Neumann KH750 rattle, second replacement with the same issue

[arescec]

Got KH80 + KH750 from Thomman Germany and I am already on the replacement KH750. Both showed significant rattle at low volume, even when just using MA1 to calibrate.
Both the original and replacement woofer had the exact same issue so I wonder if it is a faulty batch.

Here is the sample playing at pretty low volume:

There also seems to be minimal low end, no cone movement and just this extreme distortion / rattle. Anyone else had this?

 

[Arindal]

Does not sound like a typical sharp rattle problem in a very narrow frequency band, but but rather like some major leak, unscrewed amp/driver or something major with the cabinet.

Do you have the possibility to run a sine sweep and identify in which frequency bands the rattle is excited?

 

[arescec]

Does not sound like a typical sharp rattle problem in a very narrow frequency band, but but rather like some major leak, unscrewed amp/driver or something major with the cabinet.

Do you have the possibility to run a sine sweep and identify in which frequency bands the rattle is excited?

Yes, I did run it. It was unable to produce frequencies below some 60Hz, works best for higher frequencies than that. The volume is extremely limited and no cone movement was ever observed. I had to crank the input to get it to produce any 30Hz-50Hz sound and when it did it hit protection almost immediately. Both speakers had the exact same issue. Note that this happens with MA1 software too.

 

[ProAktiv]

I am running three KH 750s in different configurations and never had this problem. I also never read about such a problem with the KH 750 before. This is definetly something to contact Neumann directly. They are usually very supportive.

 

[arescec]

I am running three KH 750s in different configurations and never had this problem. I also never read about such a problem with the KH 750 before. This is definetly something to contact Neumann directly. They are usually very supportive.

I found 4-5 instances of this between reviews, forums (including two on this one - unresolved) and YouTube so not that infrequent. Some people even got the rattle after some time, got it in for repair and then got it again. But glad to hear that it is not a widespread issue. I know the quality is not the best (from the durability standpoint) since they are using super cheap capacitors that are red flagged in genera,l so all in all not that encouraging so far.

 

[respice finem]

I'm curious how they will resolve it (and how long my Neumanns will last).
The old Klein+Hummel were almost "immortal", so were their successors so far (mostly).
But as in any company, at some point the "not so sunny days" are there...

One thing's for sure, brand reputation is a fragile asset.

 

[williamr]

Two KH750s with the same problem suggests that you might look at something in your own system set up, especially if the problem is identical in both cases. Just making a "random" comment based on statistical inference.

 

[Waxx]

Two KH750s with the same problem suggests that you might look at something in your own system set up, especially if the problem is identical in both cases. Just making a "random" comment based on statistical inference.

I would also think about that, also on how you decribe the problem. Can you move the sub to another setup and try it there (even not aligned) if you have the same problem? This to avoid that you send a good sub back because something else was wrong in your system.

 

[arescec]

I would also think about that, also on how you decribe the problem. Can you move the sub to another setup and try it there (even not aligned) if you have the same problem? This to avoid that you send a good sub back because something else was wrong in your system.

The setup is Yamaha AG06 MkII that works just fine with KH80. KH80 has deeper bass, less distortion and 5x more volume so doubtful of it being the setup but will try with a differebt laptop and soudcard, just in case KH750 is sensitive to something.

Edit:
Tried with Audient sound card, different cables, different laptop. Same issue. Meanwhile the KRK 10-3 G4 that I also have, with the same cable and power plug - just re-connecting from one to the other - has not mechanical rattle or what sounds like scraping and has 3x the input sensitivity even when the KH750 is set to high input and -2 gain.
Neumann said that they encountered this issue before when the woofer was dropped in shipping from more than 1.5 meters and they actually did not even ask me to troubleshoot, just told me to send it back.

 

[Curvature]

There was an issue with the plastic cabinets where the back panel was loose and vibrated in the KH80s and KH150s, though less instances of that with the latter. I would have thought their manufacturing solved those issues after they were reported.

Edit: Just read the post above.

