Measuring Sound Waves

[reamer]

I need an adequate formula that can be used to determine the distance a sound wave will travel where the following are known: Power in KHz that's used to drive the wave, the peak to peak echo measurment in Millivolts out, tested in 10 foot increments. These units of measure were taken using an ocilliscope. I do not wish to use a scope everytime I fire a unit and have at my disposal a testing machine that really does not tell me what any given unit under tests actual range is. My goal is to determine distance with the following parameters taken from the sonar testing machine: Power in KHz, echo width, minimum range. For these units I wish to attain a consistant 100 foot range.
Has anyone experience with this?

 

[MadMango]

Your post is a bit vague.

The speed of sound in dry air is 331.45m/s, plus variations for temperature, pressure, humidity, and CO2 concentration.

Since you mention sonar, I am assuming you are finding the speed of sound in water. It varies for fresh or salt water at a given temperature. The following link gives 6 different formulas for sound speed in water.

http://www.phys.washington.edu/~wilkes/soundspd.html

Ray Reynolds
Senior Designer
Read: faq731-376
"Probable impossibilities are to be preferred to improbable possibilities."

 

[GregLocock]

I think you need to research and understand two things

1) attenuation of sound waves in water

http://freespace.virgin.net/mark.davidson3/TL/TL.html

2) the sonar equation

http://solmar.saclantc.nato.int/detect/index.html?activesonar.html

the latter controls what signal is detectable by your receiver, the former gives you some idea of the likely attenuation at 100 feet.



Cheers

Greg Locock

 

[IRstuff]

Your usage of units is confusing. "Power in kHz" ?

Power is measured in watts. kHz is a unit of frequency

TTFN

 

[reamer]

I used the word "sonar" to get action on the thread only. The measurement is not taken in water but in air. Of the frequency in Hz insted of power as above I stand corrected. Greg is the link to the "sonar equation" the same for "in-air" measurement?
Ray or Greg, when talking frequency, is the following statement true? The response to my test yielded a responsivity level of 4,000 nR? If so is this a frequency reading? What does nR mean?
Hal

 

[MadMango]

Disclaimer: I haven't messed with electronics or radar theory since my Navy days (10+ years ago), so I might be way off base.

I know of nR (nanoroentgen) to be the measurement of net radiation, the difference between incoming and outgoing radiation strengths. Radition is a form of energy or power, but I think radition is different than transmitt frequency or received frequency.

Frequency is always measured in hertz, be it Ghz or Khz or other. You post is a bit confusing, it's like asking for 8lbs of water instead of a gallon of water.

4,000nR is how much power your equipment is seeing, but does not correlate to frequency. The frequency shouldn't change from your emitter, unless you are talking about a doppler signal (that's an entirely different discussion). The amplitude of your signal will be affected due to attenuation through the air and dB filter differences in your equipment, but frequency should remain the same.

With all that said, sound still travels roughly 331.45 meters per second, regardless of frequency or power of the signal. If I did my math right, it only takes 91.9ms for sound to travel 100 meters. What's this mean... I dunno, now I'm confused.

Ray Reynolds
Senior Designer
Read: faq731-376
"Probable impossibilities are to be preferred to improbable possibilities."

 

[GregLocock]

Attenuation of sound in open air is well known, a google search should find it, as it found the other references. The sonar equation is pretty much the same as the radar equation, so I imagine that it will apply in air, with a bit of thought.

I have never see a responsivity measure, and don't know what nR units are. nanoRadians? possibly, but unlikely. NR is Normalised Responsivity, in another field.



Cheers

Greg Locock

 

[reamer]

Thanks for your help Guy's I learned a little but no what the mythical resonsivity means.
):
Hal

 

[MadMango]

The term "resonsivity" makes no sense to me. Are you talking about resonance or responsitivity now?

Maybe to reduce the confusion on this, you could repost your original question, explaining your test set-up and what you hope to accomplish... instead of just looking for a formula.

Also, going off your background as "mechanical", you might want to pull a consultant in on your testing, or do some added research on the subject. Sounds like you are a "fish out of water".

Ray Reynolds
Senior Designer
Read: faq731-376
"Probable impossibilities are to be preferred to improbable possibilities."