# Homework Help: Loudspeaker cone problem

1. Dec 13, 2004

### saltrock

AA loud speaker cone is connected to a AC signal genetator.When the frequency of the signal genetor is alterned the amplitude of the cone changes.why?
My working:
As the frequency increases the amplitude decreases because there is less change in the magnetic flux and vice versia....I am a bit confused about the relationship between the amplitude and frequency...

can you please give me some scientific evidence to lead me in the correct path.Any help would highly be appriciated

2. Dec 13, 2004

### Andrew Mason

In a loud speaker, current passes through a coil. As the frequency increases, the inductive reactance increases, which opposes current flow (when frequency decreases, reactance decreases, thereby reducing opposition to current). This change in current would have a proportionate change on the magnetic force driving the cone, thereby chaning the amplitude (distance the cone moves per vibration period (T=1/f)).

AM

3. Dec 13, 2004

### Loren Booda

Also, mechanical resonances, often represented by Bessel functions, vary (nonlinearly?) the efficiency of the cone surface with repect to frequency.

4. Dec 13, 2004

### pack_rat2

That's true to a slight extent, but isn't sufficient to explain the fairly large decrease in cone displacement vs freq. Speakers normally have pretty low reactance at audio frequencies. The main cause of the reduced amplitude is the mass of the system. The mass must be accelerated by the force from the magntic field produced by the coil. If that force changes more quickly, the cone is less able to follow it.