dB and sound pressure

[H]

I can't quite grasp the connection between microphone sensitivity and
sound pressure level.

I am trying to use a plain electret microphone to detect a BB gun
bullet breaking through the paper target.

The bullet creates a pulse of about 2.5V measured directly on the
microphone's output. The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.

How loud is that sound, measured in the normal, everyday dB scale?

 

[John Fields]

On Thu, 10 Sep 2009 21:49:21 +0200, H <not@availab.le> wrote:

I can't quite grasp the connection between microphone sensitivity and
sound pressure level.

I am trying to use a plain electret microphone to detect a BB gun
bullet breaking through the paper target.

The bullet creates a pulse of about 2.5V measured directly on the
microphone's output. The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.

How loud is that sound, measured in the normal, everyday dB scale?

---
http://www.google.com/search?hl=en&source=hp&q=microphone+sensitivity&btnG=Google+Search&rlz=1R2GPEA_en&aq=f&oq=&aqi=

 

[Phil Allison]

"H"

I can't quite grasp the connection between microphone sensitivity and
sound pressure level.

I am trying to use a plain electret microphone to detect a BB gun
bullet breaking through the paper target.

The bullet creates a pulse of about 2.5V measured directly on the
microphone's output.

** That electret mic is not handling the pressure, 2.5 volts is well
outside its linear range.

The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.

How loud is that sound, measured in the normal, everyday dB scale?

** Would be over 146 dB SPL, if genuine.

( 8 dB + 44 dB + 94 dB )



....... Phil

 

[Phil Allison]

"BobG"

The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.
========================================

I thought the 0dB pressure reference was 1mw/10 dynes/cm^2 ??


** Mic sensitivity used to be quoted in mV per microbar, where
1 microbar = 1 dyne per sq cm = 0.1 Pa.

1 bar is very close to the standard atmospheric pressure and air
pressure was for a long time quoted in millibars by weather bureaus.

The above mic works out as 0.63mV per ub - which is to say that
a 74 dB SPL at 1 kHz would cause the mic to output 0.63mV rms.



...... Phil

 

[BobG]

 The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.
=======================================I thought the 0dB pressure reference was 1mw/10 dynes/cm^2 ??

(I know that 1mw across 600ohms is .775v. Sound guys have a head full
of numbers like that)

 

[Bob Masta]

On Fri, 11 Sep 2009 11:18:12 +1000, "Phil Allison"
<phil_a@tpg.com.au> wrote:

"H"
I can't quite grasp the connection between microphone sensitivity and
sound pressure level.

I am trying to use a plain electret microphone to detect a BB gun
bullet breaking through the paper target.

The bullet creates a pulse of about 2.5V measured directly on the
microphone's output.


** That electret mic is not handling the pressure, 2.5 volts is well
outside its linear range.



The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.

How loud is that sound, measured in the normal, everyday dB scale?


** Would be over 146 dB SPL, if genuine.

( 8 dB + 44 dB + 94 dB )

This is indeed the instantaneous SPL (assuming, as
you note, that the 2.5V is correct). Just a note
to the OP, however, that this number will not
correlate well with "loudness" since the sound is
very brief. It will certainly sound a *lot*
softer than (say) a rock band whose output
measures 146 dB SPL on a sound level meter.

Another issue that seems to be generally
overlooked by the general public is that SPL
measurements give the loudness at the specific
location of the measuring mic. In most cases, SPL
falls off greatly with distance (unless you are
very close -- in the "near field" -- to a very
large sound source, for example).

I suspect the OP's microphone was closer to the
target than a typical listener's ear. And since
the listener will surely not be in the near field
(which in this case is probably an inch away or
less), the sound fall-off will be roughly a square
law.

Some formulas for working with sound:
<http://www.daqarta.com/dw_0mdd.htm>

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!

