# 60 hz



## JohnJSmith (Apr 25, 2010)

I'm beginning work on acoustic treatments for my living room, so I've been using REW to try and get some before/after waterfalls. I noticed I have what appears to be a constant 60 hz signal. It's really obvious when I move the time window out to 1.5 seconds.









http://optimus.incorrect.org/images/60hz.png

Any ideas what I should look for? Ground loop? Could X10 cause that?


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## grn1969c10 (Sep 18, 2008)

Do you "hear" anything? Any appliance such as a refrigerator, fish tank air pump, air circulation blower, etc. could emit a 60Hz hum that might be picked up by the measurement mic. I didn't notice where you were from, but I will assume 60Hz power is the standard.

Matt


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## JohnJSmith (Apr 25, 2010)

Nope, I can't hear anything at all. And yeah, I'm in the US.


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## grn1969c10 (Sep 18, 2008)

I don't know anything about X10. A quick google search brought up a smarthome device that apparently communicates across the house using existing power wiring. The comunications probably utilize a much higher frequency than 60Hz to avoid interference, so I doubt that the X10 has anything to do with the persistent 60Hz noise you are seeing.

Are your sound card calibration and loopback graphs clean? (As in no 60hz problems.) I'm still thinking your mic is picking up ambient hum in the room, but if that is not the case, maybe you can list your sound card and measurement mic models and somebody else will know how to isolate the cause.

Matt


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## kflory (Feb 6, 2010)

Do you know if it was coming from the room? 

Or noise interjected into the signal path?


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## grn1969c10 (Sep 18, 2008)

> Do you know if it was coming from the room?


The graph shows the 60Hz signal at more than 66db. Assuming the levels are reasonably calibrated with a sound level meter, that should be audible. Yet he doesn't seem to hear it.



> Ground loop?


Try taking an REW measurement with the sub amp unplugged and see if the 60Hz noise is still sitting there all by itself. That could eliminate the soundcard output signal and the sub amp itself as possible sources of the buzz.

Matt


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## laser188139 (Sep 19, 2009)

Another possibility, if you are on a laptop, is trying taking the measurement running the laptop off battery instead of line power. 

Bill


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## JohnJSmith (Apr 25, 2010)

Cool, I found my hum. It turned out to be my HTPC. It runs continuously, so I'd tuned out the noise. After I shut it off, I couldn't believe how loud it had been. 

Here's something odd: I unplugged my MFW15's while hunting the sound. One of them made a really nasty humming noise when I plugged it back in. The hum gradually faded after a while. The other sub didn't do that.


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## JohnJSmith (Apr 25, 2010)

Well, I spoke too soon. As it turns out, I have more than one problem. I thought I was done after I shut off the HTPC, but I saw the same 60hz signal while taking new measurements this evening. It turns out that plugging the laptop's sound card into the receiver's aux input produces a buzz in the laptop's input. I only found one of the problems last night because I'd unplugged the cord to wander around the room with the meter.

I'm not sure if there's anything I can do about this one. The noise is present on batteries, and plugging the laptop into the same circuit as the receiver only helps a little bit.


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## kflory (Feb 6, 2010)

Just throwing out a few idea for you...

Do you have the laptop plugged in or are you running on batteries?

You may want to try unplugging and running off the batteries (in case you are getting a ground loop between the two).

That would be the easiest way to check, but if you conclude that is the case, and that you need to be plugged in either for the laptop or HTPC where you don't have that option, try plugging then both into the same wall outlet (if not already) see if that addresses it. I suspect if the two outlets are on separate circuits, that could exacerbate the problem.

You may also want to do a measurement in loop back mode and confirm it is not being injected by your laptop itself (I doubt this is the case, but may be worth doing just to completely rule out).
hat addresses it.

Food for thought. Good luck!


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## grn1969c10 (Sep 18, 2008)

John, is your receiver connected to a TV? If so, try disconnecting the coax from the back of the TV and see if it helps with a measurement. That is one common cause of ground loop noise.

Matt


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## JohnJSmith (Apr 25, 2010)

kflory said:


> Do you have the laptop plugged in or are you running on batteries?


Yeah, same problem both on batteries and when plugged in. I tried plugging it in to the same circuit and even to the same surge protector.



kflory said:


> You may also want to do a measurement in loop back mode and confirm it is not being injected by your laptop itself (I doubt this is the case, but may be worth doing just to completely rule out).


Yep, no love there either. I did the soundcard calibration with a loopback before I got started.

The RTA is really invaluable here. I can watch the spike appear and disappear as I plug the audio cable in and pull it out.



grn1969c10 said:


> John, is your receiver connected to a TV? If so, try disconnecting the coax from the back of the TV and see if it helps with a measurement. That is one common cause of ground loop noise.


Ahh, good idea! I'll try that out.


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## jbjb (Jun 21, 2009)

Glad I found this thread.

I also extended my time window to 1.5 sec and I saw a similar spike in my waterfall. Mine is centered at 50Hz (which is the freq of my power here in Malaysia).

I'm running REW on my battery powered laptop. Using the Behringer UCA 202 sound card.


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## JohnJSmith (Apr 25, 2010)

Just to follow up, I got a Denon AVR-4311ci today, and it doesn't exhibit the same behavior for whatever reason.


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## laser188139 (Sep 19, 2009)

Congratulations on picking up the 4311. What were you using previously?

Bill


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## JohnJSmith (Apr 25, 2010)

laser188139 said:


> Congratulations on picking up the 4311. What were you using previously?


Thanks.  The old one is an HT-R160.


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## cast55 (Dec 30, 2010)

This Rane document on system interconnection has helped me solve all sorts of ground loop problems with my equipment. Even if it doesn't solve your particular issue, it's a good read.

http://www.rane.com/note110.html

-Sean


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## grn1969c10 (Sep 18, 2008)

Thanks for the link Sean. I added that one to my library.

Matthew


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