KS Kuecke Tertia D70 woofer membrane repair

[vrobec]

Hello all!

I noticed in one of my Tertia D70's 12" woofer membrane there is a 3-4 cm long crack. The outer textil layers are ok, but the middle (harder) layer is cracked.
Does it affects the sound and how can it be repaired?

Here is video showing the membrane.


https://www.youtube.com/watch?v=Jv0F2OeA4cA

[RMC]

Hi vrobec,

Here's a suggestion for you, but subject to the fact I don't know this driver: cost, cone material, etc. Still better to have a crack than a hole in a cone.

RE: Does it affects the sound

It may affect the low-frequency sound if air passes by the crack even if the outer textile seems ok (textiles usually let some air pass through). A loudspeaker enclosure is supposed to be a COMPLETELY sealed cabinet, except for a vent in a vented enclosure. Even tiny spaces anywhere on a cabinet will affect to some extent box losses and bass reproduction.

RE: The outer textil layers are ok, but the middle (harder) layer is cracked

First, I suggest that you work on the BACK side of the cone since the textile on the front side looks ok and you don't want to compromise this.

Step one: I would put a VERY THIN coat of glue just to seal the crack. No bump or thickness in the glue line, it should be flat, maybe spread a little at the time in/on the crack with a finger or a small brush. When the glue has cured inspect both sides of cone with light to see if any gaps left in the glue, if so correct the issue. Put no pressure on cone to inspect as this may crack the glue line... That first sealing is to prevent air passing by the crack.

Step two: I would then glue a pretty thin piece of cloth, on back side of cone, over the crack to give the repair some strength and durability. That thin piece of cloth must be a little wider and longer than the crack itself (the crack and its immediate vicinity are weak points, but the rest of the cone is the stronger remaining part from which you can get some strength with the larger glued cloth to prevent the crack from opening again). I assume thin cotton cloth may be easier to glue than synthetic fibers?

I think that type of repair is easy, low cost, should do the trick and last a long time when properly executed. This could save your driver and not show on the front side of the woofer. Plus it would not add much cone mass.

By analogy for step two, think of a "Band Aid" length wise covering a skin cut...

Good luck, regards,

Richard

[vrobec]

Hi vrobec,

Here's a suggestion for you, but subject to the fact I don't know this driver: cost, cone material, etc. Still better to have a crack than a hole in a cone.

RE: Does it affects the sound

It may affect the low-frequency sound if air passes by the crack even if the outer textile seems ok (textiles usually let some air pass through). A loudspeaker enclosure is supposed to be a COMPLETELY sealed cabinet, except for a vent in a vented enclosure. Even tiny spaces anywhere on a cabinet will affect to some extent box losses and bass reproduction.

RE: The outer textil layers are ok, but the middle (harder) layer is cracked

First, I suggest that you work on the BACK side of the cone since the textile on the front side looks ok and you don't want to compromise this.

Step one: I would put a VERY THIN coat of glue just to seal the crack. No bump or thickness in the glue line, it should be flat, maybe spread a little at the time in/on the crack with a finger or a small brush. When the glue has cured inspect both sides of cone with light to see if any gaps left in the glue, if so correct the issue. Put no pressure on cone to inspect as this may crack the glue line... That first sealing is to prevent air passing by the crack.

Step two: I would then glue a pretty thin piece of cloth, on back side of cone, over the crack to give the repair some strength and durability. That thin piece of cloth must be a little wider and longer than the crack itself (the crack and its immediate vicinity are weak points, but the rest of the cone is the stronger remaining part from which you can get some strength with the larger glued cloth to prevent the crack from opening again). I assume thin cotton cloth may be easier to glue than synthetic fibers?

I think that type of repair is easy, low cost, should do the trick and last a long time when properly executed. This could save your driver and not show on the front side of the woofer. Plus it would not add much cone mass.

By analogy for step two, think of a "Band Aid" length wise covering a skin cut...

Good luck, regards,

Richard

You helped a lot. I will do what you suggested. Thank you very much!