 

[steve]

On Sep 11, 5:32 pm, N0S...@daqarta.com (Bob Masta) wrote:

On Fri, 11 Sep 2009 11:18:12 +1000, "Phil Allison"





phi...@tpg.com.au> wrote:

"H"
I can't quite grasp the connection between microphone sensitivity and
sound pressure level.

I am trying to use a plain electret microphone to detect a BB gun
bullet breaking through the paper target.

The bullet creates a pulse of about 2.5V measured directly on the
microphone's output.

**  That electret mic is not handling the pressure, 2.5 volts is well
outside its linear range.

 The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.

How loud is that sound, measured in the normal, everyday dB scale?

**  Would be over 146  dB SPL,  if genuine.

 (  8 dB  +  44 dB  +  94 dB  )

This is indeed the instantaneous SPL (assuming, as
you note, that the 2.5V is correct).  Just a note
to the OP, however, that this number will not
correlate well with "loudness" since the sound is
very brief.  It will certainly sound a *lot*
softer than (say) a rock band whose output
measures 146 dB SPL on a sound level meter.

Another issue that seems to be generally
overlooked by the general public is that SPL
measurements give the loudness at the specific
location of the measuring mic.  In most cases, SPL
falls off greatly with distance (unless you are
very close -- in the "near field" -- to a very
large sound source, for example).  

I suspect the OP's microphone was closer to the
target than a typical listener's ear.  And since
the listener will surely not be in the near field
(which in this case is probably an inch away or
less), the sound fall-off will be roughly a square
law.

Some formulas for working with sound:
http://www.daqarta.com/dw_0mdd.htm

Best regards,

Bob Masta

              DAQARTA  v4.51
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
           FREE Signal Generator
        Science with your sound card!- Hide quoted text -

- Show quoted text -

----------------------------------------------------------------------------------------------------



Since we are on the topic of sound units, I would like to know what is
the output level (in volts, db, etc.) from a walkman earphone,
compared to, say, a small pocket radio.

Thanks

Steve

 

[Michael A. Terrell]

BobG wrote:

On Sep 12, 4:28 am, steve <kvst...@gmail.com> wrote:
Since we are on the topic of sound units, I would like to know what is
the output level (in volts, db, etc.) from a walkman earphone,
compared to, say, a small pocket radio.
=============================================
Go get a radioshack db meter and make some sort of acoustic coupler
from the earbuds to the mic, note spl level for some particular music
clip.. long sustained power chord??. Then measure volts during same
passage, and resistance of coil. Since 8 ohm speakers have about 6 ohm
resistance, I claim if the resistance is say 24 ohms, you can use 32
ohms as the estimated impedance. Calc power. V^2/Z. Repeat same calcs
for other transducer. Now you can compare sensitivites by repeatedly
doubling the power and adding 3dB of the weaker signal until the mWs
are the same. I think the earphone transducer is 'more efficient' at
delivering a certain spl per mW because of the inverse square law
relationship of transducer to eardrum.

Harbor Freight has a similar meter:

<http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92282>
$22.95


--
You can't have a sense of humor, if you have no sense!

 

[BobG]

On Sep 12, 4:28 am, steve <kvst...@gmail.com> wrote:

Since we are on the topic of sound units, I would like to know what is
the output level (in volts, db, etc.) from a walkman earphone,
compared to, say, a small pocket radio.
============================================Go get a radioshack db meter and make some sort of acoustic coupler

from the earbuds to the mic, note spl level for some particular music
clip.. long sustained power chord??. Then measure volts during same
passage, and resistance of coil. Since 8 ohm speakers have about 6 ohm
resistance, I claim if the resistance is say 24 ohms, you can use 32
ohms as the estimated impedance. Calc power. V^2/Z. Repeat same calcs
for other transducer. Now you can compare sensitivites by repeatedly
doubling the power and adding 3dB of the weaker signal until the mWs
are the same. I think the earphone transducer is 'more efficient' at
delivering a certain spl per mW because of the inverse square law
relationship of transducer to eardrum.

