trying to work out ohms on cabinet build

[crazyboy]

Hi guys

Great forum you have here

hopefully this will be a good first post..

Ok ive been looking at a cabinet that im trying to replicate but im struggling to under how the ohms law is working i'll try and explain

the cabinet has a 8 ohm impedance

the bit i dont understand is the fact that the components are as follows

15" 350wrms driver 8ohms
compression driver 8ohm
crossover for use with 8ohms

now as i understand if you wire 2 x 8 ohm speakers in parallel you make 4 ohms
and if you wire in series you would get 16 ohms

so how have they come up with a total impedance of 8 ohms

is it because the use of the crossover

thanks
steve

[chris661]

Ok - there's a few reasons, so I'll try to cover them all.

The first is that it's considered 8 ohm nominal impedance. It's a number that's vaguely central to the impedance curve of the speaker. They're usually 4 or 8 ohm, so most will round to the nearest of those two.

The second reason is that a crossover is designed so that the drivers don't end up playing the same thing. Because of this, the impedances don't actually interract at all.

So, if you have a woofer of 8 ohm, cross it over to a tweeter of 8ohm, they will have no effect on one another. An easier way to think about it - picture 2 amps, on running the woofer, one running the tweeter. They'll each see 8ohm.

The problems occur when more than one driver is playing the same frequency range. Putting 2 8ohm woofers in parallel will indeed give 4 ohm.

Hope this helps

Chris
PS - Welcome to the forums.

[crazyboy]

Chris
Thanks for a nice and easy put response i will carry on building now

with the crossovers

once again thanks