Note: I know many think tap tuning is a bunch of hooey. I don't know enough to cast a vote. However, I'm posting this for those that might be interested.
I tried Siminoff's tap tuning method on the top when I was doing my build. Had some good preliminary results when shaping the tone bars. Then things became inconsistent and I stopped.
Decided today to measure the frequencies of the top and back since it's now assembled in-the-white (but no strings). I held it by the neck and tapped, roughly in the center, 3 times with Siminoff's recommended felt covered wooden mallet.
Attachments are an MP3 sound file and two PDFs with the frequency spectrum of the loudest tap. I used the PC program Sound Forge 9 to do the analysis. At the bottom of the page you see that the peak frequency of all three taps was the same.
Front: 308 Hz
Back: 306 Hz
Siminoff's book says the goal is a D#4 (311.13), so I'm pretty close. FYI, I don't intend to try any tweaking.