 

[Phil Allison]

"Bob Masta"
"Phil Allison"

"H"
I can't quite grasp the connection between microphone sensitivity and
sound pressure level.

I am trying to use a plain electret microphone to detect a BB gun
bullet breaking through the paper target.

The bullet creates a pulse of about 2.5V measured directly on the
microphone's output.


** That electret mic is not handling the pressure, 2.5 volts is well
outside its linear range.



The microphone's data sheet specifies a
sensitivity of -44dB, where 0dB is defined as 1V/Pa.

How loud is that sound, measured in the normal, everyday dB scale?


** Would be over 146 dB SPL, if genuine.

( 8 dB + 44 dB + 94 dB )


This is indeed the instantaneous SPL (assuming, as
you note, that the 2.5V is correct). Just a note
to the OP, however, that this number will not
correlate well with "loudness" since the sound is
very brief.

** The OP clearly asked for a SPL in dB.

Learn to read sometime - pal.

I suspect the OP's microphone was closer to the
target than a typical listener's ear.

** You bet it was.

And THAT is THE place he wants to read the SPL.

( snip rest of this wanker's irrelevant drivel )




..... Phil

 

[Phil Allison]

"steve" <kvsteve@gmail.com


The problem is that I am in India, which is thousands of miles away
from a Radio Shack.

There are db meter suppliers here, but could be rather expensive (for
El Cheapo, like me..?).

During better times, I had acquired a frequency meter, along with a
volt meter, which could also be used.

Since I have access to computers, an alternative could be to use
software.


** Make sure to get yerself some well calibrated software....

Idiot.



....... Phil

 

[steve]

On Sep 12, 11:33 am, BobG <bobgard...@aol.com> wrote:

On Sep 12, 4:28 am, steve <kvst...@gmail.com> wrote:> Since we are on the topic of sound units, I would like to know what is
the output level (in volts, db, etc.) from a walkman earphone,
compared to, say, a small pocket radio.

============================================> Go get a radioshack db meter and make some sort of acoustic coupler
from the earbuds to the mic, note spl level for some particular music
clip.. long sustained power chord??. Then measure volts during same
passage, and resistance of coil. Since 8 ohm speakers have about 6 ohm
resistance, I claim if the resistance is say 24 ohms, you can use 32
ohms as the estimated impedance. Calc power. V^2/Z. Repeat same calcs
for other transducer. Now you can compare sensitivites by repeatedly
doubling the power and adding 3dB of the weaker signal until the mWs
are the same. I think the earphone transducer is 'more efficient' at
delivering a certain spl per mW because of the inverse square law
relationship of transducer to eardrum.

----------------------------------------------------------------------------------------------------

Yes, thanks.

The problem is that I am in India, which is thousands of miles away
from a Radio Shack.

There are db meter suppliers here, but could be rather expensive (for
El Cheapo, like me..?).

During better times, I had acquired a frequency meter, along with a
volt meter, which could also be used.

Since I have access to computers, an alternative could be to use
software.

Steve

 

[Bob Masta]

On Sat, 19 Sep 2009 23:30:31 -0700 (PDT), steve
<kvsteve@gmail.com> wrote:

On Sep 12, 11:33=A0am, BobG <bobgard...@aol.com> wrote:
On Sep 12, 4:28=A0am, steve <kvst...@gmail.com> wrote:> Since we are on t=
he topic of sound units, I would like to know what is
the output level (in volts, db, etc.) from a walkman earphone,
compared to, say, a small pocket radio.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Go get a radioshack db meter and make some sort of acoustic coupler
from the earbuds to the mic, note spl level for some particular music
clip.. long sustained power chord??. Then measure volts during same
passage, and resistance of coil. Since 8 ohm speakers have about 6 ohm
resistance, I claim if the resistance is say 24 ohms, you can use 32
ohms as the estimated impedance. Calc power. V^2/Z. Repeat same calcs
for other transducer. Now you can compare sensitivites by repeatedly
doubling the power and adding 3dB of the weaker signal until the mWs
are the same. I think the earphone transducer is 'more efficient' at
delivering a certain spl per mW because of the inverse square law
relationship of transducer to eardrum.

