What is the difference between ultrasonic & subsonic sound ?

I think they’re two completely different things..

Subsonic is any speed lower than the speed of sound (so you could say aircraft flight at airspeeds lower than the speed of sound in air is subsonic flight).

Ultrasound is sound with a frequency greater than the upper limit of human hearing (Ultrasonic is an adjective referring to ultrasound).

Here’s where I get put in my place by Harp… ;)

damien is correct ; ), but “subsonic” can also mean sound having a frequency below audible range (better referred to as “infrasonic” to avoid confusion).

Aahhhh…

Sound waves travel at a constant velocity in air (at sea level)-approximately 1,130 feet/sec., although in scientific terms one could mistakenly use the terms to suggest velocity of objects other than sound waves, as in the velocity of aircraft.

In those cases, the more familiar terms are hypersonic and subsonic as in describing if an object travelling through air exceeds the speed of sound.

That is a different measurement than a sound’s frequency (the rate at which a sound wave vibrates). In that case, the terms ultrasonic and subsonic describe sound energy that “vibrates” at a rate above or below the audible hearing range for humans (known as the Sound Frequency Spectrum).

Typical “perfect” hearing for most humans translates to hearing vibrations that range from 20 vibrations (cycles) per second (expressed in Hertz), to an upper frequency “ceiling” of 20,000 Hertz.

Frequencies above 20,000 Hz are said to be ultrasonic, while freqencies below 20 Hz are described as subsonic. Earthquakes often have a resonant frequency below 20 Hz (somewhere between 15–18 Hz), while many ultrasonic sounds are heard by other animals (dogs, for example, often can hear and respond to ultrasonic frequencies).

Light is similarly described, as in the terms infrared (below the lowest light frequencies-red being the lowest in the visible spectrum), and ultraviolet (violet being the upper range of visible light frequencies). Our eyes can’t see these frequencies but they’re there (electronic equipment can see them).

sounds like someone wants Fluther to do their homework.

SdffreQ gets an A, for having written the essay.

ultrasonic – above speed of sound
Subsonic – below speed of sound
Sonic – speed of sound

*Usually objects travel below the speed of sound. Fast objects like Concordes travel above speed of sound. For example when we are in a air plane travelling at subsonic and when a Concorde passes us, we would hear the sound of the Concorde approaching to us way before the Concorde actually fly pass us. THis is because the sound wave generated by the concorde is travelling ahead of the concorde itself. After the concorde moved away, we wouldn’t be able to listen any of the concorde sound. THis scenario assumes that we are able to listen to the outside sound from inside the airplane. In a subsonic case, for example when we are in a car, when an ambulance passes us, we could listen to the sound of ambulance before and after it passes us. This is because the sound wave is surrounding and travelling with the ambulance.

Hi mea05key,

Nice description! One detail I want to point out: your first part of the description, where the Concorde is approaching (I’m assuming by Concorde you mean an airplane travelling toward you that is flying at hypersonic speed), from your vantage point (being in another airplane), you would not hear any sound.

I found an interesting link that takes into account the Doppler effect, however, at hypersonic speeds, the sound will never reach you as the Concorde travels away from your aircraft either.

http://www.kettering.edu/~drussell/Demos/doppler/doppler.html

My theory (guess) is, all you would encounter as the two aircraft pass each other is a single sonic boom (from the pressure), but thereafter, you would not hear the Concorde sound (as you indicated).

In the case of subsonic sound, your ambulance analogy describes Doppler shift, however, the dip in the pitch of the sound is attributed to the added velocity of the approaching ambulance (the sound wave’s frequency is shifted up), and a dip in the frequency as the ambulance travels away (the sound is shifted lower by the subtractive effect of the escape velocity, offsetting the speed of sound). The factor is that the object creating the sound (the ambulance) is not travelling above the speed of sound, thus, the sound is heard, but shifted. Also, the description of the ambulance is somewhat different, if we assume our vantage point is stationary. If we make a similar comparison, maybe it would be that if we were on a road in a car, traveling in the opposite direction of the approaching ambulance, the Doppler effect would still be in effect, but we would be able to hear both the approaching and departing sound because we’re subsonic.

my brain hurts now, and I have to drive home 90 minutes from work

Nice pontificating with you :)