Focal Kanta No. 2 Speakers hum with speaker with speaker cable disconnected

Is there construction work or other environmental noise in your neighborhood?

Thanks for the reply... No there isn't any in close proximity to the house.  

There have been situations where home alarm systems have cased issues 

with individuals equipment. If you have one try shutting it down.

Thanks for the suggestion, no home alarm either.

It’s specifically the left speaker, even with no speaker cable connected. It being the left speaker makes it a bigger issue, as it’s closest to the analog setup. So any noise generated by the speaker (plugged/unplugged) is causing a sort of feedback with the phono.

Right speaker is dead silent, even when connected to the amp. Is it safe to assume that this rules out any power leakage from the power amp (Parasound JC-5) to the speakers?

SKW OCC speaker cables, QED reference 40 RCA and XLR interconnects

That is very odd! I’m sure you tried it but it goes away when you unplug the phono? 

With the speaker disconnected, short the speaker terminals.  Does the problem magically go away??

Swap the speaker positions (place the right speaker in the exact same spot to the half inch). Does the right speaker now hum and the left stay quiet? If so, then there is something inductively coupled to the speaker. Is there a basement underneath? There may be an alarm panel under that location. Or a loose wire connection in an electrical junction box (especially a 240V feed) under the speaker or in a wall near the left speaker. There is no way -- other than inductive coupling -- a speaker cone can move if nothing is connected to the terminals.

If the left speaker continuous to hum after swapping places then call an exorcist.

@mofojo the hum is independent of the phono. I did unplug the phono’s power and umbilical cord, so zero power. I think this hum is what’s causing the phono to hum in the first place.

@erik_squires Thanks Erik! I give it a try.

@gs5556 You might be onto something, the electrical wiring is indeed 240v and running through the wall approximately the same height same as the speaker terminals. Maybe the power line is emitting RFI/EMI in this instance, and the speaker is picking it up. Left speaker is around 3ft. off the back wall and 2.5ft off the side wall.

In the Stereophile review of the Wilson SabrinaX, JA noted that they hum even when not connected to anything.  I was stunned that such an incompetent design would be released.  Even if it were masked while playing music, it’s still noise.

your speaker is apparently picking up an external field.  I suppose you could cover the speaker with mu-metal, but…

Yeah it's troubling to hear that even speakers at Wilson's price point can have design flaws that cause it to pickup interference. 

I think @erik_squires nailed it. I shorted the speaker terminals and indeed the hum dissipates completely. I'm not knowledgeable enough to make a diagnosis, but this kind of points to an internal issue, possibly a leaky/noisy cap? By shorting it, I guess it's being discharged, so no humming. The phono hum is hopefully going to be resolved if this is sorted. Right speaker is silent, so it's just limited to a single speaker.

Thank you all for the suggestions and help. It wouldn't have occurred to me to try out some of proposed tests. I'll reach out to my dealer and update him on this, hopefully he can source a new crossover and install it.

Regards,

Faisal

Lets see what eric has to say since it was his test, he probably has a diagnosis.  But shorting the speaker terminals just provides a lower impedance path for the signal and doesn't really explain where it comes from.  

The crossover can have large inductors that will produce a voltage if they are in a moving magnetic field (near a generator, large electric motor, or transmission line for example).  But you'd know if you had a large piece of electrical equipment near your speaker.  If it was something external, such as a transmission line, you'd likely hear it in both speakers. 

Hopefully eric has seen this before and knows what it likely is.

Jerry

Hey Faisal,

I'm afraid that your test result only makes things weird. :)  This points to the crossover (most likely a coil) is picking up a strong magnetic field.  The issue is that the current has no place to go so it builds up a voltage on the driver, hence the hum.  Honestly I've never head of this happening,  I can imagine this would cause a number of issues depending on whether your amp used negative feedback on the output or not, and whether the outputs were balanced or not.

At this point this appears to be magnetic induction.  Two things to try to further prove this.  Turn the speaker around and on it's side.  See if the hum vanishes or is minimized or maximized in one location.  Move the speaker to another place in the room/home.  Is it possible you have a high current wire in the wall behind it?? AC units, dryer or the wiring from the service entrance??

PS: It’s most likely an inductor, or coil, is acting as the antenna. They couple to magnetic fields better in some alignments than others. That’s why crossover designers will often turn the coils on the board in different directions. If you think of the coild’s direction as a pencil going through the center, there’s up, horizontal and vertical directions on a board. Here’s what I mean:

So you can see the desinger used all 3 directions to minimize coupling. If you have a strong EMF field, turning the crossover around (well, your speaker) should change how well it is coupling to the EMF. Of course, the drivers themselves are coils... < sigh>

Image from audiojudgement

PPS - I'm assuming this issue is happening to a well made speaker.  If you swap the speakers, the new speaker in that place should develop the same problem, if not, it's possible you have something funky in the speaker that makes it susceptible.

I once had a Focal speaker with a broken inductor wire, for instance.  It was nearly impossible to see and only impedance testing revealed what was going on.

PPS - Of course, remove the shorting wire when you do these tests. :) 

Fair enough... It might be too early to start celebrating. Though I did move the Left speaker to a different spot in the house, far away from the listening room and the hum was still there but disappeared when shorted. No high-voltage or transmission lines within a few miles of the house. No radio towers/cell towers close by either, and I believe they operate at a much higher frequency range (MHz/GHz) than the speaker can pickup. If that was the case, wouldn't both speakers be affected equally? Right speaker hasn't been moved at all and doesn't hum, whether connected to amplifier or not. No large electrical equipment.

