new KEF KC62 dual 6.5" subwoofer

[Willem]

I have had similar issues with my KEF Kube8b using the subwoofer output of an amplifier. I still have occasional issues using the high level output, but only rarely. Conversely, sometimes the sub does not turn off when it should.

 

[prmfeddema]

Just wondering whether this wake up issue also occurs when using the wireless module?

 

[Willem]

Mine is wired.

 

[kokoon]

I'll check mine with wireless module, I have it but didn't try yet. I can't see why that would behave any differently though.
The thing with my MANUAL input is, I'm feeding it the same LPFed signal as when using LFE input, so it's not any hotter or anything.

 

[prmfeddema]

i wouldn’t be surprised if the wake up problems disappear as it will receive a digital signal - i suspect that the wake up issues come from an a/d converter on the lfe input

Edit/additon: the fact that the wireless module has it's own connector on the KC62 leads me to suspect it has it's own circuitry - hence it might be feeding the data directly to the DSP and bypassing the LFE input (otherwise the wireless received would be on the LFE input). I'm very interested in your observations

 

[kokoon]

Are you sure the wireless module interfaces digitally with the sub?

 

[prmfeddema]

No i’m not, kef would need to confirm that.
let’s assume it is not bypassing the lfe/rca analog input: then you would simply connect the receiver on the lfe or rca inputs, no need for a separate connector... hence my assumption that the extra receiver connector is likely to bypass some of the analog/digital converters...

on the other hand the kw1 tech specs state an “audio output level” of 2v - this would then confirm johzerosix observations that a voltage of at least 1,1v is needed which in turn leads to the suspicion that it links back into the lfe input...

https://eu.kef.com/products/kw1-wireless-subwoofer-adapter-kit

 

[prmfeddema]

I've been battling this Standby issue since I got mine a month ago. In LFE mode, it needs a good, strong, regular LFE signal to stay awake. This doesn't happen in MANUAL mode. My preamp speaks in Volts (not gain) and I have to provide >1.1V, depending on crossover frequency. I'm surprised you still have problems with such a (relatively) high crossover; mine is <50Hz.

when diving into the tech details of the KW1 wireless received (and how this might connect internally): the tech specs state that the receiver has a 2V output. Now i do not know whether the KW1 interfaces digitally to the KC62 electronics or through the LFE connector internally - but is seems to be strange coincidence given your experiences with wakeup issue / voltage. This would suggest if you'd use the KW1 wireless transmitter & receiver the wakeup issues might disappear...guess we need to test this.

 

[kokoon]

when diving into the tech details of the KW1 wireless received (and how this might connect internally): the tech specs state that the receiver has a 2V output. Now i do not know whether the KW1 interfaces digitally to the KC62 electronics or through the LFE connector internally - but is seems to be strange coincidence given your experiences with wakeup issue / voltage. This would suggest if you'd use the KW1 wireless transmitter & receiver the wakeup issues might disappear...guess we need to test this.

I guess 2V is just the max rated output voltage, it should probably be the same as the input voltage on the transmitter module.

 

[Ingenieur]

those crossover frequencies don't look right, that's a big gap

Doesn't it add between?
That is not even an octave so if the slope for each is 6 dB/Octave for example the hi pass would be down 6 at 35 Hz and the lo pass down 6 at 90 Hz.
At the midpoint ~ 57.5 Hz
Hi pass ~ - 2.1 dB
Hi pass ~ - 1.7 dB
That sums to 91 dB using 90 as a base

Lo pass is 24 dB/Oct
Down 8.5 dB at 57.5 Hz
No slope given for the HPF

 

[Willem]

However, most subs have rather steeper filter slopes. So just measure response.

 

[kokoon]

Doesn't it add between?
That is not even an octave so if the slope for each is 6 dB/Octave for example the hi pass would be down 6 at 35 Hz and the lo pass down 6 at 90 Hz.
At the midpoint ~ 57.5 Hz
Hi pass ~ - 2.1 dB
Hi pass ~ - 1.7 dB
That sums to 91 dB using 90 as a base

Lo pass is 24 dB/Oct
Down 8.5 dB at 57.5 Hz
No slope given for the HPF

The crossover filters are generally done so there's already 6dB attenuation at nominal stated frequency, so that should add up to zero gain if you set both LPF and HPF to the same freq. Afaik.

