencies. The Decca Tree works by taking advantage of the HF beaminess of the sphere-mounted moni in an M50.

Josephson and Schoeps both sell add-on spheres for use with small (but not fractured PZM small) omnis. Think 20-22mm diameter bodies.

normanstrong wrote:

Why won't small omnis work in a Decca
tree? I really need to know.

Because small omnis have truly omni polar patterns, even at high frequencies. The Decca Tree works by taking advantage of the HF beaminess of the sphere-mounted moni in an M50.

Josephson and Schoeps both sell add-on spheres for use with small (but not fractured PZM small) omnis. Think 20-22mm diameter bodies.

"Scott Dorsey" wrote in message
...
normanstrong wrote:
Scott Dorsey writes:

BUT, since a small omni won't work worth a damn in a Decca tree
anyway, it
is sort of academic.

Now you have my attention. Why won't small omnis work in a Decca
tree? I really need to know. Thanks,

Because you won't get any amplitude differences between channels,
just
exaggerated phase differences. What makes a Decca tree work the way
it
does is the directionality at high frequencies that you get from the
M-50.

The original idea of the Decca tree was to use the beaminess of the
M-50
to your advantage, and it does so very well. But it does not work
very
well with mikes that have significantly different characteristics.

Interesting. Is it true that the M-50's were all facing forward? If
so, I fail to see how the beaminess will work. Or are the mikes
facing outwards? Perhaps I should read up a bit more on the subject.
It was my understanding that the Decca tree depended strictly on time
of arrival cues.

Norm

"Scott Dorsey" wrote in message
...
normanstrong wrote:
Scott Dorsey writes:

BUT, since a small omni won't work worth a damn in a Decca tree
anyway, it
is sort of academic.

Now you have my attention. Why won't small omnis work in a Decca
tree? I really need to know. Thanks,

Because you won't get any amplitude differences between channels,
just
exaggerated phase differences. What makes a Decca tree work the way
it
does is the directionality at high frequencies that you get from the
M-50.

The original idea of the Decca tree was to use the beaminess of the
M-50
to your advantage, and it does so very well. But it does not work
very
well with mikes that have significantly different characteristics.

Interesting. Is it true that the M-50's were all facing forward? If
so, I fail to see how the beaminess will work. Or are the mikes
facing outwards? Perhaps I should read up a bit more on the subject.
It was my understanding that the Decca tree depended strictly on time
of arrival cues.

Norm

"normanstrong" wrote in message ...

Interesting. Is it true that the M-50's were all facing forward? If
so, I fail to see how the beaminess will work. Or are the mikes
facing outwards? Perhaps I should read up a bit more on the subject.
It was my understanding that the Decca tree depended strictly on time
of arrival cues.

Norm

When I set up a decca tree, I face the side mics slightly forward, but
mostly outward. The front mic is positioned straight ahead. With standard
omnis that lack the beaminess, you don't end up with the exaggerated timing
differences between microphones. Low frequencies on the M50 are quite
omni-directional, but as you go higher in frequency, you get more
directionality.

The higher frequency information is what will often give us the directional
information in a stereo configuration. With a lack of directionality on a
good set of omnis, all frequencies are going to all microphones and
therefore you loose some of your imaging. If you are effectively cutting
off certain parts of the sound from certain microphones, you'll end up with
a much better image.

I can't afford a set of M50's (or even M150's) so I've had good luck with
the Schoeps MK21 capsule for decca tree work. I find that while it is an
approximation of the pattern in an M50, they are one of the closer mics out
there to the pattern I'd want.

--Ben

--
Benjamin Maas
Fifth Circle Audio
Los Angeles, CA
http://www.fifthcircle.com

Please remove "Nospam" from address for replies

"normanstrong" wrote in message ...

Interesting. Is it true that the M-50's were all facing forward? If
so, I fail to see how the beaminess will work. Or are the mikes
facing outwards? Perhaps I should read up a bit more on the subject.
It was my understanding that the Decca tree depended strictly on time
of arrival cues.

Norm

When I set up a decca tree, I face the side mics slightly forward, but
mostly outward. The front mic is positioned straight ahead. With standard
omnis that lack the beaminess, you don't end up with the exaggerated timing
differences between microphones. Low frequencies on the M50 are quite
omni-directional, but as you go higher in frequency, you get more
directionality.

The higher frequency information is what will often give us the directional
information in a stereo configuration. With a lack of directionality on a
good set of omnis, all frequencies are going to all microphones and
therefore you loose some of your imaging. If you are effectively cutting
off certain parts of the sound from certain microphones, you'll end up with
a much better image.

I can't afford a set of M50's (or even M150's) so I've had good luck with
the Schoeps MK21 capsule for decca tree work. I find that while it is an
approximation of the pattern in an M50, they are one of the closer mics out
there to the pattern I'd want.

--Ben

--
Benjamin Maas
Fifth Circle Audio
Los Angeles, CA
http://www.fifthcircle.com

Please remove "Nospam" from address for replies

normanstrong wrote:


Interesting. Is it true that the M-50's were all facing forward? If
so, I fail to see how the beaminess will work. Or are the mikes
facing outwards? Perhaps I should read up a bit more on the subject.

They are toed-out, a varying amount depending on the room.

It was my understanding that the Decca tree depended strictly on time
of arrival cues.

If you depend only on time of arrival cues, you get great imaging below
around 1KC or so, and no imaging above that range. Your brain can't sort
out phase differences at high frequencies, so you need to preserve intensity
differences as well as phase differences in order to get a complete soundstage.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

normanstrong wrote:


Interesting. Is it true that the M-50's were all facing forward? If
so, I fail to see how the beaminess will work. Or are the mikes
facing outwards? Perhaps I should read up a bit more on the subject.

They are toed-out, a varying amount depending on the room.

It was my understanding that the Decca tree depended strictly on time
of arrival cues.

If you depend only on time of arrival cues, you get great imaging below
around 1KC or so, and no imaging above that range. Your brain can't sort
out phase differences at high frequencies, so you need to preserve intensity
differences as well as phase differences in order to get a complete soundstage.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Benjamin Maas wrote:

I can't afford a set of M50's (or even M150's) so I've had good luck with
the Schoeps MK21 capsule for decca tree work. I find that while it is an
approximation of the pattern in an M50, they are one of the closer mics out
there to the pattern I'd want.

I actually was surprised at how well the 1" B&K measurement mikes work. With
a ball around them, they are beamy enough to be surprisingly effective. Have
you ever tried any of the Gefell stuff? I have heard some of their large
diaphragm omnis used in a Decca tree and it sounded very close to the classic
Decca sound.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Benjamin Maas wrote:

I can't afford a set of M50's (or even M150's) so I've had good luck with
the Schoeps MK21 capsule for decca tree work. I find that while it is an
approximation of the pattern in an M50, they are one of the closer mics out
there to the pattern I'd want.

I actually was surprised at how well the 1" B&K measurement mikes work. With
a ball around them, they are beamy enough to be surprisingly effective. Have
you ever tried any of the Gefell stuff? I have heard some of their large
diaphragm omnis used in a Decca tree and it sounded very close to the classic
Decca sound.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."