Hey,
this might be a silly question, but I simply have no explanation...
Most 2440 and 2441 alnico-drivers which have the original 16ohm diaphragms installed, measure something between 7-8ohms... far away from factory-specs.
And 2405H ferrit slot-drivers which have the original 8ohm diaphragms installed, measure something between 6-7ohm.... so pretty close to factory-specs.
Any help....
Thanks a lot,
Olaf
It's called "nominal" (in name only) impedance because it's pretty much meaningless, plus, what you are measuring the is DC resistance of the voice coil, which isn't the same as impedance anyway. Just be happy knowing your drivers are measuring correctly.
8=16 from JBL...Originally Posted by Dr.db
please take a look at
http://www.audioheritage.org/vbullet...-2404-077-2405
Please check out your universal meterHey,
this might be a silly question, but I simply have no explanation...
Most 2440 and 2441 alnico-drivers which have the original 16ohm diaphragms installed, measure something between 7-8ohms... far away from factory-specs.
And 2405H ferrit slot-drivers which have the original 8ohm diaphragms installed, measure something between 6-7ohm.... so pretty close to factory-specs.
Any help....
Thanks a lot,
Olaf
46 lover
No!
Impedance is a complex number as represented in the plot below. This is the plot of a JBL LE14H-3 which is nominally an 8 ohm woofer. If you were to put an ohm meter on it you would measure a DCR of 5.94 ohms.
If that isn't confusing enough, once you mount the woofer in a cabinet the impedance will change rather significantly.
The long and the short of it... if you can't measure actual impedance plots and are designing passive networks... then don't sweat the impedance number. To the typical user the number is of virtually no significance.
Widget
Si!
Actually "8=16 from JBL" means that foilcals are stamped indifferently by JBL 8ohms or 16 ohms for the same voicecoil (and the same acoustical load... eg 2405 horn/phase plug + rear load).
And yes, i agree that 8 or 16 are the impedance numbers with no significance when designing Xover...
(and i teach the complex impedance with DC resistance plus coil self effect vs frequency plus additional mechanical and acoustical (radiation) terms from driver itself and its load (eg added stiffness due to the closed box volume (like a spring))
http://www.audioheritage.org/vbullet...l=1#post200233
and my own (old) impedance measurement performed on E145 drivers showing the coil contribution in impedance value at "high" frequencies
I realize you understand and yes it is true that in the past on certain models JBL was inconsistent with their foilcals, but most people don't get the significance of impedance at all. In the scope of this thread 8 ohms does not = 16.
I bet many here will take a cursory look at that impedance plot and think, "geez, that speaker has a terrible frequency response"... I've gone to the trouble to post the plot hoping that at least one person out there will now understand that DCR is the resistance of the coil at 0 Hz and not it's impedance.
Widget
Are these both 8 ohms but labelled as 8 or 16? Is there some date when they really did put diaphragms with different DCR values into the drivers for 8 and 16 ohm versions?
I understand that in the 1960s JBL called the LE14A a 16ohm woofer at first, and then later it was 8ohm woofer - I have a few of each, and they all have about the same DCR, and the measured impedance is the same (after replacing the foam)
Modern JBLs use G,H, or J as the last letter to signify the impedance. G=4 ohms, H=8 ohms, J=16 ohms.
In the past they used A and B and others but they were inconsistent.
Widget
Thanks a lot for all your replies!!
You guys brought some light in my confusion....
The intention of my question was the following;
I got a pair 2405 ( labeled 16ohm , Alnico ) and a pair 2440 ( labeled 16ohm ) mounted to a 2390 horn/lense....
JBL claims the 2405 to be 105db/1w and the 2440 mounted to the 2390 to be 107db/1w. Due to the fact that I personally hate the sound of resistors in a passive crossover, I was wondering if these two drivers would match in terms of loudness when connected to the same amp-channel....
I apprehend the midrange will be a little too loud....
So my idea was to swap the 16ohm Alnico-2405 against an 8ohm Ferrit-2405.... Due to the lower impedance the 2405-8ohm should receive more power from the amp than the 2440-16ohm and compensate the lower efficiency....
But I am on the wrong track, ain`t I ?
Yep.
Resistors are your friend.
Widget
my understanding again is there will be no major difference (alnico/ferrite debate out) when the two drivers have the same voice coil, same diaphragm ...
Have you any DCR measurement on the two to confirm ?
Sorry guys, I believe i missed a post of yous, respectively I didn`t get it right.
So 2405-alnico and 2405h-ferrit have the identical voicecoils, but different labels on the back. Sorry for that extra turn
I have no current measurements of MY DRIVER`s, cause they´r stored somewhere at my parents place...
OK, so these actually ARE different then, and not just a change in label? I'm asking because I'm wondering if 2426Js would be just as good to use as 2426Hs (in for example, DIY 4425s or 4430s). (so the H and J versions would have different voice coils, if they do have different impedances?)
regarding these animals and one connecting pin of the voice coil is red marked for 16 ohms (J) while green marked for 8 ohms (H)
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