Had a thought. It is a bit of a pain, and some times risky even when you think you have limited the sweep bandwidth, to test a tweeter directly on an amp to get the response and phase for crossover design, SOP is to add a blocking cap, but now you have a 90 degree phase shift in the phase measurement
Could one just plop the data into Excel and add 90 degrees to make a valid acoustical phase component?
Could one just plop the data into Excel and add 90 degrees to make a valid acoustical phase component?
You only get a 90 degree shift in the stopband of the filter that you make by adding the capacitor. If you could measure the magnitude and phase of the voltage across the tweeter and the sound pressure, then you can calculate the transfer from voltage to sound pressure by dividing them (complex division, equivalent to dividing the magnitude of the sound pressure by the magnitude of the voltage and subtracting the phases).
As MarcelvdG says: only at infinitely low frequency. (In practice you don't get there.) It is 45 deg at the -3dB point. And you will want to set the -3dB point VERY far below the frequency range of interest so it does not mess-up your measurements.
And when you do, it doesn't protect the tweeter very well (although it can still save the tweeter if there is a large DC voltage at the amplifier output for whatever reason). I think two measurements and a complex division is the only way to protect the tweeter and measure accurately.