Equations relating to a loudspeaker?

[doomsdaydave1]

Hi guys, although this is for a class project, this isn't really a traditional homework question, so the mods can move this if they like, though.

I scrapped some hard drives and made a stereo speaker set for a physics project, but now to complete this project I need to relate some equations for it.

Assuming this is the most basic magnet/coil/membrane speaker, what would be a basic (algebra) equation that I could use to determine, say, air pressure? Or some other measurable quantity that results from "turning it up."

Thanks.

 

[toombs]

This is actually quite a complicated problem, but let's just see here. The membrane can be modeled using a driven damped harmonic oscillator. The driving force is given by the force on the coil due to the current and magnetic field. The Lorentz force law for conductors should work for that. The air pressure can be estimated by dividing the force by the membrane's surface area. This is the important quantity for volume. I believe the volume perceived by animal (human included) ears is proportional to the logarithm of the pressure, so that an exponential increase in peak pressure is perceived as a linear increase in volume.

That should get you started.

 

[brollysan]

You could also use diffraction to justify the size of the loudspeaker, the reason bass speakers are so large for instance is that for low frequencies single-slit diffraction requires a large slit for the intensity of the sound to be localized in a narrow angle-range.