[[email protected]]

I understand that the more directional a mic is, the
more the bass will be exagerated as you get
quite close to the sound source.

But is the inverse true? Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?

[Don Pearce]

On 27 Jul 2006 00:27:46 -0700, wrote:

I understand that the more directional a mic is, the
more the bass will be exagerated as you get
quite close to the sound source.

But is the inverse true? Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?

No. In the far field all mics are nominally flat. Individual mics may
or may not have bass rolloff, but that is nothing to do with the polar
pattern.

Bass boost for directional mics is due to the fact that air velocity
does not follow an inverse square law in a sound field where the
radius of curvature is comparable to the wavelength. Pressure is
inverse square all the way to the source. Directional mics use a
combination of velocity and pressure, with omnis pure pressure and
figure eights pure velocity. Cardioids and hypercardioids are a
mixture of the two.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Phil Allison]

**Groper alert.


Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?



** At 30 feet there is no " proximity effect " - at all.

The mic's response will simply follow the published curve.

If you want more bass - just turn of that knob on the desk.




........ Phil

[[email protected]]

So why then do they say that an omni will be better at
retaining the bass when distance mic'ing, for example,
an orchestra?

[Mike Rivers]

wrote:
So why then do they say that an omni will be better at
retaining the bass when distance mic'ing, for example,
an orchestra?

They do?

An omni generally has flatter frequency response than a cardioid mic so
it more realistically captures the environment. Bass goes everywhere.
If you suppress it from one direction (like behind a cardioid mic) it
might sound like you haven't "preserved" it all.

[Don Pearce]

On 27 Jul 2006 04:29:21 -0700, wrote:

So why then do they say that an omni will be better at
retaining the bass when distance mic'ing, for example,
an orchestra?

"They" say all sorts of things. Choice of mic when distant miking is
generally not do with bass, but with how the room sounds. If it has a
really good acoustic, and the music needs it, go for an omni. If the
room is not great, but you have to use a distant mic, then go for a
directional mic. But bear in mind that the frequency response off axis
is generally nicer with an omni. Also, in general omni mics have more
low frequency extension than directional mics, usually limited only by
the electrical parameters.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Adrian Tuddenham]

Don Pearce wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Phil Allison]

"Adrian Tuddenham"


Which direction is off-axis with an omni?



** Any direction that in NOT on the central axis - ****WIT .






........ Phil

[Don Pearce]

On Thu, 27 Jul 2006 13:15:12 +0100, lid
(Adrian Tuddenham) wrote:

Don Pearce wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

Any direction that isn't normal to the diaphragm. Omnis are only omni
up to a few kHz - you can't fight geometry.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Scott Dorsey]

wrote:
I understand that the more directional a mic is, the
more the bass will be exagerated as you get
quite close to the sound source.

Right. Therefore many cardioids have a built-in bass cut, to compensate
for this.

But is the inverse true? Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?

For the most part, this is true, but for different reasons than the
proximity issues. It's much easier to build an omni capsule with
good low end than a cardioid.

The data sheet on a good microphone should have a chart on it which
lists the free-field response of the microphone (that is, the response
to a distant sound source). Some manufacturers will also include
response to a nearby source so you can see how the proximity effect
works with that mike. For the most part, data sheet plots are very
smoothed so you can't see details, and SOME manufacturers will fudge
the low end measurements completely because they don't have a chamber
capable of making the proper measurements. But guys like DPA and
Neumann can be more or less trusted for this sort of thing if you
understand the charts are usually third-octave measurements.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

wrote:
So why then do they say that an omni will be better at
retaining the bass when distance mic'ing, for example,
an orchestra?

It may not be. But it's easier to build an omni with a good low end
than a cardioid with a good low end. You can get a B&K 4145 that is
+/-1dB down to 2 Hz... you can't build a cardioid like that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Adrian Tuddenham wrote:
Don Pearce wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

That depends how omni the omni is. Lots of omnis aren't very omni.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Don Pearce wrote:
On Thu, 27 Jul 2006 13:15:12 +0100, lid
(Adrian Tuddenham) wrote:

Don Pearce wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

Any direction that isn't normal to the diaphragm. Omnis are only omni
up to a few kHz - you can't fight geometry.

Oh, yes you can. Check out the B&K mikes with the bullet-shaped incident
compensation devices, for instance. They make your omnis a lot more
omni at high frequencies.

Funny thing, though, I often find I prefer omnis to be a little bit beamy
for orchestral work.
--scott


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

[Don Pearce]

On 27 Jul 2006 09:50:13 -0400, (Scott Dorsey) wrote:

Don Pearce wrote:
On Thu, 27 Jul 2006 13:15:12 +0100, lid
(Adrian Tuddenham) wrote:

Don Pearce wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

Any direction that isn't normal to the diaphragm. Omnis are only omni
up to a few kHz - you can't fight geometry.

Oh, yes you can. Check out the B&K mikes with the bullet-shaped incident
compensation devices, for instance. They make your omnis a lot more
omni at high frequencies.


Well, they work by making the effective diameter much less, the
geometry for that diameter still applies. The bullet is a device for
improving the diffraction around the probe tip.

