Noise from Subwoofer

[Ron Nielson]

This question pertains to noise in my subwoofer, not in my car, but in my house.

The Phoenix house was built in 1947 and did not contain a ground circuit to any outlets. I inherited the house from my mother about 12 years ago and had some interior remodeling done, mainly in the kitchen area where 2 walls were moved. The wiring in that area was done under the current code and now has a ground circuit at each receptacle. On the other side of that kitchen wall is the living room, where my subwoofer is plugged into a grounded receptacle. The AVR receiver is plugged into a receptacle in the old part of the house, with no ground circuit. Output from the reciver to the subwoofer is a patch cord, up thru the living room wall behind the receiver into the attic, over to the kitchen/living room wall, and down to the subwoofer.

I hear noise from the subwoofer with no apparent input from the AVR receiver. When music is playing you don't hear the noise or perhaps it is buried in the music, but when the music stops, there is a nondescript noise coming from the subwoofer. The noise is not a buzzing, electronic hum or static, just varying noise. Maybe like a microphone rolling over a piece of carpeting. Hard to describe.

What is causing this subwoofer noise? and what is the fix?

 

[2004LB7]

Well since we can't hear it, it must be you

But 99% of the time it's a ground issue. Sometimes it's not the plug ground but internal or on the board, etc. could also be a bad ground on the input side too. Try adding an additional ground wire to the input ground and see if it lowers the noise. You can also try jumping the input and ground together to see if it's a floating input noise.

Do you know what class amplifier it is? A, B or D are most common with D being the most common for newer ones. A being mostly relegated to professional amps, and B for cheaper or not as new.

Class of amplifier can sometimes help in figuring the source of noise.

 

[N2BRK]

For S&G grab an adapter to take the 3 prong cord and change it to 2 prong. Plug it in and see if the noise stops. I did this with my powered sub.

 

[2004LB7]

For S&G grab an adapter to take the 3 prong cord and change it to 2 prong. Plug it in and see if the noise stops. I did this with my powered sub.

You probably had a ground loop issue and killed it by removing the ground at the plug

 

[PureHybrid]

What did they do with the new wiring at the panel? Dedicated to the ground rod or bonded?

 

[N2BRK]

Of course I did.

If he takes off the ground and it goes away, then it could be a ground loop acting as an antenna and picking up RF from the 60cycle or another device with poor shielding. If it doesn't go away, then it could be another device or a dimmer switch putting noise on the power line and you go from there. I'd still test it by putting a 2 prong adapter on and seeing what it does or doesn't do.

 

[Ron Nielson]

I believe my mom had a few 3-prong to 2-prong adapters around. I'll try one if I can find them. Hardware store close by if I can't. I'll let you know how it goes. Found one and no noise/rumble so far.

Truck electronics need ground to complete a circuit, but houses do not. I thought that the ground in a house was there to prevent shocks to people from a device where there is no neutral circuit present. 240V receptacles like a clothes dryer don't have grounds either. Why would anything to do with the ground on the subwoofer cause any problems? What do I need to understand?

 

[jlawles2]

I had a similar issue when I had the Velodyne. Adding https://www.crutchfield.com/S-8IJUifNA1Di/p_119MPSW200/Monster-Power-SW-200.html (no longer available but there is probably a substitute) killed the noise.

You need to unplug the RCA feeding the subwoofer to determine if it's power feed or RCA noise you are hearing. Once you determine if it's RCA or power, then you can combat the issue.

 

[2004LB7]

I believe my mom had a few 3-prong to 2-prong adapters around. I'll try one if I can find them. Hardware store close by if I can't. I'll let you know how it goes. Found one and no noise/rumble so far.

Truck electronics need ground to complete a circuit, but houses do not. I thought that the ground in a house was there to prevent shocks to people from a device where there is no neutral circuit present. 240V receptacles like a clothes dryer don't have grounds either. Why would anything to do with the ground on the subwoofer cause any problems? What do I need to understand?

(Warning: long reply ahead )

This is a case of terminology. Vehicle ground is technically the neutral or negative. House ground is indeed connected to the earth. The center tap of the transformer that is providing the power to your house is the neutral. This is also the part the connects to the earth ground. So in an event that a rouge hot wire touches the frame or metal case of an appliance the ground wire is supposed to carry enough current back to this center tap of the transformer to overload the circuit breaker or fuse and cutting off the power

When it comes to electronics, ground is often used as a shielding from electromagnetic interference and stray current. Basically any waves trying to pass through the case get shunted down to ground. Otherwise they can induce a voltage on the input stage of the amp and then get superimposed on the signal.

