Another impedance question regarding tweeters

[capnjim]

So I just found out I got scammed a while back.
I bought an 8 ohm aguilar GS115 cab from a seller who said he bought it new.
I recently sold it, and the new owner just told me it has a 4 ohm RCF driver. I'm lucky I never killed an amp as I used it with an 8 ohm 2x10.
The new owner is concerned about dropping a 4 ohm speaker into a circuit designed for 8 ohms. Can this harm the tweeter or speaker?
It always sounded good to me, but I didn't use it a lot.
It does have the aguilar label which says its an 8 ohm cab.
Did Aguilar ever use RCF drivers?
Thanks

[staindbass]

no. it wont hurt it. are you sure it was replaced? can you be sure they didnt use rcf as stock? (i dont recall aguilar manfacturing its own speakers, few do, not even ampeg)when you add a crossover to a tweeter its ohms go way up when measured with a multimeter. into the hundreds and doesnt change the impedance of the total system like putting two woofers in parallel will. ask him if he measured the speaker with a meter. an 8 ohm speaker will not measure 8 ohms on a meter. its nominal impedance. and 8 ohm measures from 4.6-6.9 ohms with a meter. a 4 ohm measures somewhere in the vicinity of 2.1-3 ohms. they always measure lower. some manufacturers may use a 4 ohm tweeter to match efficiency, and the crossover capacitor is smaller too. (cheaper).

[capnjim]

Thanks staind, its tough to tell whether or not its original. He gets exactly 4 ohms when measuring across the speaker.
he also has a 4 ohm Aguilar 4x10. I suggested he measures at the output jack for each cab, if they are the same, then the 15 is indeed a 4 ohm. If the 15 is even slightly higher, it could still be an 8 ohm cab and is most likely original.

[will33]

Tell him to measure the actual speaker terminals of the 15 and not just at the jack. The filter parts for the tweeter can throw off the meter reading.

[capnjim]

He did, he gets 4.0 ohms from both cabs. So my 8 ohm aguilar was actually a 4 ohm cab.
I'm lucky I didn't kill any amps!
How would one set up 2 4 ohm cabs to give 8 ohms? I think the jacks on the speakers are wired parallel?

[will33]

Disconnect the 15 and measure it by itself, then you'll know for sure. Don't know if it's the original speaker or not but someone around here will have the same cab. Try putting "Aguilar 15" or something in the thread title to catch their attention and compare it with yours.

[will33]

Make or buy a series speaker cable to get them to 8 ohms.

[will33]

1 plug to plug in amp with 2 cables coming off it. Both cables won't fit in plug so splice in a few inches back.

Hook + of amp plug to + of one cable.... - of amp plug to - of the other cable.....then connect the remaining open + and - together.

Looks like a big Y when it's done. Make the legs long enough to reach the bottom cab when stacked.

[capnjim]

Thanks, I will pass that on, but the buyer is actually happy the cab is a 4 ohm, he has a GBE 750 which will run at 2 ohms and he loves the way his 2 aguilar cabs sound together.
Thanks for all the help.

[will33]

Ya, I just re-read that. If he was gonna chain to a 4ohm cab he must have a 2ohm amp and can run it like it is. 4ohm min. amp would need the series cable.

[projectMalamute]

You are not measuring impedance, you are measuring resistance. You should be seeing about two thirds of the nominal impedance of the speaker.

4 ohms resistance for an 8 ohm driver is on the low side but possible. An actual 4 ohm driver would read 2 and change.

[BassmanPaul]

Originally Posted by projectMalamute

You are not measuring impedance, you are measuring resistance. You should be seeing about two thirds of the nominal impedance of the speaker.

4 ohms resistance for an 8 ohm driver is on the low side but possible. An actual 4 ohm driver would read 2 and change.

But he is also measuring the crossover which will lower the reading even more.

[projectMalamute]

Originally Posted by BassmanPaul

But he is also measuring the crossover which will lower the reading even more.

Depending on what the crossover is, sure.

In any event I would not take a reading of 4 ohms on a multimeter and conclude that I am looking at a 4 ohm box.

[billfitzmaurice]

Originally Posted by BassmanPaul

But he is also measuring the crossover which will lower the reading even more.

The crossover doesn't show up with a DC resistance measurement because capacitors don't pass DC. Even if they did it still wouldn't affect the reading. However, if the cabs have true crossovers rather than just simple high pass filters on the tweeters the 4 ohm woofer response will be AFU using it on an 8 ohm crossover.

[will33]

If you subtract the couple tenths or more that are probably in the leads on his meter it's a 4 ohm woofer assuming it's a cheapish meter like most of us have.

It's a 15 + tweet bass cab, I doubt there's a lowpass.

[capnjim]

The main thing is it measures the exact same as his 4 ohm 4x10, which makes it a 4 ohm cab, I guess I learned not to trust what people tell you when you buy something.