Funny thing, though, I often find I prefer omnis to be a little bit beamy
for orchestral work.
--scott

Quite, there is very little of musical value that arrives from behind
at high frequency - generally just unwanted noises.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Frank Stearns]

lid (Adrian Tuddenham) writes:

Don Pearce wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

Depends on the omni & frequency. Some become much more directional on axis
at HF. (This a key aspect of what makes the Decca Tree work, for example.)

Published polar patterns from reputable manufacturers will provide a
starting point.

Frank Stearns
Mobile Audio
--

[Jens Rodrigo]

Don Pearce wrote
Pressure is inverse square all the way to the source.

At the doupled distance from the sound source the
sound pressure is halved in the direct field.
I call that pressure law 1/r.
I think there is nothing inverse squared.
Look he p ~ 1/r
http://www.mathdaily.com/lessons/Inverse-square_law

Cheers Jens

[Don Pearce]

On Thu, 27 Jul 2006 17:33:44 +0200, "Jens Rodrigo"
wrote:

Don Pearce wrote
Pressure is inverse square all the way to the source.

At the doupled distance from the sound source the
sound pressure is halved in the direct field.
I call that pressure law 1/r.
I think there is nothing inverse squared.
Look he p ~ 1/r
http://www.mathdaily.com/lessons/Inverse-square_law

Cheers Jens

Quite right - it is the sound power that obeys the inverse square -
the pressure is 1/r.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Anahata]

Jens Rodrigo wrote:
Don Pearce wrote

Pressure is inverse square all the way to the source.

Look he p ~ 1/r
http://www.mathdaily.com/lessons/Inverse-square_law

Interesting. If you read on beyond that reference, it says that sound
*intensity* ~ 1 / (r squared)

Of course that's power, which is different from pressure in the same way
that electrical power has a square law relationship with voltage.

If only they expressed it in decibels, there wouldn't be any ambiguity...

Anahata

[Jens Rodrigo]

Anahata wrote:
Jens Rodrigo wrote:
Don Pearce wrote:
Pressure is inverse square all the way to the source.
Look he p ~ 1/r
http://www.mathdaily.com/lessons/Inverse-square_law
Interesting. If you read on beyond that reference, it says
that sound *intensity* ~ 1 / (r squared)
Of course that's power, which is different from pressure
in the same way that electrical power has a square law
relationship with voltage.


But my ears and the microphone of my sound level meter
are sensitive to the sound pressure and not sensitive to
sound intensity. They feel the inverse 1/r law and no square.

Cheers Jens

[Bob Cain]

wrote:
I understand that the more directional a mic is, the
more the bass will be exagerated as you get
quite close to the sound source.

But is the inverse true? Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?

Yes, but this is not about proximity effect. Any gradient mic will
have a LF rolloff. For equal intensity soundfields, the difference in
sound pressure between two points (the approximate pressure gradient)
gets less and less as you go down in frequency. It is avoidable above
a given knee by tuning of other mic parameters but it will eventually
set in as you go down. An omni is a pressure sensor rather than a
pressure gradient sensor so does not suffer from this LF rolloff.

The various patterns are made by the mix of an omni component and a
gradient component within the capsule. The fig 8 has no omni
component and is pure gradient. The hypercardiod has less omni in the
mix than a cardiod and the cardiod has an equal mix of the two. It is
this relative mixing that accounts for the ordering you describe.


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein

[Laurence Payne]

On 27 Jul 2006 00:27:46 -0700, wrote:

I understand that the more directional a mic is, the
more the bass will be exagerated as you get
quite close to the sound source.

But is the inverse true? Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?

No.

[Laurence Payne]

On 27 Jul 2006 04:29:21 -0700, wrote:

So why then do they say that an omni will be better at
retaining the bass when distance mic'ing, for example,
an orchestra?

Do they?

A mic designed for close vocals may be designed with a bass roll-off
in order to reduce proximity effect. That would make it unsuitable
for distance use.

[Laurence Payne]

On Thu, 27 Jul 2006 13:15:12 +0100, lid
(Adrian Tuddenham) wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

Precisely ! :-)

[Karl Winkler]

wrote:
I understand that the more directional a mic is, the
more the bass will be exagerated as you get
quite close to the sound source.

But is the inverse true? Say I'm 30 feet from a loud sound
source. I point a mic directly at the source from
30 feet away. Is it correct to say that an omni will
get me the most bass pickup, a cardioid a bit
less bass, a hyper yielding even less bass than
the cardioid, and a figure-8 getting the least
bass of them all?

In a general sense, you are on the right track. As others have pointed
out, most directional mics are rolled off deliberately so that within
their "normal" working distance (usually less than a meter) they are
relatively flat (due to proximity effect). But even at a meter, most
show significant rolloff. Omni mics indeed to not have proximity effect
and thus if they are designed to have flat bass response, they have it
at any distance. The typical high quality omni mic has flat bass
response down to or below 20 Hz, while a cardioid mic may be down 20 dB
at 20Hz at 1 meter.

The reasons engineers choose omnis for orchestral work IMO does have
something to do with this, along with other reasons.

Karl Winkler
http://www.lectrosonics.com
http://www.giovanniquartet.com

[hank alrich]

Laurence Payne lpayne1NOSPAM@dslDOTpipexDOTcom wrote:

(Adrian Tuddenham) wrote:

...bear in mind that the frequency response off axis
is generally nicer with an omni.

Which direction is off-axis with an omni?

Precisely ! :-)

Yes, and that depends on what portion of the spectrum is being
considered.

--
ha