View Full Version : Update or rework of 4412 crossover or tweeters?

Dave Dunbar
05-31-2012, 08:24 PM
I posed my questions here about two years ago, and the consensus was that I needed better gear feeding my 4412s. So I've majorly upgraded the audio chain. I now have an Adcom 555 amp (just tweaked by a great shop), a McIntosh C27 pre-amp (ditto), a Cambridge Audio CD player (as well as a Sony EX) and an HD Technologies MusicStreamer II+ DAC. So I am now sure I'm feeding my JBLs a nice clean audio signal (BTW, the new gear made my L110s sound much better!).

I'm still not convinced that my 4412s are sounding 100% the way they originally did, especially on the upper mids and highs. I got them from a radio station, and the chief engineer told me the tweeters "might" have been redone at some point in their life. He had no idea if they used JBL parts. He was quite sure the crossovers had never been touched. The only thing I've done is have the woofer surrounds re-done.

On a high percentage of material the 4412s are just dynamite, but on some stuff, the upper mids and highs sound just plain harsh. Especially on high-energy passages and female voices. It's much less harsh with the improved equipment, but there's still more harshness than I think should be there. I've taken the CDs from which I get the harshness to the homes of friends with modern high end systems, and they sound far less harsh. Heck, even the L110s are smoother on the high end.

There is zero question about the bottom on my 4412s...it's remarkably clean, tight and robust. I get the kind of bass my friends have to use expensive subs and bi-amping to acheive, and they still envy the bottom on the JBLs.

I listen mostly to high-quality reissues from the 50s to the 70s, and the gear I've got is great for "vintage" playback. The age and quality of the gear is intentional. Trust me - good modern gear wouldn't have cost much more.

I have two areas which may be at issue; the crossovers and the tweeters. I don't have a way of knowing if my suspicions are correct. I'm in Cincinnati, and we don't have a really good, top quality audio repair shop here (I've had to lug my stuff to a shop in Columbus!). I've read here in the forum that caps go bad over time and should be replaced. But posters also say this can affect the sound in a negative way, or hurt the resale value of the speakers. Re-sale doesn't concern me; I will direct the executor of my estate to sell them. I'm wondering if it's bad caps that could be causing the harshness I hear. My tweeters are also suspect. They may or may not have been redone, and may have been done by someone who didn't really know how to do it to JBL factory specs.

How can I tell for sure if anything is amiss? Could bad caps cause the harshness I hear? Is there a way to test this? How about the tweeters? How can I know if they're right?

I don't know if I've seen any JBL service shops posting on the forum (except for one, and he hasn't responded to private e-mails or calls). Would I be out of line to ask members to suggest good shops who really know what they're doing? I really want these speakers to be totally right. I love so many things about them, and I will always be wondering if they're totally right, unless and until I can find someone who really knows these speakers who can suggest the correct path here.

Thanks in advance for any suggestions.

Mike F
05-31-2012, 08:58 PM
You may want to determine if the tweeters are in fact original and in proper working order. If you have access to a sweepable sine wave generator, it would help in troubleshooting.
Faulty tweeters can certainly sound funky at some frequencies and quite normal at others, a sweep of the tweeters operating range is a good start.

You make no mention of particular offending frequencies, a spectrum analyzer would be useful, perhaps your issue lies in the upper midrange and not the tweeter range.
The 4412 has a relatively balanced response, how are you running the onboard attenuators?

05-31-2012, 09:26 PM
Don't know but I'll suggest:

Some insist the 035ti can have issues as they age caused by deterioration of the foam plug behind the diaphragm.

Can you post a photo of your tweeters? Anyone in the area that could swap tweets with you? Those are pretty common among vintage JBLs. And your 4412s also have L-pads that could be dirty and causing problems. I hope you can sort it out. The 4412s should be a source of joy rather than aggravation!