B&C 6PEV13 question

[vj]

it says they are 8 ohm...if i wire 2 in parallel, it should make 4 ohm correct? when i wire 2 in parallel, it reads 2.6 ohms on my DMM. is that the load my amp will see? i need to know so i know which amp i have to order for these

thanks

[Æ]

> it says they are 8 ohm...if i wire 2 in
> parallel, it should make 4 ohm correct? when
> i wire 2 in parallel, it reads 2.6 ohms on
> my DMM. is that the load my amp will see? i
> need to know so i know which amp i have to
> order for these

A lot of advertised "8 ohm" woofers, tweeters, or whatever are not really truly 8 ohms.
Many that are marked 8 ohms are really closer to 6 ohms than they are to 8 ohms. In fact some are even closer to 5 ohms!
8 ohms isn't an exact number, kind of a just ballpark figure, more of a category.
Generally 8 ohms is the home category and 4 ohms is the car category.
If your DMM says 2.6 ohms, then your amp will really be "seeing" something closer to a 3 ohm load. Trust your DMM.

[vj]

ok thats what i thought

> A lot of advertised "8 ohm"
> woofers, tweeters, or whatever are not
> really truly 8 ohms.
> Many that are marked 8 ohms are really
> closer to 6 ohms than they are to 8 ohms. In
> fact some are even closer to 5 ohms!
> 8 ohms isn't an exact number, kind of a just
> ballpark figure, more of a category.
> Generally 8 ohms is the home category and 4
> ohms is the car category.
> If your DMM says 2.6 ohms, then your amp
> will really be "seeing" something
> closer to a 3 ohm load. Trust your DMM.

[Paul K.]

Your DMM is measuring the d.c. resistance of the two paralleled drivers, not their impedance, and their impedance could easily be at or near 4 ohms.
Paul

> it says they are 8 ohm...if i wire 2 in
> parallel, it should make 4 ohm correct? when
> i wire 2 in parallel, it reads 2.6 ohms on
> my DMM. is that the load my amp will see? i
> need to know so i know which amp i have to
> order for these

> thanks

[vj]

> Your DMM is measuring the d.c. resistance of
> the two paralleled drivers, not their
> impedance, and their impedance could easily
> be at or near 4 ohms.
> Paul

i have my DMM set to ohms, it still is dc resistance? whats the difference? sorry im dumb

[Chris Roemer]

> i have my DMM set to ohms, it still is dc
> resistance? whats the difference? sorry im
> dumb

This isn't the exact answer, but it'll do.

Your DMM has a battery in it (9v?, or maybe 1 or 2 AA which would be 1.5v or 3v). It measures DC RESISTANCE by applying voltage through the leads and the load, measuring the current flow, and displaying it as Ohms (according to Ohm's Law). Your DMM does this with DC since that's what's powering it (the batteries). It doesn't create AC for the load, which could be used for measuring AC IMPEDANCE.

Trouble is, even if it DID generate AC, impedance varies with frequency. That's why you look at impedance vs. freq. plot graphs when designing a crossover.

Anyhoo, (ROT in GENERAL) is that if something has an AC impedance of 100 ohms, then it'll measure a DC resistance of 100 x 1/sq.rt.(2), which would be 100 x 1/1.414, which is 100 x .707, which would be about 71 ohms.

Proportionately, a driver that would have 8 ohms of impedance at a given freq. (let's say, 500 Hz) would show a DC resistance (as on your DMM) of 8 ohms x 0.7, or 5.6 ohms (which a lot of meters just report as 6 ohms).

[Paul K.]

Chris' explanation is on the mark and if you use his rule of thumb for comparing an AC impedance measurement to a d.c. resistance measurement of the same part, you can multiply the 2.6 ohms of d.c. resistance you measured by 1.414 and see that the likely impedance of your paralleled drivers is ~3.7 ohms, close enough to 4 ohms to likely be an okay load for your amplifier.

And, hey, you're not dumb; you just haven't yet acquired some specific knowledge.
Paul

> i have my DMM set to ohms, it still is dc
> resistance? whats the difference? sorry im
> dumb