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View Full Version : JBL L-300 Summit woofer re-foam problem



keenyoung
07-16-2012, 11:33 PM
I just did a surround re-foam on my JBL Summit L300 woofers. I followed the sticky in the DIY forum using Rick Cobb's kit with the CD. It went well, and the speaker coils pretty much aligned themselves like the instructions said they would. I ran the tone at high volume (about 1/4 inch cone travel) until the glue was dry. They both sounded great, until I picked them up off the counter. One of them continued to sound great, but the other one started clicking like crazy. If I put it back on the counter, or cover the rear vent with my hand, it again sounds great.

It doesn't seem to be a side clearance issue with the driver, it seems like the whole cone is bottoming out. When I hold the speaker completely vertical, or with the cone pointing slightly down, it sounds fine no mater how I spin it around it's axis. It does sound good up to about 60 watts in any orientation. Unfortunately, the L-300 speaker case front is NOT completely vertical, it tilts slightly back.

It does appear that the cone sits slightly (very slightly) lower in the basket than the one that sounds good.

Anyone have this problem before? I hate to have to re-cone the damn thing, but is that my only option?

Thanks much,
Keen

hjames
07-17-2012, 05:18 AM
Cone position is determined by the surround AND by the spider - maybe the spider on that woofer has sagged?

Have you had these speakers since new or did you buy them elsewhere used?
Maybe one of the woofers was replaced at some point and doesn't fully match (re: usage, not model info)

No flames meant - just a thought ...



I just did a surround re-foam on my JBL Summit L300 woofers. I followed the sticky in the DIY forum using Rick Cobb's kit with the CD. It went well, and the speaker coils pretty much aligned themselves like the instructions said they would. I ran the tone at high volume (about 1/4 inch cone travel) until the glue was dry. They both sounded great, until I picked them up off the counter. One of them continued to sound great, but the other one started clicking like crazy. If I put it back on the counter, or cover the rear vent with my hand, it again sounds great.

It doesn't seem to be a side clearance issue with the driver, it seems like the whole cone is bottoming out. When I hold the speaker completely vertical, or with the cone pointing slightly down, it sounds fine no matter how I spin it around it's axis. It does sound good up to about 60 watts in any orientation. Unfortunately, the L-300 speaker case front is NOT completely vertical, it tilts slightly back.

It does appear that the cone sits slightly (very slightly) lower in the basket than the one that sounds good.

Anyone have this problem before? I hate to have to re-cone the damn thing, but is that my only option?

Thanks much,
Keen

speakerdave
07-17-2012, 01:42 PM
My guess is that your tone drive was excessive. You don't need that much to center the voice coil, which is an event of magnetics happening in the gap. The excessive travel was tugging on the new surround, and it may have pulled in a bit asymmetrically where the hold was not as strong as elsewhere. Or it may have pulled all around and the foam is in effect deflecting the spider (a really soft one). Or maybe the spider had sagged over time. I would try refoaming it, but I would first examine the spider carefully for tilt or pushup on one side. I've never done it, but I've heard said a hair dryer will soften a spider enough to help it remember it's true self. You would want to have a setup all ready to hold the cone in place while it cools. Very carefully identical pieces of stryofoam very carefully identically placed between the frame struts and the back of the cone may work. I suggest these heroic efforts because if those cones are the original 136a cones you will have to recone both of them if you do one.

keenyoung
07-17-2012, 02:01 PM
My father bought them new. They are one serial number apart. The woofer cones are definitely the same, and I know he never had work done on them. They have been sitting unused with rotted foam for probably 15 years, but they were working fine before that. They have been sitting in a basement with a fairly constant temp and humidity level. I'm not sure why one spider would sag and not the other, but I suppose it's possible. It is definitely the coil bottoming.

Is there any way to determine the spider position without pulling the cone?

Thanks,
Keen



Cone position is determined by the surround AND by the spider - maybe the spider on that woofer has sagged?

Have you had these speakers since new or did you buy them elsewhere used?
Maybe one of the woofers was replaced at some point and doesn't fully match (re: usage, not model info)

No flames meant - just a thought ...

speakerdave
07-17-2012, 02:06 PM
My father bought them new. They are one serial number apart. The woofer cones are definitely the same, and I know he never had work done on them. They have been sitting unused with rotted foam for probably 15 years, but they were working fine before that. They have been sitting in a basement with a fairly constant temp and humidity level. I'm not sure why one spider would sag and not the other, but I suppose it's possible. It is definitely the coil bottoming.

Is there any way to determine the spider position without pulling the cone?

Thanks,
Keen

The spider should look level.

The foam rotting may have been different on the two woofers, supporting one cone less than the other.

edgewound
07-17-2012, 02:08 PM
My father bought them new. They are one serial number apart. The woofer cones are definitely the same, and I know he never had work done on them. They have been sitting unused with rotted foam for probably 15 years, but they were working fine before that. They have been sitting in a basement with a fairly constant temp and humidity level. I'm not sure why one spider would sag and not the other, but I suppose it's possible. It is definitely the coil bottoming.

