2 x 6 ohms = 8 ohms???????

[PaulWarning]

just been messing about with my Celestion F30 audio speakers, both the mid range and bass drivers are marked 6 ohms, well they're identical actually, yet the specs say these speakers are 8 ohms, can this be right?

[Ian Savage]

[quote name='PaulWarning' timestamp='1352148474' post='1859457']
just been messing about with my Celestion F30 audio speakers, both the mid range and bass drivers are marked 6 ohms, well they're identical actually, yet the specs say these speakers are 8 ohms, can this be right?
[/quote]

It can; impedance and DC resistance are different things, impedance varies with frequency whilst DC resistance is, well, resistance at DC. I'd guess that the speakers are stamped with 6 ohms because that's their DC resistance, whilst 8 ohms would be their nominal impedance.

[PaulWarning]

[quote name='Ian Savage' timestamp='1352150504' post='1859492']
It can; impedance and DC resistance are different things, impedance varies with frequency whilst DC resistance is, well, resistance at DC. I'd guess that the speakers are stamped with 6 ohms because that's their DC resistance, whilst 8 ohms would be their nominal impedance.
[/quote]
Right think I sort of understand that, but if 2 speakers have nominal inpedance of 8ohms how can 2 of them be 8 ohms? unless they're nominal impedance is 4 ohms, could nominal impedance be less than DC resistance?

[3below]

One is not connected

[flyfisher]

Could be that a passive crossover needs to be accounted for as well?

[3below]

On a more serious note

[url="http://www.epanorama.net/documents/audio/speaker_impedance.html"]http://www.epanorama.net/documents/audio/speaker_impedance.html[/url]

gives possible explanation of the situation. 6 Ohms would be DC resistance, nominal impedance is 1.3 (roughly) x DC resistance = 8 ohms.

I do not know the validity of that estimation.

[PaulWarning]

now I'm confused.

[Phil Starr]

Ok the speaker has a coil inside the magnet which is what makes the cone move when the amp pushes electricity through it. The coil has a resistance because uncoiled it is a long thin bit of wire and thin wire resists electricity.

Coils do something else though they have inductance, they resist the passage of high frequencies and the higher the frequency the more they resist.

So to work out the total resistance you add the two together, resistance and inductance and this gives the speakers [b]impedance [/b]which is what the manufacturers give as 4,8, or 16 ohms.

This means the impedance is always bigger than the resistance you measure. Actually as it varies with frequency an 8ohm speaker may be less than 8 ohms at one frequency and 80 ohms at another. If you look the specs of drive units they usually say [b]nominal[/b] 8 ohms. If you look at a graph of impedance you'll see what I mean [url="http://www.eminence.com/pdf/Kappalite_3015LF.pdf"]http://www.eminence.com/pdf/Kappalite_3015LF.pdf[/url]

If you have two 6ohm resistance speakers then they are 8ohm units and the cab is probably 4ohms or it could be 16ohms.

[PaulWarning]

that what I thought, with no science to back it up, I found something else out that's odd, they're biwired, if I take off one of the terminals on one speaker the bass unit stops working, if I take off the same wire(not exactley the same wire, if you know what I mean) on the other speaker the mid range and the bass speaker stops working, i.e just leaving the tweeter, spooky huh?

Edited November 6, 2012 by PaulWarning