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jonbach@pugetsystems.com
science forum beginner
Joined: 02 Apr 2006
Posts: 4
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 Posted: Sun Apr 02, 2006 11:27 pm Post subject:
Semi-Accurate Measurement of <20dB Levels
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I'm looking for a good way to measure the noise levels of quiet
computers in dB(A). Since it is very expensive to get a decibel meter
to measure levels that low (and even with no budget limitation, I can't
even find one!), I'm looking into alternatives.
I'm thinking about just using a parabolic amplifier for our microphone,
and then calibrating to known levels. Am I just missing something, or
is that a solid route to getting the measurements I need?
I don't need absolute precision, but need it close enough that I can at
least have confidence about the numbers I get!
Thank you,
Jon Bach
Puget Custom Computers
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http://www.pugetsystems.com
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DaveL
science forum beginner
Joined: 11 Nov 2005
Posts: 37
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| Posted: Sun Apr 02, 2006 11:56 pm Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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I no expert, so maybe I should not comment, but it would seem to me that you
could move the decibel meter closer to the source and then used a formula to
calculate the decibels at a farther distance.
DaveL
<jonbach@pugetsystems.com> wrote in message
news:1144020439.539510.20330@v46g2000cwv.googlegroups.com...
| Quote: | I'm looking for a good way to measure the noise levels of quiet
computers in dB(A). Since it is very expensive to get a decibel meter
to measure levels that low (and even with no budget limitation, I can't
even find one!), I'm looking into alternatives.
I'm thinking about just using a parabolic amplifier for our microphone,
and then calibrating to known levels. Am I just missing something, or
is that a solid route to getting the measurements I need?
I don't need absolute precision, but need it close enough that I can at
least have confidence about the numbers I get!
Thank you,
Jon Bach
Puget Custom Computers
------------------------------------
http://www.pugetsystems.com
------------------------------------
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jonbach@pugetsystems.com
science forum beginner
Joined: 02 Apr 2006
Posts: 4
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| Posted: Mon Apr 03, 2006 1:23 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Very true....but measurements are usually taken from 1 meter...with
that plan I worry about getting a measurement of just a component of
the computer instead of the computer as a whole. |
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jonbach@pugetsystems.com
science forum beginner
Joined: 02 Apr 2006
Posts: 4
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| Posted: Mon Apr 03, 2006 1:26 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Though I suppose I run the same risk with the parabolic microphone, if
it has a well defined "target" area. Maybe only testing it will tell
me for sure! Kind-of an expensive test though, if it doesn't work
well. |
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Tom Harper
science forum beginner
Joined: 09 Jul 2005
Posts: 16
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| Posted: Mon Apr 03, 2006 1:43 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Which frequency are you hoping to measure less than 20dB?
It should not be difficult to find a SLM with this kind of sensitivity,
although it would have to be a proffessional quality one. You could
hire the meter if it was only a one off measurement.
Tom |
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jonbach@pugetsystems.com
science forum beginner
Joined: 02 Apr 2006
Posts: 4
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| Posted: Mon Apr 03, 2006 2:24 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Whatever frequencies you can hear  It is intended to be a
measurement of the quietness of the computer...pretty subjective. |
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Herb Singleton
science forum beginner
Joined: 04 May 2005
Posts: 46
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| Posted: Mon Apr 03, 2006 4:24 pm Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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In article <1144020439.539510.20330@v46g2000cwv.googlegroups.com>,
jonbach@pugetsystems.com wrote:
| Quote: | I'm looking for a good way to measure the noise levels of quiet
computers in dB(A). Since it is very expensive to get a decibel meter
to measure levels that low (and even with no budget limitation, I can't
even find one!), I'm looking into alternatives.
|
In addition to finding an SLM/mic combo that can measure that low (you
should be able to find 1-inch mics with a self-noise lower than 10 dBA)
you also need to have an *environment* where the ambient noise levels
are lower than 20 dBA. Do you have access to an anechoic chamber or some
other area where the ambient noise levels are that low?
Herb |
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avare
science forum beginner
Joined: 27 Mar 2006
Posts: 4
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| Posted: Tue Apr 04, 2006 6:35 pm Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Several products are the market that will measure to that level. The
big problem I am detecting is that you are not familair with what you
hoping for entails. The usual way is to determine total power level
using a REVERBERATION chamber, and then measuring the directivity of
the sound using an ANECHOIC chamber. Aside from their name
descriptors, the chambers themselves are very quiet. All three things
(live acoustics, dead acoustics, and quiet acoustics) are expensive.
Good luck!
