Noise filter eliminates hum AND subwoofer?

Abquid

CarAudio.com Newbie
Jun 19, 2019
4
0
I recently had a new subwoofer installed in my 2007 Honda Civic Coupe EX. I also have a new Kenwood HU. After the sub was installed, I noticed what seemed to be a ground hum every time I turned on the car and released my parking brake.  The hum would continue as long as the engine was running, but not when it was off. Anyway, I took it back to the Car Stereo place and they said it needed a Noise Filter to remove the ground hum. They installed this and it did get rid of the hum, but it also seems to have made the subwoofer almost gone. I can barely hear it unless I crank it up all the way, and even then it's not great. Before the filter, I used to be able to keep it at +1 and be happy; now I have to keep it at least +6 and often to +10. Am I going crazy or is the filter attenuating the subwoofer sound?

 

Abquid

CarAudio.com Newbie
Jun 19, 2019
4
0
I took my car back to the installer, a popular chain here in CA. I showed him even when he turned up the subwoofer there was little sound change.

His first solution was to EQ all of the lowest frequencies up and leave it at that. But it seemed to me this was just compensating and would be unbalancing the overall sound. I said this wasn't acceptable, so he took out the old amp that powered the sub. The gain on it was turned up all the way. Apparently this amp was underpowered, and this is why putting the noise filter in was lowering the sub. His next, and final method was to put a new, more powerful amp in to drive the sub. I did this, (for an additional $100) and the problem of ground hum AND subwoofer attenuation was gone.

So, in a way, the problem is solved but I am very bummed out at the expensive solution. It seems to me if they had put in an adequate amp to begin with I wouldn't have had these ground hum and missing subwoofer issues. All told, I wouldn't go back there, but at least I finally  have a working sub.

 

wew lad

wew lad inc
Mar 22, 2015
5,722
48
MA
I took my car back to the installer, a popular chain here in CA. I showed him even when he turned up the subwoofer there was little sound change.

His first solution was to EQ all of the lowest frequencies up and leave it at that. But it seemed to me this was just compensating and would be unbalancing the overall sound. I said this wasn't acceptable, so he took out the old amp that powered the sub. The gain on it was turned up all the way. Apparently this amp was underpowered, and this is why putting the noise filter in was lowering the sub. His next, and final method was to put a new, more powerful amp in to drive the sub. I did this, (for an additional $100) and the problem of ground hum AND subwoofer attenuation was gone.

So, in a way, the problem is solved but I am very bummed out at the expensive solution. It seems to me if they had put in an adequate amp to begin with I wouldn't have had these ground hum and missing subwoofer issues. All told, I wouldn't go back there, but at least I finally  have a working sub.
Yep. You've learned a good lesson today on what gain is though. If you have it pegged to max all it's doing is amplifying the noise floor. The proper ratio of input signal to output signal is important. At least you didnt have a hard problem to fix. Chasing down ground loops when gains are proper is a f*****g pain.

You've also learned that to get the right amount of power for the sub stage you need 2-3x the power rated on the box.

 

Boomin_tahoe

Hurtin' feelings errrday.
Jul 24, 2005
15,249
132
WA
I took my car back to the installer, a popular chain here in CA. I showed him even when he turned up the subwoofer there was little sound change.

His first solution was to EQ all of the lowest frequencies up and leave it at that. But it seemed to me this was just compensating and would be unbalancing the overall sound. I said this wasn't acceptable, so he took out the old amp that powered the sub. The gain on it was turned up all the way. Apparently this amp was underpowered, and this is why putting the noise filter in was lowering the sub. His next, and final method was to put a new, more powerful amp in to drive the sub. I did this, (for an additional $100) and the problem of ground hum AND subwoofer attenuation was gone.

So, in a way, the problem is solved but I am very bummed out at the expensive solution. It seems to me if they had put in an adequate amp to begin with I wouldn't have had these ground hum and missing subwoofer issues. All told, I wouldn't go back there, but at least I finally  have a working sub.
Expensive situation....welcome to the world of car audio. Where we deal with that on a constant basis.

 

audioholic

not a moderator
Aug 31, 2003
24,109
636
Parts Unknown
Where did everyone on this forum get the idea that you need to run 2x-3x the rated power to a speaker to overcome impedance rise? Impedance rise is frequency dependent, and highly affected by the enclosure design. Just saying to throw tons of power at a speaker will lead to power compression issues and thermal failure of voice coils. Its a much more complex topic than most people here seem to be giving it credit for.

*steps off soapbox*

 

Abquid

CarAudio.com Newbie
Jun 19, 2019
4
0
I don't know much about car stereo equipment, but here it is as I understand it.

Originally, the stock Honda 8" sub and factory amp.

First, this was replaced with a Micro Road Rage Amp 150w, and a Pioneer 2-ohm, 150W/600W 8" sub. The subwoofer sounded good, but there was a pronounced hum.

Ground hum was found to be due to "underpowered" MicroRR amp (gain was turned all the way up). A Metra ground-loop noise filter was added to eliminate hum, but this also cut most of the subwoofer out.

Finally, an Infinity Primus 6002A 280w amp replaced the Micro Road Rage Amp. I think it sounds better, and there is no need for the noise filter anymore.

 
Last edited by a moderator:

audioholic

not a moderator
Aug 31, 2003
24,109
636
Parts Unknown
Ground hum was found to be due to "underpowered" MicroRR amp (gain was turned all the way up). A Metra ground-loop noise filter was added to eliminate hum, but this also cut most of the subwoofer out.
So the shop's explanation was that they sold you an insufficient product initially, which they tried to compensate for by turning the gains artificially high. Which led to a noise threshold issue, which they tried to compensate for with a noise filter. This is the type of work you get when you have your cousin install your system in his driveway, not the work of a professional shop.

 

Abquid

CarAudio.com Newbie
Jun 19, 2019
4
0
Yes...I took it into a popular chain here (SoCal). I had read Yelp! reviews and they were pretty good.

It's too bad--their work looks pretty clean. But I agree that the way the amp troubles were handled was pretty bad customer relations. Does anybody know of a good auto stereo shop in West LA, other than Aaron and Exekiel's?

 

nauc

CarAudio.com Veteran
Mar 22, 2005
3,010
22
Home
shops that give a crap about being successful, should watch this and apply the info..



 

slide95

CarAudio.com Newbie
Mar 22, 2019
9
0
Hi
to be a ground loop problem one or more devices attached to the unit would have to be grounded,so try a battery powered source like a phone or ipad as a sole source and see if you still get a hum.

 

slide95

CarAudio.com Newbie
Mar 22, 2019
9
0
Hi
to be a ground loop problem one or more devices attached to the unit would have to be grounded,so try a battery powered source like a phone or ipad as a sole source and see if you still get a hum.
to be a ground loop problem one or more devices attached to the unit would have to be grounded,so try a battery powered source like a phone or ipad as a sole source and see if you still get a hum.

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