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Natural Science Forum / Physics / Acoustics / September 2005



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In-ear microphones

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M J Carley - 13 Sep 2005 16:22 GMT
As it says in the title, I'm trying to source in-ear microphones for
use under a motorcycle helmet. Bruel and Kjaer make a set but I would
like to know if there are any others available which I could consider.

Thanks.

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Didier A. Depireux - 13 Sep 2005 18:31 GMT
> As it says in the title, I'm trying to source in-ear microphones for
> use under a motorcycle helmet. Bruel and Kjaer make a set but I would
> like to know if there are any others available which I could consider.

Etymotic's mikes work well, we have
http://www.etymotic.com/pro/er7c.aspx
You might also consider
http://www.etymotic.com/pro/er10c.aspx
depending on what you are looking for.

                        Didier

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Baltimore MD 21201 USA                           Fax: 1-410-706-2512

The Ghost - 13 Sep 2005 20:06 GMT
> As it says in the title, I'm trying to source in-ear microphones for
> use under a motorcycle helmet. Bruel and Kjaer make a set but I would
> like to know if there are any others available which I could consider.
>
> Thanks.

Max SPL?  Noise floor?  Frequency range?  Distortion?  Stability and
sensitivity to environmental factors?  Calibration requirements?  Cost
constraints?

http://www.knowlesacoustics.com/knowlesacoustics-
apps/specialty_productdetail.do?product_id=7
The Ghost - 13 Sep 2005 20:09 GMT
> As it says in the title, I'm trying to source in-ear microphones for
> use under a motorcycle helmet. Bruel and Kjaer make a set but I would
> like to know if there are any others available which I could consider.
>
> Thanks.

http://www.knowlesacoustics.com/images/data_sheets/FG.pdf
Tony - 14 Sep 2005 11:24 GMT
> http://www.knowlesacoustics.com/images/data_sheets/FG.pdf

How do you calibrate these?

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- but please don't use it, reply to the group.

The Ghost - 14 Sep 2005 20:53 GMT
>> http://www.knowlesacoustics.com/images/data_sheets/FG.pdf
>
> How do you calibrate these?

I don't like the use of the term calibration because it means different
things to different people.  If you mean, how does one measure sensitivity
and frequency response, the methodology will depend on both the frequency
range and the accuracy that is required.  The sensitivity and frequency
response of the Knowles FG can be measured to better than 0.5dB accuracy
over the frequency range from 20Hz to 20KHz in a small cylindrical coupler
utilizing a Bruel & Kjaer 4136 as a reference microphone and a back-driven
Bruel & Kjaer 4134 as a sound source.  Alternatively, you can measure it
under free-field conditions (using the method of substitution) against
either a Bruel & Kjaer 4135 at normal incidence or a Bruel & Kjaer 4136 at
90-degree incidence. In both approaches you will have to correct for the
magnitude and phase characteristics of the reference microphone that is
used.

 
GregS - 14 Sep 2005 21:45 GMT
>>> http://www.knowlesacoustics.com/images/data_sheets/FG.pdf
>>
[quoted text clipped - 15 lines]
>
>  

Are there any charts of their response curves on the internet?

greg
The Ghost - 14 Sep 2005 22:42 GMT
> In article <fd%Ve.36785$s35.6255@fe09.news.easynews.com>, The Ghost
> <theghost@hotmail.com> wrote:
[quoted text clipped - 23 lines]
>
> greg

Representative frequency response (pressure) plots for the various versions
are given in the data sheet at:

http://www.knowlesacoustics.com/images/data_sheets/FG.pdf

Because of its very small size, there is very little difference between the
pressure response and the free field response, and then only at the higher
audio frequencies (10KHz-20KHz).  If you need to know the free field
response for various angles of incidence at high frequencies you will have
to measure it directly for each capsule because there is considerable
variability in the pressure response itself at high frequencies.

 
Angelo Campanella - 16 Sep 2005 20:56 GMT
> How do you calibrate these?

    I think this has been answered OK with the pressure coupler comment.

