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Neumann KH750 crack?

Liftro

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Hello everyone, I explain my problem. This afternoon playing with my 3 year old I noticed a crack in my subwoofer which I have not noticed before. I have a basement of about 30m2 where I have my studio set up a pair of Neumann KH120A next to the Neumann KH750 subwoofer. I share the basement with my son, he has all his toys there and we usually play there a lot. Leaving aside whether it was the child's fault or not, my main question is does this crack affect sonic reproduction? Is it possible that due to the vibrations (I really like drum n bass and electronic music with a lot of low end) it continues to break even more? Can I fix It someway?Thank you very much for your help.
IMG20230904195404.jpg
 

Joffy1780

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Hello everyone, I explain my problem. This afternoon playing with my 3 year old I noticed a crack in my subwoofer which I have not noticed before. I have a basement of about 30m2 where I have my studio set up a pair of Neumann KH120A next to the Neumann KH750 subwoofer. I share the basement with my son, he has all his toys there and we usually play there a lot. Leaving aside whether it was the child's fault or not, my main question is does this crack affect sonic reproduction? Is it possible that due to the vibrations (I really like drum n bass and electronic music with a lot of low end) it continues to break even more? Can I fix It someway?Thank you very much for your help.View attachment 309746
Have you tried contacting Neumann direct for advice?
 
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Liftro

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Have you tried contacting Neumann direct for advice?
I'm a little embarrassed because I haven't contacted them yet.. :D
First I wanted to know some ideas around here and if anyone has had a similar problem... Also I think I'm out of warranty.
 

Joffy1780

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I'm a little embarrassed because I haven't contacted them yet.. :D
First I wanted to know some ideas around here and if anyone has had a similar problem... Also I think I'm out of warranty.
I think even if you are out of warranty, Neumann would be able to advise as to whether the crack will widen or worsen, or whether it will affect the sound.
 

Sokel

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Does it have any other marks of misbehavior?
Cause it sure doesn't seem like someone hit it,it seems like the cracks caused by humidity or bad assembling.
Subs are built like tanks,it would take tremendous effort to crack it intentionaly,that's a a very odd situation.
 

DVDdoug

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is does this crack affect sonic reproduction?
I would assume so, but since you can't tell...

I would at-least try gluing it and/or maybe Neumann will sell you a replacement driver or maybe you'll need "authorized service". With a woofer/subwoofer it's important to use an exact replacement because a different woofer will have different Thiele-Small parameters and it won't be optimized for the box and an active speaker may have built-in EQ optimized for the particular driver & box.

If you glue it, the mass of the glue will also change the parameters, but not that much. And the voice coil may be out of alignment, etc.
 

Sokel

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I would assume so, but since you can't tell...

I would at-least try gluing it and/or maybe Neumann will sell you a replacement driver or maybe you'll need "authorized service". With a woofer/subwoofer it's important to use an exact replacement because a different woofer will have different Thiele-Small parameters and it won't be optimized for the box and an active speaker may have built-in EQ optimized for the particular driver & box.

If you glue it, the mass of the glue will also change the parameters, but not that much. And the voice coil may be out of alignment, etc.
It's not the woofer as I see it,it's the box that cracked.
 
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Liftro

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Does it have any other marks of misbehavior?
Cause it sure doesn't seem like someone hit it,it seems like the cracks caused by humidity or bad assembling.
Subs are built like tanks,it would take tremendous effort to crack it intentionaly,that's a a very odd situation.
No not at all. Since I installed it, it has not moved and I can assure you that there were no unforeseen events when it came to putting it in the basement.
 
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Liftro

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Since Sokel mentioned humidity... In the winter the basement was 17 degrees but now in summer it does not go below 27, would this difference in degrees have anything to do with it?
 

BrokenEnglishGuy

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Since Sokel mentioned humidity... In the winter the basement was 17 degrees but now in summer it does not go below 27, would this difference in degrees have anything to do with it?
I dont think so
Here in the summer you can go up to 40° and in the winter like 10°C
 

RobL

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It looks like a glue joint failed on one of the mitered corners. If it’s out of warranty I’d just get some two-part epoxy resin and inject it into the crack with a syringe.
 

dfuller

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More than likely it's just a bad glue joint. It happens from time to time.
 

Anthony LoFi

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Hi Liftro
I believe your best option is to contact Neumann directly with photos clearly showing the crack and other photos of all sides of the speaker cabinet trying to show that there has been no impact damage.
Neumann sell to the professional market even though you may be using this for your own semi professional use. They would be concerned
I believe they would want to find out if its a production run problem where other units may also be affected.
This kind of problem raised in an ASR forum would certainly get their attention. They are proactive in sending products to Armir for review and I believe would treat your problem seriously.
I take it you are the only or first owner of this sub.

You may wish to run a low frequency sweep of the sub only to hear any audible effects of the crack.
You could also tell if the crack is still sealed or cone movement air is leaking out of the fracture.
All the best. Love to know how you get on.
 

JaapD

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I would definitely try to repair it. The box should be airtight and resonance-free, meaning: solid construction.

I can’t see it from the picture, is the box made out of wood? If so then apply generic white wood glue in the crack, as much as you can and over the complete length, possibly by pressing from the bottle directly in the crack. Any excess glue can be easily wiped off. Let is sit and dry without using. Then you’re fine.



Cheers,

JaapD
 
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Liftro

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First, thank you very much for all the answers. You are the best. I think that first I will contact the Neumann company and see what they advise me. Depending on what they answer, I will do one thing or the other, knowing that I am a person who likes to fix things on my own, I can try some advice that you have given me. I will also test to see if it affects the sound. About the box I'm not sure... I would say that is made of wooden sheets maybe? And yes, unfortunately I am the second owner of the subwoofer but the person who sold it to me has always had it in his professional studio. Also during transport nothing happened since I have the original box and the original protections and they are fine. That would be all responding to various posts. I post another pic... a little zoom out. I will keep you informed about the progress. Thank you.
IMG20230904195343.jpg
 
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