Custom JBL/Altec Build - LE15A Woofers "Frozen"

[Kingsin7]

Hello AK
I recently purchased a custom speaker set that was built by a UC Berkeley engineer back in the 70s. The set features:

15" JBL LE15A woofers (8ohm)
15" JBL PR15 Passives
JBL 075 tweeters (16ohm)
Altec 802D Mids (16ohm)
Altec 811B Horns

The crossovers were made from scratch as were the cabs. There are two large "bass coils" hooked into the XO in each cabinet.

I bought these speakers in the Bay Area where they auditioned great. I unhooked and tested all drivers with my meter, and they all checked out.

I was forced to remove the protruding horns to be able to fit both cabinets into my truck (had the camper shell on), where I put them on their sides facing each other.

I hauled these massive speakers into my garage and hooked them up to find neither of the woofers were functioning. Upon opening the cabs up, I found connections in the custom XO's had come apart in places during transit. The XO's were the only weak link in this setup as they are home made and frankly Mickey Moused, though I admittedly could never have built them myself and commend the engineer that created them. Lots of lamp wire and exposed connections (pictured)...

I re-soldered the connections where needed but the woofers still wouldn't come on. If I cranked the power slightly they would activate in a horrid muffle and I quickly shut the amp off. After some head scratching I noticed they were both virtually frozen stiff when unpowered... There is (very) slight play when manually moving the voice coil in and out by pulling on the cones.

I hooked in another woofer to each speaker and it worked fine.

So, here I am trying to figure if this is an easy fix or if a reconing job is needed. Local quote is about $400 for new cones/foam...

What I really want to know, more than anything, is how they got frozen. Whether this was due to the shock of transporting them the 60 miles to my home (never happened before) or something to do with the XO wiring being disconnected in places when first powered on back at my house...

Any advice will help!
Thanks,
Steve

 

[Zonker92]

Stiff, ossified Lansalloy surrounds. Probably hard as rocks. Refoam. Do not use brake oil.

 

[Kingsin7]

The surrounds are hard, but no harder than they were when the woofers worked before I hauled them home. They do need replacing but I can just barely move the voice coil in and out on either woofer when applying very firm, even pressure pulling the cones upward with my hands on their backsides...

 

[Zonker92]

I deleted my earlier reply, but I just cannot see how the voice coils could be frozen: (1) They do move a bit; and (2) the magnets are screwed on so they should not have shifted. Plus, the surrounds are clearly ancient and rock-hard, and both woofers are doing the same thing. And it's not the spiders, because spiders don't do that. The mechanical system is simple so it's pretty easy to narrow things down.

Maybe when you auditioned them the room was emphasizing the bass, or the program material, or the tone controls were turned way up, or your amp is less powerful or your bass is turned down lower or your room has less bass ... dunno.

Again, my money is on the surrounds. But if you're not convinced, run them directly off an amp and try a tone generator (e.g., a smartphone app); start out at low volume, see what happens. Just make sure the vent on the back of the magnet can breathe.

 

[donprice]

It is likely the driver or surrounds did not change. The listening environment did. Not sure if that explains everything but there is little reason to believe they performed to spec in the last 10-20 years. Replacing the lansalloy surrounds with a proper fitting foam might solve your .main problem for much less than reconing.

What zonker92 said.

 

[Kingsin7]

Zonker, Donprice
I assure you the problem does not lay with the surrounds. I used a Marantz 1060 to test the speakers at the seller's home. The speakers performed very well with that 30wpc amp, and I even ran a frequency test off Youtube which started at 20Hz and ended at 20KHz. The woofers performed beautifully. I also played quite a bit with the low/mid/high tone controls on my 1060 while testing them with different forms of music.

At home, I hooked them up to a 150wpc Mac 2155. The woofers will not produce any sound at low power and make a scary rumble at med-low power. I've also ran the woofers straight to the amp as you suggested, but to no effect. That amp currently has 3 sets of ESS speakers hooked into a speaker selector box and all work fine so I know the problem is with these woofers.

If you guys were here right now and tried to forcibly move the voice coil in and out with your hands you would agree they are frozen and that by no means do the old surrounds make any difference in this particular case. You would make the funny face I made trying to apply a lot of force pulling those cones upward while getting virtually no give and at the same time trying not to break anything... Maybe I live on an old Indian burial ground or something.