    Also, be aware that the B&K pistonphone kit includes adapters for 1/4"
and 1/8" microphones. The 0.1" diameter of the knowles unit implies that
a thin tape wrap around it should provide a snug fit into the B&K
pistonphone adapter. Note also that virtually all calibrators
manufactured in the US and worldwide have all adhered to the standard
adapter set practiced by B&K for some decades. This would be my choice...
    Calibrators emitting a calibration level of 94 dB (1,000Hz), 102 dB
(1,000Hz), 114 dB (250Hz) and 124 dB (250Hz) are available today.

    Angelo Campanella
The Ghost - 17 Sep 2005 04:03 GMT
>> How do you calibrate these?
>
[quoted text clipped - 14 lines]
>
>      Angelo Campanella

The FET buffer that is built into the Knowles FG mic has an output dc
operating point that sits at approximately 300mV above ground.  Since the
nominal sensitivity of the FG is 25mV/Pa, the maximum peak symmetrical
sound pressure that can be applied to FG and avoid clipping is
approximately 10Pa or equivalently 114dB SPL.  Consequently the sensitivity
of the FG can not be accurately measured using a pistonphone such as the
Bruel & Kjaer 4220 which produces 124dB SPL.  In fact, exposing the FG to
124dB SPL (ie 10dB overpressure) may actually damaged it.
Bob Cain - 17 Sep 2005 06:48 GMT
>>>How do you calibrate these?
>>
[quoted text clipped - 23 lines]
> Bruel & Kjaer 4220 which produces 124dB SPL.  In fact, exposing the FG to
> 124dB SPL (ie 10dB overpressure) may actually damaged it.

This can be enhanced.  The internal FET is a source follower
with external connection to the drain, to the source and to
the ground side of the 22k source resistor.  It is self
biased such that Ids is a weak function of Vds (quiescent.)
 Thus, a higher Vs can be used and additional resistance
can be placed between the "ground" connection and circuit
ground to effect a higher bias point and wider signal swing.

The Knowles engineer I communicated with about this capsule
in Feb 2003 said that the Vs max in the data sheet is
conservative and that the buffer's quiescent Vds should not
actually much exceed 3V so that with a supply of 6V and
additional source resistance adjusted to split that at the
source, the 22.4 mV/Pa (-53 dB Re 1V/.1Pa) sensitivity
specified on the data sheet gives, before electrical
clipping, 133.5 dB SPL max.

It is possible, though not terribly likely that the
diaphragm can physically clip at the backplate before this
limit but since this is a back electret design such physical
contact would not be destructive due to the dialectric
electret coating on the backplate.

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

                                             A. Einstein

The Ghost - 19 Sep 2005 01:58 GMT
> This can be enhanced.  The internal FET is a source follower
> with external connection to the drain, to the source and to
[quoted text clipped - 20 lines]
>
> Bob

There is no such thing as a free lunch.  If you demand a higher SPL limit,
you need to prepared to accept more distortion, which you conveniently fail
to mention.  However, in light of yor past record of technical
incompetence, that minor oversight is certainly undersandable.  

That having been said, you still don't know squat about microphone
calibration.
Bob Cain - 19 Sep 2005 11:56 GMT
> There is no such thing as a free lunch.  If you demand a higher SPL limit,
> you need to prepared to accept more distortion

Of course.  I doubt anyone thought otherwise so it goes
without saying.

> That having been said, you still don't know squat about microphone
> calibration.

Depends on what kind of calibration.  I know lots about
finding the audio band impulse response (frequency response)
of a microphone and compensating it because that is what is
important to my work and it is that to which I refered.
Absolute sensitivity calibration is, of course, different
and more useful for other applications like noise
measurement.  I surmised the former and you are probably
correct that he intended the latter.

You simply don't know how to be civil, do you?  A pity.

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

                                             A. Einstein

The Ghsot - 21 Sep 2005 02:01 GMT
ship....snip


> You simply don't know how to be civil, do you?  A pity.
> Bob

I am civil to those who are civil to me.  The real pity is that you fail to
recognize your own blatant hypocrisy.  You have been posting defmatory
comments about me on the internet for the past five years.  You now falsely
accuse me of criminal behavior here and elswhere on a regular basis.  And
you have the audacity to criticize me for not being civil to you.  Your
arrogance is unbelievable and is clearly only superseded by your obvious
denial of reality.  

