Everything I read (non-JBL) says DC current to a speaker pushes the dome or diaphragm outwards. Yet, when I check a know original JBL driver, I get the opposite. I've heard that JBL often wired drivers out of phase, could this be what I'm experiencing?
Thanks,
Eric
Yes, I've seen all the older JBL is wired so + to the black pushes out (backwards of norm)
The new stuff is + to the red term so be careful and double check stuff with very low DC voltage (1 or 2 volts) for quick pulses only. I was taught this by a tech at Unistage many years ago. He said you don't want to heat the coils or cause damage by prolonged application of higher DC voltage. So I've always followed this.
(I'm not a JBL tech! I've just always used them when possible. For something like 40 years now)
I'm still wondering what might have provoked JBL to polarize their speakers the other way round. For comptibility reasons I changed polarity in my 2225H subwoofers by reversing the internal hookup cables.
Best regards!
I use a 9 volt as well. It moves big cones enough that you can clearly see their direction. I doubt keeping it hooked up very long will do any damage to low end drivers, just not enough wattage.
For compression drivers, I will unscrew the diaphragms. Hit terminals quickly with 9 volt (could probably get away with 1.5v). The diaphragm will either stay put or jump slightly. You won't see any movement of the actual diaphragm surface and I'm guessing if you did, you'd probably be in trouble. I keep it quick, DC (0 Hz) isn't anything a mid or high driver like.
Did they do this with all their older gear? LE15A, LE8T, 375, LE85, 175, 075, 077, etc.? I'm assuming they had to or their own speakers would be out of phase. I wonder when they made the change and if any info was ever sent out regarding mixing and matching new with old, especially with studios and sound reinforcement companies who might need to stick a newer driver in a cabinet with older drivers.
Eric
I retired from pro sound years ago. Back then it was known that their equipment was wired the other way +. Recently I started building another sound system for kicks. I couldn't help noticing that the wiring sticker on the speakers proclaimed that a positive voltage to the red term would produce outward movement of the cone, or something like that.
So that was on some used JBL's that I just got. They are years old now. So I can only guess at when the change happened. My older woofers (2226 for example) made in the eighties were before the change. So when did they release the newer neodium type woofers? (like maybe the #2258 or newer stuff?) I think that's when the change occurred?
That is great!Originally Posted by robertg
So a 2242 18" woofer is opposite the 2241 18" woofers. I have a good idea now with that of why I missed it.
Thank you I copied it for reference!
I always check stuff first as I was always afraid of recons not matching. I didn't realize it took place so long ago.
Always made me wonder on compression drivers. The 2451, for example, is listed as "negative" - but the diaphragms for those are physically compatible with drivers not listed as "negative", and the coated versions of the 2451 diaphragm are popular today as replacements for other 4" drivers. And what about TruExtent? Their 4" diaphragms are listed to work in most all 4" JBL drivers, ones JBL lists as both "positive" and "negative".
Most guys here will be able to do measurements to see if a driver is suddenly out of phase after a diaphragm swap, but looks to me like a potential source of confusion.
I was wondering about the 2450 and 2451 series drivers. They originally had the polarity flipped. Did the production of replacement diaphragms at some point correct that? Would they retain it to conform with the original product?
here's the same idea.
There are mistakes! From discussion here, seems like about 1 in 50 is backwards. I have a pair of 2241Hs and they are different in that one moves the cone out with + on red while the other goes in as it should. I checked with a compass and the polarity of the magnet is reversed on the former.
Rats! Now I come back to look at this sheet again and it's deleted!
I thought I saved a copy on my computer but it's not there.
Not deleted, just moved.
Here's a new link to the Tech Note on JBL Polarity Conventions.
https://adn.harmanpro.com/site_eleme...5_original.pdf
Remember "Polarity" and "Phase" are not interchangeable terms. Although, if polarity of one or multiple drivers is reversed, the system might be out of phase. If the polarity is reversed on two of the same systems, they will be out of phase.
Edgewound...JBL Pro Authorized...since 1988
Upland Loudspeaker Service, Upland, CA
Thank you! Although the first link didn't work here on this site, it did save the link on my computer that still worked. I thought it wouldn't?
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