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How drivers work?

post #1 of 6
Thread Starter 
Hi, I have a somewhat technical question to people who know speaker design.

How exactly does the changing voltage translate to diaphragm excursion?

The "secondary school physics" model of a dynamic driver I always imagined is like this:
The air pressure (and diaphragm?) form a close-enough-to-linear spring. Applying voltage to voice coil induces (almost) linear current and Lorentz force moves the diaphragm to the point where it gets equalized by diaphragm's spring force. From linearity of both forces it easily follows that this point is linear to input voltage.

However, I'm not sure how to fit mass into this picture. I guess it should introduce some treble roll-off and phase shift, but how much of them in real world?

Has anybody seen models used by people who actually build this stuff? How it is possible to make all of this insanity sound even close to good? :)
post #2 of 6

Here you go:

 

http://en.wikibooks.org/wiki/Engineering_Acoustics/Moving_Coil_Loudspeaker

 

se

post #3 of 6
Quote:
Originally Posted by mich41 View Post

Hi, I have a somewhat technical question to people who know speaker design.

How exactly does the changing voltage translate to diaphragm excursion?

The "secondary school physics" model of a dynamic driver I always imagined is like this:
The air pressure (and diaphragm?) form a close-enough-to-linear spring. Applying voltage to voice coil induces (almost) linear current and Lorentz force moves the diaphragm to the point where it gets equalized by diaphragm's spring force. From linearity of both forces it easily follows that this point is linear to input voltage.

However, I'm not sure how to fit mass into this picture. I guess it should introduce some treble roll-off and phase shift, but how much of them in real world?

Has anybody seen models used by people who actually build this stuff? How it is possible to make all of this insanity sound even close to good? :)

 

I think there should be a certain amount of back emf to consider into the model, and also the material properties of the cone may influence the amount of linearity in the speaker, and also the damping of the system.

 

 

I guess what you need to consider is a model with damping, in response to a periodic force :

m x(dot) + c x(dot dot) + k x =  F cos (2pi f t) 

 

Using the Laplace transform, it should be possible to get the solution for frequency response and phase shift.

post #4 of 6

Here's your electrical model right here:

 

 

se

post #5 of 6
Quote:
Originally Posted by Steve Eddy View Post

Here's your electrical model right here:

 

 

se

 

I'm wondering how is the material property translated into the electrical model. For instance, the material used for subwoofer may not be the same as the one for woofers, or mid range drivers and tweeters. That, and the desired decay response may be different for each driver.

Is it just changing the values of the components above? Or a different kind of a model?

post #6 of 6

some speaker building books, websites will explain dynamic loudspeaker driver Theil-Small parameters (how mass, spring constant are translated to electrical equivalents)

 

parts express, other driver resellers often show the parameters for the products they carry

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