Standing waves :
The condition for standing wave is that 2L = n
, where n = 1, 2, 3, . . .
A few standing-wave modes for an organ pipe open at both ends. The arrows show the direction in which air moves for half the cycle, whereupon the mode reverses. Both ends of the tube are at atmospheric pressure and there are pressure nodes at both.
Standing sound waves in a tube:
Condition: n = 2/n * L, for n = 1, 2, . . .
All harmonics are produced.
A few standing-wve modes for an organ pipe open at its lower end. The arrows who the direction in which air moves for half the cycle, whereupon the modes reverse. The dashed lines indicate the displacement nodes and antinodes.All brass instruments are closed at one end by the mouth of the player.
Anti nodes at one end
Condition: n = 4/(2n-1) * L, for n = 1, 2, . . .
Only ODD harmonics are produced.
Standing waves in closed tubes
all harmonics
only odd harmonics
Wave Velocity: v = 20.1 ( T ) 1/2
T is the Kelvin temperature of air in tube.
Remember:Room temperature is 292 K
Frequency: ( v =* f )
n = 1, 2, 3, 4, . . .n = 1, 3, 5, . . .
"Standard" pitch: A = 440 Hz
Wave Term | Colloquial | |
---|---|---|
amplitude
|
= | loudness |
frequency
|
= | pitch |
attenuated
|
= | damped |
Sound travels at known velocity.
Speed of sound in Air :
Sound travels faster in warmer air
Sound travels slower in cooler air
Water
(remember demonstration where a wave front of water wave was bent due to different depths of the ripple tank. Examlpe for sound: Ship horn in fog can be heard a longer distance due to temperature variations in the air.)
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