In the following, we show that not all methods of equalization are created equal. In particular, using a series notch reduces distortion, which does not happen with alternative methods. The proposed circuit results in an extremely clean low-pass response combined with low distortion

Set of drawings for the SPK5 construction and Port Flange .stl file.

The SPK5 Crossover kit is designed to provide a 2nd order acoustic low pass function for the woofer and 2nd order acoustic high pass function for the tweeter to provide well behaved transition from one driver to the other in the crossover region, both on- and off-axis.
Target alignment for the total acoustic response is a flat output from the box tuning frequency throughout the audio band.
The electrical response of the filter when loaded with the drivers (drivers’ terminal voltage) is shown in Figure 2 to be ~9dB/octave.

SPK5 is intended as demonstration platform for the PTT6.5W04 transducer.
The design is deliberately kept very simple: a small ported wooden box, traditionally shaped with a simple 12.5mm chamfer for management of edge diffraction, and a passive cross over at ~3.2kHz. Although extremely simple, with numerous possibilities for enhancement by the skilled speaker designer, the SPK5 design very successfully demonstrates the tremendous improvements in sound quality which is possible to achieve when using the long-stroke ultra-low-distortion PTT6.5W04 woofer from PURIFI Transducer Technology.

SPK4 is intended as demonstration platform for the PTT6.5W04-01A transducer.
The design is deliberately kept very simple: a small ported wooden box, traditionally shaped with no particular management of edge diffraction, and a passive cross over at ~2.5kHz. Although extremely simple, with numerous possibilities for enhancement by the skilled speaker designer, the SPK4 design very successfully demonstrates the tremendous improvements in sound quality which is possible to achieve when using the long-stroke ultra-low-distortion PTT6.5W04 woofer from PURIFI Transducer Technology.

The relationship between the non-linear phenomenon of ’reluctance force’ and the position dependency of the
voice coil inductance was established in 1949 by Cunningham, who called it ’magnetic attraction force’. This paper
revisits Cunningham’s analysis and expands it into a generalised form that includes the frequency dependency and
applies to coils with non-inductive (lossy) blocked impedance. The paper also demonstrates that Cunningham’s
force can be explained physically as a modulation of the force factor which again is directly linked to modulation
of the flux of the coil. A verification based on both experiments and simulations is presented along discussions of
the impact of force factor modulation for various motor topologies. Finally, it is shown that the popular L2R2 coil
impedance model does not correctly predict the force unless the new analysis is applied.