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How fast are drivers? - Page 2

post #16 of 19
10/11/09 at 11:03am
Quote:
Originally Posted by JaZZ View Post
A membrane vibrating with 1 kHz and an excursion of 1 mm (±0.5 mm) has an average speed of 1000 x 2 mm = 2 m/s (triangle waves). I can't calculate the sinc function, but the estimated maximum speed of a 1 kHz sine wave will be about 4 m/s (= 14.4 km/h) at the zero crossings in this case. But note that an excursion of ±0.5 mm at 1 kHz means a rather extreme volume level for a headphone driver.
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For the 1 mm (±0.5 mm) excursion of a 1 kHz sine wave, the maximum speed is 3.14 m/s. If you know the displacement amplitude (X = 0.5 mm) and the frequency (f = 1000 Hz) of then you can calculate the velocity amplitude (V), which is V = X*2*pi*f. Similarly, acceleration amplitude (A) is A = X*(2*pi*f)^2. I'm not sure what a more reasonable excursion for listening levels at this frequency would be, but whatever it is, the corresponding peak velocity with be reduced by the same factor. So back to the original question, the drivers aren't going anywhere near the speed of sound.
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post #17 of 19
10/11/09 at 11:27am
Thread Starter 
Quote:
For the 1 mm (±0.5 mm) excursion of a 1 kHz sine wave, the maximum speed is 3.14 m/s. If you know the displacement amplitude (X = 0.5 mm) and the frequency (f = 1000 Hz) of then you can calculate the velocity amplitude (V), which is V = X*2*pi*f. Similarly, acceleration amplitude (A) is A = X*(2*pi*f)^2. I'm not sure what a more reasonable excursion for listening levels at this frequency would be, but whatever it is, the corresponding peak velocity with be reduced by the same factor. So back to the original question, the drivers aren't going anywhere near the speed of sound.
Lol, i didnt understand even a bit of what you said there

But, 3,14*3,6= ~11 km/u. Isnt that like a bit 'too' slow?

A side question: How can something that moves 11 km/u makes sound that travels with ~1000 km/u
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post #18 of 19
10/11/09 at 1:50pm
Quote:
Originally Posted by miloxo View Post
Lol, i didnt understand even a bit of what you said there

But, 3,14*3,6= ~11 km/u. Isnt that like a bit 'too' slow?

A side question: How can something that moves 11 km/u makes sound that travels with ~1000 km/u
It isn't too slow, because speed of sound is not the same thing as the particle (or driver) velocity. Think of it this way, there is a steel bar that is pushed at one end. The opposite end of the bar will begin to move with the end being pushed almost instantaneously (there is a very small time delay due to the elasticity and density of the bar), no matter how slowly the one end of the bar is being pushed. The small time delay between when the one end of the bar is pushed and the other end moves depends on the speed of sound (around 5000 m/s for the compressional wave in steel for this case) and is independent of the speed at which the bar is pushed, which would be much slower in this example. Its basically the same thing happening with the driver in air. The driver locally pushes the air at a relatively slow speed, but the relative motion is transmitted much faster (at the speed of sound) since the as the air displaced by the driver moves it displaces the air in its path. Hopefully this makes some sense.
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post #19 of 19
10/14/09 at 8:21pm
Would the speed of a driver not totally depend on which car he or she was driving?

-Nkk
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