The Axis VoiceBox Extended Bass System (EBS) is not a subwoofer. It is a true bass extender that is designed to not be spectrally flat with respect to the rest of the frequency spectrum. Therefore it should not be treated like a subwoofer if you have a DEQX speaker/room correction processor in your audio system.
This post tells you what you should do instead. The process described here applies also to the Axis VoiceBox Floorstander (FLS).
It is assumed that the room has been acoustically treated so that undesirable reflections are controlled as much as you are able or willing to do.
Put the speakers at their intended locations in the room. If using a pair of EBS, stack a VBS on top of each EBS — centre the VBS on the top of the EBS, with the front baffles of both flushed. Slip a thin sheet of neoprene rubber between the VBS and EBS to provide some acoustic isolation and to prevent the VBS from sliding off if it is accidentally bumped.
Integrate the EBS with the VBS. Use the method described in the EBS user guide. For our demo room and living room at home the best crossover point is at the 12 o’clock setting. And the best volume setting is at 9.30. Yes, that low! These settings may not be ideal for your listening room, so please take the time to do extended listening and tweaking with a good variety of well recorded/mastered tracks.
Tip: If the bass sounds boomy, slow and lacking in detail try decreasing the EBS volume (the same amount for both units). You will know when you get it right because the difference between right and wrong is startlingly obvious.
Move the stacks further into the room if they are not at least 1 metre from the rear wall and respective left and right walls. The further away from the walls the better. Set up the measurement microphone as described in the DEQX user guide. A speaker-to-microphone distance of 1 metre will do. Remember to put soft, acoustically absorbent material on the floor between the loudspeaker stack and the microphone.
Perform measurement of the loudspeakers, treating each stack as a single full-range loudspeaker. Do not treat the EBS units as separate subwoofers, which implies that you must not connect them to the DEQX processor’s subwoofer outputs.
Create a filter set and upload it to the DEQX processor.
Move the loudspeaker stacks back to their original locations.
Power-off both EBS units.
Perform room EQ using only the VBS units.
And that’s it! You can now power-on the EBS units and use your test tracks to verify that your crossover and volume settings for the EBS units are still valid. With any luck you won’t have to adjust either one.
It will take a really bad room to require so much EQ near the crossover point that the crossover frequency needs to be moved. If this is the case you should repeat the loudspeaker correction and generate a new filter set.