Grounding a Powered Subwoofer Causes Volume Increase

I have an Audioengine S8 powered subwoofer.  It uses an IEC C7 connection for power.  That means that it does not directly connect to ground. Since I was using Earth-Ground boxes for my Audioengine HD6s, I thought maybe the Subwoofer would benefit being grounded. Audioengine stated that any analog amplifier they use is single-ended.  The sub is a class D amp, but that doesn't mean it isn't analog.

Unfortunately, there are no banana plugs on the sub.  The only in/outs are USB, Stereo Mini-Pin and RCA. According to the instructions the sub only needs one RCA input to receive audio from the source; the right RCA. However, I am using both the left and right RCA inputs. 

Using a voltmeter, I was able to determine that the left RCA terminal could successfully be connected to ground. I used a 16awg silver-plated (not tin) copper wire and wrapped one end around the left RCA input.  I connected a spade on the other end and connected that to my power distributor's Chassis Ground Port.  When I did this, the volume of the subwoofer increased significantly.


Not that it's a bad thing to have more volume on my just doesn't make sense.  I have one thought, and it's probably wrong, but it was the only thing that registers.  I read somewhere that with subwoofers, an increase in signal voltage will increase the volume the woofer produces.  Which is why it is best to use both RCA inputs as doing so doubles the input voltage.  The power distributor's chassis ground is connected to the Earth-Ground boxes that are attached to the powered speakers. I tested the signal produced on that line and it fluctuates at .199 - .200 volts. Is it possible that once I connected the sub's left input RCA to Chassis Ground, that it is borrowing that voltage and thus the volume increased?  I cannot imagine that grounding to chassis would suddenly cause the audio signal to increase in volume.


I have no clue but if you are adding grounds to something that doesn't require a ground, I'm thinking you should know the answer to that question. I don't know what is going on but something is and that may be important. Call the sub company and ask that question. 


I think I figured it out. I am not certain, but I think I nicked the volume knob slightly when I was attaching the ground.  Whereas that would better explain the volume increase, it wouldn't explain how bass at that volume was not distorted as it had before, which is why I set it to the volume I had it originally.

Why doesn't it need grounding? I contacted Audioengine and their engineers said all their analog amps are single-ended.  That means only one input is handing the audio signal and the other is just a ground loop.

No experience with the equipment you use/d, but when I demoed another grounding unit, I noticed a subtle, though noticeable increase in the 'blackness' of the system-like, less noise in the background. 

Perhaps this is what you are noticing.-Maybe not increased volume, but enhanced definition.


Yeah, that would make sense. On the Audioengine HD6 and A2+, they'd have a faint "hiss" when they were on and no audio signal was present. This hiss would go away once audio was present and wouldn't appear in quiet moments in a song.  Audioengine claimed this was normal as the hiss was representative of the constant power being used.  On a subwoofer, it cannot "hiss" but that doesn't mean there wasn't some form of signal in constant use when no audio signal was present. On the HD6, that hiss disappeared when I grounded it, so it's entirely possible I did the same on the sub.


I discovered that banana plugs fit perfectly in stereo-mini-plug ports.  This subwoofer has a stereo mini-plug input that I am never going to use.  So I changed the spade to a banana plug and now I am sending any signal or noise that touches the stereo mini-plug port to shared chassis ground (which also connects to various ground boxes).