---------------------------------------------------------------------------=
-------------------------

Yes, thanks.

The problem is that I am in India, which is thousands of miles away
from a Radio Shack.

There are db meter suppliers here, but could be rather expensive (for
El Cheapo, like me..?).

During better times, I had acquired a frequency meter, along with a
volt meter, which could also be used.

Since I have access to computers, an alternative could be to use
software.

Steve

My Daqarta software includes a sound level meter
option, but please understand that you can't
measure an absolute sound level (like SPL) without
a complete calibrated system. The first thing you
will need is a calibrated microphone. A properly
calibrated microphone is expensive. Some
3rd-party suppliers will sell inexpensive mics
that they have calibrated, but you will pay for
their labor. (In other words, you may pay $100
for a $10 mic that they have calibrated.)

If you don't really need precision and are just
looking for comparisons (as you mention in your
original post), you can use an uncalibrated
microphone. The SPL reading won't really be true
SPL, but you can compare the *difference* between
SPL values obtained from different sources
measured with the same mic... with a few caveats:

First, note that microphones don't usually have
flat frequency responses. Since most people want
to measure the total sound over a particular
frequency range (A-weighted, etc), you might get
bogus comparison results if one sound source has a
different frequency response than another... one
might be putting out more power in a region that
the mic doesn't respond well to, while the other
might be emphasizing a region that the mic is
boosting.

If you are selecting a microphone for this, look
for "omnidirectional" as opposed to
"unidirectional" (or "cardioid", etc), since the
latter sacrifice frequency response to obtain
directionality.

You may be able to buy an inexpensive raw mic
cartridge for a few dollars, and make your own
mic. The Panasonic WM-61A is a good choice for
flat response over a wide frequency range, though
it is not especially sensitive.

Also, with software sound level meters you must
either always run with the sound card sensitivity
at maximum (so you know where you are) or you must
calibrate the sound card input controls. Daqarta
can do that automatically, using a loopback
connection from the output. It may take 10-15
minutes or more as it scans over the control
range, but when you are done you can change ranges
and Daqarta will keep track of the attenuation so
its displays compensate.

The above refers only to the *relative*
attenuation of the sound card mixer controls, so
that Daqarta knows when you've set (say) 20 dB of
attenuation that the input must have been 20 dB
larger than what it is measuring. This is a
completely separate issue from *absolute*
calibration, so that it knows what reading
constitutes one Volt, etc. There is a separate
procedure for that, which requires that you either
have a known source or a known measuring device.
You'd need both relative and absolute calibration,
along with a microphone calibration, to measure
true SPL.

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!

 

[H]

On Fri, 11 Sep 2009 12:32:11 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

( 8 dB + 44 dB + 94 dB )

This is indeed the instantaneous SPL (assuming, as
you note, that the 2.5V is correct).

I just did the measurement again. It is correct. I also tried changing
the distance between impact and microphone. At about a foot (the size
of the sheet of paper I am using for a target), I still get about 1V
peak.

Just a note
to the OP, however, that this number will not
correlate well with "loudness" since the sound is
very brief.

I understand that. The pulse is about 40us long, so it'll probably
sound like tiny pop, just like you'd expect when something pierces a
sheet of paper at high speed.

It will certainly sound a *lot*
softer than (say) a rock band whose output
measures 146 dB SPL on a sound level meter.

I can't hear it at all over the mechanical noise from the rifle
itself. The important thing here is that the signal is very strong, so
it should be easy to detect it and feed to a microcontroller for
timing measurements.

Thanks everyone for the comments.