Is there any way to determine the spider position without pulling the cone?

Thanks,
Keen

The spiders can sag due to age and use. The spiders used on the 136A is lighter than the spec' new recone kit C8R2235. It's possible to replace both the surround and spider but it's a tedious job. Some prefer this route to maintain the original voice coil length and spec as long as the original coil is in good shape...and save a couple hundred bucks in the process since the OEM kits are the major cost of a recone.

speakerdave
07-17-2012, 02:12 PM
It's going to take some fooling around, but I would try to save it. The exact equivalent cone kit is no longer available. My experience with the 4333a with original 2231's says that every effort should be made to restore the original cones. The 2235 replacement cone kit JBL specifies for this speaker is good, better in some ways, but it is a little different. You will have to do them both.

keenyoung
07-17-2012, 02:23 PM
Darn. I ran at 1/4 inch cone travel because that was the upper limit suggested by Mr. Cobb, and I wanted to be damn sure to get it right. Live and learn, I guess.

Hmm. Visually, the edge of the new foam has the same gap to the edge of the basket on both speakers, and they are both really centered on the basket. This and the fact that the coil is definitely bottoming on the case leads me to believe that the spider must have shifted.

How would I inspect the spider without removing the cone? As for the hairdryer trick, are you suggesting doing this with the speaker sitting on the coil end, or upside down with the basket on the desk?

I really don't want to recone the pair, but I know the new woofers are different.

Thanks,
Keen



My guess is that your tone drive was excessive. You don't need that much to center the voice coil, which is an event of magnetics happening in the gap. The excessive travel was tugging on the new surround, and it may have pulled in a bit asymmetrically where the hold was not as strong as elsewhere. Or it may have pulled all around and the foam is in effect deflecting the spider (a really soft one). Or maybe the spider had sagged over time. I would try refoaming it, but I would first examine the spider carefully for tilt or pushup on one side. I've never done it, but I've heard said a hair dryer will soften a spider enough to help it remember it's true self. You would want to have a setup all ready to hold the cone in place while it cools. Very carefully identical pieces of stryofoam very carefully identically placed between the frame struts and the back of the cone may work. I suggest these heroic efforts because if those cones are the original 136a cones you will have to recone both of them if you do one.

speakerdave
07-17-2012, 02:30 PM
Hold the woofer up and look across the spider between the struts of the frame. It should not look dished or uneven.

stony22
07-17-2012, 02:38 PM
just food for thought, have you checked the tinsel leads to make sure it's not slapping the cone or spider. I've had that happen by after removing the speaker, I grabbed the basket and didn't realize that I bent the lead close to the cone, but does make a slap/bottoming sound at volume. Good luck. TONY

speakerdave
07-17-2012, 02:41 PM
. . . . As for the hairdryer trick, are you suggesting doing this with the speaker . . . .

I'm not suggesting any technique for this, because I haven't done it; I was just passing on a passing comment one of our members dropped in a post in the past. He may chime in here when he gets off work. It may be Custer's last stand, so I'm not recommending you try it until you get some more-experienced advice. Remember before anything gets wrecked, edgewound can replace the spider for you.

speakerdave
07-17-2012, 02:44 PM
Darn. I ran at 1/4 inch cone travel because that was the upper limit suggested by Mr. Cobb, and I wanted to be damn sure to get it right. Live and learn, I guess.

Hmm. Visually, the edge of the new foam has the same gap to the edge of the basket on both speakers, and they are both really centered on the basket. This and the fact that the coil is definitely bottoming on the case leads me to believe that the spider must have shifted . . . .

I perhaps a bit overstated the case. It was just one possibility. You likely didn't do anything wrong, but I do think 1/4 inch is way more than necessary. You just need to have the magnetic fields acting on each other to center the coil. Perhaps to a point more current is better, but I think not so much.

keenyoung
07-17-2012, 04:42 PM
Tip of the hat to all who suggested spider sag. I can definitely see it cup down in the center. The spiders on both speakers do, but the rattling one is much more pronounced.

So speakerdave, do you know the thread on this possible spider sag repair? Or perhaps the member name of the gentleman who commented on it?

Many thanks,
Keen



I'm not suggesting any technique for this, because I haven't done it; I was just passing on a passing comment one of our members dropped in a post in the past. He may chime in here when he gets off work. It may be Custer's last stand, so I'm not recommending you try it until you get some more-experienced advice. Remember before anything gets wrecked, edgewound can replace the spider for you.

speakerdave
07-17-2012, 05:07 PM
Read this:

http://www.audioheritage.org/vbulletin/showthread.php?21567-Can-you-repair-a-pushed-in-speaker

I have fairly decent manual skills, but there are things in that thread I wouldn't try.

keenyoung
07-17-2012, 05:35 PM
Yeah. I don't know about using MEK. I used that stuff to get the old glue off the baskets, and wound up dizzy even with good ventilation.