BTW, were you still beating your x at the time she dumped you, or were you
only verbally and psychologically abusing her?    
Bob Cain - 14 Sep 2005 19:21 GMT
>>As it says in the title, I'm trying to source in-ear microphones for
>>use under a motorcycle helmet. Bruel and Kjaer make a set but I would
[quoted text clipped - 3 lines]
>
> http://www.knowlesacoustics.com/images/data_sheets/FG.pdf

These are great little capsules.  I've used them for
measuring headphone response at entrance to the ear canal.
www.digikey.com was my source for them.  If you get them be
sure and spend the extra dollars for the leaded ones.
Soldering leads to the tiny things is extremely difficult
with a high probablility of destruction.  The solder pads
also detach very easily.

If you need to calibrate them against a reference mic they
can be mounted nearly coincident with it.  Because of their
tiny size, their effect on the sound field is negligable in
the audio band.

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

                                             A. Einstein

@.@ - 16 Sep 2005 00:19 GMT
> If you need to calibrate them against a reference mic they
> can be mounted nearly coincident with it.  Because of their
> tiny size, their effect on the sound field is negligable in
> the audio band.
> Bob

You clearly don't know much about the subject of microphone calibration.
Bob Cain - 16 Sep 2005 00:58 GMT
Gary Sokolich wrote:

His usual venom.

"" is actually Gary Sokilich.  He stalks me in all usenet
groups in which I participate.  Please ignore him and this
most recent marker of his stalking.

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

                                             A. Einstein

robert bristow-johnson - 16 Sep 2005 01:34 GMT
> Gary Sokolich wrote:
>
[quoted text clipped - 3 lines]
> groups in which I participate.  Please ignore him and this
> most recent marker of his stalking.

Bob, the best way to ignore him is to really ignore him.  at least that's
how i see it.  maybe if someone gets sucked into a bad post of his, we can
try to respond to that person (or that person and every other poster in that
thread save Gary) directly with e-mail.

now i will try to practice what i preach.

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r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

Gary Sokolich - 16 Sep 2005 02:28 GMT
> Bob, the best way to ignore him is to really ignore him.  at least
> that's how i see it.  maybe if someone gets sucked into a bad post of
> his, we can try to respond to that person (or that person and every
> other poster in that thread save Gary) directly with e-mail.
>
> now i will try to practice what i preach.

Thank you for that profound commentary.  Now go wipe that brown streak off
your nose.
Bob Cain - 16 Sep 2005 07:39 GMT
>>Gary Sokolich wrote:
>>
[quoted text clipped - 10 lines]
>
> now i will try to practice what i preach.

I hear you but if you read his response to my marker you may
understand why I've decided to mark all his stalking posts.

His bald face lies won't stand up to any scrutiny but should
I need to show the truth of the matter, as may become
necessary, I want to make it relatively easy.  I should have
begun doing it long ago but...

I'm really sorry for the noise but there are good reasons.
What I can absolutely promise is that I will make no more
than one such response to each offense.  They should be easy
to skip over without giving them any attention.

Bob
Signature


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

                                             A. Einstein

Gary Sokolich - 19 Sep 2005 02:46 GMT
> I hear you but if you read his response to my marker you may
> understand why I've decided to mark all his stalking posts.

The truth of the matter is that your so-called "marking" is just your
latest tactic, involving lies and false assertions, in your ongoing and
five year old obsessive crusade to besmirch and defame me on the internet.    


> His bald face lies won't stand up to any scrutiny but should
> I need to show the truth of the matter, as may become
> necessary, I want to make it relatively easy.  I should have
> begun doing it long ago but...

Actally, began doing it long ago. I have a two-inch thick three ring binder
documenting the lies, false accusations, defamatory and libelous statements
about me that you have made on the internet during the past five years.  
Based on the record it is your bald faced lies that won't stand up to
scrutiny.


> I'm really sorry for the noise but there are good reasons.

Name one.

> What I can absolutely promise is that I will make no more
> than one such response to each offense.  

Translation: you will make no more than one annoying and offensive response
to my each of my posts.

> They should be easy
> to skip over without giving them any attention.
> Bob

Excuse me while I reach for an air sickness bag because the truth of the
matter is that creating attention is your sole purpose.


