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Default mic question (bass boost/phase)

hello everyone,

some mic designs like large-diaphragm cardioid condensers will have the
bass response boosted if you put the mic very close to the sound
source.

is this because of phase issues?

i learned that the presence peak that many mics have is due to phase
stuff inside the capsule, so i was wondering if this is somehow related.

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Scott Dorsey
 
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wrote:

some mic designs like large-diaphragm cardioid condensers will have the
bass response boosted if you put the mic very close to the sound
source.

is this because of phase issues?


It's because of the cardioid pattern. I think how the proximity effect
works is discussed in the FAQ. I know there was a long discussion of
this here a couple years ago.

EV used to also have a nice discussion of this on the glossy sheet for
the RE-20.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Justin Ulysses Morse
 
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In article , Scott Dorsey
wrote:

wrote:

some mic designs like large-diaphragm cardioid condensers will have the
bass response boosted if you put the mic very close to the sound
source.

is this because of phase issues?


It's because of the cardioid pattern. I think how the proximity effect
works is discussed in the FAQ. I know there was a long discussion of
this here a couple years ago.

EV used to also have a nice discussion of this on the glossy sheet for
the RE-20.
--scott



Here, read this:
https://www.neumann.com/infopool/dow...i=docu0002.PDF

ulysses
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wow, thanks for the link!

that's some thick, meaningful reading. i will read it bit by bit.

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David Satz
 
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Generic, the bass boost that you're talking about is called "proximity
effect." Unfortunately its cause is difficult to explain concisely. It
involves [a] the gradual change in shape of the wavefronts as sound
radiates outward from a point source (or something like one), and [b]
the fact that any pressure gradient transducer is exposed to the sound
field at more than one point.

A sound that originates in front of the diaphragm will eventually reach
the back of the capsule, too, but only after it has traveled a greater
distance. When a sound source is very close to the diaphragm and in
front of it, the inch or so of extra path length for the sound to reach
the back of the diaphragm (or the rear diaphragm in a dual-diaphragm
capsule) is proportionately quite significant. The sound waves are
spreading out in all directions, and the wavefronts, which initially
tend to be sharply curved near the sound's point of origin, tend to
flatten out gradually as the sound travels.

Try sketching a set of concentric circles plus a one-inch straight line
that intersects each of them in turn, and you'll see what I mean--the
farther the circles get from the point of origin, the more nearly the
section of arc will approximate the one-inch straight line.

Now if a wave is more nearly spherical when it strikes one side of the
capsule but more nearly plane when it strikes the other side, there
will be a greater resulting force than if the wavefront had the same
shape on both sides. The output of a pressure-gradient transducer is
proportional to the difference between the sound pressure at the front
and back of the capsule. So ultimately it's that discrepancy in
wavefront shape between the front and back of the capsule that causes
the bass boost.

As a corollary, note that a cardioid has no proximity effect 90 degrees
off axis, and that a supercardioid or a figure-8 will have stronger
proximity effect than the corresponding cardioid.

--best regards



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Bob Cain
 
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David Satz wrote:

Now if a wave is more nearly spherical when it strikes one side of the
capsule but more nearly plane when it strikes the other side, there
will be a greater resulting force than if the wavefront had the same
shape on both sides. The output of a pressure-gradient transducer is
proportional to the difference between the sound pressure at the front
and back of the capsule. So ultimately it's that discrepancy in
wavefront shape between the front and back of the capsule that causes
the bass boost.


I'd thought this too but came to wonder why the effect, as
described, would be at all frequency dependant.


Bob
--

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

A. Einstein
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