JBL Compression Driver Diaphragm Polarity?

[mefisto]

Greetings all,

I cannot spot a color on either terminal of the diaphragm, how do I determine a correct polarity?

Kindest regards,

M

[Robh3606]

What are you trying to do why is the driver open??? You can verify polarity looking at the impulse or step response.

Rob :)

[grumpy]

Bottom right... small residual amount of green (?)

[Earl K]

Greetings all,

I cannot spot a color on either terminal of the diaphragm, how do I determine a correct polarity?

Kindest regards,

M


There's ( obvious to me ) green paint on the lowest terminal ( seen in your posted pic ).

Connect the internal red wire to that diaphragm terminal (having the green paint ).

:)

[Robh3606]

Good Eye!

Rob :)

[Mr. Widget]

There's ( obvious to me ) green paint on the lowest terminal ( seen in your posted pic ).

Connect the internal red wire to that diaphragm terminal (having the green paint ).
10 points Earl!


Widget

[mefisto]

Hi Robh3606,

I am not sure, what you are asking; as written, I am trying to determine, how to connect the wires between the cover terminals and the diaphragm terminals. Thank you for the recommendation re impulse/step response

Hi grumpy, EarlK,

I am afraid that this is an artifact of the lightning reflection from the protective plastic partially covering the terminal copper lead. Here is a close-up of the terminal. Now, I have lowered color sensitivity, so I may be wrong.


Kindest regards,

M

[grumpy]

That's all there is. The green shown is exactly the green used for indication. Would appear (color, translucence) something like clear green cellophane.

[sebackman]

Agree with all above. Colored dot terminal (here Green) is for the Red lead.

Which is negative in these old JBL units. Black is positive in the sense of moving the diaphragms towards the exit. The green spot means 8 ohms and if red 16 ohms diaphragm.

If there indeed are no visible markings you can also use a small AA or AAA battery (only 1.5V) and connect to the diaphragm and with the back cap open you can see the diaphragm moving ever so slightly towards the exit or backwards when looking close. The connector that create movement towards the exit from plus at the battery is the black lead.

[mefisto]

Hi grumpy,

you are correct, it is a plastic-like piece, partially covering the lead from the diaphragm's winding to the diaphragm"s terminal. Thank you very much for the clarification.

Hi sebackman,

thank you for the reply.

However, something does not appear to be correct. Both of the diaphragms measure , 4 Ohms (at DC), but according to your post it should be an 8 Ohm diaphragm.

I am also rather confused with the coloring. Since the black terminal, when correctly connected to the diaphragm, will move the diaphragm towards the phase-plug, when connecting to an amplifier, it should be connected to the output and not to the ground. I may consider swapping the terminals-to-diaphragm so that I have the accustomed configuration.

Kindest regards,

M

[Robh3606]

4 ohms DCR is correct for an 8 ohm

Rob :)

[mefisto]

Hi Rob,


4 ohms DCR is correct for an 8 ohm

Rob :)

Thank you for your reply.

I was wondering because I remember to have read that the standard requires that impedance does not drop below 80% (or was it 70%?), of declared nominal impedance under any conditions. Even the more relaxed standard would result in 5.6 Ohms.

But, I will take your expertise and consider it an 8 Ohm. In fact, after having thought about it, it makes sense because voice coil being, well a coil with inductance, will just cause the magnitude of impedance rise as a function of increasing frequency.

Kindest regards,

M

[sebackman]

Hi,

Attached is the impedance of a naked (no horn) 2450SL 8 ohm driver (green dot) over the frequency spectrum.

Most older JBL's used a reverse color scheme on their speaker components. This goes for both woofers, mids and drivers. They used black terminal for positive phase whereas most other used red.

https://www.audioheritage.org/vbulletin/showthread.php?477-Reversed-Polarity-on-JBL-Speakers-When-Did-It-Start-and-Why&highlight=polarity

[mefisto]

Hi sebackman,

thank you for posting the impedance, this further confirms Robh3606's post.

Would it be possible to post a the impedance curves in a format that I can further process, e.g., *.csv, *.xls, and the like?

Kindest regards,

M

[sebackman]

Hi mefisto,

Sure, what driver core, what diaphragm and on what horn? I may have something if you use modern JBL stuff. Happy to share.

The horn loading will of course completely change the impedance curve.

kind regards
//Rob

[mefisto]

Hi sebeckman,

thank you for your generous offer.

The driver's core is 2450SL, and I have two diaphragm types - D16R2441 and another, a designation of which I do not know, it is Aquaplassed (dome only) Ti diaphragm depicted in my first post.

The wave-guide is, unfortunately, nonstandard in that I have modified B52 - PHRN1014 by (i) replacing the 1 in throat with re-calculated and printed throat 1.5 in and (ii) adding a round-over to the mouth, cf. the attached pictures. As such, I do not believe that there is anything comparable.

Saying that, for my current purpose a measurement of the driver only, e.g., SPL, Impedance would be sufficient.

Kindest regards,

M

[sebackman]

Hi,

I have no idea how such horn would load a 2450SL driver.

Attached is the impedance (curve and data) of a 2450SL coated smooth Titanium (here called "D2" out of 9 drivers measured) on a JBL VTX F15 wave guide #5006815.

Kind regards
//Rob

[mefisto]

Hi sebackman,

thank you very much.

Kindest regards,

M