BK XXLS 400 Subwoofer- Using both high pass connection on AMP and low level connection on AVR


Novice Member
Hi all,
First of all thank you to all the people offering so much precious information.
I have been gathering parts (mostly used ones) for my home cinema/audio system for the past two months without much previous experience and the information I found here by reading through old posts was very helpful.
However I can't seem to find clear information on the following issue:
My aim for the current setup: 5.2.2 and 2.1 for music.
Dali Opticon 6 (fronts);
Dali Opticon Vokal (centre);
Dali Spectre 2 (Rear Surround);
Q Accoustics 3020i (as front downward firing Atmos);
Subwoofers: BK monolith (ported) & BK XXLS400 (sealed)
AVR: Yamaha RX-V 685;
Integrated amplifier: Arcam SA30;

The Opticon 6s are connected directly to the Arcam SA30 for music. The Arcam SA30 is connected (in processor mode) to the Yamaha AVR front preouts for movies.
The Monolith is connected (LFE mode) to one of Yamaha's two subwoofer preouts.
The XXLS400 is connected on the ARCAM SA30 (speaker terminals) via the high filter cable.

Initially the aim was to use the XXLS400 just for music (2.1) via the low level input, however I found the sound to be better via the high level input.

Then just for curiosity I connected the XXLS400 to the AVR (via low level) in LFE mode together with the Monolith and I was very impressed how well they work together. The monolith is in the corner next to the couch (right side - practically right next to the main listening position on the couch). The XXLS400 is behind the left Opticon 6 and under the left Q3020i, almost in the corner area diagonally opposite from the Monolith. The Monolith is amazing and I find it better for movies than the XXLS400 (tried them separately and the scene in Oblivion where Jack/Tom lands to repair that drone in the football field - with the Monolith you feel the ship landing on top of you). That being said, together somehow they sound amazing (with xxls400 added it brings something to the front stage that gave me and my partner chills and she did not know about the change so her instant feedback was unbiased.)
Apologies for the long intro. Now for to the issue at hand:
I want to continue to use the XXLS400 for music with the Arcam and also use it for movies with the AVR.
What are the risks of leaving the high level connection to the Arcam SA30 and the low level (for LFE mode) to the AVR.

I am asking because I tested to see by having the Monolith connected to the AVR (Low level) and the XXLS400 connected to the ARCAM (via high filter and with no direct low level connections to the AVR). I was expecting the XXLS400 (in LFE mode) not to produce any sound in movies, however it still did.
What are the risks of something going wrong if I use both connections? I could probably use it like that for music by turning up the high level gain and turning off the low level gain and do the oposite when the AVR is on for movies (high level gain down and low level gain up). However I don't want to break something. What would happen if both high and low connections gains were turned on when watching a movie?
I am asking because when the AVR was on and I touched the back of the XXLS400 I got a small electrostatic shock. I used to get that before on the AVR and ARCAM SA30, however since I bought a Tacima 6 power conditioner it stopped. The only item not connected to the Tacima 6 is the Monolith (connected to a wall socket).
This is why I am asking if having the XXLS400 connected both to the ARCAM and YAMAHA could break something?

Also as a side question: Because I just got the XXLS400 today, while shortly testing it with a low frequency sound on youtube I noticed the driver flapping a bit at the 20hz range when the gains was turned a bit high. Is that normal behaviour (the driver bottoming because of the constant low hz long vibrations) or a sign of it being partially blown etc? I just very shortly tested that as I don't think it was a good idea to test it like that in the first place and I did not want to torture it with those continous low level sounds. From 30hz onward it sounds perfectly fine. The reason I did the test is because I was a bit troubled how low the volume output is on it compared to the Monolith. But it's probably because it is a sealed sub, right?

Thank you and apologies for the long post.

Kind Regards,

Deleted member 39241

Hi Pat. BK do explicitly support their subs being connected by both high and low level connections at the same time, so it's fine to do that.

The high level connection is blended to the mains via the controls on the sub itself, and the low level is bass managed, and room corrected by the AVR.

I'm not sure from your video whether that is a fault or expected behaviour, it sounded like there is a bit of a rattle, but that could be because the driver is not front or forward firing whilst you took the video. You could send the video to BK and ask them?

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