I used a Radio Shack spl meter with the downloaded test tones and was able to get some sound(very little)at a true 20 Hz. However, a friend of mine who was assisting me is a retired Physics professor seriously doubts the accuracy of the high dollar Radio Shack meter especially with sounds that low. I used the YPAO feature on my Yamaha receiver to calibrate each sub independently. I found that it did a good job of integrating the sub with the rest of my Paradigm monitors. Although I thought I was doing pretty good by ear alone. I still like the remote bass control built into the reciever that I am constantly tweeking depending on what source or recording I am listening to. It's amazing the variances in recording quality between cds specifically the amount of bass a track may or may not contain. Other than the test tones and some recordings of some pipe organs(which the quality is terrible) I was hard pressed to find any material with anything that low. I would like to do more listening especially with the VTF-3 in max extension mode. Lord of the Rings has some good stuff and so does Pearl Harbor but I don't think any of it goes that low. I am not an expert by any stretch and I leave all professional reviews up to those who are. Being more of an amateur enthusist I have learned alot. No matter how technical or objective a listener tries to be it really comes down to a subjective matter-what sounds good to the individual. I know both of these subs sound great to me.