Speaker impedance question:

[Cogs]

How come my JBL 2215s are labeled 16Ohms each but measure 8.6 & 8.4?

[Bill Moore]

Rob, you're measuring resistance, and the speaker is rated as "X" ohms impedence. Both will vary with frequency. Most 8 ohm speakers I've checked, run around 6.8 ohm resistance, and the 4 ohm will run around 3.2 ohm resistance.
I guess I haven't checked a 16 ohm, so I'll remember your measurement.

[phantomman]

They've prolly been re-coned as 8's.

My 16Ω D130Fs both show a DCR measurement of 15.8Ω.

[Offshore Angler]

Phantoman is correct. Impedance is the same as resistance in this case.

Only other thing I could think of is if the cabinet was rated 16 Ohms and they are two 8's in series(?)

Oh, and as an anal-retentive point, "Ohms" should be capitalized. Just one of my pet peeves, like when people use "dampened" for "damped".

[phantomman]

Oh, and as an anal-retentive point, "Ohms" should be capitalized. Just one of my pet peeves, like when people use "dampened" for "damped".

Right you are.

However, it would seem that expediency has overtaken proper lexicon, going back at least four decades now. My vintage RCA Receiving Tube Handbook uses no capitalization for any measurement units developed by a specific physicist or scientist whether it be "henries", "farads", "amperes", or "ohms".

Such is "life in the fast lane", I suppose......

[Cogs]

Nothing is quite as goofy as "ohmage", though-

[Wilko]

That "anal retentive point" goes against most, if not all published style guides.

"All units, including those that are named for a person, have a lower-case first letter when written out (not abbreviated). Thus, write "ohm, farad, coulomb, volt, ampere, hertz" for units."

[steve25]

The 2215A model is a 8 ohm driver, the 2215B model is a 16 ohm driver.
These have a frequency responce that is rated only up to 1200 Hz as they are intended for recording monitoring use as a true woffer.
As such they have low distortion and are not as effifciant as a 130 or 140 serise 15 incher, in fact even the 140 instrument serise bass driver goes up higher in Hz the the 2215 model.

[Bill Moore]

I looked a a few speaker spec. sheets, and all have a dc resistance rating,(Re) listed. They are all over the place, but always lower than the rated impedence. So I measured a few speakers that I have, with my trusty Fluke 87.
'66 C12N 6.1 ohm
EV SRO15 5.2 ohm
JBL G-135-8 4.2 ohm
Weber 12A125A 6.4 ohm
Mojo BV30H-8 6.7 ohm
Peavey Sheffield 1230 6.4 ohm
'69 Oxford 12 6.4 ohm
EVM12L 5.1 ohm
EVM15L 4.9 ohm
EVM15B 5.3 ohm
EV Proline18 5.4 ohm
Fender 025923 7.2 ohm

I also had a few 16 ohm drivers, and they too were all over the place.
CV ER-122 11.4 ohm
Cletron 10" (4) 7.0- 7.4 ohm
Altec 806 horn driver 12.6&12.7 ohm

So I guess you can't be sure, as I once thought by measuring DC resistance, you'll need to look up the spec for the particular speaker.

[Cogs]

They are 2215Bs

[steve25]

95% of the time a 8 impeadance rated driver will check in between 4.2 and 7.8 ohms on a resistance meter, a 16 ohm driver will go between 8.4 and 13.8.

[Bill Moore]

http://www.jblpro.com/pub/obsolete/2215.pdf Here's a link to the spec sheet.

[limbe]

A speaker has an impedance which consists of a resistive part and an inductive part.If you just measure the resistive part with a VOM you will get a value that´s slightly lower than the impedance.I remember from the old days that speakers sometimes were marked with just the resistance.For instance a 4 ohm speaker (impedance) would be marked 3.2 ohm (the resistance.)

[aclempoppi]

Yep, these are AC units. So it's a combination of resistance(which doesn't change) and reactance(which is frequency dependent and does change). If the speaker is measured by DC or AC resistance, it's measurement cannot exceed that groups name. Or else it is bumped up to the next higher common group. Same holds true for the next lower common group. So a speaker measured at 8.2ohms is put in the 16ohm bin, and the 7.9ohm speaker and 4.2ohm speaker goes into the 8ohm bin. Art