Andre |
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Raoul Duke
science forum beginner
Joined: 03 Oct 2005
Posts: 10
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| Posted: Mon Apr 10, 2006 5:15 pm Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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"avare" <avare@hotmail.com> wrote in news:1144175728.069525.273960
@u72g2000cwu.googlegroups.com:
| Quote: | Several products are the market that will measure to that level. The
big problem I am detecting is that you are not familair with what you
hoping for entails. The usual way is to determine total power level
using a REVERBERATION chamber, and then measuring the directivity of
the sound using an ANECHOIC chamber. Aside from their name
descriptors, the chambers themselves are very quiet. All three things
(live acoustics, dead acoustics, and quiet acoustics) are expensive.
Good luck!
Andre
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Definately go with a sound intensity map of the whole computer -in 3D of
course! |
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Greg Locock
science forum Guru Wannabe
Joined: 28 May 2005
Posts: 111
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| Posted: Thu Apr 13, 2006 9:07 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Raoul Duke <RaoulDuke@PoloLounge.ca> wrote in
news:Xns97A172891999CRaoulDukePoloLoungec@198.80.55.250:
| Quote: |
Definately go with a sound intensity map of the whole computer -in 3D of
course!
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Just in case you were tempted to take that seriously, that is a waste of
time.
Cheers
Greg Locock |
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Angelo Campanella
science forum Guru Wannabe
Joined: 08 May 2005
Posts: 226
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| Posted: Sat Apr 15, 2006 3:31 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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jonbach@pugetsystems.com wrote:
| Quote: | I'm looking for a good way to measure the noise levels of quiet
computers in dB(A). Since it is very expensive to get a decibel meter
to measure levels that low (and even with no budget limitation, I can't
even find one!), I'm looking into alternatives.
|
The suggestion by DaveL is practical. First of all, you need to be
aware of the normal threshold of hearing, which, in octave bands, is a
few dB positive at 1000-4000Hz and rises above and below that frequency
range (takes more level to be heard).
Figuring that you want to have your measurement apparatus to have a
noise floor below that by as much as 10 dB, then you need to have the
sound level meter system to have a threshold around 0 dB in that
1000-0000 Hz range. The only microphones I have ever had tat comes close
to that is a 1" condenser microphone. The 1/2" mics have a noise floor
about 10 dB and more above that.
But getting closer to the computer equipment is the most reliable way
to get good data. Since you are willing to settle for "Approximate"
values, extrapolation by inverse square law will give you he answers you
want. For instance, If you measure various peripherals or the CPU box or
a lap top, at a distance of one foot from what you believe to be the
noise center (fan discharge opening, etc., then if you want the vale
that should be at one meter, that's about 10 dB less.
| Quote: | I'm thinking about just using a parabolic amplifier for our microphone,
and then calibrating to known levels. Am I just missing something, or
is that a solid route to getting the measurements I need?
|
The problem with a parabolic "amplifier" (I think you mean a "parabolic
reflector") is that it has gain proportional with frequency; another
variable you do not want to fuss with at this stage. Just find a good
quiet room (I can get about 27 dBA at night in my home office), and set
your existing equipment microphone closer and closer to a test unit.
When the measured level rises 6 dB when you halve the distance, you know
you are getting proper data (the test sound is well above the room
background.)
| Quote: | I don't need absolute precision, but need it close enough that I can at
least have confidence about the numbers I get!
|
You might tell us what the "noise floor" of you unit is (just cover the
microphone with an inactive calibrator, and read what's indicated).
Also get few close-up readings and tell us the result. You can measure
right up to any surface (I have often measured about 1/2" from walls
that I hear sound coming from). Just keep the microphone out of any air
currents (if you can feel an air current on you cheek, it is too much).
Place the microphone an inch or two aside from that blast. (I can feel
such a mini blast coming out of this T43 Think Pad, side discharge.
Angelo Campanella |
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Angelo Campanella
science forum Guru Wannabe
Joined: 08 May 2005
Posts: 226
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| Posted: Sat Apr 15, 2006 3:32 am Post subject:
Re: Semi-Accurate Measurement of <20dB Levels
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Greg Locock wrote:
| Quote: | Raoul Duke <RaoulDuke@PoloLounge.ca> wrote in
news:Xns97A172891999CRaoulDukePoloLoungec@198.80.55.250:
Definately go with a sound intensity map of the whole computer -in 3D of
course!
Just in case you were tempted to take that seriously, that is a waste of
time.
|
i.e. bigger is not always better.
Sound Intensity lines pockets of instrument makers and professors.
Ang. C. |
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