Unfortunately, even when merely plugged in, the Belkin is generating noticeable chassis hum. It seems to consist primarily of 60Hz and 240Hz. Perhaps the kitchen at 240Hz.
I tried putting a damped metal plate on top and it only decreased the level at 240Hz by about 1dB. But putting an oversized piece of 3/4" plywood dropped hum by more than 3dB, from 27.6 to 24.3dB. I'm using RTA app on iPhone to make these measurements. A Weighted SPL is more or less at residual either way.
It seemed to be best if I covered entire top of Belkin with slight overhang on both sides, especially on air intake vent side. Moving toward the wall but uncovering back was worse by about 1dB.
The Belkin manual warns about leaving 1" of space on all sides, but says nothing about the top (which has no vent holes).
Funny that the Belkin in living room on dedicated outlet seems quieter, but that could result from the stack of equipment on top, or the position in the room, or different room modes in the room.
Refrigerator or A/C make enough noise that the hum is not noticeable when they are running, though the refrigerator also shows big (bigger) spike at 240Hz.
Also, when cable box is plugged it, possibly not even "on", it makes more noise than Belkin, can't even tell Belkin is making noise.
It is seeming to me that the old MonsterPower 2000 strip *also* made some hum, that seems to be a property of all line filters that use inductors (need to retest this).
It is also seeming to me that both TV and cable box are quieter with Belkin than they were with MonsterPower 2000, but this is nothing like a controlled comparison, and I was mostly running Sony also.
I'm concluding that the low level hum is not important now that I am damping it down with big piece of particleboard on the surface of the Belkin, and the particleboard top is also nice for putting power strips on.
I tried putting a damped metal plate on top and it only decreased the level at 240Hz by about 1dB. But putting an oversized piece of 3/4" plywood dropped hum by more than 3dB, from 27.6 to 24.3dB. I'm using RTA app on iPhone to make these measurements. A Weighted SPL is more or less at residual either way.
It seemed to be best if I covered entire top of Belkin with slight overhang on both sides, especially on air intake vent side. Moving toward the wall but uncovering back was worse by about 1dB.
The Belkin manual warns about leaving 1" of space on all sides, but says nothing about the top (which has no vent holes).
Funny that the Belkin in living room on dedicated outlet seems quieter, but that could result from the stack of equipment on top, or the position in the room, or different room modes in the room.
Refrigerator or A/C make enough noise that the hum is not noticeable when they are running, though the refrigerator also shows big (bigger) spike at 240Hz.
Also, when cable box is plugged it, possibly not even "on", it makes more noise than Belkin, can't even tell Belkin is making noise.
It is seeming to me that the old MonsterPower 2000 strip *also* made some hum, that seems to be a property of all line filters that use inductors (need to retest this).
It is also seeming to me that both TV and cable box are quieter with Belkin than they were with MonsterPower 2000, but this is nothing like a controlled comparison, and I was mostly running Sony also.
I'm concluding that the low level hum is not important now that I am damping it down with big piece of particleboard on the surface of the Belkin, and the particleboard top is also nice for putting power strips on.
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