KEF KC62 Subwoofer Owners Thread

JohnnyZeroSix

Standard Member
Given the increasing ownership of KEF's new Uni-Core mighty mouse, I thought I'd try to launch a thread to collate any ownership issues.

I'd like to start off with a concern I have over the LFE input: it's much noisier than on the MANUAL input!

Naturally, people might suggest generic Ground issues, but it's not a 50Hz hum; it's more of a random "ruffling" static noise, which completely disappears when the switch is moved from LFE to MANUAL. (The latter means the KEF's 4th-order Low Pass filter is being used instead of the Amp's).
It can't be the amp grounding otherwise it would show up on either switch position...?
My amp is a Devialet 220 Pro, which means I can set up a LP filter at source with a slope of my choosing.

I'd appreciate if a fellow owner could turn theirs up to at least notch #30 (or full volume!) and report if there's any noise difference between LFE & MANUAL. By the way, mine is connected in MONO to this phono input only.

I am getting a second one this week; I'll be very disappointed if it's a common design fault!
 

JohnnyZeroSix

Standard Member
Well, the second one is the same, so at least I don’t have a faulty unit. I’ll be posting an REW sweep of the two together shortly, but the short story is that they almost reach 90dB below 20Hz together!
 

JohnnyZeroSix

Standard Member
Some more curiosities discovered:
1. The output to the 2nd subwoofer is inverting; so you must invert the phase of the attached one
(presuming I haven't missed any DIP-switch settings notes). I don't think this is my room characteristic, as my two REL's didn't need to be set opposite-phase in the same positions.
2. I have measured inconsistent responses to the LP crossover dial; when changing by 2-3 notches, the freq response doesn't change at all; then it will suddenly change a lot with the next notch up.
3. If the unit is re-powered, it seems to initially put out slightly less volume

I think KEF's DSP control is a little too A.I. ... Is there a Neural Net in there, KEF?

LFE NOISE
KEF have asked me to give them a full setup description, and suggested the Ground Lift button for my noisy LFE input. But that makes it much worse! Its not a ground hum, its static noise. I must stress that it's very faint and acceptable below 12'oclock on the volume dial, but it's annoying with <40Hz source crossovers and high volumes.
 
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JohnnyZeroSix

Standard Member
Here's some measurements with KC62's near rear corners, using UMIK-1 mic.
GREY=PMC 25.23 speakers ; BLACK=one sub; BLUE = both subs; RED = too loud for me!
Twin_KC62_measurements.PNG
 

Fillius

Well-known Member
Here's some measurements with KC62's near rear corners, using UMIK-1 mic.
GREY=PMC 25.23 speakers ; BLACK=one sub; BLUE = both subs; RED = too loud for me!View attachment 1475387
Do you have a lot of room treatment? That's an impressively flat response (compared to mine) without any room EQ.
 

JohnnyZeroSix

Standard Member
Well observed! Yes, I do have a lot of GIK Acoustics products in my living room. Corner traps and wall panels. I would say it has halved all the peak/trough variations in my room .
 

Vendo91

Standard Member
I am looking into this subwoofer for my home theater. I have REL T7i and I am using high level and LFE on it. I want to add KEF as an additional sub, for movies.

As you can also use high level on KEF, how to connect both REL and KEF on high level? As I assume both have different input impedance, is it recommended to connect both at the same time (Excuse my ignorance ) ? Any help would be appreciated. Thanks!
 

JohnnyZeroSix

Standard Member
I was thinking along very similar lines as you initially. But I’m not convinced that movie LFE is the KEF’s true forte. If I were you, I wouldn’t be trying to hook up the KEF by high-level as well if it’s for movies. As you say, the impedance issues must make it complex.
Although, the electrical side of me might say that those input impedances must be very low* in order not to affect the amp or main speakers too much. I don’t use high-level input because I need control over the relative phase of the subs vs the speakers, using time delays in my amp.

*or is that very high...?
 
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JohnnyZeroSix

Standard Member
Thankyou, Benza. I did some more location experiments and found that some parts of the room - near walls - make it worse than others. I can't tell if its boundary magnification, or going near to behind-wall mains wiring! In fairness, my REL's also made a little low-level hum at half volume via their LFE input.
 

