Speaker Question

[far0n]

What's the physical difference between say two 15" speakers, one 4 ohm and one 8 ohm. Does one have a larger magnet or coil windings? Just curious.

[Mr. Foxen]

Two different ones, or two otherwise the same ones? If they are ifferent it can be everything, if they aer the same, its just the coil winding, which can affect other specs, usually in a fairly minor way.

[far0n]

Yeah same cones, just different impedence. I'm assuming the 4 ohm cone will have more windings?

[Mr. Foxen]

To keep all the other stuff the same, you need about the same number of windings, since that related to the amount they will 'magnetise' when current passes through. In practice, I dunno if that happens.

[BILL POSTERS]

Not really sure which is actually used, but to half the impedance, you would need either thicker wire, or less of it ie. less turns,

In practice, its probably a combination of both.

[Bill Fitzmaurice]

[quote name='far0n' timestamp='1327342003' post='1509645']
Yeah same cones, just different impedence. I'm assuming the 4 ohm cone will have more windings?
[/quote]If anything less, but that assumes the two coils use the same wire gauge, and you can never assume anything. In any event if you need to know the end result difference modeling software will tell you.

[Phil Starr]

To lower the resistance you need less wire or thicker wire or a combination of both. Manufacturers use all sorts of methods and if you are a major manufacturer you can get all sorts of impedances made up. If you are a home builder then beware, Most manufacturers do their design work on 8ohm speakers and the magnet gap is designed to work with an 8 ohm coil. To make a 4 or 16 ohm option the coil is changed with the 4 ohm version shorter reducing the excursion the speaker can cope with before distorting. The 16 ohm coil is often longer giving more excursion but at the expense of having more of the coil outside the magnetic field reducing efficiency and decreasing the control the magnet has over the speakers movement. This doesn't have to happen but completely re-tooling is expensive and just changing the voice coil by adding or subtracting turns isn't.

As BFM says you need to check before using a speaker in a design, the 4 ohm and 8 ohm models probably won't be the same.