I've looked at the links on the Sonotube page. The FAQ on equalizing with a BFD uses Acoustisot ETF. Another link allows a free trial of Spectra software. The corresponding link for Radio Shack SPL meter correction values is no longer active. Yet another link lists RS meter correction values. My question ... Are there significant differences in the software. I have been hearing about TrueRTA. How does it compare to Acoustisoft & Spectra? Can I use the RS meter with TrueRTA? How does the RS meter compare to a mic & preamp. And, one more, do the values listed for the RS meter work for the digital version also? I would certainly like to go with a RS SPL meter (vs. a separate mic & preamp), at least intially. Building an IB sub and speakers is taxing my budget enough. Thanks, Steve V.