Current drive of speakers and
2. Measurement of distortion of speaker current
3. Measurement of speaker distortion with voltage and current drive
4. Measurement of tweeters
3. Measurement of speaker distortion under voltage and current drive
After we have seen that there is much higher distortion of speaker current with voltage drive, compared to distortion of the driving voltage, it is logical to measure with microphone at acoustical side of the speaker, to confirm or disprove an assumption that linear current drive should result in decreased speaker distortion. The amplifier was prepared that is easy to be switched between voltage and current mode.
Distortion test was performed at speaker terminals voltage 1 - 2Vrms. The voltage was checked before every measurement
First, harmonic distortion of the amplifier used was tested, in a current mode, voltage mode, at all frequencies and always with 2Vrms at speaker terminals. THD of the amplifier was between 0.001% and 0.006%, depending on driving mode and frequency. Harmonic components had fast decay and all of them were far below speaker distortion.
The measurement was performed with ECM8000 microphone placed in 9cm distance from the woofer membrane. All measurements were repeated to check their credibility. Measurements in higher distance were also done to exclude influence of microphone distortion.
continue - measurement of tweeters
Pavel Macura, 01/2015, 12/2018