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invstbiker
10-28-2008, 07:14 PM
I've recently previewed a YOU TUBE article whereby the guy was re-installing speaker mounting screws using brass screws vs steel screws and then using an inch-pound torque wrench. I'm not interested in replacing stock screws with brass screws, but I was wondering if JBL used a torque spec on their 70 vintage monitor transducers? More snake oil or is there some fact to what this guy is saying? Any help/comments appreciated.

Hopefully the link below loads automatically.

http://www.virtualdynamics.ca/the-oddiophile-eps--1/

grumpy
10-28-2008, 08:35 PM
Even and sufficient pressure against a presumably flat surface (baffle) is
always a good idea. Uneven torque -could- distort a frame, as could
unnecessarily high torque values. I would guess that the driver mounting
process changed over the last 60+ years, but "sufficient" likely means
tightening the fasteners until the gasket is 'squished' (to form a seal)
and the frame very near or just in contact with the baffle.

Getting reliable/consistent torque values driving fasteners into even precisely
placed t-nuts would be tough. It is a useful question, but in practice I use my
torque "arm", check for alignment, binding, and visual clues.

Regarding the link... dude is putting brass machine screws where there were
coarse wood-type threads without installing machine-thread inserts... perhaps
that was the equivalent of a video-typo. Sound difference? Not going there...

invstbiker
10-28-2008, 08:43 PM
Thank you Grumpy, what you say below is, well, common sense and I have used that approach on many projects. My question really has to do with "back in the day", did JBL have a torque spec for screws, or did they use the below, common sense approach?




Even and sufficient pressure against a presumably flat surface (baffle) is
always a good idea. Uneven torque -could- distort a frame, as could
unnecessarily high torque values. I would guess that the driver mounting
process changed over the last 60+ years, but "sufficient" likely means
tightening the fasteners until the gasket is 'squished' (to form a seal)
and the frame very near or just in contact with the baffle.

Getting reliable/consistent torque values driving fasteners into even precisely
placed t-nuts would be tough. It is a useful question, but in practice I use my
torque "arm", check for alignment, binding, and visual clues.

BMWCCA
10-28-2008, 08:54 PM
We did learn from Harvey Gerst here on the list that Fender caused all sorts of problems torquing their JBL speakers in their amps improperly, which led to JBL wallowing out gap so it wouldn't bind, and then labeling the product the "F" series. I go with the "torque-arm" method, too.

3dbdown
10-29-2008, 02:07 AM
Correct about the Fender JBL's.......When we tested them in the QA booth, we always placed physical pressure on the frames during the 20 Hz test signal, to make sure the VC's didn't rub, since Fender pressure mounted them in their amp cabinets.

As far as torque specs on the transducer mounting screws, we never published any. Obviously the production line had specs on the pneumatic drivers, but that was for consistency in installation as well as insuring compressibility of the gaskets. Snug and a 1/4 turn is sufficient, unless youhear air leaks, most commonly from old gaskets. Whenever I remove my woofers, which isn't often, I replace the noodle gaskets anyway. Cork gaskets don't normally deform, and I've never had a problem.

Definitely a good idea to tighten in a pattern, however, like the heads on a car, to avoid any possibility of frame warpage.

FWIW

Rick (JBL #12)

BMWCCA
10-29-2008, 06:38 AM
Definitely a good idea to tighten in a pattern, however, like the heads on a car, to avoid any possibility of frame warpage.Lug bolts and nuts, too. But then many would suggest using a torque wrench in those applications.

3dbdown
10-29-2008, 02:48 PM
Precisely why I have my Snap-On Dial-Back torque wrench in the shop!

PioneerGuy75
11-02-2008, 06:08 PM
I think I hear my wall ringing too..............Perhaps I should pull all of the steel screws out of the drywall and put in brass!:banghead:

Joking of course, But it does sound a wee bit anal retentive:blah:

PioneerGuy75
11-02-2008, 09:06 PM
Reading through that website, I smell a snake oils salesman!

What is sad that so many people fall prey to stuff like that!