Hi, I recently bought an SVS subwoofer SB12-Plus a few months ago. I have tried many set up and configuration and I am still not convince that the subwoofer is sending out any sound. I have a pair of B&W tower speakers which I believe is doing all the work. What do I need to do to proof or verify the working condition of the subwoofer?

touch the driver when playing the test tones...if its moving...its on ;)

Set your AVR main speakers to small, check your LFE trim, check your SUB trim.

If you are playing the right movie or music there should be no doubt that the sub is playing. Is the subwoofer enabled on your receiver? Have you calibrated the subwoofer?

You can carefully disconnect the speaker wire to your speakers and play
a scene that should have sub. You should get bass from the sub.

Generally if your fronts are set to large, on many AVR's and pre/pro's you won't get any sub action on two channel sources and only the true LFE channel on 5.1 source.

Thank you for all the good advices. What about how you can tell if it is really working on all the sub level frequency? Will it be possible that a subwoofer circuit is broken partly when only certain frequency is working?

Here is what I have configured, I used an SPL meter to measure by playing AVIA test tone, and one of the menu allow me to send three base sound, middle, low and very low. I found that I have to change to crossover frequency to below 40 hz in order to have any response on low from all channel. If the crossover frequency is set too high, then I am missing the low range. I suspected my subwoofer is not working even though I can feel it vibrate (just a bit) not much. The subwoofer supposed to be able to send frequency above 40 hz unless I am wrong. What do you think?