Examples of Measured Distortion
All the flaws of voltage drive summarized are quantifiable and of patently detrimental level. Many of these effects also manifest themselves as clearly observable harmonic or modulation distortion mainly as a consequence of the corrupted voltage/current conversion occurring in the driver.
Though the results speak for themselves, it should be minded that measurable nonlinear distortions are only part of the whole picture of ill effects pertaining to voltage drive. There are also various feedback mechanisms that are more related to the temporal accuracy and comparable e.g. to cabinet edge diffractions whose harmfulness is widely recognized but which do not necessarily produce extraneous frequencies in the amplitude spectrum.
The acoustic measurements have been made using a dynamic cardioid microphone (Sennheiser e815 S) at 20 cm distance from the diaphragm and with appropriate frequency compensation. This kind of close-distance distortion measurements should never be made with a budget electret microphone (such as Dayton EMM-6 or Behringer ECM8000) that has a distortion-introducing FET stage in the capsule. With such mics, the real differences cannot be found out. Unfortunately, microphone manufacturers do not specify distortions for their products. To test a microphone's suitability, one can vary the measurement distance with the full modulation test signal. If the distortion decreases with increasing distance, the mic is useless for the purpose.
Example of contact resistance distortion