I can't really afford a recone right now, so I will attempt the hair dryer first, and see how it goes. If that fails, I may try the MEK, but it would definitely be last resort before a recone.

I'll report back when I get it done.

Many thanks,
Keen




Read this:

http://www.audioheritage.org/vbulletin/showthread.php?21567-Can-you-repair-a-pushed-in-speaker

I have fairly decent manual skills, but there are things in that thread I wouldn't try.

speakerdave
07-17-2012, 05:45 PM
That may be the ticket. Good luck with it.

keenyoung
07-20-2012, 05:14 PM
Well I'll be darned. It actually appears to have worked. For now, anyway.

With the speaker upside down and supported on the basket edge so the cone was free to move, I used 4 empty toilet paper rolls squished down between the cone and the frame to get the spider flat. I the hit it with a good hair dryer, for about 15 seconds through each basket hole all the way around. I let it sit for about an hour, and then repeated the heat treatment. I then let it sit over night, and then flipped it over on to the coil end. After letting it sit again overnight, it seems to have stayed flat. I played the 30 Hz tone thru it at around 100 W, and it's working fine, with no clicking or slapping. I have no idea whether it will last or not, but for now you guys have saved me a ton of time and money. Thank you VERY much!

Now on to stretching new grill cloth!

Many regards,
Keen

Earl K
07-21-2012, 02:02 AM
Great Thread !

Great Save !

Fwiw, I generally miss a lot of what goes on here at LHF during the summer .

So many thanks to Dave for posting the reference to SubWoofs ( Mikes ) thread on how to attempt a rehab on a "bagged" spider ( hadn't seen that before ) .


cheers :)

speakerdave
07-21-2012, 01:08 PM
Well I'll be darned. It actually appears to have worked . . . .

Good show.

keenyoung
07-29-2012, 05:04 PM
The new grill cloth was a challenge because of the depth of the L-300 grill frames, but they came out great.

However, my last task to finish the speakers was to glue the gaskets back onto the baskets. I did one, and ran out of glue. Anyone know what type of glue is used on a foam re-surround? I don't want to by another surround kit.

Thanks again,
Keen

SEAWOLF97
07-29-2012, 05:31 PM
The new grill cloth was a challenge because of the depth of the L-300 grill frames, but they came out great.

However, my last task to finish the speakers was to glue the gaskets back onto the baskets. I did one, and ran out of glue. Anyone know what type of glue is used on a foam re-surround? I don't want to by another surround kit.

Thanks again,
Keen

I would just use Elmers white

BMWCCA
07-29-2012, 09:34 PM
Elmer's would certainly work but Aleen's Tacky Glue from any fabric store or Walmart seems to work better in nearly every application.

badman
07-30-2012, 02:12 PM
Elmer's would certainly work but Aleen's Tacky Glue from any fabric store or Walmart seems to work better in nearly every application.

Agreed, it's much higher quality, and still inexpensive.

keenyoung
07-30-2012, 02:39 PM
Thanks for the tips. I found a local speaker repair place (Midwest Speaker Repair, MN) that will sell me an ounce of the original white Bostik cheap.

Many regards,
Keen

keenyoung
08-21-2012, 04:15 PM
Hi all,

I thought you might like to see the end result of all your help to me on these L-300s. They sound fantastic, and look pretty good too.

Thanks to all,
Keen

Krunchy
08-21-2012, 04:37 PM
They look Great :applaud: Hope you got lots of music and even if you do get more, you can never have enough. :D

Enjoy!

What gear are you using to powe the beasts?

keenyoung
08-21-2012, 07:27 PM
Heathkit AP-1800 Preamp
Pair of Adcom GFA-555 amps
Pair of Heathkit AD-1304 audio processors
Pair of SoundCraftsmen equalizers
Bob Carver Sunfire subwoofer
Dual 721 turntable with Ortofon amped stylus
Teac Tascam 122 cassette deck
Sony MDX-D5c CD player
Crappy Harmon Kardon tuner
Klipsch Chorus speakers for the front channels

Some of the bits including the speakers I got from my father's estate, some I've accumulated myself over the years.

Keen



They look Great :applaud: Hope you got lots of music and even if you do get more, you can never have enough. :D

Enjoy!

What gear are you using to powe the beasts?

Krunchy
08-22-2012, 07:59 AM
Hi Keen, Looks like you're set in all departments, now just sit back and Listen! :) & Let us know your impressions.

mech986
05-15-2013, 12:14 AM
Keen, great job on the resurround, spider rejuvenation, and the grille / cabinet work. I'm sure your father would be proud. :applaud:

BMWCCA
05-15-2013, 07:24 PM
Check the date on this thread.

The OP sold his family heirlooms right after posting here and hasn't been around since. That was over eight-months ago. :(