New Rel Carbon Special Sub “Roars” when there is no signal!

@holmz , thanks and yes I did try swapping the speakon cables, with no change.  Haven’t swapped the power cables though, will try that next.  Not expecting any change, but I’ll let you know if there is.

@bimmerman2 Talked to Rel today, yes you can have the black wire floating (you should tape it with electrical tape to avoid it accidentally coming in contact with the chassis and causing a short.

if you have a ground stud on your balanced differential amp (NOT the negative speaker terminal as that would be disastrous, you can also connect it to that. Rel recommended doing so to me on the phone today, but it’s not necessary if you don’t have any problems with ground hum.

Back to my issue, after much diagnostic troubleshooting this evening I found the problem. Turns out the position of my left sub is in close proximity to a wireless device ( I think it is a router) in the suite below, despite the thick soundproof flooring. When I move the sub either forward or backwards the noise changes to a low and constant hum. Move it far enough and it goes away entirely.

My next step is to see if Rel thinks it is worth it to source some inexpensive EMI shielding material. My thought is I can lay 1m x 1m of it (or more) it on the floor l, and then put a small rug over it so it doesn’t look bad, and the Rel can then sit on top of the rug. Not sure how effective that mesh EMI shielding is but I think it’s worth a shot.

I’ll talk to Rel tomorrow again to see if they think this is worth trying.  I’m just really glad I didn’t have to send back a defective unit and have a replacement shipped.  My wife was afraid that sound was going to break the houses windows and now the kids are absolutely terrified of my subs.  Rel, you are not helping with my popularity in my house! :)

@jetter , @lalitk I tried exactly that - swapping the left and right subs and leaving the connections in place. The problem stayed on the left, so there is definitely nothing wrong with the subs.

When sliding the sub forward or backwards the problem goes away. When I leave the sub in place and move the power and signal cables away from other wiring, then the problem remains. It’s definitely something that happens when the sub is in that exact spot, AND the speakon signal cable is connected, AND there is no signal /music playing. Weirdly, it even happens when the amp is turned off and unplugged. But disconnect the speakon signal cable and no issue when powering on! Very weird problem. But nothing wrong with the subs. I’m going to buy a roll of EMI shielding material to experiment with. It’s not too expensive, and maybe I can try multiple layers if needed. The cover with a small bit of carpet or rug for aesthetics, once the issue is resolved.

@sryeager yes it very much sounded like the end of the world! I couldn’t imagine if this happened when on the other side of the house or downstairs, with this sound blaring! I’d be already of not only the sub damaging but also random stuff in the house breaking!

Even if I fix the issue with shielding, I’m going to be forever paranoid that it will randomly return. As I mentioned, for the first bit, there was no issue.

Update:  I wonder if I can get that sound to play when my houses alarm system is tripped.  No need for monitoring with that sound playing - it would literally be impossible to be physically in the house with that roar!

I forgot to mention - just as an indication of just how loud that sound was, when the issue happened the first time and we weren’t prepared to stop it, the sound persisted for about 6-7 seconds, and the problem sub actually UNPLUGGED my other sub connected to a different outlet about 12ft away! Just incredible. I think it’s the loudest sound I’ve heard, ever.

Anyone know of the most effective brand and type of EMI shielding out there?  Seems more practical than the paint option.

So I discovered that the problem only happens if the crossover setting is set at the 12 o’clock position or higher!  It was in this position only for the burn-in process.  My normal crossover point is much lower than this position.

I still want to fix the issue but this is good news as now I don’t need to worry that the apocalypse won’t be triggered at any time during normal use!

I should also mention that after fiddling with position and the crossover and volume settings, my system sounds fantastic.  It took quite a bit of work to get to this point and I wasn’t sure I was going to get to a point where I get all the benefits people speak about when adding pairs of subs for music.  I had a small coffee table to the left of the left sub which was causing things not to gel.  When moving that coffee table away, everything clicked. What is amazing is that the benefits I notice the most don’t have anything to do with bass. The #1 biggest improvement is how solidly formed and coherent vocals become in the middle of the soundstage. 

As everyone says I found that using a pair is far better than one, as the benefits to soundstage and vocals are nowhere near as pronounced when using only one.  

Also, the one single thing I’ve not been happy with about my B&W 802 speakers is fixed - the image not follows you as you move left and right from the sweet spot.  Before the Rel’s, things fell apart even moving 2” off of the sweet spot.  What a relief. It was worth it just for that!

@audiorusty that sounds likely. I do wonder however where the offending signal is coming from. As I mentioned I feel like the sound is a 60Hz “megatone”, so likely AC from somewhere. And yes lowering the filter would stop a 60Hz tone from being produced. And it starts with a quiet rumble and builds, it’s almost surely a feedback loop. But, I do wonder how the sub “feeds back” the tone back into the offending input signal, since the output is acoustic as you say. This totally makes sense when considering turntables picking up vibration from speakers and infinitely magnifying it, but I can’t figure out how a sub would do that to itself….

I do wonder if there might be an interaction between the sub and my main speaker driver, somehow generating a micro signal on the speaker cable, which is of course connected to the high level speakon cable at the amp terminal…. That micro signal could then be fed back into the sub in perpetuity, which would infinitely increase the signal level. Probably a far fetched theory, but interesting stuff.  I suppose I could test it out by disconnecting the speaker cable from the main speaker and seeing if the problem still happens.

@holmz, sorry I didn't update you, but swapping the power cables made no change (I had also swapped the SpeakOn cables before your suggestion and there was no change).

@jetter , thanks and if that’s true I have TWO defective subwoofers (Ahem, sub-bass systems…), as the problem is always on the left even when I switch the subs.

I do have a terrible amount of coiled power cords (high end Audioquest) behind my system that I think is also a possible culprit. In fact, if my AQ Dragon feeding my amp is too clustered with my streamer’s AQ Hurricane cord, there are slight but very noticeable and annoying issues with my sound’s balance.

Keep in mind when I have my crossovers set to where I like them set, there is no issue.  The issue only happened when I set the crossover to the 12 o’clock position for burn-in.

Small update - as I mentioned I was suspecting the sub might be driving the drivers of my left main speaker and that is where the ever increasing feedback is coming from, since the speaker cables are tied to the SpeakOn cables at the amp. Of note, the issue happens even if my amplifier is completely unplugged from power.

Seems I was right - there IS an interaction with the left speaker. I tried disconnecting the left MAIN speaker cable and trying again. This time, I heard a flat 60Hz tone that did NOT build into a roar. It was flat, and not too loud. Reconnected the speaker, and the feedback loop with a building rumble was back....

My latest guess is that the sub or SpeakOn cable is picking up AC noise at 60 Hz (only when no music signal is input for some reason), and the sub is feeding that back into my left speaker, adding the amplified noise back into the speaker cables and thus the SpeakOn cable as well, which feeds the amplified noise back into the sub, creating an infinitely building feedback loop.

Seems like there are two votes to try powering the subs with one outlet.  I’ll give that at shot tomorrow.  Note however that the two subs’ grounds should  already be bonded, as  the black leads of the two Speakon cables are both connected to my amp’s ground stud as Rel recommended I do.