Voice Coil Induction and its relevance to SQ


Silver Member
Username: Scubasteve

College Park, MD

Post Number: 615
Registered: May-05
A few days ago, someone I was responding back and forth with asked about the difference in sound quality between SVC and DVC speakers. It seems like the inductance of coils in parallel and in series should have something to do with it, but I really had no idea. Is there any theoretical or experimental evidence as to which wiring method produces the quickest response?

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 10585
Registered: Dec-03
dug this up for ya

With a speaker you have 2 components of the impedance. The first is the DC resistance, it's just a function of the length and size of the wire that makes up the coil, that's it. It will be the same regardless of frequency, this is what you measure when you hook a DMM up to the speaker, and this is the Re value when you look at the T/S parameters. The second is the AC impedance that you get from basically feeding an AC signal to an inductor (the speaker's voice coil is an inductor).

See when you feed a current through an inductor it generates a magnetic field, this magnetic field is what pushes against the permanent magnetic field from the speaker's magnet and causes the coil to move. You can't change this magnetic field instantaneously though, which means the current through the inductor can't change instantaneously. When you change the voltage across the inductor quickly, the current can't follow suit, there's some impedance that keeps the current from rising too quickly, but after time it will eventually rise up all the way and you'll be at steady state again. This impedance is a function of the inductance (the Le of the driver) and the frequency (with a higher frequency, the current is trying to change directions faster, so there's more impedance).

The total impedance is equal to the square root of the DC resistance squared plus the AC impedance squared (X=sqrt(DC^2 + AC^2)). Of course with a speaker it isn't so simple, since you actually have this inductor moving through a permanent magnetic field it changes things, the actual impedance depends on a LOT more than just the frequency, Re, and Le. This is why to test the amp's output you should use a purely resistive load, one whos impedance does not change with frequency, which means that it has no inductance (non-inductive dummy load).


Silver Member
Username: Scubasteve

College Park, MD

Post Number: 619
Registered: May-05
alright, thanks glass. Probably gave me as many questions as it answered, but such is the learning process. :-)
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