Benza

Novice Member
Thankyou, Benza. I did some more location experiments and found that some parts of the room - near walls - make it worse than others. I can't tell if its boundary magnification, or going near to behind-wall mains wiring! In fairness, my REL's also made a little low-level hum at half volume via their LFE input.

But it's weird when switching to manual te noise disapears. I will send a message to KEF. I'll keep you posted!
 

PascalF

Standard Member
I have also send a message to KEF. I'm about to order a KC62 too, but i rather avoid sending it back for warranty/repairs if this is production issue. Awaiting answers....
 

Tuneoholic

Standard Member
Has anyone else had problem with the KC62 wake up. I have mine connected to Lyngdorf TDAI-1120 from sub out to LFE. Volume on the KC62 is in the middle and gain on the Lyngdorf is at 0. When watching tv it does not wake up at all and from Roon I can wake it with some really bass heavy songs. But most songs won’t wake it.
 

JohnnyZeroSix

Standard Member
Has anyone else had problem with the KC62 wake up. I have mine connected to Lyngdorf TDAI-1120 from sub out to LFE. Volume on the KC62 is in the middle and gain on the Lyngdorf is at 0. When watching tv it does not wake up at all and from Roon I can wake it with some really bass heavy songs. But most songs won’t wake it.
Interesting you were able to wake it with a signal. I could not wake my two with a big volume increase; I had to re-plug the signal cable (which causes a whump sound). Do you have yours set to LFE or MANUAL input mode?
I wonder whether providing a sub-40Hz 3rd-order crossover from my amp is making it think there's not enough signal in its normal 40Hz+ operating range.
 
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JohnnyZeroSix

Standard Member
Any update from Kef yet on these issues?
KEF asked me for my audio system wiring diagram, but I didn't want to get bogged down in grounding issues when the LFE is obviously noisier than MANUAL, even when no signal cable is plugged in to them! They haven't been back to me in the week since I replied to them with this info.
 

JohnnyZeroSix

Standard Member
In the interests of balance, I would like to state that I still think this is an amazing product and has doubled my music pleasure, making it more addictive than ever (which is really a LOT in our hobby).
It's a miraculous little box that makes other subwoofers look like clunky early mobile phones compared to today's.
I just think that in tackling the clever transducer engineering challenges, they forgot to fully test some of the basics of standard subwoofer behaviours and expectations.
As someone who tests defence software for a living, I get annoyed about missing out test cases!
 

PascalF

Standard Member
@JohnnyZeroSix : fully agree with you and i fully understand that every new product has issues - but i also expect a company like Kef to come up with remediation for these issues given the price point of this sub - also for existing owners.
I'm still inclined to buy it by the end of April (when it is stock again) and after comparing it to the SVS 3000 Micro (just for my peace of mind) - but chances are 95% that i will get the Kef as this will be linked to my LS50 W2's and is likely to integrate best.
That being said: if Kef refuses to come up with an decent answer i will likely delay my purchase.

Note that i also have queried Kef with a summary of the issues mentioned here.. and yes, i fully understand you point of view about testing (in my line of business things are likely to blow up and cause significant damage when not properly designed & tested :) )
 

Tuneoholic

Standard Member
I was using LFE mode. I tried different crossovers and different settings. No big change. My problem was that my amp was not able to increase gain on the sub signal. I’ve heard it works if you can increase the signal gain more than +5. I finally got frustrated and took the sub back to the dealer. Enough was enough.
 

PascalF

Standard Member
Thanks for the update - let's keep chasing Kef and post our experiences with the relevante reviewers.
 

PascalF

Standard Member
It's awfully quiet - still no response from Kef on these issues. Kinda strange don't you think?
 

JohnnyZeroSix

Standard Member
No, I haven’t heard back either. But I have an update: Unexpected Standby doesn’t happen in MANUAL mode! I left my two in this input mode for 3-4 days, and they didn’t drop to standby once. Then, back to LFE mode, and voila, Standby, from which they can only be woken with a strong 30Hz tone (from REW). I notice from measurement that MANUAL gives more dB’s, so I am currently experimenting with a signal voltage of 1.1V in LFE mode (1V wasn’t enough).
I’m getting close to sending these back, and I do wonder if the KF92 has similar design traits.
 
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PascalF

Standard Member
Thanks for the update - highly appreciate. I've taken the liberty to post you feedback in a reddit forum, link here >>


I still want the kc62, but as it stands now it looks like i will wait a bit more...
 

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