[[email protected]]

Ideally, I wish I could find a web-based calculator that will give the
change in loudness for increasing distanced from the source. One would
enter that the loudness is 140 dB (say) at the source, and enter than
one's ears are 50 yards away, and would get back the loudness at the
ear.

I don't need a high level of precision, just a ballpark figure.

Anybody know of such a thing, or have a spreadsheet that does the job,
or such like?

[Don Pearce]

On Sun, 6 Jan 2008 14:09:11 -0800 (PST),
wrote:

Ideally, I wish I could find a web-based calculator that will give the
change in loudness for increasing distanced from the source. One would
enter that the loudness is 140 dB (say) at the source, and enter than
one's ears are 50 yards away, and would get back the loudness at the
ear.

I don't need a high level of precision, just a ballpark figure.

Anybody know of such a thing, or have a spreadsheet that does the job,
or such like?

The basic formula is 6dB for each doubling of distance - you can write
the spreadsheet for that.

Unfortunately it isn't that simple. Indoors that formula applies up to
the room's critical distance. Further than that and the reverberant
sound is louder than the direct sound and there is no further
decrease with distance. Outdoors you rapidly reach places where
thermal gradients in the air are far more important than the simple
inverse square law.

d

--
Pearce Consulting
http://www.pearce.uk.com

--
Posted via a free Usenet account from http://www.teranews.com

[Scott Dorsey]

wrote:
Ideally, I wish I could find a web-based calculator that will give the
change in loudness for increasing distanced from the source. One would
enter that the loudness is 140 dB (say) at the source, and enter than
one's ears are 50 yards away, and would get back the loudness at the
ear.

I don't need a high level of precision, just a ballpark figure.

Anybody know of such a thing, or have a spreadsheet that does the job,
or such like?

Kind of. What is the application here?

The thing is, it depends a lot on the terrain. Sound will go a lot
farther on a nice flat desert than on a grassy surface, and a few
trees can make a mess of your estimates. On top of that, it depends
more than you'd expect on temperature and humidity. And of course
it is very frequency dependant (and this is made worse with PA stacks
that are directional at high frequencies but have no directionality
at lower frequencies).

There are some charts for ballpark stuff in one of the free pamphlets
B&K used to give out... I think it was "Noise." Turns out sound
propagating over actual terrain goes farther than you'd expect from
the inverse square law. Except when it doesn't.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Adrian Tuddenham]

Don Pearce wrote:

On Sun, 6 Jan 2008 14:09:11 -0800 (PST),
wrote:

Ideally, I wish I could find a web-based calculator that will give the
change in loudness for increasing distanced from the source. One would
enter that the loudness is 140 dB (say) at the source, and enter than
one's ears are 50 yards away, and would get back the loudness at the
ear.

I don't need a high level of precision, just a ballpark figure.

Anybody know of such a thing, or have a spreadsheet that does the job,
or such like?

The basic formula is 6dB for each doubling of distance - you can write
the spreadsheet for that.

Unfortunately it isn't that simple. Indoors that formula applies up to
the room's critical distance. Further than that and the reverberant
sound is louder than the direct sound and there is no further
decrease with distance. Outdoors you rapidly reach places where
thermal gradients in the air are far more important than the simple
inverse square law.

....and the inverse square law only applies where the source is small
compared with the distance (when the wavefront is spherical).


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Scott Dorsey]

Adrian Tuddenham wrote:

...and the inverse square law only applies where the source is small
compared with the distance (when the wavefront is spherical).

This is true for a typical PA application, where you may have a couple
horns separated by 10 feet, but you are concerned with sound levels
a hundred feet away.

However, the fact that you are on the ground and not in free space
makes an appreciable difference.

Generalizing this to a line array is left as an exercise to the folks
at Community. The math is all different, though, because you can no
longer consider it as a point source. But they will send you all kinds
of white papers about it if you ask.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Peter Larsen[_2_]]

Scott Dorsey wrote:

Adrian Tuddenham wrote:

...and the inverse square law only applies where the source is small
compared with the distance (when the wavefront is spherical).

This is true for a typical PA application, where you may have a couple
horns separated by 10 feet, but you are concerned with sound levels
a hundred feet away.

However, the fact that you are on the ground and not in free space
makes an appreciable difference.

Generalizing this to a line array is left as an exercise to the folks
at Community. The math is all different, though, because you can no
longer consider it as a point source. But they will send you all
kinds of white papers about it if you ask.

This seems simple to me ... is it big enough, calculate 6 dB loss pr.
doubling of distance, does it annoy the neighbors: calculate 4 dB loss pr
doubling of distance, in the evening calculate 6 dB amplification pr.
doubling of distance.

I have heard barking dogs and the fact of outdoor speech - not what was
said, but that people spoke - 2 miles away over a moor in Sweden at 11 pm a
summers evening and listened to Brian Wilson 10 miles from the Roskilde
Festival,that too a summers evening ... vox didn't make it, but very swining
bass and drums did and the music was unmistakeable.

--scott


Kind regards

Peter Larsen

[Don Pearce]

On Mon, 7 Jan 2008 13:59:05 +0100, "Peter Larsen"
wrote:

Scott Dorsey wrote:

Adrian Tuddenham wrote:

...and the inverse square law only applies where the source is small
compared with the distance (when the wavefront is spherical).

This is true for a typical PA application, where you may have a couple
horns separated by 10 feet, but you are concerned with sound levels
a hundred feet away.

However, the fact that you are on the ground and not in free space
makes an appreciable difference.

Generalizing this to a line array is left as an exercise to the folks
at Community. The math is all different, though, because you can no
longer consider it as a point source. But they will send you all
kinds of white papers about it if you ask.

This seems simple to me ... is it big enough, calculate 6 dB loss pr.
doubling of distance, does it annoy the neighbors: calculate 4 dB loss pr
doubling of distance, in the evening calculate 6 dB amplification pr.
doubling of distance.

I have heard barking dogs and the fact of outdoor speech - not what was
said, but that people spoke - 2 miles away over a moor in Sweden at 11 pm a
summers evening and listened to Brian Wilson 10 miles from the Roskilde
Festival,that too a summers evening ... vox didn't make it, but very swining
bass and drums did and the music was unmistakeable.

--scott


Kind regards

Peter Larsen



I think I can sum up what we have discussed he

Forget the theory, you get what you get.

d

--
Pearce Consulting
http://www.pearce.uk.com