Discussion in 'The Lansing Legacy' started by Mr.White, Feb 8, 2018.
What exactly do I need to do?
The tinsel lead needs touched up with some fresh solder. If you don't have experience with a soldering iron and/or don't have a steady hand, I'd get someone more experienced to do it for you. You don't want to slip and burn a hole in the cone or surround.
Ok. I have been wanting to learn how to solder. In the basement of my coop there is an electronics recycling bin so I have an endless supply of stuff to practice on.
A scratching sound could be the coil. Compare it to the other woofer.
This is an L19A, an A should follow the serial number, it denotes use of the later 116H ferrite magnet woofer as pictured.
A magnet shift is possible but less likely with ferrite magnets vs alnico magnets unless either sustained a hard blow or fall, but there is no evidence of that, at least on the cabinets. Since this issue has occurred over time, a slightly sagging spider due to cone/voice coil weight is more likely. Even though people suggest a 180 deg. Turn, I always suggest the woofer or cabinet be turned in 90 deg. Increments and sound quality noted in each position, also noting the actual position of the woofer orientation - note that with a colored stick on dot. At the nominal "top" of the frame. That way, if the woofer has sagged irregularly and not directly down, the best of the four orientations can be assessed and the woofer can then be rotated to that position in the normally upright cabinet.
Another thing to check is the baffle woofer cutout rebate or mounting ledge - important that it is flat, smooth all the way around so that the frame is fully supported around its circumference and when tightening, don't overtighten as that could slightly twist and distort the frame. Normally, their should be a thin paper gasket between the baffle and woofer. If not, there can be small air leaks, even though it's a vented speaker, so a very thin compressible foam gasket should then be improvised (very thin height wise draft sealing material from Home Depot or similar) or purchased from Parts Express. Don't use neoprene here because it doesn't compress, use foam like what the surround is made of. The tech sheet gives the JBL part number 52671 which is the same gasket used for other JBL 8 inch drivers like the Professional 2118, so if yours is missing, JBL Professional Parts in Northridge, CA may still have it.
http://manuals.harman.com/JBL/HOM/Technical Sheet/L19A ts.pdf
When I think of Mr. white, it reminds me of the SPECTRE villain in the Daniel Craig Casino Royale.
The tinsel could be splayed outward to avoid the spider, or the solder connection to the faston terminal heated with a soldering iron and then moved outward and held till the solder hardened. However, unless excursion limits (low low frequency and high volume) are being tested, it's unlikely the cause, but good to address it anyway.
Reconing is not difficult, but obtaining the OEM JBL recone kit and installing it correctly as a first time DIY project is difficult.
Also, in testing, you're changing the conditions when you play one Cd at regular listening volumes, then play others at reduced volumes with loudness on. The stresses on the woofer are not the same. The worst case scenario is at regular volumes with loudness on or major bass boost. The speakers will try to give you what it can but these are relatively small 8" drivers and the laws of physics will only allow so much bass and cone excursion with this design before real physical limits are reached and exceeded.
IMO, Try to test using your familiar CDs and normal listening volumes where you did hear distortion before, it may be volume or frequency related. Try using without loudness and the. Try using some bass cut and see if at the same volume level but without some bass frequencies if the distortion changes or goes away.
If these speakers can't match or reach the bass levels you desire without distortion (in both speakers), then you need a subwoofer. If it's just one speaker and not the other despite all attempts to adjust it to eliminate the distortion, then you need a new used JBL 116H woofer (easier and likely cheaper) or a full recone with OEM JBL parts.
When the problem is present on certain recordings it's more pronounced on these same recordings at lower volumes with the loudness button on.
Hmm, on these recordings, try swapping the channels left to right and see if the problem follows the recording channel, not the speaker. If not, its definitely the speaker. If yes, that particular track is somehow exceeding what the speaker can do bass wise. Even at reduced volumes, the loudness control adds more bass boost as the volume is reduced. In a ported speaker, this can exceed its low frequency cutoff and the driver cone unloads.
When you test again, see if there is a lot of visual motion / vibration, or even perhaps some excessive excursion as if someone is really wobbling the cone. A much less likely issue is the amp or preamp "motorboating" or low freq. oscillating.
A question is what are your music sources - digital or analog, and if analog, tape or vinyl record system? If vinyl, there can be issues with arm-cartridge resonance, acoustic or vibration feedback, or tracking / groove wear issues which can create all kinds of audible but sometimes intermittent problems.
I've already narrowed it down to the woofer. I've already switched them and the problem followed the woofer. I've only played CDs since noticing this problem.
Just from experience with this particular woofer, the hand push method is not a good diagnosis. The VC gap is so tight that anything but perfection on your push feels like a rub.
So I've decided that I'm going to buy some brand new speakers for this system and refoam these JBLs at some point and move them into the bedroom. When I eventually do that I will report back. Thanks for everyone's help!
Here is the spec sheet for the L19's;
http://www.cieri.net/Documenti/Cataloghi/JBL/JBL - L19 (1977) - Depliant (English).pdf
Would these replacement woofers work with the L19;
No, and it's not close. That driver is intended to be used in a sealed enclosure. Your L19s are ported. Comparing the Theile small parameters again reveals they are very different drivers.
Here's the Theile small parameters for various versions of the JBL 116:
If yours are L19s, you'll want a 116A. If they are L19As, the original woofer is an 116H.
Just because a driver physically fits the opening in the front baffle does not make it a viable replacement. For that particular driver you'd need to redesign the crossover and change the cabinet tuning, and even then it won't match the sound of the original. Your L19s will no longer be L19s.
Either get your wonky woofer repaired or watch eBay for a genuine JBL replacement (116A if L19, 116H if L19A). They show up frequently and usually aren't too expensive. You can substitute a 116A for a 116H, and vise versa, but I'd recommend staying with the correct original part for authenticity.
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