The THD measurements at distance of 315 mm and voltage levels 2.83 - 8 Volt were carried out with High Pass Filter "on" (2nd order Buttreworth type, 30 Hz cutoff, HPF2-30).
The THD measurements at distance of 315 mm and voltage level 11.2 Volt were carried out with High Pass Filter "on" (2nd order Buttreworth type, 50 Hz cutoff, HPF2-50).
ZA14W08 is a child of respected John Krutke, who made a significant contribution to the support of DIY activity. Be sure to visit his website www.zaphaudio.com, where you will find a lot of interesting projects, measurements and thoughts.
ZA14W08 is a great midwoofer with even frequency response and very low THD, which can easily concur with much more priced drivers of famous brands. When comparing it to other speakers it should be remembered that its effective membrane Sd is only 68 cm2!