JBL wiring

[Will Meyer 2,374]

Fyi...

I can across this a few years ago when I was upgrading my JBL L100t speakers to the L100t3. The upgrade (T to T3) is considered a significant improvement amoung the JBL community. 

 

I've attached the technal manuals for the T and T3. As you can see, they are wired 180 degrees out of phase.

 

Common industry practice is that a positive voltage will drive the woofer outward; however, on a T a positive voltage will drive the woofer inward. This was changed on the T3 and is noted on the bottom right of page 1 of the T3 technical manual.

 

I've been told (I don't know this for sure) that early JBLs (pre T3 I'm guessing) were wired so that a positive voltage drives the woofer in.  This shouldn't cause an issues when running just one set JBLs, but I would think that running them in chorus with other speakers or subs may yeild a phase imbalance.  

 

Does anyone know any details on this?

hfe_jbl_l100t_technical_en.pdf hfe_jbl_l100t3_technical_en.pdf

[Yamacarver 806]

I think you summed it up pretty well.

From what I read there was no standard when JBL decided on this polarity and then when it was standardized, it went against him.

Then they had to switch to avoid confusion. My subwoofers are that way and you can check with a 9-volt battery.

[Rob 6,007]

I have a set of those L100t3's. Very nice speakers.

[Yamacarver 806]

On 7/23/2023 at 7:57 PM, Will Meyer said:

phase imbalance

So you merely put red to black and black to red on the older speakers if you want to use them with others.

Now if you had to replace an individual driver it might get complicated not knowing how old it was and the 9-volt battery will wreck a tweeter I think, so you would have to test for phase some other way like maybe a microphone on your oscilloscope and compare to the other speaker or see if they cancel each other out.

I have often wondered about this but apparently as long as they're all the same, that is all that matters.

When a drummer stomps the bass pedal, the pressure wave is coming at you but how does he hear it sitting behind the drum?

Edited July 27, 2023 by Yamacarver

[4krow 6,630]

 I knew it. This topic caused me to search for information of another JBL speaker that a friend of mine bought from me. I did not like the internal wiring or the switch on the back of the cabinet for single or bi-amping. Sooo, a very long time ago, I rewired everything myself, and I cringe to think of what it must looked like when I finished. my soldering skills and tools back in the day sucked. Now, I am on a mission to somehow get these rewired in a proper way. Of course, going to the JBL commemorative site has helped a bunch, but it would still be a challenging job. Now crossovers might be easier in a way but really expensive to build.

[radtraveller 283]

Have had a long held desire to build my own speakers.. just once.. no internal crossovers.

Active external crossovers with level controls for each output, individual amplification for each speaker.

Maybe open baffle, just because they look cool.

[4krow 6,630]

I agree.

 

[timmyjim 463]

On 7/23/2023 at 10:57 PM, Will Meyer said:

Common industry practice is that a positive voltage will drive the woofer outward;

It seems that JBL in particular has wrestled with this for some time.

 

Follow this link and download the Polarity Conventions tech note.  It doesn't apply directly to your models, but it does indicate that they couldn't make up their mind to the point they had to write a tech note .....

 

https://jblpro.com/en/products/4312a

 

 

[Yamacarver 806]

Here's a good article on the subject.

https://audiouniversityonline.com/speaker-polarity/

 

When pro speakers changed to the quarter inch phone plug, you could no longer swap the polarity at that end of the cable.

Doing so at the other end of the cable would render the shell of the phone plug hot. I have a pair of MR - 825's with phone plugs and I know if one gets pulled while the speaker is playing, it will short the amp on its way out of the hole. So that was just a bad idea all around and probably why they found something better.

Edited July 29, 2023 by Yamacarver
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