I'd like to point out that the hum is not heard at all unless your press your ear to the woofer/tweeter, even then it's very faint. If it didn't cause any interference with the phono, I wouldn't have noticed or cared about it. Unfortunately the quieter/more sensitive the phono is, the more these issues are noticeable/annoying.

Maybe I misunderstood.

If you unshort the speaker, does the humming come back? If so it’s an external EMF field, if not, you are right, there’s some weird ringing in the circuit. If that’s the case the best thing to do is have it examined by a pro. If you feel like digging in though you could purchase a DATS V2 from Parts Express and compare the impedance traces of both speakers. My guess is one will be wildly different.

And no, this isn't a leaky cap.  It's the opposite.  It's a cap that can't discharge.  In an amp power supply you want your caps to HOLD charge.  In a speaker you most certainly do not.  Any charges should be dissipated immediately after the signal passes. 

Power supply reserve caps are buffers.  Speaker caps are filters.  Very different expected behavior.  The only way I could see this happening is if a cap had a poor connection somewhere and therefore gets charged, but not released. 

One test to do I just thought of.  Get a multimeter, set it to DC and check your amplifier output with no signal.  Should be a few millivolts.

Just read your last post.

Sounds like a cap is getting charged and then oscillating when discharging.  It's one of two things.  Bad internal speaker connection, or DC on your amp outs.

Thanks Erik for the detailed response, and all the others who contributed.

I moved the speaker far away to see if it's a location based issue, and it didn't appear to be the case. Shorting seems to completely stop the humming any where it's been placed, so there's that tidbit.

I'll try what you suggested with speaker placement, and rotation, and I'll swap Right and Left speakers as suggested. Speaker is admittedly heavier than what the specs suggest :)

Best,

Faisal

If the speaker keeps humming no matter where it is in the room it's not an EMF field.  Do the amp measurement.

The DC output is something I considered and tested for when troubleshooting the phono hum. I purchased the DC blocker adapter that plugs between the IEC socket and power cable, no change. The Puritan Mains conditioner does a great job at filtering all nasty stuff coming in the power line, not that it's that bad to begin with. Measured the EMI/RFI interference out of the Puritan sockets and it's between 11-16mv or 0.011v - 0.016v seems negligible.

Dealer told me about a speaker he owned a few years back that kind of had similar issues with humming. Took him a while to find out the cause: oil-filled caps leaked and shorted or corroded something.

Tried measuring with a multimeter, it's super basic model, and it's measuring no DC current at the mV setting. So either my amp is 100% not leaking any DC (unlikely), or the meter is misleading, which what I think is happening.

Sorry Eric, the timeline of the posts have me answering in reverse order.

If I un-short the speaker the hum comes back, whether in the listening room or elsewhere, doesn't matter. If it's EMF and a wonky something in that speaker only, then yeah your explanation fits the bill. The only thing is, that the right speaker exhibits none of this, connected to the amp or not, so that kind of excludes the amp outputting DC, no?

I unplugged every piece of gear that emits WiFi/Bluetooth (Playstation, Apple TV, TV, Router, Philips Hue/Bridge, and even disabled the WiFi on my AV receiver, but it didn't seem to do anything with the hum. The phono is canary in the coalmine so to speak, it's amplifying whatever is being emitted by the speaker. Many orders of magnitude louder than the original hum level.

Leave it shorted for 30 minutes. If the problem comes back after removing the short it’s EMF from somewhere, and also damn weird!

If it vanishes and stays vanished it’s more likely to be a DC charge happening (could also be a combination of DC + wonky crossover).

Since it doesn’t matter where in the house it is, or how it’s turned around it is unliekly to be EMF though.

In any event, spend $40 on a multimeter and measure the DC on your amp outputs.

OP:

I think you misunderstand me.  DC on the AC input is very different. DC on the AC line causes mechanical transformer hum in the amp. 

DC on the amplifeir's output is caused by improper biasing or leaky coupling caps.  Measure the amp's output terminals.  DC should be near zero. 

Any significant DC could charge the crossover caps and cause oscilation when the input is removed.

Moved speaker, same problem... shorted the outputs, problem gone. Other speaker is (and has been) quiet.

Time to give Focal a call. Looking at their literature, they developed what they call a 'Neutral inductance Circuit" which does balancing act with the driver by making the magnetic field independent of the voice coil position, frequency or current. Something is not up to spec in that circuit  and it's the surrounding emf couples a voltage to it enough to move. 

Thanks Erik for clearing up the mix-up. The measurements quoted above are the amp’s DC offset, I chose the right speaker binding posts but the left should be the same, no? I’ll try again when I get a new meter. Forgot to ask what’s an acceptable range of values for DC offset? I saw 100mV as the maximum acceptable value on the web, any truth to this?

In the meantime, I’ll contact my dealer and Focal, and swap the right and left speakers to confirm it’s just the one speaker. Based on the what’s been mentioned above, it’s seems that there is definitely something wonky with the speaker’s crossover. Caused by their "Neutral inductance Circuit" not working as intended as @gs5556 has kindly brought up, or a malfunctioning component. So far I can’t find anything that leads me to suspect an environmentally induced hum. Quite the head-scratcher this had been.

Again, thank you all for the help!

Edit: Typo