Hello all - looking for assistance on a pair of JBL 4435's
I've been told "re-cap them!" - but why? - and how can I tell specifically? - also I have read on here that if they are the older model they have the aluminum tweeter and not the titanium - how do I tell? - serial numbers? - and the internal crossover - apparently it's pretty good?
I've looked through all the posts for answers so please don't scream at me.
Ok, now you can scream at me.
Thanks.
Are you trying to fix a problem with a recap?
A bit more than a "tweeter", I believe all 2426Hs used Titanium diaphragms but the voice coils were edgewound aluminum. Those pro networks will usually work fine for quite some time without needing any work. What's the issue? Remember, on most big 44xx or 43xx monitors, "sh*t in equals sh*t out".
". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers
Also, older 443x system did have 2421, aluminum diaphragm drivers. Small hex key to remove horn/driver to see what you have.
As far as trying to fix? - not sure - I was advised to "change the caps" after talking to a few people about the 4435's - just looking for advice from experts that after 15-120 years of age this is a regular mod to do. As far as sh*t in, sh*t out, input is 24Bit/96k optical to a Parasound Pre to a Parasound Halo A51 Amp. It drives a pair of LSR32's very nicely but the 4435's are a little much in the 63-125Hz area and a little harsh in the mid-range - yes, it could be the room and this could also be a characteristic of the monitor - I'm just trying to get them flat and as true as they can be to when they were designed.
The serial of the right is 254961 if that might shed any light.
Thanks for your help.
Matt.
You can have the crossovers gone through by a qualified tech, its easy enough to check the components. Replacing caps is sometimes done simply because its easy enough to do when the boards are on the bench, and its sometimes considered best to replace all rather than a few. But assuming properly functioning components, its not a certainty that rebuilding them will change anything.
Sounds like you have a decent enough system driving them, but that doesn't mean the source material is up to the mark. GIGO means that the music itself must be well mastered, whether its delivered in 24/96 or 16/44 has surprisingly little to do with it.
If they're on the floor, get them up a bit.
I've got them up at about 4 feet off the floor - so I'm in Los Angeles (I can see JBL Northridge from my house- can you suggest a tech in LA? - or at least a good starting point?
Thanks for your combined advice so far - very kind.
Cheers.
Originally Posted by grumpy
Once I remove the horn with a hex key what am I looking for specifically? A part or model number or just a physical indicator?
the back of the compression driver should have the part number sprayed on it in white ink
(or less likely, a "foilcal" with the part and serial number on it)
Given the serial numbers referenced in the URL below, there's a fair chance yours are aluminum diaphragms.
http://www.audioheritage.org/vbullet...l=1#post135799
Yes, took the compression driver out and not sprayed but a nice shiny jbl sticker but still labelled 2421A. Is the "A" for Aluminum?
I need the 2425H correct?
Can I just purchase something like this?:
http://www.ebay.com/itm/JBL-2420H-24...item25698e4284
I am assuming this will fit? somehow?
So is there a good reason to upgrade to the titanium compression driver or simply a personal choice? The 2421A is a little harsh.....
Thanks
Matt.
D8R2421 or D8R2425 would be the JBL Al and Ti replacements, e.g.:
http://www.simplyspeakers.com/jbl-re...m-d8r2425.html
The Al units are a bit more pricey.
You can do what you like, but you're likely to be disappointed with a $40 aftermarket diaphragm.
There have been tests done by folks here that bear this out.
Others have had good experience with replacements from Radian (1225-8), at a price between
questionably cheap and questionably expensive.
Before going that route, make sure the L-pads are clean and adjusted well (and match side to side).
This is harder than it sounds unless you have some test equipment... something a studio would have
readily available (and where these "tools" were designed to be used). A fairly small change in the
settings (don't be afraid to set them to other than "0") can change the character quite a bit.
Also, if these came from a studio environment, there's a fair chance that the stock aluminum
diaphragms have worn out (played hard) and -need- replacing. If you open the backs, there's
also a fair chance that the damping pad (open cell foam) is in poor condition and could be replaced.
Shoot, if they were ever opened up, who knows what diaphragm is in there. Might be Ti already
or some aftermarket wank job... worth checking. Not hard to look and take some pics (cap doesn't
come all the way off...wired to the rest of the driver, so be a little careful).
... and one more thing, if you like to listen at really loud levels, these may just not be your
cup of tea. I don't play mine loud enough for it to be a problem (for me), but this driver on
this horn in this system series has been noted by others here to get harsh sounding when played
at loud (too loud for me) levels.
Personally, if budget was a priority, and you've sorted out the typical 443x issues I'd be hard
pressed to recommend the JBL Al diaphragms at several hundred each, and would probably look
at the Radians before the JBL Ti units. If you happen to -like- the Ti sound better, I'd stick with the
JBL units (and probably get the whole 2425/2426H driver so the 2421A's could be set aside or traded).
(oh yeah... A stands for 8ohms, B for 16 ohms on a 2421 driver ... later drivers, both cone and compression,
used suffixes G, H, J ... for 4, 8, 16 ohms)
OK - great advice! - thank you. So, I removed the driver and took of the back of the casing - this is a pic of the diaphragm. The damping pad looks in good condition too.
Any idea what they are? - I didn't see any serial numbers.......
they appear to be JBL aluminum diaphragms. That pad is already starting to turn to goo.
Not the worst I've seen though
I'd button them back up and leave them alone, using other cores for your experimentation
(e.g., 2425 or 2426)
Oh, you mean find a complete driver and not change out the diaphragm?
Also to answer your other questions, I'm monitoring at between 70-75dB for music, not too loud at all, but still have the harsh mid-range.
So to clean the L pads you said most studios would have test equipment to do this? What kind of equipment?
if you know of any techs in LA can you let me know? Getting lots of great advice from many people but not found one yet that can change caps or check crossovers etc...
Cheers!
Cleaning (or replacing damaged) L-pads is separate from
getting them set to appropriate and matching levels
(which you may attempt to do by ear, or with the
test equipment I casually referred to).
It's a bit of careful work to get to the L-pads (have to
remove the metal plates (a bit thicker than a "foilcal")
which are glued on, then remove some screws behind it.
then the real work starts. If you don't notice any cutting
out of the sound, or odd jumps in level while turning the
controls, I'd leave them alone and concentrate on levels.
You want close to the same level coming from the
midrange and the woofer at crossover (roughly 1KHz),
so if you turn the HF control all the way down, then
alternately connect the woofer and then the
compression driver while playing a tone, you could use
a sound level meter (or equivalent mic, pre, a/d,
and computer program) to match their level by
adjusting the MF control.
Do the same for the other channel (with reasonable
disregard for the level markings).
Then turn up the HF controls to taste. If it's still harsh,
try reducing the MF controls in matching, small increments.
http://www.lansingheritage.org/image...-35/page04.jpg
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