4312As with the mid out of phase

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06-07-2020, 07:55 AM
Zeb Norris

4312As with the mid out of phase

So this is weird. I picked up a set of 4312As a few years back. But they have just never sounded right to me. I poked around a little when I first got them, but everything looked OK. I didn't like them as much as my Centurys, so they went in my office. Where they still didn't sound right.
We moved and they got put in use for the media room. I was watching an episode of Monk and everything sounded wrong. His voice sound liked there was nothing but upper mid. And the imaging had always been super unstable.
So I looked at them again, but this time with a ton of knowledge from this site and Audio Karma. It turns out the tabs of the mid... 104H-3s... were wrong. It has the "genders" of the tabs reversed. Plus was on the left side of the speaker as the wiring diagram shows. But it's tab accepted only the negative wire. I tested the speaker; + moves the cone forward as stated in the tech sheets for the 104H-3. Has anyone else encountered this?
So anyway I got in there are put another set of connectors in the wires so I can easily change the polarity/phase.
They sound SO MUCH BETTER now. I could go on and on about the difference between my early 70s Centurys and my mid-80s 4312As... now that the midrange speaker is in phase. Much flatter than the Centurys. Piano and voices in particular benefit from the improved mid-range. Loads of bass, but not so peaky at 70Hz. They're mirror imaged... and as a result the imaging is spectacular.
This is my first post. I'll post some pics If I can figure out how to do that...
06-07-2020, 08:01 AM
Zeb Norris

Lol anyone know how to post pics?
06-07-2020, 08:41 AM
Odd

How to Add Images and Attachements to Posts
06-07-2020, 01:24 PM
grumpy

Missed the AK storyline, so this may be old hat:

Check the woofers? Perhaps a previous owner got them in backwards (push terminals vs sized tabs?)
... as it’s supposed to be wired out of phase with the other drivers (black stripe to neg terminal), and is run wide open (no crossover filtering) so lots of driver overlap.

https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Jbl-4312A-L-Technical-Manual.pdf
06-07-2020, 02:56 PM
Zeb Norris

Thanks Grumpy, but everything else was correct.
06-07-2020, 03:00 PM
Zeb Norris

3 Attachment(s)

Here's what I found, and how I proceeded. Made it easy to switch back.
06-07-2020, 03:33 PM
grumpy

Glad you got it sorted! Factory mistakes have happened.
06-09-2020, 08:09 PM
DavidF

I hesitate to go down the driver polarity path on this but should add some background on your situation.

Agree that the terminals, male and female, on the mid driver are reversed according to the tech sheet illustration.

On this vintage of JBL drivers the male terminal is the "positive" terminal in the broad industry sense. A positive signal to the male terminal will cause the driver cone to move outward. It appears you confirmed this.

Your system follows JBL convention that is the reverse of everyone else as to driver polarity. The tech sheet shows all three drivers wired in the same polarity. Your conversion reversed the mid polarity relative to the tweeter and woofer.

As to whether this is correct per design, I don't think it is. Since you much prefer the sound with the mid reversed, then it makes sense to leave it as so.
06-10-2020, 05:10 AM
Zeb Norris

Quote:

Originally Posted by DavidF

I hesitate to go down the driver polarity path on this but should add some background on your situation.

Agree that the terminals, male and female, on the mid driver are reversed according to the tech sheet illustration.

On this vintage of JBL drivers the male terminal is the "positive" terminal in the broad industry sense. A positive signal to the male terminal will cause the driver cone to move outward. It appears you confirmed this.

Your system follows JBL convention that is the reverse of everyone else as to driver polarity. The tech sheet shows all three drivers wired in the same polarity. Your conversion reversed the mid polarity relative to the tweeter and woofer.

As to whether this is correct per design, I don't think it is. Since you much prefer the sound with the mid reversed, then it makes sense to leave it as so.

Agree it doesn't make much sense. It's not like just MY mids have a "male" connector on the positive terminal. But that IS positive, as I confirmed with a AA battery. After the change the wiring is as illustrated in JBL's wiring diagram.

I tried a AA battery on the entire speaker, but the crossover network only put the power to the woofer.

Anyway, I do know enough about the sound of out-of-phase drivers to be confident they are now correct. Huge improvement. Now they sound a lot more like my Centurys. Smooth response to a frequency sweep, as opposed to a volume dip or hole in the crossover zone.

But it's bizarre.
06-10-2020, 07:04 AM
Zeb Norris

Quote:

Originally Posted by Zeb Norris

Agree it doesn't make much sense. It's not like just MY mids have a "male" connector on the positive terminal. But that IS positive, as I confirmed with a AA battery. After the change the wiring is as illustrated in JBL's wiring diagram.

I tried a AA battery on the entire speaker, but the crossover network only put the power to the woofer.

Anyway, I do know enough about the sound of out-of-phase drivers to be confident they are now correct. Huge improvement. Now they sound a lot more like my Centurys. Smooth response to a frequency sweep, as opposed to a volume dip or hole in the crossover zone.

But it's bizarre.

I've been hesitant to re-cap them... thinking if that was required, I would update the entire crossover instead.

Question; could a failed capacitor in the crossover change the speaker phase? They ARE 1986 speakers.