sound meter

Mon Apr 26 14:28:50 AKDT 2004

Actually 3dB is double the sound POWER level.  It is a factor of square root of 2 (1.41x) on sound pressure level (SPL), which is what a sound meter typically measures.  The lowest limit of a difference in sound level that the human ear can detect is usually taken to be about 1 dB (1.12x on SPL), and that is under ideal conditions where one sound comes right after the other.

Where you first listen to one engine, stop it, take the time to move it out and bring in another airplane and start another engine with different frequency content etc. - not being able to discern a 3 dB difference in SPL is not unexpected.  That doesn't mean you can't hear a difference.  The human ear is incredibly sensitive to tiny changes in pitch (frequency content).  But for quantitative assessment of sound amplitude its pretty pathetic.  Differences in frequency content and duration change the perceived sound amplitude, called loudness as opposed to sound level.

I agree it would be nice to have a low cost calibrator, but for the same reasons low cost sound meters aren't real accurate, low cost calibrators wouldn't be any better. 

Ed

John Ferrell <johnferrell at earthlink.net> wrote:
As the Site Director at Worlds in Pensecola, I watched the noise checks very
carefully. There was at least one instance where my ears could not percieve
the difference between 94 and 97 db. Of course that is irrelevant since I
got my hearing aids last year...

It would be nice to have an affordable calibration device for the RS meters.
They work well as comparison devices.

John Ferrell
http://DixieNC.US

----- Original Message ----- 
From: "Tony Stillman" 
To: 
Sent: Monday, April 26, 2004 11:52 AM
Subject: Re: sound meter

> Brian:
>
> Do you realize that 3 DB is DOUBLE the sound level? That's not even
> close.....
>
> Tony Stillman
> Radio South
> 3702 N. Pace Blvd.
> Pensacola, FL 32505
> 1-800-962-7802
> www.radiosouthrc.com
> ----- Original Message ----- 
> From: "Brian Young" 
> To: 
> Sent: Monday, April 26, 2004 8:34 AM
> Subject: Re: sound meter
>
>
> > Do they calibrate the meter at the NATS?
> >
> > I think the RS meters are within spec if they are +/-
> > 3DB.
> >
> >
> > --- "ed.schummer" wrote:
> > > Couldn't agree more. Most of these meters work
> > > pretty well when measuring
> > > relative levels of pink noise, such as in
> > > calibrating control room levels to
> > > a SMPTE standard, or such. The problem comes up
> > > when there is a dominant
> > > frequency that is much louder than the others, as
> > > often occurs with our
> > > planes. We once tested a bunch of these meters, and
> > > although on average
> > > they were pretty good, I have seen as much as 6 dB
> > > difference from one meter
> > > to another at single frequencies, both meters
> > > calibrated to the same level
> > > with pink noise....
> > >
> > > Ed
> > >
> > >
> > > ----- Original Message ----- 
> > > From: "Ed White" 
> > > To: 
> > > Sent: Sunday, April 25, 2004 5:22 AM
> > > Subject: Re: sound meter
> > >
> > >
> > > > At work I have access to a large acoustics test
> > > lab
> > > > and borrowed a portable calibrator. My RS sound
> > > meter
> > > > was off up to + AND - 3 dB. It varied
> > > considerably
> > > > with frequency. At lower frequencies (<1 KHz) it
> > > read
> > > > low by 2-3 dB, at higher frequencies (>1 KHz) it
> > > read
> > > > high by 2-3 dB. Pretty much varied all over the
> > > > place.
> > > >
> > > > The message is don't get hung up on 95 dB vs. 96
> > > dB.
> > > > The RS meter will give you a ballpark absolute
> > > value,
> > > > and as Earl said will give you decent relative
> > > > measurements.
> > > >
> > > > Ed
> > > >
> > > > --- "Del K. Rykert" wrote:
> > > > > My radio shack soundmeter was off by almost 3 dB
> > > > > when it was calibrated.
> > > > >
> > > > > Del
> > > > > ----- Original Message ----- 
> > > > > From: Earl Haury
> > > > > To: discussion at nsrca.org
> > > > > Sent: Saturday, April 24, 2004 9:05 AM
> > > > > Subject: Re: sound meter
> > > > >
> > > > >
> > > > > Steve
> > > > >
> > > > > It matters a lot. The rules specify dB-A, so
> > > use
> > > > > the A scale. Without a calibrator most sound
> > > meters,
> > > > > even the expensive variety, are really only good
> > > for
> > > > > comparative measurements. So - use it to find
> > > what
> > > > > makes the airplane quieter but don't get fixated
> > > on
> > > > > the absolute number without a calibrated
> > > reference.
> > > > >
> > > > > Earl
> > > >
> > > >
> > > >
> > > >
> > > >
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