How to determine proper JBL polarity

[Kay Pirinha]

It's pretty standard now I believe, that pin #2 on a XLR input is positive. I swear when I got started years back, pin #3 was hot? I found some old adapter XLR to stereo 1/4" cords I made many years ago and I had to swap the hot wires to work with modern stuff.I just was making a new system and also found that I had some of my drivers out of phase. So this issue seems current for me. I got a pair of JBL/Selenium 2" drivers to test. Someone removed the rear cover on one and rotated the diaphragm 90 degrees. It wasn't blown just re-installed incorrectly. I got lucky there. So while inside I tested for polarity. I just used an old AAA battery very quickly to observe diaphragm movement. I've never done that before and I'm wondering if I should continue that practice? On my normal JBL cone woofers, I feel that quick pulses of low DC volts (1 volt) won't hurt them. I don't hold on long enough to heat anything up. Just to double check polarity.

Ok, let's do the math: Assuming a fully charged AA or AAA cell, you apply a power of 1.5[V]²/8[Ω] = 0.28 watts. That really won't hurt, even after a longer period. But, as I've never done it before with a disassembled CD: Is any diaphragm movement clearly enough to see?

Best regards!

[engineerjoe]

Ok, let's do the math: Assuming a fully charged AA or AAA cell, you apply a power of 1.5[V]²/8[Ω] = 0.28 watts. That really won't hurt, even after a longer period. But, as I've never done it before with a disassembled CD: Is any diaphragm movement clearly enough to see?

Best regards!

I saw it move! Most guys back in the day used a 9 volt to a 1/4" plug because it was so easy. I was warned not to use it on horn drivers for prolonged periods. So I stayed with that.
Using that formula, I think I will continue when inside a driver of unknown polarity.
I was going on and on about sound systems without knowing if the OP was into large sound systems, studio, or just for home stereo use! Very sorry.
I like to ramble.

[Eric M.]

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.

[engineerjoe]

http://www.jblpro.com/ProductAttachm...eN1V12C_v5.pdf

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.

[edgewound]

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.

[engineerjoe]

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 by out of phase.

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?

[edgewound]

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?

The new Harman by Samsung is rearranging everything to how they see fit.

Progress.

Google searches will most likely be of help. That's how I found this link. Finding old resources that used to be easy to find...is no longer so easy.

[engineerjoe]

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?

[engineerjoe]

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.

here's the same idea.

[Kay Pirinha]

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?

Why should they have altered anything? It would make refurbishing an old driver even more confusing.

Best regards!

[engineerjoe]

Yes, that would make sense! …. if they did do that.
How about the knock offs?

[Kay Pirinha]

Sorry, I dunno . But why should they differ as the possibility of confusing also applies to them?

Best regards!