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Mac Forum / General / Portable Macs / January 200660 hz hum from "noise cancelling" headphones
My wife got a Kensington Noise Canceling headphone set for Christmas. Strangely, in use there is considerable 60 Hz hum, which kind of ruins things when one is listening to audio which has quiet passages. In testing on my iBook, I discovered that the hum only happens when the iBook is line powered. If operating off of battery, the hum goes away. This also turns out to be true with her PC laptop. I've never noticed any sort of hum in the audio from either iBook or PC, so it seems strange the headphones would be picking up any hum. Anyone have this kind of experience with NC headphones? Recommendations for NC headphones that work well?? I'm not sure if I'm noticing that much of a noise cancellation effect either when I try to use them in a family room with the TV going, etc.  SignatureClem "If you push something hard enough, it will fall over." - Fudd's first law of opposition > My wife got a Kensington Noise Canceling headphone set > for Christmas. Strangely, in use there is considerable 60 Hz [quoted text clipped - 13 lines] > either when I try to use them in a family room with the TV > going, etc. Bose Quiet Comfort 2 is good but outrageously expensive. Noise cancelling is effective at repetetive low frequencies, for noise such as airconditioning, engine noise, electric motors and stuff. Interestingly my QC2s don't keep out all the fan noise from my Powerbook. You have to rely on the padding to quieten TV etc. 60 Hz hum is usually some kind of earth loop. What other equipment is connected to the power and plugged into your Mac? How is your Mac power brick earthed? What happens when you plug it into a different socket? SignatureTo de-mung my e-mail address:- fsnospam$elliott$$ PGP Fingerprint: 1A96 3CF7 637F 896B C810 E199 7E5C A9E4 8E59 E248 >>My wife got a Kensington Noise Canceling headphone set >>for Christmas. Strangely, in use there is considerable 60 Hz [quoted text clipped - 13 lines] >>either when I try to use them in a family room with the TV >>going, etc. One thing I failed to note is that the hum only occurs with the headphones NC on (and the laptop on AC power.) > Bose Quiet Comfort 2 is good but outrageously expensive. These Kensingtons were about $40 (USD). Anyone have experience with NC headphones in the $40-$60 range? I'm trying to figure out if these are defective or not. > Noise cancelling is effective at repetetive low frequencies, for noise > such as airconditioning, engine noise, electric motors and stuff. > Interestingly my QC2s don't keep out all the fan noise from my > Powerbook. > > You have to rely on the padding to quieten TV etc. The padding is fairly effective. > 60 Hz hum is usually some kind of earth loop. Which make this strange because I can't figure out where there'd be a loop. This should be like a bird on a power line. I can sort of see where Steven might get a loop if his powered speakers had their own power supply. > What other equipment is > connected to the power and plugged into your Mac? Just incandescent lighting a sleeping HP Laserjet 4L and a few other electronic do-dads with their own brick(ette)s. > How is your Mac power brick earthed? It is on a power strip into the wall. Standard US 3-prong outlet & power strip, but the iBook's PS is a two prong non-polarized plug, so I guess it is not grounded at all. It is electrically isolated? Hum occurs with plug in either orientation. >What happens when you plug it into a different socket? I took it to other outlets in the house where there aren't any electronic loads. No difference. I'm trying to figure out whether these are defective or is this a common phenomenon with NC headphones. (Can't believe it is. Certainly crummy audio...) SignatureClem "If you push something hard enough, it will fall over." - Fudd's first law of opposition > >>My wife got a Kensington Noise Canceling headphone set > >>for Christmas. Strangely, in use there is considerable 60 Hz [quoted text clipped - 16 lines] > One thing I failed to note is that the hum only occurs with > the headphones NC on (and the laptop on AC power.) Have you connected the headphones to a different audio source to see whether the problem follows the 'phones around? SignatureLater, John johajohn@indianahoosiers.edu 'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk. >the headphones NC on (and the laptop on AC power.) > > Have you connected the headphones to a different audio source to see > whether the problem follows the 'phones around? Strangely, they don't hum when plugged into the bedroom LCD TV, just the iBook or Toshiba laptop. :-/ I think I shall give Kensington tech support a call on this before I try to return