Sound and the Decibel

Marc O'Brien · Joined: 23 Jan 2008 Posts: 91

It all has to do with the area under the waves curve squaring with the
amplitude and then the area covered by the wave square-rooted with the
diameter on account of the d² component of the formula for the area of
a sphere.

Cool.

A sound twice as loud as the last, a Bel, by pressure ratio, has an
area under its curve 10 times that of the last. The square root of 10
is 3.16 meaning the pressure ratio has to increase by 3.16 in order
that the sound becomes twice as loud as the last.

To increase the area under the curve by 10 we have to have 10
identical sound sources. So one sound source becomes twice as loud, or
increases by 10 decibels or 1 Bel or ten 10ths of twice as loud, when
we stand 10 identical sound sources together.

Two identical sound sources double the area under the curve. This
means each dimension of the two area dimensions of the curve increase
by square-root 2 which is 1.414, this means the pressure ratio
increases by 1.414. Doubling the area under the curve increases the
sound pressure level by 3dB

Sound pressure and sound pressure level are not the same thing...

Archived from group: alt>hvac

Jeffrey Lebowski · Joined: 14 Jan 2008 Posts: 15

"Marc O'Brien" wrote in message@u10g2000prn.googlegroups.com...

> Sound pressure and sound pressure level are not the same thing...

http://forums.winamp.com/showthread.php?threadid=242059

--

.p.jm · Joined: 07 Aug 2007 Posts: 527

On Tue, 26 Feb 2008 07:50:56 -0800, "Jeffrey Lebowski"
wrote:

>
>"Marc O'Brien" wrote in message
>@u10g2000prn.googlegroups.com...
>
>> Sound pressure and sound pressure level are not the same thing...
>
>http://forums.winamp.com/showthread.php?threadid=242059

"How loud is 138 dB? Very, Very, VERY LOUD!
138 dB C-weighted is approximately equal to 30,000 Watts of sound
power.

The Chrysler Air Raid Siren is the loudest sound signaling device ever
built. The threshold of pain is 130 dB, anything above that level
causes immediate ear damage. The Chrysler Air Raid Siren produces that
level of sound nearly 200 feet in front of the projectors. "

One might question the wisdom of a protective device whose design
basically assures permanent injury to those it would try to
protect ....

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Tony Hwang · Joined: 07 Aug 2007 Posts: 207

Marc O'Brien wrote:

> It all has to do with the area under the waves curve squaring with the
> amplitude and then the area covered by the wave square-rooted with the
> diameter on account of the d² component of the formula for the area of
> a sphere.
>
> Cool.
>
> A sound twice as loud as the last, a Bel, by pressure ratio, has an
> area under its curve 10 times that of the last. The square root of 10
> is 3.16 meaning the pressure ratio has to increase by 3.16 in order
> that the sound becomes twice as loud as the last.
>
> To increase the area under the curve by 10 we have to have 10
> identical sound sources. So one sound source becomes twice as loud, or
> increases by 10 decibels or 1 Bel or ten 10ths of twice as loud, when
> we stand 10 identical sound sources together.
>
> Two identical sound sources double the area under the curve. This
> means each dimension of the two area dimensions of the curve increase
> by square-root 2 which is 1.414, this means the pressure ratio
> increases by 1.414. Doubling the area under the curve increases the
> sound pressure level by 3dB
>
> Sound pressure and sound pressure level are not the same thing...
>
>
>
Hey,
Be cool yourself. That is HS physics stuff!

Jeffrey Lebowski · Joined: 14 Jan 2008 Posts: 15

wrote in message@4ax.com...
>
> The Chrysler Air Raid Siren is the loudest sound signaling device ever
> built. The threshold of pain is 130 dB, anything above that level
> causes immediate ear damage. The Chrysler Air Raid Siren produces that
> level of sound nearly 200 feet in front of the projectors. "
>
> One might question the wisdom of a protective device whose design
> basically assures permanent injury to those it would try to
> protect ....
>

Mildly ironic yup.

--

Marc O'Brien · Joined: 23 Jan 2008 Posts: 91

On Feb 26, 4:06 pm, .p.jm@see_my_sig_for_address.com wrote:
> On Tue, 26 Feb 2008 07:50:56 -0800, "Jeffrey Lebowski"
> wrote:
>
>
>
> >"Marc O'Brien" wrote in message
> >@u10g2000prn.googlegroups.com...
>
> >> Sound pressure and sound pressure level are not the same thing...
>
> >http://forums.winamp.com/showthread.php?threadid=242059
>
> "How loud is 138 dB? Very, Very, VERY LOUD!
> 138 dB C-weighted is approximately equal to 30,000 Watts of sound
> power.
>
> The Chrysler Air Raid Siren is the loudest sound signaling device ever
> built. The threshold of pain is 130 dB, anything above that level
> causes immediate ear damage. The Chrysler Air Raid Siren produces that
> level of sound nearly 200 feet in front of the projectors. "

I've always read that 120dB is the pain threshold. 130dB is permanent
damage.

By the way, just for scribbles, 120 dB is 20 Pascals and 130dB is 63
Pascals.

> One might question the wisdom of a protective device whose design
> basically assures permanent injury to those it would try to
> protect ....

Surely it does not try to protect anyone within its own danger zone?
It would be mounted away from people sufficient to prevent any persons
injury. A gun is also a dangerous defensive device but you don't point
it at yourself when you pull the trigger.