OK. Here we go.
As said above, I couldn't help making adjustments to the sub to try and get the best (in my opinion) out of each recording. But there lies madness. My view now is, get it all set up for as flat a response as you can, then at least it's as the sound engineer wanted. Leave it alone after that.
So, this is how I set up my sub-woofer. Might not be the best way – but it worked for me– YMMV – etc etc.
Step 1. Obvious really. Make sure your main 2 speakers are in phase. Of course they are. But it won't do any harm just to check. Out of phase and the bass will be all to cock before you start. There's loads of test tones on the internet, but I used these here:
Click on the Loudspeakers Polarity Audio Test link. I found the more useful tests to be the 75 Hz tone and the guitar. I downloaded them (right click /save link as), then squirted them through my Squeezebox. You can put them on cd if you want.
Step 2. See what the manufacturer says about the bass roll off on your mains. This is a frequency response graph for the the ESL57.
Looks easy peasy, doesn't it? Let the sub take over below 50 Hz – job done. Well no. I thought it best to check what my 40 year olds actually did. So, look on the above test tones web site for “Low Frequency Response and Subwoofer Audio test (10-200 Hz)”. Play this through your speakers with your sub turned off. It is a sweep from 10 to 200 Hz with a voice announcement every 10 Hz. When I listened to it, I realised they had forgotten to put the tone on as there was nothing. Well, nothing till 60 Hz, and then only quiet. Started properly about 70 Hz which makes me think as well as the treble panels I replaced last year, maybe the bass panels need looking at.
Step 3. It's then a case of turning on your sub and setting the crossover frequency at this point , 70 Hz in my case. Then play the sweep again. You're looking for a constant sound level from 20 Hz to well in to where your mains are doing all the work. It takes a few goes and you need to concentrate. Adjust the sub's volume control until you're happy it's as flat as you can get it. I was quite surprised at how loud I had to have the sub to get a flat line. I had previously had the crossover up at 100 Hz (so I could REALLY hear it, like you do), but turned down in volume otherwise it was overpowering. But now it was below what my mains were producing, it needed some power.
Step 4. Adjustment of phase. My sub is a BK XLS200 and has phase infinitely adjustable from 0 to 180 degrees. Others have just 2 settings, 0 and 180. The important point is to make the adjustment so that when you're playing a tone at the CROSSOVER frequency, it sounds loudest. So in my case, I downloaded a 70 Hz tone and got someone to twiddle the phase knob until it was loudest. You need someone to do the twiddling as you are sitting in position 'A' listening. Again, a bit of concentration is needed. To help me, I downloaded an app called Sound Meter. It's very sensitive. Don't know whether it really helped but it's great fun seeing how loud farts can be or how quiet (or not) the house is. Make sure your phone, and you, stays still during the test.
Step 5. Now that you've altered the loudness of your sub with the phase change, you need to revisit step 3 to ensure the sweep is still smooth. If you have introduced a peak try reducing the crossover frequency a little.
Step 6. Play your favourite track. As I have said, I knew I had it right as soon as I did this. As every one says, you shouldn't notice the sub. But you sure as hell know when it's not there.