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Martin
Martin, Electrical Engineer
Category: Home Improvement
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Experience:  Design, construct, fix and grow stuff around and in the home.
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I have some studio monitors that are magnetically shielded

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Hi,
I have some studio monitors that are magnetically shielded and are plugged into this Furman power conditioner/surge suppressor:
https://www.sweetwater.com/store/detail/PLPLUSDMC
However, my setup is near my kitchen and every time the refrigerator compressor or dishwasher motor kicks on or off, the studio monitors pop.
My questions:
1. What is the cause of this popping?
2. Is it airborne or on the electrical line?
3. Can it damage my equipment even though my equipment is plugged into a pretty potent power conditioner?
4. How to solve it?
Thank you.

Hi. Does those speaker are connected to an amp or is the amp integrated into one of them?

Customer: replied 8 months ago.

Hi,

They are self-powered speakers, so I believe they have amps in them. They are KRK Rokit 6 units with the following specs:


Specifications



  • Configuration: 2-Way

  • System type: Active Studio Monitor

  • Low-Frequency: 6" Aramid Glass Composite woofer

  • Mid-Frequency: N/A

  • High-Frequency: 1" soft dome tweeter

  • Frequency Response :48Hz - 20kHz

  • Max Peak SPL: 107 dB

  • Amplifier Class: Class A-B

  • Power Output :68W

  • High Frequency: 18W

  • Mid-Frequency: N/A

  • Low Frequency: 50W

  • Input Impedance (Ohms): 10 K Ohm balanced

  • HF Level Adjust: -2dB, -1dB, 0, +1dB

  • System Volume: (-30dB - +6dB)

  • Indicators: Power

  • Input Connectors:

    • Unbalanced RCA

    • Balanced 1/4" TRS

    • Balanced XLR



  • AC Power Input: Selectable 110V-120V / 220V-240V (50Hz - 60Hz) or 100V (50Hz - 60 Hz)

  • Enclosure Construction: MDF

  • Finish: Black vinyl wrap

  • Port Configuration: Front firing slot port

Yes they are active (at least the generation model 3 spec i am reading).

"1. What is the cause of this popping? "
Electromagnetic noise AND electrical noise. When a currentis made to stop too fact, a small arc is produced (a bit like a spark plug). This cause an energy dirac that is very rich in harmonics. Yes it can sometime damage electronics but it is less a problem with modern equipment (it was especially a problem with 80's CMOS chip).

2. Is it airborne or on the electrical line?
Both, but significantly airborn as it if partially absorbed by the inductance of long cable.
An insulation transformer help to isolate from the electrical. Also putting ferromagnetic bead on the electrical cable at the cause and then the closer to the speaker AC cord can also absorb some. Connecting the speaker with an optical cable would help but i don't see such an input on those (as that also isolate). That mean isolating the unti that give the sound to the speaker is also needed.

3. Can it damage my equipment even though my equipment is plugged into a pretty potent power conditioner?
As i mentioned, yes it can. Harmonics make thing heat more than they should (very slighly but resistor evaporate faster so an equipment may last 30 year instead of 60) and capacitor chemistry can change (that can cause failure earlier, like 2-6 years)

4. How to solve it?
Like i mentioned. Also making a faraday cage around electrical wire reduce the antenna effect. Metal piping grounded is great for that (a cheap way would be grounded aluminum foil. The orientation of power cord and every electrical wire (if they are parallel the more they will transmit to each other). Electrical device called softstart are used in industrial environment when motor need to much starting current.

Also. If the setup is behind the freezer (i don't know yet if it is in front or behind it), you could make a aluminum foil barrier to reflect the compressor emission without that even showing.

Customer: replied 8 months ago.

Thank you for your interesting and informative responses. The speakers are in front of me on my desk and the fridge/freezer is behind me on opposite wall. I will take your suggestion about putting isolation transformer and ferromagnetic beads on cable.

I isolated the issue to the XLR cables connecting from my Firewire Audio Interface into the monitors. If I disconnect the XLR cables from monitors, but leave power to monitors turned on, there is no more pops. When I re-connect XLR (even if audio interface is turned off), the pops come back.

So anytime XLR cable is plugged into the audio interface + monitors, even if audio interface is turned off, the speakers pop. As soon as I disconnect from audio interface, no more pop.

Perhaps something is wrong with the audio interface shielding?

Is it OK to plug power conditioner/surge suppressor into isolation transformer?

yes, as long as the equipment powered by the transformer does not exeed the transformer power rating. It also need to be a 1:1 ratio (the definition of a power transformer but i need to mention it because you don't want to increase the tension :)).

About XLR, sometime issue like than can happen. the pin 1 and the sheild are not always connected so on some setup the sheild is not present with that cable.

Customer: replied 8 months ago.

Thank you Martin. Can you please review this transformer and let me know if it's correct for this problem and also if it is OK to connect the Furman power conditioner to it?

Isolation Transformer:

https://www.amazon.com/gp/product/B00006HPHN/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Power Conditioner:

https://www.sweetwater.com/store/detail/PLPLUSDMC

Thank you very much,

Igor

It should be ok but the power condition seem rated at 1800W (15A x 120V). The transformer is 500W, so you must not connect for more than 500W of stuff to it. Note that an insulation transformer is expensive and cost a lot in transport fee (it is heavy) so try all other solution incrementaly and use this as the last one. I say that because you already have a power conditioner so a lot of the problem may come from the air.

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