375/2440 differences

[vernb]

Everywhere in here it says that the 375/2440 were identical and identical to 376/2441, but when I look at JBL litterature the shipping weight of the 375 was 6lbs more than that of the 2440. Why is that?
Someone is trying to tell me the 375 has a bigger magnet, but that can't really be true, since they are supposed to be twins.

Can someone shed a light on this please? Did they just use a heavier box for shipping the 375??? a lot heavier???

regards
Verner

[Mr. Widget]

The 6 lbs is due to a lack of consistency in JBL's literature. There are also varying flux densities too if you look hard enough. The two drivers are essentially identical. During the long production run of the 375 and later 2440s there were several small changes made. Different back caps, different internal dampening materials and a general loosening of the tolerances in the later production units. As JBL increased production quantities into the '70s they apparently did loosen some of the driver's tolerances slightly to aid in manufacturing. I don't know this first hand but it has been reported here and it seems to be backed up by anecdotal evidence. That said. there are no fundamental differences between any of these drivers and those that claim a '67 375 is better than a '77 2440 are probably basing it mostly on lore and legend.


Widget

[subwoof]

I just disassembled a group of 2440 drivers for cleaning / remag and found a number of internal differences in the way that the centering ring and also the phase plug assembly's are made. This would account for a small difference in weight but there are NO differences in the actual performances between the blacks and the grays.

When I get the second computer up + running with photoshop I will post pictures of the internal variations I have seen. There are probably a few more with the early 375's and such.

I have seen some different packaging over the years but it's been a very long time since a 275 came into the shop in an original box....you can attribute the weight difference to that jbl standard, "typo"

sub

[SMKSoundPro]

I just disassembled a group of 2440 drivers for cleaning / remag...sub


Dear Subwoof,

Where can a driver mag be remagged? Inquiring minds want to know?

Thank you!

Scotty.

[subwoof]

JBL professional does it cheap.

I think edgewound knows someone around there. I think bruce edgar does it too but unknown if for others.

I have mine done in mass since it's only one day shipping from here.

sub

[SMKSoundPro]

Thank you for the information!


Scott.

[4345]

Subwoof. I have some 2441's that have a little corrosion on them. Also, the foam on the top cap rotted and has been removed. They work, but are not so pretty. Can JBL pro clean them as well?

[Robh3606]

They work, but are not so pretty. Can JBL pro clean them as well?

If everything is working well, no cracked throats as an example I would not ship them. I would do any cosmetic work myself if it is something that could be done by me. Those are heavy drivers and one good drop and you can shift a magnet, crack a throat or both. The worst part is it can happen on the way back from JBL. Shipping is always a high risk operation especially with these drivers.

Rob:)

[Mr. Widget]

I agree with Rob here... actually I frequently agree with him. :)

I have shipped 2441s a few times and I am always a bit nervous. They really do not like shock. A good drop and they will need to be shipped back to Northridge for a rebuild. I have been there. :(

If you do ship them, always ship them in individual boxes. I double box them with the inner box floating in a tightly packed 2" layer of styrofoam peanuts... one of the few uses of those things where they really work well. They form a bit of a cushion for the inner box.


Widget

[TechLab]

Regarding remagnetizing drivers... I have a large 450v capacitor discharge magnetizer, and a 190mm (7.5") ID fixture, so can remagnetize almost any compression driver or cone driver, back to (or better than) factory specs. It was designed for ceramic magnets, so has huge excess ability when charging alnico. Sadly, I cannot charge neodymium without an expensive cobalt flux shaper, which I can't afford. I check polarity and condition with a Walker gaussmeter, before and after, as long as there is access to the gap, and my 0.9mm (36 thou) probe will fit. The early 375/2440 had a 38 thou gap, while later 2440/2441 gaps were 41 thou. A broken throat means certain magnet damage. Tests on dozens of 2440/2441s indicate that with no physical damage, it is rarely useful to recharge them. The aspect ratio of the internal alnico ring is relatively tall, and the voice coil is both short, and not subject to high currents, eliminating 3 important discharging factors. On the other hand, in recharging hundreds of alnico woofers, it is rare to find one that does not benefit, sometimes dramatically, from a fresh charge. I have NEVER found an alnico JBL 50 or 75mm (2 or 3") coil JBL woofer that did not need it, along with almost all alnico 100mm (4") coil units. Sorry I'm so far from Alaska, but isn't everything far from Alaska?.

[Mr. Widget]

"Sadly, I cannot charge neodymium without an expensive cobalt flux shaper..."

I just had to quote that line... I'm going to have to figure out a way to use it conversationally. :D


Thanks for the info... seems in line with other info posted here.


Widget

[cooky1257]

I have a large 450v capacitor discharge magnetizer, and a 190mm (7.5") ID fixture,

Whatever you do do not install it into a DeLorean, heaven knows where you'll end up.

[JohnK]

The difference is that if you wanted 375's & got a 2440's it will be in the back of your mind that you don't have 375's all the time you are listening to them.

[Maron Horonzakz]

Yes but you can smile that you got them at half the price.:D

[Guido]

Whatever you do do not install it into a DeLorean, heaven knows where you'll end up.


THIS IS PRICELESS :rotfl:

[John]

The difference is that if you wanted 375's & got a 2440's it will be in the back of your mind that you don't have 375's all the time you are listening to them.

That,s when it time to call it a day.:banghead: