After Switching Speakers, My Subwoofer Causes a Humming Noise on All Denon x3700h connected Speakers

[peterjedi]

Denon identified the issue as a ground loop problem, but here's what's puzzling me:

1. My Paradigm Studio 5.1 channel speaker setup previously worked flawlessly. After switching to Revel speakers, I removed the Paradigm speakers and connected everything except the Revel Sub B112V2, which hadn’t arrived yet. Initially, the receiver produced no sound, but after restarting all components, it started functioning normally.

2. Two weeks later, I received the Revel Sub B112V2 and plugged it in. That’s when the humming noise began across all speakers. I contacted Revel, but they were not very helpful, and Denon identified the issue as a grounding loop. Since my previous setup worked perfectly (same cable) and I’m using the same power strip, the problem seems unlikely to be related to the power source (cable) or plug.

3. I’m wondering if the absence of a sub initially caused some kind of reset in my receiver, and now plugging the sub back in is leading to the grounding issue. Microsoft Copilot suggested resetting the receiver as a potential solution, but before taking that step, I wanted to see if there are other recommendations to resolve the issue.

Thank you,

Peter

 

[kyuu]

A ground loop doesn't mean there's an issue with your power source or plug, and the fact that your previous setup didn't have this issue doesn't mean that your new setup couldn't. Unfortunately, a lot more information about your setup (how everything is connected, the actual model of the previous subwoofer (passive speakers are unlikely to be at fault in a ground loop or other hum issue)) would be needed to be able to diagnose the problem.

One thing I might suggest right off the bat is connecting a wire between the signal ground screw on the Denon and either your power ground or to one of the screws on the plate amp on the back of the Revel subwoofer to see if that helps.

 

[DVDdoug]

Two weeks later, I received the Revel Sub B112V2 and plugged it in. That’s when the humming noise began across all speakers. I contacted Revel, but they were not very helpful, and Denon identified the issue as a grounding loop. Since my previous setup worked perfectly (same cable) and I’m using the same power strip, the problem seems unlikely to be related to the power source (cable) or plug.

"Two weeks later" sounds like you didn't have the subwoofer (or the same subwoofer) in the "previous setup". It could be related to how the ground connection is handled in the different subwoofers. i.e., The signal ground may now be connected to the power ground.

Does the hum go-away when you unplug the sub? How about if you just touch the RCA grounds together without plugging it in? (I'm assuming it's an RCA connection.)

You can also try breaking the power ground with a "cheater plug". (That should be just a temporary experiment to confirm a ground loop problem. It's a safety ground.)

You might need a ground isolation transformer.

 

[peterjedi]

A ground loop doesn't mean there's an issue with your power source or plug, and the fact that your previous setup didn't have this issue doesn't mean that your new setup couldn't. Unfortunately, a lot more information about your setup (how everything is connected, the actual model of the previous subwoofer (passive speakers are unlikely to be at fault in a ground loop or other hum issue)) would be needed to be able to diagnose the problem.

One thing I might suggest right off the bat is connecting a wire between the signal ground screw on the Denon and either your power ground or to one of the screws on the plate amp on the back of the Revel subwoofer to see if that helps.

I’m currently using the Denon X3700H AVR. In the past, my setup included Paradigm Studio 60 V5 speakers for left and right channels, a Studio CC590 V5 center speaker, ADP-590 V5 for left and right surround channels, and a Studio Sub 12 V5 subwoofer. My old sub was calibrated with Paradigm Perfect Base Kit.

I sold my Paradigm 5.1 setup and upgraded to Revel speakers, including the F226Be for left and right channels, the C426Be for the center channel, and the S16 for the surrounds. However, the Revel B112V2 subwoofer is delayed and will arrive in two weeks. So, no sub at this point.

Initially, I encountered issues with the receiver when the subwoofer wasn't connected. There was no sound, and I had to power the receiver off and on several times before the speakers began producing audio.

Two weeks later, I received the Revel B112V2 subwoofer. After plugging in the power cord and connecting the single RCA cable to the sub, I began hearing noises coming from all the LCR speakers. I'm unsure if the issue extends to the surround speakers, though the noise from them is less noticeable.

So far, I've tested a new RCA cable, switched to the receiver's pre-out Sub 2, and replaced the plug with an in-wall outlet. Unfortunately, none of these changes have resolved the issue.

