4412 Weak Bass (re foam issue?)

[Paul_M]

Would that be Millersound in Lansdale?

Ah yes :-)

[Ian Mackenzie]

http://www.audioheritage.org/vbullet...p?10645-128H-1
https://www.google.com/amp/s/m.wikih...edance%3famp=1

Assuming the driver does not measure to spec you won’t know for sure if it’s the spider or the surround but it’s likely the surround based on service history.

If the driver does meet spec start looking else where ie swap out the preamp and power amp.

Order a Rick Cobb surround and other necessary tools & glues and either get someone to install it properly and nicely (not a rush job if you want a nice cosmetic appearance) or follow re foam instructions recently posted on the forums.

Re test the driver resonance as above after breaking in the driver with some usage.

I hope this helps.

If there is a forum member nearby who is well practiced in testing woofers it might be worth a road trip ( and a few beers) to figure it out.

[BMWCCA]

Ah yes :-)

They have a great reputation for re-building vintage drivers with no factory support or spare-parts availability. Nearly every repair experience I've heard of from them seems to involve a replacement spider to create a somewhat Franken-speaker product. Not saying they aren't talented but they seem to always focus on spider replacement. Not saying that it's not possible to be the problem, but I find it hard to believe that the issue with your JBLs is the spider.

[Robh3606]

Nearly every repair experience I've heard of from them seems to involve a replacement spider to create a somewhat Franken-speaker product. Not saying they aren't talented but they seem to always focus on spider replacement. Not saying that it's not possible to be the problem, but I find it hard to believe that the issue with your JBLs is the spider.

I find that kinda odd as a "worn" spider may be an issue as far as centering the coil but it certainly will not raise Fs if anything it will lower it. Almost every re-foam I have done has been within a couple of hertz from spec using Rick Cobb surrounds. Some have been lower which makes sense if the spider stiffness is lower from use as the two and cone mass determine the Fs of the driver. I have a pair of 128H-1 I did re-foams on will post the Fs results.

Rob

[Ian Mackenzie]

That makes sense.

Maybe if the drivers are run on a sine wave at 30 hertz for a reasonable period they might loosen up.

You can down load an app on an iPhone to do that.

[Robh3606]

Just ran one of the re-foamed 128h-1 and the T/S table has it as 20 Hz. My driver came in at 20.4 Hz so basically right on the money. This is cold with no run in at all from storage right to the measurement.

Rob