Power supplies for the amps or other electronics will often have a center tapped transformer or other reference point for ground that can help shunt any inbalance in current to ground. So if you have a bad ground the current has nowhere to go but down the power supply lines and into the electronics thus effecting the sound. Another issue is ground loops where there is one or more ground wires all trying to carry current to ground. But it's exceedingly difficult to get everyone of them the exact resistance so if one ground wore has more resistance then another it can cause some of the current to flow backwards through the electronics to another ground wire then to ground. This is another source of interference. Sometimes just disconnecting one ground will allow all the current to flow one way and out a single ground conductor. Typically the correct way to ground electronics is a star connection. Where all the individual grounds come together to one solid connection then one wire from there to the earth. If there is multiple lines running to earth, then you literally create a circle pathway and current can go in circles

Another source of noise in amplifiers is placing unbalanced signal wires near other high powered circuits. This is normally manifested in the infamous buzz. But with today's digital circuits being more common higher frequency interference is becoming more common

 

[Ron Nielson]

Thanks Jason. I think I understand. So I'm thinking if both the receiver and sub are plugged into the same grounded receptacle, that would be a good place to start. Both units would have the same electrical power inputs and grounds and all should be good under that setup, true?

Well, I've been testing for a few hours now and do not hear that noise that was the subject of my question. However, now I think I may have a blown speaker. Turning up the low pass filter gain to 5 or so, the speaker does not sound good with some sounds. I watched Outdoors with the Morgans and Mike was using his new excavator. The sound of the tracks while moving sounded like a microphone was right at the track in the sub, but from the front speakers, it just sounded normal, like you would expect. I also watched several music videos, pro-recorded videos, and didn't hear anything like that. Some homegrown recordings seem to have some problems, just based on the sub sounds. I have no idea if true.

You need to unplug the RCA feeding the subwoofer to determine if it's power feed or RCA noise you are hearing. Once you determine if it's RCA or power, then you can combat the issue.

I can unplug the RCA from the sub but then I wouldn't be able to hear it. Or are you saying just unplug the RCA, leave the sub on, maybe even turn it up, and see if I hear bad sounds? I'm guessing so. I tried it, RCA unplugged, no noise at all, except if I turned the low pass filter gain to 5 or above, I could barely hear a very small 'tick' sound, about 1 per second or so. I had my ear right up to the driver, so the sound was almost not heard. My conclusion is that it is RCA noise, right?

I think I might try running an extension from the receiver surge protector and plug that into the grounded circuit by the subwoofer, so that they should have common electrical supplies. That will have to wait until tomorrow, getting a little late to disturb the wife tonight.

This is the amp for the sub: https://www.daytonaudio.com/product/1030/spa500-500w-subwoofer-plate-amplifier

Thanks for all the help and information guys

 

[2004LB7]

Thanks Jason. I think I understand. So I'm thinking if both the receiver and sub are plugged into the same grounded receptacle, that would be a good place to start. Both units would have the same electrical power inputs and grounds and all should be good under that setup, true?

No guarantee that there is no ground loop issue. That why it was suggested above to use the adapter without the ground to see of it breaks the ground loop and clears the noise

Well, I've been testing for a few hours now and do not hear that noise that was the subject of my question. However, now I think I may have a blown speaker. Turning up the low pass filter gain to 5 or so, the speaker does not sound good with some sounds. I watched Outdoors with the Morgans and Mike was using his new excavator. The sound of the tracks while moving sounded like a microphone was right at the track in the sub, but from the front speakers, it just sounded normal, like you would expect. I also watched several music videos, pro-recorded videos, and didn't hear anything like that. Some homegrown recordings seem to have some problems, just based on the sub sounds. I have no idea if true.

Speaker coils that are burning out can make weird noises shortly before they go out completely

I can unplug the RCA from the sub but then I wouldn't be able to hear it. Or are you saying just unplug the RCA, leave the sub on, maybe even turn it up, and see if I hear bad sounds?

Yes

I'm guessing so. I tried it, RCA unplugged, no noise at all, except if I turned the low pass filter gain to 5 or above, I could barely hear a very small 'tick' sound, about 1 per second or so. I had my ear right up to the driver, so the sound was almost not heard. My conclusion is that it is RCA noise, right?

Could be unless it is a dieing speaker as discussed above

I think I might try running an extension from the receiver surge protector and plug that into the grounded circuit by the subwoofer, so that they should have common electrical supplies. That will have to wait until tomorrow, getting a little late to disturb the wife tonight.

This is the amp for the sub: https://www.daytonaudio.com/product/1030/spa500-500w-subwoofer-plate-amplifier

Thanks for all the help and information guys

You can also try feeding the amp with something battery powered like your phone to see if it is clear or still noisy. That would be a pretty good method to isolate the two but still get sound to test with

 

[Ron Nielson]

What did they do with the new wiring at the panel? Dedicated to the ground rod or bonded?

