Why not? If you measure directly with a soundcard, the power is so small it cannot damage any tweeter. If you do the measurement throughh an amp, you will need to make sure the power rating is not exceede. However, if you do teh measurement via a 100 ohm resistor (I believe it's the recommended value, the tweeter receives less than 1% of the power delivered by the amp. You may burn the resistor, but never the tweeter.