Natural Limits to high frequencies?

Archived from groups: rec.audio.pro (More info?)

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

Archived from groups: rec.audio.pro (More info?)

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

Archived from groups: rec.audio.pro (More info?)

"Ty Ford" <tyreeford@comcast.net> wrote in message
news:kPydnWe5JZvHt33fRVn-sw@comcast.com...
> On Thu, 21 Jul 2005 12:20:16 -0400, studiorat wrote
> (in article <1121962816.471971.256150@g44g2000cwa.googlegroups.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.

Archived from groups: rec.audio.pro (More info?)

Ty Ford wrote:
> On Thu, 21 Jul 2005 12:20:16 -0400, studiorat wrote
> (in article <1121962816.471971.256150@g44g2000cwa.googlegroups.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

Archived from groups: rec.audio.pro (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:rPSdnZ7bU7ELIH3fRVn-3A@comcast.com...

> 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

Archived from groups: rec.audio.pro (More info?)

"Arny Krueger" <arnyk@hotpop.com> 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