When the remodel work was done, new wiring was attached the old 100amp service. The next year or so, The electrical supply was replaced with 200 amp service, new box of course, and there is a ground now. I'll have to look and see what they did with the ground and neutral from the box.

 

[Ron Nielson]

Of course I did.

If he takes off the ground and it goes away, then it could be a ground loop acting as an antenna and picking up RF from the 60cycle or another device with poor shielding. If it doesn't go away, then it could be another device or a dimmer switch putting noise on the power line and you go from there. I'd still test it by putting a 2 prong adapter on and seeing what it does or doesn't do.

At this point, the receiver has no ground (I just looked and the receiver cord is only a 2-prong cord), and the sub has no ground due to the 2-prong adapter added to the grounding plug.

 

[jlawles2]

Correct Ron. Trying to isolate the issue to power supply or if it's some how traveling through the RCA. I've picked up noise in the RCA on short runs just by it getting shifted too close to power wires (I believe there were some other issues in power feed also) and being looped.

The way you are describing that removing the RCA from the sub and you are not hearing a steady buzz says the noise is probably traveling through the RCA cable. If you disconnect it from the source leaving the sub end connected and the noise is present, then the RCA or its routing is suspect. If the noise goes away, then the noise is coming from the source (receiver) most likely. You can try an alternative source as suggested and even a completely DC powered signal source (portable electronic of some type) to verify the noise is truly from the AC powered source.

I have noise isolation filters on the TV and Receiver to help isolate and kill the errant noises from the wall power. I also have them plugged into a USP with voltage correction (we have unpredictable power sag and drops) which help increase the life span.

 

[N2BRK]

Have you tried another RCA cable? Have you tried using an extension cord to plug sub and receiver into the same outlet and seeing if that helps?

As for the descriptions above - they are SPOT on. The only other thing I can add is that poorly grounded or ground loop issues can cause the ground wire to act as an antenna and bring in noise. That's why were were trying to disconnect the ground on the plug and break up it's resonance length as well as getting rid of possible different potentials to ground between the two units.

 

[Ron Nielson]

Have you tried another RCA cable? Have you tried using an extension cord to plug sub and receiver into the same outlet and seeing if that helps?

I don't have another RCA. It's about 25 ft long, the best I remember- up one wall across in the attic and down another wall.

I used an extension cord, plugged the sub and the receiver into one end, and tried both receptacles with the other. No difference between the two receptacles.

Then I pulled the RCA from the receiver and removed it from the hole in the back of the cabinet holding the receiver, where all the cables exit the unit. Reattached the RCA to the receiver. Separating the RCA made a definite difference. But I just barely have enough RCA length to run it to the receiver because the entire back of the unit is a lath metal with only a 1 1/2 inch hole for all the cables to go thru. I will drill another couple of holes to get some separation for the cables but need to get another hole saw. There is possibly a similar problem with cables going thru the wall up to the attic that I will address.

Now, what I have discovered is that there must be a lot o


f garbage sound in amateur video on YouTube. Pro recorded videos, like a recent awards show, Miley Cyrus, sounds very good, but the general guy recordings, Outdoors with the Morgans, has problems. Commercials sound good. Blast off with SpaceX is AWESOME.

Thanks for all the help, time, and suggestions from everyone.

 

[2004LB7]

Play a little music to test the sound.

Hotel California
Money For Nothing
And the 1st 35 seconds of rage against the machine take the power back

these are some songs I go to when testing sound systems for clarity and base response.

 

[N2BRK]

I cannot listen to Hotel California without changing the words to Hotel Coral Essex.

Once I saw Revenge of the Nerds when they went to Mexico and were looking for the Hotel Coral Essex, it was all over. HAHAHAHA. If you haven't seen the movie (shame on you) the place was a DIVE and some of the letters on their sign were burned out, so it just read:

HOT__
_ORAL
__SEX

 

[1FastBrick]

I cannot listen to Hotel California without changing the words to Hotel Coral Essex.

Once I saw Revenge of the Nerds when they went to Mexico and were looking for the Hotel Coral Essex, it was all over. HAHAHAHA. If you haven't seen the movie (shame on you) the place was a DIVE and some of the letters on their sign were burned out, so it just read:

HOT__
_ORAL
__SEX

Source: https://www.youtube.com/watch?v=qcSObbhqMUY&ab_channel=FrankieForeal

 

[Ron Nielson]

What did they do with the new wiring at the panel? Dedicated to the ground rod or bonded?

I just looked at the box. Each of the neutral and ground terminal strips was grounded to the copper ground rod.