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Speaker repair

pflash4001

pflash4001

Dec 2, 2011
2,166
169
#1
I wasn't really sure where to put this, so here it goes....I have a JBL monitor that suddenly got really noisy. When I opened it up I saw there is a 1 1/2-2 inch tear down the cone about 2 inches from the edge. I looked up repairs online and ran across several sites suggesting brushing in thinned adhesive to penetrate the paper cone then patching it using spray adhesive and a patch made from tissue paper, used dryer sheets, or coffee filter about 1/2 in larger than the tear on each end. Have any of you heard of this or tried it? If so, what were your results? Please let me know your thoughts on this. I'm a but skeptical myself, but if it's already torn, I may try anyway since the only other option would be a full recone anyway.
 
#3
No harm in playing around with it and if it works you will have a cool practice driver but I wouldn't gig with it with out a back-up cab (not very realistic IMO) as I would never believe such a repair to be totally reliable long term. I toyed with repairing a few damaged cones over the years with decent results but never trusted the cone(s) for live bass guitar use. I have repaired numerous stereo speakers and a few PA drivers but the PA speakers always broke again (to much stress I believe). You can't really make it worse than it is by trying, and the driver can still be re-coned if/when you are ready...
 
#4
Changing the mass of the cone will change the T/S parameters a bit and that will affect the sound in some way. I think raising the mass of the cone raises it's resonant frequency?? Maybe someone more familiar can correct me but I am sure changing the cones mass will change it's resonant frequency somewhat. In a stage MI cab it probably doesn't mean much but in Hi-Fi or studio use repaired cones are frowned on by many...
 
#8
Hi.

While the methods You describe are perfectly valid, the choice of the patch material IME quite isn't.

Every cone material nowadays is made out of reinforced something or other, You want that reinforcement on the patch as well. Otherwise the failure repeats itself and re-repair will be more difficult.

Newspaper paper is somewhat oriented because of the printing requirements, You can verify that by trying to tear strips out of it. You want the strand direction to be perpendicular to the tear. Obviously.

A thin inpregneable cloth of any kind is my preferred material, the patch is then stronger than the cone.

Added mass to the moving parts will lower the resonant frequency somewhat, but the effect is IME neglible in MI/PA use. If the patched area is large, I have glued a "balancing patch" on the opposite side of the cone, but that's more for "just in case" than anything else since the air gaps tend to be rather large in MI/PA motors.

Regards
Sam
 
#10
Hi.

pflash4001 said:
I considered the backside patch too. In a 1-2 inch tears to you think that laundry sheet fabric would be too heavy to use on both sides?
Click to expand...

I did mean on the opposite side of the dustcap.
IMLE a sandwich structure isn't usually necessary in anything but high stressed subs. Or if there are pieces missing.

The laundry sheet should be OK, as is non-stretchable band-aid cloth.

Regards
Sam
 
#11
I have done a few cone patches with great results. Luckily, I had old cones of the exact same type (JBL D120f) laying around for the patching material. The cones eventually got very brittle from age and finally gave out totally (tore loose from the voice coil. I sold them as is for someone else to recone.

I kept the patch to minimum size, but place equal portions in a quadrant around the cone (sorta like balancing a tire).

I also had another speaker develop a tear along the surround a few times over the years and would just apply a glue on both front and back, working it into the split. After 15 years this speaker, too, finally gave out when someone played an active bass through my amp and I forgot to depress the -15dB pad switch! Bought a new replacement and placed the original in my closet for future recone.

On both occasions I used a 2-part epoxy adhesive. Can't remember the brand... something from my workplace. Had a little bit of flexibility to it, like a dark grey rubbery texture.
 
#13
Hi.

pflash4001 said:
I see what you men now, I think...you're saying to patch the tear and then put another patch opposite the repair on an undamaged section to "balance" it out, right?
Click to expand...

Right.

But, as I said earlier, that's just for peace of mind. The structure of the PA/MI drivers is so stiff and heavy, that an imbalance like a relatively small patch won't IME affect anything.

Regards
Sam
 
#17
bassmeknik said:
Changing the mass of the cone will change the T/S parameters a bit and that will affect the sound in some way. I think raising the mass of the cone raises it's resonant frequency?? Maybe someone more familiar can correct me but I am sure changing the cones mass will change it's resonant frequency somewhat. In a stage MI cab it probably doesn't mean much but in Hi-Fi or studio use repaired cones are frowned on by many...
Click to expand...

The repair goes on the "outside" of the cone..... Ts ratings effect the porting and internal volume of the enclosure

IF you're that much of an audiophile - your concern altered the theil rating of the atmosphere - not the speaker enclosure

It's a gigging monitor - not a hearing evaluation/testing stations for an audiologist
 
#19
MNAirHead said:
Obviously while trying to demonstrate your extensive education you for got to test what you're saying

The repair goes on the "outside" of the cone..... Ts ratings effect the porting and internal volume of the enclosure

IF you're that much of an audiophile (and have that much of an impact on the universe) - your concern altered the theil rating of the atmosphere - not the speaker enclosure

It's a gigging monitor - not a hearing evaluation/testing stations for an audiologist
Click to expand...


Very funny, but you took that wrong. TS ratings are designed into the DRIVER that's why the cab requirements are different for different models of driver. If you change the driver you also change the box requirements.

Where did I say the repair goes "inside" the cone?

The OP's driver is in a monitor, so the repair is not likely to make much difference, Did I say it would re-write history and cause the end of the world as we know it? Oh, sorry you took that wrong.
 
#20
Putting ANY additional mass on a driver's cone will make a measurable difference in the T/S parameters. "Measurable" by scientific instruments not necessarily by your ear...

The patch will change the drivers response. Period. It will not however be a large noticeable change in response unless you get carried away with the glue and patch material.

Thanks T-Bird I stand corrected, adding mass to the cone will lower the resonant frequency.
 

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