Think I have a sub problem


Active Member
So yesterday evening I turned my tv and av receiver on, both myself and my wife said that sounds tinny. Checked the sub (BK p12-300), the was light on, dials in correct place as I would expect. Tried playing white noise using the channel level test, I used to get a nice rumble when I select sub, now I just get a very faint noise if I get really close to it. I put a blu ray on, it’s clear there is some bass there but it’s as if the gain has been turned down 50%. I even tried increasing the sub level to max on the avr and it’s not making much difference at all.

I checked all avr settings, (Dennon 2400h), cross overs 80, all set to small, audyssey on reference. I know none of this would have changed as I am the only one who uses it. I even reset the avr then loaded the setting back on, no difference. Also unplugged sub and checked connections. There are no other noises from the sub, it is just not outputting at the volume it has been. It was last used Saturday night, and I played a film the day before.

I will ring BK this afternoon, has anyone come across this before or have any suggestions? Sub is only 7 months old.


Active Member
Sounds like a possible dead amp. One way to test a sub without question is with a jack to phono cable. You can plug this directly into the sub from a phone and rule out anything else. It's possible the AVRs sub output has died, but that's pretty much unheard of. Subwoofer amplifiers on the other hand, they die all the time. Warranty is good though, if you perform the test as described above and go to BK armed with that, they may just send you a replacement amplifier out, assuming you're happy to swap it out which is incredibly easy to do.


Active Member
Ok, So I spoke to Tom at BK, he suggested trying a different source like my phone, so I plugged my phone in to the sub and changed the filter to in. Played a few songs to test and it is outputting what I think is decent volume/bass. I’ve never done this before so not sure whether it is sounds right or not. If the amp was dead, would I get nothing at all?

Also using the single phono lead I touched the end with my finger and the sub creates a slight buzzing noise which again should indicate sub is fine.

Tried listening to TV through it again and there is just no LFE at all unless I turn the volume up really high then you can start to hear it and feel the cone moving. I even tried optical as well as ARC with same result.

Tried xbox using the dolby app to play the amaze clip, really deep bass towards the end with the thunder and presence throughout.

Tried youtube and Amazon prime video both on the TV apps and I’m convinced they sound how they should but can’t be certain, same with xbox. The sub is creating effects and cone is moving a reasonable amount even playing at the same volume as the TV.

Tried a couple of blu rays with same results as youtube and Amazon.

Test tone through sub still inaudible unless I crank the volume up.

It doesn’t make sense how I get a different result using tv and youtube/Amazon. The sound signal gets sent the same way to the avr and uses the same settings, how could this be different?

I re ran Audyssey again using the phone app so I could see the results better, all the graphs look fine. Have checked all the settings and they are where they should/used to be. I think the Audyssey tone through the sub sounds quieter though but can’t be sure.

So the main problems are, test tone inaudible, TV LFE effects not present/extremely quiet. Possible reduced LFE on other sources.

I’m going to call Denon today to see if they have any ideas. The only other thing I could do then is take my av receiver to Richer Sounds and to see we can try it in the demo room using a sub of theirs and that should then tell us whether it is an AVR or sub problem.


Active Member
You haven't disabled dynamic eq have you? That would reduce the bass.


Active Member
It’s always been disabled. I checked all sources today again and am confident apart from tv audio they all sound as they should. V strange.


Well-known Member
Interested in the outcome of this. I have a BK XXLS400 and for some reason it seems to just 'loose' the connection of the bass. Pull the phono out, plug it back in and all is well again.


Active Member
I’m no further forward with this yet. All other sources are fine. I’m going to have a play the weekend but will keep this thread updated.

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