I also have a Revel B110V2, which was mistakenly sent to me initially. When I connected it, the same issue occurred. After upgrading from the Paradigm 5.1 system to the Revel 5.0 setup, could this change be causing a problem with the receiver? Connecting either the Revel B112V2 or B110V2 subwoofer results in a humming noise.

 

[peterjedi]

"Two weeks later" sounds like you didn't have the subwoofer (or the same subwoofer) in the "previous setup". It could be related to how the ground connection is handled in the different subwoofers. i.e., The signal ground may now be connected to the power ground.

Does the hum go-away when you unplug the sub? How about if you just touch the RCA grounds together without plugging it in? (I'm assuming it's an RCA connection.)

You can also try breaking the power ground with a "cheater plug". (That should be just a temporary experiment to confirm a ground loop problem. It's a safety ground.)

You might need a ground isolation transformer.

Somewhere after upgrading the Revel Speakers, I removed the Studio Sub 12. Now plugging the new sub causes humming noise on all the front speakers.

Yes, the humming noise stops when I unplug the subwoofer. Using the same cable with the B112V2, the humming persists as long as the receiver is connected to the subwoofer, regardless of whether the subwoofer is powered on or off. When using the B112V2’s power cable with the B110V2 and connecting the receiver to the B110V2, the humming noise also occurs. However, if the subwoofer is turned off or unplugged, the noise disappears. I also tested with new power cable from B110V2 box, it gives the same humming noise.

 

[kyuu]

Studio Sub 12 V5 subwoofer

After finding a picture of the back of this sub, one difference between this and the Revel sub jumps out at me immediately. Here is the relevant bit from the Paradigm sub:

And here is the corresponding bit from the Revel sub:

Notice the difference? Paradigm is a class II device with no ground, while the Revel is a class I device with a ground. So before, you weren't developing a ground loop due to the Paradigm having no connection to ground. Now that you have the Revel sub with a ground connection, a ground loop is occurring. This has nothing to do with the quality of the power cable or the outlet or power strip, so messing with those will not resolve the issue.

The Denon is a class II device like the Paradigm with no connection to ground. Giving it a ground connection via the screw on the back labelled "signal ground" may help, as I recommended in my last post. Alternately, you can try one of the ground isolation transformers from the link above.

Or you can search around for information on diagnosing and resolving ground loops, which are a common issue in the audio world and much has been written about it. I'm not an expert on the subject unfortunately.

 

[peterjedi]

Thank you @kyuu and @DVDdoug

There was no signal ground that I could find on the Revel B112V2.

I purchased RECOIL MGLI 2-Channel RCA Stereo Ground Loop Noise Isolator at https://www.amazon.com/dp/B0D8PF1V5W?ref=ppx_yo2ov_dt_b_fed_asin_title

This fixed the humming noise from all the speakers.

 

[kyuu]

There was no signal ground that I could find on the Revel B112V2.

Right, I suggested trying any of the screws on the amplifier plate. However...

I purchased RECOIL MGLI 2-Channel RCA Stereo Ground Loop Noise Isolator at https://www.amazon.com/dp/B0D8PF1V5W?ref=ppx_yo2ov_dt_b_fed_asin_title

This fixed the humming noise from all the speakers.

Glad that worked for you. Given how cheap that is, I'd worry a bit about if it's introducing distortion in the bass frequencies. It claims it doesn't... but it's small and cheap.

Edit: Remembered where I saw the issue with a small, cheap ground isolation transformer causing serious bass distortion issues. Look at this review. Not the same product, but I would be surprised if the tiny transformers in that RECOIL were able to avoid saturating the same way. I would do some tests to make sure it's not doing anything gnarly to your subwoofer's signal. Easiest way would be to use a tone generator like this one to see if you can hear anything odd in the lower frequencies. And make sure you can hear anything at all under ~50Hz (heed the advice to be careful with your volume when doing this).

 

[peterjedi]

Right, I suggested trying any of the screws on the amplifier plate. However...

Glad that worked for you. Given how cheap that is, I'd worry a bit about if it's introducing distortion in the bass frequencies. It claims it doesn't... but it's small and cheap.

Edit: Remembered where I saw the issue with a small, cheap ground isolation transformer causing serious bass distortion issues. Look at this review. Not the same product, but I would be surprised if the tiny transformers in that RECOIL were able to avoid saturating the same way. I would do some tests to make sure it's not doing anything gnarly to your subwoofer's signal. Easiest way would be to use a tone generator like this one to see if you can hear anything odd in the lower frequencies. And make sure you can hear anything at all under ~50Hz (heed the advice to be careful with your volume when doing this).

