Most other ESLs damp this HF resonance by including a small series resistance of 1-2 ohm in the primary circuit. This is not immediately obvious, but at 24Khz, the 560pF caps and the mid panel capacitance are essentially short circuits provided the electrical path for the damping. The resonance is damped by the 150K resistor(junction 9 & 14). The sum of the winding capacitance and tweeter panel capacitance in combination with the leakage inductance(145mH) forms a 2nd order LP network just above the audio band at about 24Khz. The diaphragm resonance with Q of 2 or 3 provides equalization for the bottom octave or so. The addition of baffling around the panels and small side wings keeps the response from falling quite this quickly. Either way you look at it, the response remains flat until about 1kHz where there is a 2nd order LP network formed by the leakage inductance (46H) and the panel capacitance(400pF).īelow 300Hz, the response would still fall at 6dB/octave. Looking at it another way, the RC filter puts a 6dB/oct LP filter on the voltage reaching the bass panels.

The 6 x 180K resistors in series with the Bass Panel effectively provide current drive above about 300Hz and flatten the response of the bass panels. Ignoring diaphragm resonance, the bass panels have a natural 6dB/oct rising response. The KLH Nine had a similar loading choke.įor the brief description below to make sense, you must understand that an ESL panel that is small relative to listening distance has a response that naturally rises 6dB/octave when driven from a voltage source response is flat when driven from a current source. Without the loading choke, the impedance in the mid-bass region might have been high enough to cause problems with some tube amps of the day.

It is my understanding that most tube amplifier output stages do not like to be driven at high levels without some amount of loading…internal tube arcing can occur. The purpose of the loading choke was to reduce the magnitude of the impedance peak that occurs at the low-to-mid frequencies of all transformer driven ESLs.

The values were taken from the Baxandall description…actual production values may vary slightly. See attached ESL-57 schematic to which I have added the transformer leakage inductance and winding capacitance since they are directly involved in how the crossover works. For a complete understanding of the ESL-57 crossover as well as its acoustic design I would highly recommend reading the description by Peter Baxandall on pages 169 – 179 of “Loudspeaker and Headphone Handbook”, J.

Hifishark esl 57