Recent Design Improvements for the Focal Transmission Line Speakers and the Fostex ML TQWT Speakers For the ML TQWT the cabinet I built, there is definitely a baffle step around 300 Hz that has resulted in a somewhat weak bass response. I measured the as-built units using LAUD and verified the measured results using Paul V's software. Two options were available, a correcting circuit or a set of "wings" for the baffle. I decided to use a corrective circuit. So after reading the LAUD measured impedance and SPL (at 1 m and 1 watt) into MathCad, I designed a Zobel for across the driver terminals and an inductor and resistor (in parallel) and placed them in series with the driver. I have improved the bass performance significantly at the expense of SPL efficiency (93.5 dB droped as low as 87.5 dB). I have plenty of power so this is not a real problem. One other interesting side effect is the 12 to 16 ohm (depending on the R inserted) constant impedance above about 100 Hz. Based on these results I also added BS correction for my Focal-TLs. Download the Acrobat pdf "Recent Design Improvements for the Focal Transmission Line Speakers and the Fostex ML TQWT Speakers" with the entire story at www.quarter-wave.com <frequency response graphs here>

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Martin J. King is a lead engineer at Intermagnetics General Corporation a manufacturer of the superconducting magnets used in Magnetic Resonance Imaging machines. His primary job responsibilities involve performing computer analyses and simulations (closed form solutions, numerical solutions, and finite element analyses) aimed at solving product design and manufacturing problems.