Woofers ruined or no?.

[clwinbe]

I’ve restored many JBL speakers over the years. I’ve always used a guy here in Utah that’s been working on JBL drivers for 40 years. He’s taken woofers that looked like a lost cause and brought them back to “museum” grade. He’s an artist. All of the JBL woofers that he’s done always has the proper surround glued to the rear of the cone.

im seeing a bunch of JBL raw speakers and mounted in cabinets that appear to have the foam surrounds glued to the front of the cone. I would think this would be done to try and hide damage done from trying to clean off the old foam. Some of the work is really shoddy. I’ve bought many 708g-1 woofers that had been butchered, then my guy fixes them.

Is the foam attachment location a factor for proper woofer operation? It’s really upsetting to see a fine speaker hacked by a “I think I can do it” owner.

[JeffW]

It's harder to put them on the rear of the cone.

[HCSGuy]

Re-foaming on the front wrecks the value of the driver, but generally not the performance. I would worry about it on a driver with an underhung voice coil, especially a small driver like a 2108, but that’s a pretty rare bird. I sold off some LE14H-1’s that had been re-foamed on the front a few years ago for $175each. If they had been properly re-foamed on the back of the cone, it would have been more like $250 at the time, and over $300 now. Make sure it’s done right.

[Chris Brown]

Is the foam attachment location a factor for proper woofer operation?

Absolutely. The magnet has a gap, in which the voice coil operates. The resting position of the voice coil, which is attached to the rear-center of the cone, is obviously influenced by the surround foam. When you put the foam on the front instead of the rear, you are changing the resting position of the cone, pushing the cone (and the voice coil) inward by several millimeters at least.

Consider the "XMax" specification. This variable represents the maximum limit of cone travel while the voice coil is still properly within the magnet gap. The voice coil (or part of the voice coil) can leave the magnetic gap, but distortion rises quickly at that point. Most woofers have an XMax in the range of 4-8 millimeters. Every millimeter matters. So while the tiny distance that the cone is pushed inward due to an improper refoam might seem trivial, it does actually matter.

Further consideration would be the "XMech" specification. XMech is a superset of XMax. While XMax represents the maximum extent of cone travel while the voice coil is still properly within the magnet gap, XMech represents the absolute maximum limit of cone travel. With most woofers, XMech would be defined as when the voice coil slams into the pole piece of the magnet, letting out a very loud "POP!". While exceeding XMax can result in additional distortion, reaching XMech can result in physical damage to the voice coil. By putting the foam on the front, you are pushing the cone inward, reducing the XMech of the woofer in most cases.

[SEAWOLF97]

It's harder to put them on the rear of the cone.

can't agree with that ... for me , rear is easier.

on the front , you have to push foam onto cone while drying

on the rear, I weigh down the cone a bit , so it's pushing into the foam.

[JeffW]

can't agree with that ... for me , rear is easier.

There's gotta be some reason they're sticking them on the front...

[SEAWOLF97]

There's gotta be some reason they're sticking them on the front...

because most other makers do. JBL does too on some car ones.

[grumpy]

Rip and strip. It's much faster, much less training/expertise. End of story. Shop saves $$, customer may also.
Until recone kits disappeared, this was just a band-aid to prolong service less expensively.

Context: Yes, I got burned once, and I'm still pissed off about it.

... I should also reiterate that many drivers have their surrounds attached to the front by design... including some of the the older LE14 models (IIRC).

[clwinbe]

Rip and strip. It's much faster, much less training/expertise. End of story. Shop saves $$, customer may also.
Until recone kits disappeared, this was just a band-aid to prolong service less expensively.

Context: Yes, I got burned once, and I'm still pissed off about it.

... I should also reiterate that many drivers have their surrounds attached to the front by design... including some of the the older LE14 models (IIRC).

I hate when that happens. My guy has saved six woofers that were butchered by eBay folks. Find your happy place.....breath.....Bastards

[toddalin]

because most other makers do. JBL does too on some car ones.


JBL does this on a lot of stuff now, including the new L100 classics (butyl rubber), though it would seem than much of this technology has trickled down from their "professional" automotive line.

Putting the foams on the front, where designed for rear installation, can also limit the cone's travel and ultimately, its maximum volume level.

[JeffW]

Still puzzles me why anybody would take a driver that had the surround on the rear of the cone and stick a new one on the front of the cone because other mfgs or even other JBL drivers were done that way. Seems like if it came in with surround on the rear, it should go out with surround on the rear. :dont-know:

[grumpy]

Again... cheaper/faster, but not better. Usually.
Sometimes the backside has already been trashed or bad glue used.
Should be a last resort though.