Hello Kyuu,

I conducted test tones using the YouTube app at 20 Hz, 23 Hz, 24 Hz, and 27 Hz, with each tone becoming progressively louder. At 20 Hz, my front speakers produced some noise, which is understandable given that the 6.5" bass drivers aren't designed to handle such low frequencies. Overall, everything sounded fantastic. I performed the tests alongside a musician and technical expert, who confirmed there was no hissing or humming. He remarked that the sound quality was excellent. Based on this, I believe the "RECOIL MGLI 2-Channel RCA Stereo Ground Loop Noise Isolator" lives up to its claims. I'm extremely satisfied with my purchase!

Before conducting my bass frequency tone test, I ran Audyssey. It flawlessly played all the tones across all the speakers.

Disclaimer: I lack the equipment to test sine waves or perform other evaluations on the Ground Loop Noise Isolator to identify any corruption or frequency loss. My assessment is based purely on my auditory perception.

20 Hz:

23 Hz:

24 Hz:

27 Hz:

20 Hz - 150 Hz:

20 Hz - 20,000 Hz:

 

[kyuu]

At 20 Hz, my front speakers produced some noise, which is understandable given that the 6.5" bass drivers aren't designed to handle such low frequencies.

Your mains shouldn't have been producing any noise at all at 20Hz, the AVR should be crossing over to the sub well above that.

 

[peterjedi]

Your mains shouldn't have been producing any noise at all at 20Hz, the AVR should be crossing over to the sub well above that.

I just double checked. Only my center channel is making some low-level noise, not LR. I posted Audyssey XT32 results on this forum:

https://www.audiosciencereview.com/forum/index.php?threads/audyssey-on-revel-5-1-speakers.62281/

 

[peng]

I just double checked. Only my center channel is making some low-level noise, not LR. I posted Audyssey XT32 results on this forum:

https://www.audiosciencereview.com/forum/index.php?threads/audyssey-on-revel-5-1-speakers.62281/

Have you made sure the speaker cables, interconnect signal cables and power cords are well separated the way they are laid?
If the sound quality with the isolator is not changed then you are good to go but as mentioned, it would have effects, on paper for sure. You may also try using the isolator with the subwoofer signal cable only and see if that works too, because if they work then there is no point using it with the LR speakers.

 

[peterjedi]

Have you made sure the speaker cables, interconnect signal cables and power cords are well separated the way they are laid?
If the sound quality with the isolator is not changed then you are good to go but as mentioned, it would have effects, on paper for sure. You may also try using the isolator with the subwoofer signal cable only and see if that works too, because if they work then there is no point using it with the LR speakers.

Hello Peng,

I am only using the isolator with the sub RCA cable. Nothing else. My cables are jumbo together. Not sure if it is causing issues. I will try to untangle. Do you think a better RCA sub cable would help?

 

[peterjedi]

Hello Peng,

I am only using the isolator with the sub RCA cable. Nothing else. My cables are jumbo together. Not sure if it is causing issues. I will try to untangle. Do you think a better RCA sub cable would help?

Hello Peng,

I ordered a new RCA cable, Monolith by Monoprice 6ft RCA Cable https://www.monoprice.com/product?p_id=18535. This made no difference. I still hear noise on 20 Hz from my center Channel Revel C426Be.

The mid base makes the most noise 5-1/4" (130mm).

The 4 Low-frequency base Four 6.5" (165mm) vibrates and makes a little noise.

Could my mid-bass be faulty, or is the noise isolator unintentionally directing low frequencies exclusively to the center channel of my receiver?

My center crossover is 40 Hz.

My Audyssey Muti-EQ for center is 20 Hz - 20k Hz. Could this be related?

Thanks for your help!

 

[kyuu]

40Hz is rather low. Are the left/right speakers set to the same crossover frequency?

 

[peterjedi]

40Hz is rather low. Are the left/right speakers set to the same crossover frequency?

Fronts set at 40 Hz and Surrounds set to 60 Hz.

I have all my Audyssey settings in this post -> https://www.audiosciencereview.com/forum/index.php?threads/audyssey-on-revel-5-1-speakers.62281/