 

[Ingenieur]

However, most subs have rather steeper filter slopes. So just measure response.

I think KEF is giving numbers to those who just want to plug and play.
The LPF is steep, 24/Oct
The HPF imo is not so steep, but they give no spec.

 

[Ingenieur]

The crossover filters are generally done so there's already 6dB attenuation at nominal stated frequency, so that should add up to zero gain if you set both LPF and HPF to the same freq. Afaik.

I'm pretty sure that KEF's calculator is based on the filters they designed.
Their LPF is 24 dB/Oct, no spec for the HPF

So the LPF is likely down 3 at 45 and 8-10 at ~58 Hz.
But the numbers they give must add to ~ 1 (relative).

 

[prmfeddema]

I guess 2V is just the max rated output voltage, it should probably be the same as the input voltage on the transmitter module.

Hmmm.. i wonder why that should be the case as there is a A/D (24 bit/48khz) converter & wifi transmitter in the module.. unless Kef decided to go for max compatibility and reconverting the digital signal back to analog at the receiver end..but then a separate connector does not make sense as using a standard usb + lfe/rca connections on the sub is much cheaper..

I'd really love to have a chat with a Kef engineer to discuss the design decisions in this kind of product

 

[goldenears]

but then a separate connector does not make sense as using a standard usb + lfe/rca connections on the sub is much cheaper..

Standard connections do not allow vendor lock-in. I wonder how much that factored into the design decisions. Not saying they're Apple, but this is an Apple standard tactic, and it has worked well financially for them as a fellow hi-end product manufacturer.

 

[prmfeddema]

Standard connections do not allow vendor lock-in. I wonder how much that factored into the design decisions. Not saying they're Apple, but this is an Apple standard tactic, and it has worked well financially for them as a fellow hi-end product manufacturer.

Not sure if they have apple or similar tactics as there are plenty of wireless adapters on the market that will connect through the RCA plug... anyway.. we'll see when i get mine...probably one more week to go

 

[goldenears]

That's true.

It does stop people from being able to use the Kef wireless adapter with other subs though.

I'll agree with you that it was an interesting design decision and I'd also like to know what motivated it.

 

[prmfeddema]

Someone from the Roon community has been so kind to provide a workaround. Copy/paste :

From the Roon community someone has come up with a workaround.

Link to the article >> https://community.roonlabs.com/t/using-kef-ls50-wireless-ii-with-a-subwoofer/157545/17

Content (copy/paste)
Select the sub option in the KEF Connect app and make a note of the sub out low pass filter setting.
Adjust the sub out low pass frequency to the highest setting (so all the way to the right)
Adjust volume/gain as mentioned in the app
Switch sub to MANUAL mode rather than LFE
Adjust the sub’s onboard crossover dial to the frequency noted in step 1
This will send a wider bandwidth signal to the sub, and is significantly ‘out of the way’ of the sub’s own filter to not cause cascading. With the higher bandwidth, there should be more signal at a high enough output to help trigger the sub and keep it on. If you listen at lower volumes (3 o’clock on the sub has done me well personally with the kind of music I listen to at around 40 volume on LS50WII), then you may also consider increasing the sub gain on the app and reducing the volume dial on the crossover to compensate.


----- and some app settings

Ben - WOW, WOW your suggestion works!, thank you so very much.
Did all your suggestions - not sure what 3 means, but I’ve set the KC-62 sub volume to maximum and now the sub (once kick-started with a brief, very loud sound until the white-led comes on) stays on!
You are an absolute star!
To help anyone else with my setup - here are my app settings:
Bass extension - Standard
Subwoofer channel - Mono
High-pass frequency - 70 Hz
Sub out low-pass frequency - 250 Hz
Sub gain - 0 dB
Sub polarity, Desk mode, Wall mode - all off
The sub even stays on when the music has been paused and will (I guess) stay on unless or until you either turn the LS50 WIIs ‘off’ or they also time-out through non-use.
Even quiet BBC Classical music doesn’t allow the sub to ‘time-out’ as it used to

 

[prmfeddema]

@napilopez jus wondering how you are progressing with your review