Two related questions for our audio gurus:

1. What's the upper frequency range for acoustic sound - sound through free
air? I know it's a lot higher than we can hear, but is there some physical
threshold where the wavelengths are too short to travel as sound?

2. How does this relate to the distance traveled? ISTR that the higher the
frequency the more energy would be absorbed as it travels through the air,
like a variable low pass filter. Can you actually predict that if you are X
distance from a sound source, then you won't be able to pick up signals
above F frequency?

No particular application, I'm just curious.

Sean

"Sean Conolly"
Two related questions for our audio gurus:


** Why don't you use Google or a Physics NG ??


1. What's the upper frequency range for acoustic sound - sound through
free
air? I know it's a lot higher than we can hear, but is there some physical
threshold where the wavelengths are too short to travel as sound?


** Why don't you use Google or a Physics NG ??


2. How does this relate to the distance traveled? ISTR that the higher the
frequency the more energy would be absorbed as it travels through the air,
like a variable low pass filter. Can you actually predict that if you are
X
distance from a sound source, then you won't be able to pick up signals
above F frequency?

No particular application, I'm just curious.


** See:

http://www.earthworksaudio.com/f_wpa...undabsorb.html


Looks like even at 1 MHz sound transmits well for a few cms.





.............. Phil

Yes, proof of ultra sonics traveling over long distances can be seen by
the fact that a dog whistle carries over a very long distance too...
I'd didn't know dogs did that, but there Ya go.
Every day's a School day...
DS

On Thu, 21 Jul 2005 12:20:16 -0400, studiorat wrote
(in article .com):

Yes, proof of ultra sonics traveling over long distances can be seen by
the fact that a dog whistle carries over a very long distance too...
I'd didn't know dogs did that, but there Ya go.
Every day's a School day...
DS


They have a keener sense of smell too, but for humans, HF diffuse more
quickly than lower frequencies.

Ty Ford



-- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
stuff are at www.tyford.com

"Ty Ford" wrote in message
...
On Thu, 21 Jul 2005 12:20:16 -0400, studiorat wrote
(in article .com):

Yes, proof of ultra sonics traveling over long distances can be seen
by
the fact that a dog whistle carries over a very long distance too...
I'd didn't know dogs did that, but there Ya go.
Every day's a School day...
DS


They have a keener sense of smell too, but for humans, HF diffuse more
quickly than lower frequencies.

And remember that dog-whistles are bloody loud.
Just because we can't hear them doesn't mean they
aren't putting out a strong wavefront.

Ty Ford wrote:
On Thu, 21 Jul 2005 12:20:16 -0400, studiorat wrote
(in article .com):


Yes, proof of ultra sonics traveling over long distances can be seen by
the fact that a dog whistle carries over a very long distance too...
I'd didn't know dogs did that, but there Ya go.
Every day's a School day...
DS



They have a keener sense of smell too, but for humans, HF diffuse more
quickly than lower frequencies.

Diffusion and absorption depend not the least on the sensor.
SPL variation with frequency and distance will be exactly
the same at a dog's ear as at a human's ear.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

"Sean Conolly" wrote in message

Two related questions for our audio gurus:

1. What's the upper frequency range for acoustic sound -
sound
through free air? I know it's a lot higher than we can
hear,
but is there some physical threshold where the wavelengths
are
too short to travel as sound?

I suspect the real problem is a matter of transducers. IOW
the air is willing, but the equivalent of microphones and
loudspeakers for such high frequencies are impractical.

A little google searching (you should try it some day!) and
I found that this source has transducers running in the 100
MHz range.

http://www.cdint.com/Selection.shtml

2. How does this relate to the distance traveled? ISTR
that
the higher the frequency the more energy would be absorbed
as
it travels through the air, like a variable low pass
filter.
Can you actually predict that if you are X distance from a
sound source, then you won't be able to pick up signals
above
F frequency?

I don't think that ultrasound has to travel very far, or
travel in air to be useful. Consider an ultrasonic thickness
gauge. Consider in-ear-monitors. Consider near field
monitors.

This article says the following:

http://www.earthworksaudio.com/tech/hf_sound.pdf
"For air at room temperature and "normal" humidity (65%), a
1 kHz sound wave has to travel an astonishing 20 miles (35
km) to loose 6 dB!"

"Since the loss is proportional to the square of the
frequency, the distance the sound has to travel to loose the
same 6 dB (at 10 KHz) will be 100 times (10kHz/ 1kHz
squared) shorter, or just over 1,100 feet (350 m)."

"Bob Cain"

Ty Ford wrote:

They have a keener sense of smell too, but for humans, HF diffuse more
quickly than lower frequencies.

Diffusion and absorption depend not the least on the sensor. SPL variation
with frequency and distance will be exactly the same at a dog's ear as at
a human's ear.



** Depends on the species of dog too - some have big ears with
directional horns attached like the German Shepard while others have have
ears that are kinda covered up with sound absorbing flaps like the Labrador
and Bassett.

The ultrasonic hearing "range" of dog species is a sadly neglected subject
;-)




........... Phil

"Arny Krueger" wrote in message
...

A little google searching (you should try it some day!)

I never seem to come up with the right terms to search on, sadly.


This article says the following:

http://www.earthworksaudio.com/tech/hf_sound.pdf
"For air at room temperature and "normal" humidity (65%), a
1 kHz sound wave has to travel an astonishing 20 miles (35
km) to loose 6 dB!"

"Since the loss is proportional to the square of the
frequency, the distance the sound has to travel to loose the
same 6 dB (at 10 KHz) will be 100 times (10kHz/ 1kHz
squared) shorter, or just over 1,100 feet (350 m)."

This exactly what I'm looking for, thanks!

Sean

"Arny Krueger"
"Sean Conolly"


This article says the following:

http://www.earthworksaudio.com/tech/hf_sound.pdf


** Same link I posted yesterday.

I even did the calc for 1 MHz too.




.......... Phil

"Arny Krueger" wrote:
|
|http://www.earthworksaudio.com/tech/hf_sound.pdf
|"For air at room temperature and "normal" humidity (65%), a
|1 kHz sound wave has to travel an astonishing 20 miles (35
|km) to loose 6 dB!"

But remember, the article also states:

"Remember that we are talking about the absorption loss only, i.e.
actual loss of acoustic energy through friction and other mechanisms,
not the inverse square law reduction in level resulting from spreading
of the sound over larger and larger area as one moves away from the
source."

This causes a much greater loss. The difference in level between 1
foot away and 1 mile away is 140db (according to my rusty (not trusty)
slide rule. (20 log(sqr(5280/1)) This swamps the 6 db above!

Phil