 

[Kingsin7]

My garage has a linoleum floor, storm windows, fully finished... Guys, I'm tellin' ya - it's not the room and it's not the surrounds. These things are stiffer than the first time I discovered late night cable...

 

[drbiggles]

Hmm, I know when moving speakers, one should put them on their backs. This way, the driver can bounce with the vehicle as it cruises home. If the speakers are set on their sides, voice coil damage can happen. I don't know much about vintage JBL drivers. But the little I do know is that some have very tight clearances in there. Maybe the voice coil had too much bounding on its side.

Biggles

 

[Kingsin7]

Thanks Biggles
Yea, I always place speakers upright or on their backs, but these things were massive and had to be placed on their sides... It was all highway and I have Bilsteins on my truck... Really lost on this one since I've transported dozens of pairs of speakers in the past with no issue. I shoved a pair of huge VMPS Super Tower/R's on their sides into the back of a rented Jeep once and drove them from SF to Sacramento. Those have 15" and 12" woofers in each cab and I had no problems when I got home.

I'm also wondering if the design of these particular woofers make them susceptable to shock...

 

[Kingsin7]

Is it possible that since some wires were disconnected within the XO when I initially hooked them up at home, that when I attempted to power the speakers the woofers could have each received some wild bad signal which froze the voice coils up? If perhaps there was a crossed wire?

I know it would be crazy to happen to both at the same time but each homemade XO had wires that came loose... I once fried a ribbon tweeter by using a bad RCA cable between an amp and preamp and accidentally turning the amp on when the volume was way up, so...

 

[tubed]

The cones on my LE15a's didn't move freely until a light coat of DOT3 brake fluid was applied.
Diligently.

 

[Leben]

If you touch the cones lightly while they are playing can you feel vibration? Btw, do this at your own risk. Just something that has worked for me to see if they are “working”.

Edit: I have some LE14a speakers that previously had lansaloy surrounds. Old lansaloy gets hard, there was a huge difference when I refoamed mine.

 

[Leben]

Btw, nice find on the speakers and best of luck getting sorted.

 

[CopperWizard]

My bet is on you wired them back up incorrectly. Double check.

 

[baco99]

I don't know how this would happen to you, but it sure sounds like the drivers are frozen. And you need a recone to remedy the problem, regardless of what that is.

 

[Kingsin7]

The cones on my LE15a's didn't move freely until a light coat of DOT3 brake fluid was applied.
Diligently.

Tubed,
Did the cones not move at all when force was applied?

 

[tubed]

They moved but not enough as the surround still had some give, not rock hard.
They work fine with the DOT3.
I am rooting for stiff surrounds rather than chernoblyed voice coils.

 

[Kingsin7]

Alright guys I'm halfway there. I massaged both woofers by pushing and pulling on the cones for some time. There was still just barely any give on one and the other was frozen solid. I then ran another frequency test with my high wattage amp plugged directly into the woofers. I ran it over and over again, and gave it much more juice than last time. I had muffled sound coming out so I pushed them a little harder to get them going.

The frozen woofer would not come on until my preamp was at about half volume (the Mac power amp is 150wpc). It then loosened up and although neither woofer sounded "good" they were producing sound when the amp was at low power.

I brought the giant refrigerator cabs back into the garage and installed one woofer into the cab. HOLY CRAP! It worked!

One woofer still sounded awful, so I think I'll have to attempt to oil it tomorrow. I am not ruling out that I re-hooked-up the XO incorrectly, so I'll check for that in the morning.

I do think oiling them and working them in/out certainly would have broken them free in the first place.

I'll have to assume the shock of moving them after they had been sitting idle for 30 or 40 years is what caused them to get jammed up...

I have to say, the one speaker working sounds absolutely beautiful. I played some Brubeck in mono on it and still had my ESS AMT1A speakers plugged into the speaker selector box. I'm not the biggest fan of ESS (don't get me wrong they're good, and relatively plentiful up here in Sacramento where they were originally manufactured), but when I switched over to them their low end was not even comparable and the Heils too bright and unbalanced sitting next to this working JBL/Altec...

I'll report back when I get both working 100%
I'll be ordering new surrounds from Simply Speakers tomorrow as well.

Thanks everyone for the help and goodnight!

 

[DavidF]

The picture I get in mind is that the ride back to your place jostled some debris into the voice coil gap. But it does not make sense in thinking where the debris came from or got into the gap??

 

[tubed]

Rust, perhaps?