help for JBL 4425 crossover problem

[electronicguest]

Have a problem with JBL 4425 crossover.
R201 (LPad nr. 2) N36-58450 (8ohm/30W) have a very very little influence, close to zero, almost non-existent.
In my opinion for my JBL 4425 speakers R201 is not justified.
In JBL4425 Specification Document can see another things if you study the control range chart - high.

http://www.jblpro.com/pub/recording/4425.pdf

Made some schematics design research, and redesigned the circuit, see the pictures:

R201 made a short-circuit for R4 and put 8uF capacitor to negative pole.
total resistance varies from 0 to 5,714 ohm
Did I miss something ?
There is someone who has JBL 4425 to tell me if turn High Frequency Level knob - LPad 2 (R201) from minimum to maximum
how effective in correcting sound is ?

[mech986]

http://www.audioheritage.org/html/profiles/jbl/4430-35.htm

Study the concepts of the 4430/4435 crossover which were designed before the 4425. Dave Smith designed the 4430/35 and its primary network. The 4425 was designed by Greg Timbers so his solution may more be along the lines of the 4315/433x/434x style although those are all multiway with discrete tweeters and horn mids.

[mech986]

http://www.jblproservice.com/pdf/Network%20Schematics/3124%20Network.pdf

Here is the original 3124 network, much cleaner than the pdf exploded diagram:

http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4425LR.pdf

Before blaming the crossover, do you have fully functioning 2416H drivers with original JBL diaphragms in them? Aftermarket diaphragms are notoriously poor in frequency extension and response. If Radian makes a replacement, that may be acceptable. All of this is strictly for the original 2-way design and once you have the original 2 way design working properly with the crossover, then you can work on integrating the supertweeter. Once you start adding on a super tweeter, you have a bunch more interactions to deal with unless you biamp it with another separate passive or active crossover and amp, which might be the cleanest way to go rather than tap signal off the primary crossover and have a passive unit there. Greg Timbers has commented on adding a 2402/05/04 type tweeter with simply a 15-30W amp and active crossover or simple first order capacitor.

[johnlcnm]

Not so sure we are on the same page. I assume you are talking about the pot marked as 12kHz. You should be able to hear the level change. I sure can on my pair of 4425s. 12kHz is about the limit of my hearing though. I do have the Radian diaphragms in a pair of 2426 drivers in mine. My preferred adjustment is -0.5dB. The Radians are supposedly a tad hotter at the high end.

Regards,

John

[electronicguest]

Thank you very much for the explanations. I did not blame the crossover just because
JBL never did bad things. I used carefully selected components and checked the final assembly for several times.
All it's perfect. We are talking about the pot marked as 12kHz as you said.
I asked myself the same question if I have the original JBL diaphragms
in my 2416H drivers and I don't know what to answer. I intuited that non original JBL
diaphragms can be some different but I did not know that the replace for non original JBL diaphragms
can be so poor in response. Seems that's a very big difference.
See the pictures and please tell me more about my JBL diaphragms. Looks non original ?
Keep in touch.

[johnlcnm]

Those look to be original. The diaphragms are part of the end cap. Usually the aftermarket junk uses round magnet wire, not flat wire like JBL. That is at least one of the signs that it is aftermarket. I went to the 2426 because the diaphragms are separate from the back cap. Radian no longer makes their aftermarket back cap for the 2416. Somebody here, maybe Zonker, used a plastic pipe cover glued to the back of the driver when he installed the Radian diaphragms. The 2426s used to be cheap as they were common in the professional sound business. The 2426 also uses the annular phase plug which according to JBL is an upgrade over the hole type plug. The 4430, and I believe 4435 use the 2426 compression driver.

Regards,

John

[electronicguest]

Thank you for the answer. I found for sale Radian diaphragms for 2416 here in Romania

https://www.thomann.de/ro/radian_12258.htm

98 Euro/piece. Will buy 2 these days.
Have another question. Which it's the role of the 2 x 100 Ohm/10W resistors in parallel with
low frequency speaker ? I never saw that before.
I guess that a lot of bass power drop here.

Keep in touch

[johnlcnm]

My guess: Those resistors reduce the rising impedance of the woofer due to the voice coil inductance. Cheaper then using a resistor and capacitor in a compensating network. Sometimes referred to as a Zobel.

Regards,

John

[electronicguest]

thank you very much for your help.
keep in touch.

[script56]

8216082161I have solved similar problem for Jbl 4430 and 4435. You can remove crossover from cabinet and test every resistor and capacitor with multimeter (ohms for resistor and capacitance setting for caps). I would remove crossover board and clean the rotary switch that sets internal and external crossover. Spray deoxit on metal part above board where switch setting sets into plce. Also clean the top of switch where the ball sets into place. Even though this is not electrical part, it can still effect performance if ball does not set into place due to corrosion etc. this problem I solved twice. If you need pics let me know. With the 44xx series, I would always clean switch before anything else.