 

[arescec]

There was an issue with the plastic cabinets where the back panel was loose and vibrated in the KH80s and KH150s, though less instances of that with the latter. I would have thought their manufacturing solved those issues after they were reported.

Edit: Just read the post above.

This is not rattle from the cabinet, this is extreme distortion from the speaker. Either damaged coil, shifted magnet or faulty amplifiers. I DIYed enough speakers to know what cabinet rattle sounds like. And besides, it can not produce enough vibration to be felt on the cabinet. My phone speaker has about the same sound loudness and bass in fact, minus the distortion. Neumann said to send it back as it can not be remotely repaired.

Must be a faulty batch from Thomman or the post is playing rough with heavy packages.

 

[Everett T]

This is not rattle from the cabinet, this is extreme distortion from the speaker. Either damaged coil, shifted magnet or faulty amplifiers. I DIYed enough speakers to know what cabinet rattle sounds like. And besides, it can not produce enough vibration to be felt on the cabinet. My phone speaker has about the same sound loudness and bass in fact, minus the distortion. Neumann said to send it back as it can not be remotely repaired.

Must be a faulty batch from Thomman or the post is playing rough with heavy packages.

What output are you using to drive the sub and how are you controlling the filters? A little more detail about your setup might help, but I tend to agree with others, two defective subs from a company that has a good history with QC would make me look elsewhere. I'd plug in another source (your phone or cd player) to the sub and see if the issue persists.

 

[574stereo]

This sounds like a slipped magnet. The sub must have been dropped in transit?

 

[arescec]

This sounds like a slipped magnet. The sub must have been dropped in transit?

Probably, check this other post: https://www.audiosciencereview.com/...-kh80-kh750-or-kh120-kh750.62877/post-2375448

 

[gxvfnk]

Probably, check this other post: https://www.audiosciencereview.com/...-kh80-kh750-or-kh120-kh750.62877/post-2375448

What did Thomann/Neumann end up doing?

 

[arescec]

What did Thomann/Neumann end up doing?

Asked to return it even if I was open to debugging, good support i have to say.

 

[arescec]

Got a third one from a local shop and experiencing the exact same issue. At this point it is probably a setup issue somewhere but I am really not sure what could cause a subwoofer to rattle/distort so much from the speaker side (not back panel). Any ideas?

Current chain:
PC -> Yamaha AG06 -> KH750 -> KH80
Using Adam Hall cables in between. The interface is driven through the USB. No distortion on KH80 (alone), KRK 10-3 G4 or headphones using the same interface, only the KH750 is "farting"

 

[arescec]

Got a 3rd one from a local store and it has the same issue, if a little bit less severe. In contact with Neumann and they now have the initial woofer and it looks like driver damage.
Will keep the thread updated as I get the info.
Went over the setup on the phone and everything checks out and they think it is something with the shipping in the region of the world as they had this happen before.
It seems like the woofer might be super sensitive to shipping and the Croatian post is doing something that does not go well with the woofer.

 

[DanielT]

Got a 3rd one from a local store and it has the same issue, if a little bit less severe. In contact with Neumann and they now have the initial woofer and it looks like driver damage.
Will keep the thread updated as I get the info.
Went over the setup on the phone and everything checks out and they think it is something with the shipping in the region of the world as they had this happen before.
It seems like the woofer might be super sensitive to shipping and the Croatian post is doing something that does not go well with the woofer.

What is your local shop doing? Do they break/abuse the speakers before sending them to customers? A joke but who knows maybe it's not? Three broken speakers, hmm can it really be a coincidence?

Your hypothesis about the Croatian postal service maybe BUT don't they send the speakers to your local store /shop first? You might think the local store should test them (especially if they know about the problems with the Croatian postal service) and see if there are any problems? Are the speakers then sent to you from your local shop via parcel or do you pick them up on site?

 

[boxerfan88]

In contact with Neumann and they now have the initial woofer and it looks like driver damage.

Oh wow.

Normally subwoofer drivers are quite resilient.

All 3 units from same shop with same faults ... maybe that batch in their inventory is damaged?