I've done all Eric Wallin's mods to my RS meter. Basically that includes replacing all of the electronic components, and using the panasonic WM-60AY mic mounted on the end of a microphone boom (piece of rod homemade). I use this setup with the Speakerworkshop program, and I have always gotten consistant results from this combination. I think it works very well and is a great and cheap way for a DIYer to make meausrements. I think RS has stopped selling this meter though, but you could just build a little preamp such as the one Wayne posted a link to instead. If you have an RS meter, the RS meter works as the preamp and is more sensitive/higher gain when you select a lower decible band, so you won't need to build a seperate pre-amp.

Adrian