Eric Wallin's Radio Shack SPL meter modifications:

I'm reasonably confident that Eric has done the mods. But to be honest, I never liked the performance of the little RS SPL meters. I see them as a way to get ballpark figures, but nothing more.

As for electro-mechanical specs, they're not quite as hard to get as response measurements because they don't include the acoustic domain. If you have a good signal generator and a scope or meter, you can obtain reasonably good T/S specs. I don't expect home measurements to be as reliable as those obtained at large shops with better systems. But still, you're really just measuring electrical values, and the mechanical transformation is reflected in them, showing electro-mechanical specs. There isn't as much outside influence as there is when making acoustic measurements, so you can usually expect decent results.

I think the best thing you can do to reduce ambiguity is to verify with more than one measuring instrument, and to ensure you can reliably repeat your measurement values.

Wayne

Distance to boundaries depends on the frequency range of interest. For example, if you're concerned with the interaction between components at a crosover above 300Hz, then a few feet distance from boundaries is plenty. You can gate the microphone input so that reflections are ignored.

About the subwoofer, I assume you're talking about the flux-stabilized B12. Eminence has already built a first prototype and found that the shorting ring reduced 2nd harmonics by more than 10dB, so that part was a success. But to get the reduction of harmonics down to the lowest frequencies requires a larger flux stabilization ring, so they are working on another type of magnetic structure. They'll build a second prototype using a structure that allows a larger ring, and they've told me that we're looking at around the end of the summer for a timeframe on that.

Thanks for your help.