them. SignatureClem "If you push something hard enough, it will fall over." - Fudd's first law of opposition >> the headphones NC on (and the laptop on AC power.) >> [quoted text clipped - 6 lines] > I think I shall give Kensington tech support a call on this > before I try to return them. I'm finding a few more links on this, now that I have a better idea what to Google for: http://www.livedigitally.com/?p=546 << My single biggest complaint about the Solitudes came when using them at home (again, if you are just using the units in flight, this will not apply to you) with my laptop charging. It took me a little while to notice a bit of a background humming noise, but once I became aware of it, it was intolerable. Apparently it happens when your sound source is plugged into a wall with a three-pronged plug. The company refers to this as a “ground hum” but I found it quite noticeable. Actually, I suspect that this author has it slightly wrong. My guess is that his laptop power adapter is two-pronged and his laptop is floating, like ours. Thread from 2002 describes our problem very well and even suggests a fix: <http://groups.google.com/group/comp.sys.laptops/browse_frm/thread/d4b57ecce38eca 1a/5b3477abef79f283#5b3477abef79f283> << I found a fix/workaround. If I ground out the laptop (through connection of a USB connector from a powered USB hub, or an external monitor) the hum goes away. It looks like this laptop's ground is floating and inducing noise into the noise cancellation amplifiers. -Carl Indeed grounding the computer seems to work. I touched a wire from the headphone ground sleeve to ground on the power strip and the hum went away. Is there a downside to grounding a laptop? Only thing I can think of is making it more of a static target in winter... I'm still curious as to whether most noise canceling headphones are prone to this hum pickup or is it only some models... I still haven't called Kensington and asked them about it. Guess I'll try Monday... SignatureClem "If you push something hard enough, it will fall over." - Fudd's first law of opposition > >> the headphones NC on (and the laptop on AC power.) > >> [quoted text clipped - 24 lines] > is that his laptop power adapter is two-pronged and his laptop is > floating, like ours. It could happen with 2- or 3-prong connectors, depending on the circumstances, though it's not terribly important to this particular case. [snip] > Indeed grounding the computer seems to work. I touched a wire from > the headphone ground sleeve to ground on the power strip and the hum > went away. Is there a downside to grounding a laptop? Only thing I > can think of is making it more of a static target in winter... Proper grounding of electrical equipment is only a disadvantage in the sense that it costs time and money to do. Improper grounding can have results ranging from the inconsequential to the catastrophic. Know what you are doing before attempting to "graft" a ground onto your iBook. SignatureLater, John johajohn@indianahoosiers.edu 'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk. >Clem >"If you push something hard enough, it will fall over." > - Fudd's first law of opposition OK, totally OT but you put it in my head and I can't get rid of it: "What goes in must come out." - Testicle's Deviant to Fudd's First Law SignatureArt Gorski * Mac Integration Staff * Rice University * Houston, Texas Remember to remove NOSPAM from address when replying via email > I'm trying to figure out whether these are defective > or is this a common phenomenon with NC headphones. > (Can't believe it is. Certainly crummy audio...) Try the etymotics ER6i. About $80 if you shop. Compact, excellent noise isolation and sound that at least equals the Bose. Unlike the NC phones which cancel sounds that are mainly below 1-0.5 khz, the etymotics provide a nearly frequency independent 25 db drop in background noise. The only downsides: The etys function as earplugs with tiny speakers built in. Some people find this uncomfortable. Also, they are SO noise isolating that you cannot hear anyone speak to you, a horn honking, or the phone on your desk. This is a bug or a feature, depending. However, the sound is just fabulous. > My wife got a Kensington Noise Canceling headphone set > for Christmas. Strangely, in use there is considerable 60 Hz [quoted text clipped - 13 lines] > either when I try to use them in a family room with the TV > going, etc. I have had problems like that with powered speakers I had used iBook. It is an impedance mismatch. It is either high or low, if it is wrong you could get that. SignatureThe only good spammer is a dead one!! Have you hunted one down today? (c) 2005 I Kill Spammers, Inc. A Rot in Hell Co. |
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