There has been some discussion about our mid panel on other AC forums, and I have more details from the designer for Sonigistix, Dragslav Colich, on the panel's performance parameters.
As pointed out elsewhere, the Level 9/Sonigistix panel was in production for about 4 years and over 300,000 units were manufactured. Most went into computers, Kia automobiles, and high-end multiway speaker systems of which the VMPS RM series are the best known. The panel has a low Fs (below 200Hz), high sensitivity, high output levels, excellent power handling and durablility, and very low moving mass (less than 1g per panel).
Just how much linear travel this panel exhibits has been subject of some discussion. When I inquired about "Xmax" Level 9 gave me the figure of 3.5 mm. However, there are more considerations that linear travel in the middle of the diaphragm. As the magnetic gap increases, so does maximum linear travel, but (as in cone dynamic speakers) efficiency suffers. In addition, high excursions weaken the tension of the diaphragm and will cause it to flatten, curl and loosen up, resulting in high THD when driven hard. Plus, high excursions mean high flexure rates and fatigue of the aluminum traces which can also lead to failures.
Our panel has a rear damping sheet (none on the front, unlike the BG Neo 8 where the diaphragm is sandwiched between two damping sheets and has little to no free travel). Given the presence of the damper and the thickness of the diaphragm the peak to peak displacement for maximum SPL is about 1.3mm. Within these parameters diaphragm excursion is linear and uncompressed down to the resonant frequency. Multiplying the number of drivers in an array increases output and even gives the designer the option of lowering the crossover point.
Dragslav relates that many different arrays were built with our drivers early on with excellent results. For example, one array of 192 (!) panels allowed a dipole to generate 105dB SPL at 2m down to 80Hz, more than an octave below fundamental panel resonance.
Our measurements of the frequency response of the panel show linearity typically +/- 2.5dB, Fs of 166Hz and THD below 1% right down to cutoff, which is typical of high quality cone dynamic drivers. Since the panel is almost 3" wide we roll it off at 6dB/oct with a series lowpass filter at 6.9kHz in order to improve HF directivity.
Buzzing, loss of diaphragm tension, and thermal overload are the typical failure modes of planar LF drivers. As is clear from the above, the panel's design is a careful balance of sensitivity, maximum linear excursion, THD, LF cutoff, and distortion. Our panel has proven to be a good performer of outstanding sound quality and reliability (less than 1% total failure rate from all causes.) Currently we use 12 dB (from series first order networks) highpass filters in the 280-300Hz range, after first engineering some new WCF cone woofers better suited for use with our mid panels.
I'll be happy to relay further questions you might have to Dragoslav, who dislikes participating in on-line discussions due to their volatility and open-ended nature.