Gary Sokolich - 16 Sep 2005 02:25 GMT
> "" is actually Gary Sokilich.  He stalks me in all usenet
> groups in which I participate.  Please ignore him and this
> most recent marker of his stalking.
> Bob

The truth of the matter is that you have been stalking and harassing me on
the internet for the past five years.  Furthermore, as the Google record
clearly demonstrates, when it comes to technical commentary, you are the
one who should be ignored.  
Porky - 16 Sep 2005 03:12 GMT
>> "" is actually Gary Sokilich.  He stalks me in all usenet
>> groups in which I participate.  Please ignore him and this
[quoted text clipped - 5 lines]
> clearly demonstrates, when it comes to technical commentary, you are the
> one who should be ignored.

 The record does indeed speak for itself, and it speaks loudly and clearly
against you Dr. Sokolich, as anyone who has done the research knows. I've
been killfiling any message you post in alt.music.home-studios, where you've
been trolling ever since you followed Bob Cain there, so I don't even see
your posts there anymore..
 I've been lurking here for a while, watching you post knowledgably in one
post and then spout vitriolic insults in the next, and I'm now certain that
you have serious mental issues and I think you should seek professional
help. Bob is posting on-topic, in response to others here, and it is you who
are attacking him, as everyone here can plainly see. If you don't like Bob,
or me, or anyone else, why not just ignore them? They certainly aren't
attacking you.
I apologize to everyone else, and I'll now go back to lurking. Don't bother
to reply Dr. Sokolich, or the Ghost, or "", or Wondering, or whatever other
alias you may choose because you're now in my killfile here as well.
The Ghost - 17 Sep 2005 02:58 GMT
>>> "" is actually Gary Sokilich.  He stalks me in all usenet
>>> groups in which I participate.  Please ignore him and this
[quoted text clipped - 25 lines]
> other alias you may choose because you're now in my killfile here as
> well.

The record also speaks loudly and clearly against you Mr. Mike Rieves.  
Specifically, it reveals a litany of insults, false and defamatory
assertions, and ad hominem attacks that you have bestowed upon me during
the past couple of years.   Your posting record in alt.music.home-studio
well as your present post here demonstrates unequivocally that the art of
vitriolic insults is your sole forte.  Accordingly, you are hardly in a
credible position to be pointing the vitriolic insult finger at me.  
Furthermore, on the basis of the record of your past posts in
alt.music.home-studio, if commenting knowledgeably in one post and then
spouting vitriolic insults in the next is an indication of serious mental
issues and the need for professional help, then you too have serious mental
issues and are in need of professional help.   As a matter of
clarification,  I did not "follow" Bob Cain to alt.music.home-studio as you
falsely assert.  The truth of the matter is that I what I followed to
alt.music.home-studio was the controversial discussion involving the
Doppler distortion issue, portions of which were cross-posted to several of
the audio groups.   As far as liking you and Bob, your are right.  I don't
like either of you and I have nothing but the utmost contempt for both of
you; and both of you have either explicitly stated or demonstrated in your
past posts that the feelings are mutual.   Regarding the issue of my
attacking Bob Cain, the truth of the matter is that Bob Cain has been
harassing and attacking me on the internet for the past five years.  As
both you and Bob Cain know, I am not one to turn the other cheek, and Bob
Cain can expect more of the same venom that he has repeately dished out my
way in the past.  Finally, as someone who has a long-standing history of
posting under the alias "porky" with an email address of noham@nospam.com,
you are hardly in a position to criticize anyone for faking their true name
and email address when posting.  Furthermore, while I do not know how/why
you selected "porky" as your user name, you have certainly lived up to the
label as a swine in every/all sense/meaning of the word.  
Porky - 17 Sep 2005 04:15 GMT
<snipped>

> Furthermore, while I do not know how/why
> you selected "porky" as your user name, you have certainly lived up to the
> label as a swine in every/all sense/meaning of the word.

  I chose the name "Porky" because it sounds like "por que" which is
Portuguese for "why" or "for what", which reflects my inquisitive nature. It
has nothing to do with swine. Have a nice life, Gary...
 
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