The most crucial aspect is avoidance of any drive unit output overlap/crossover in the aurally sensitive 2-3 kHz range; this is the Achilles heel of the majority of the majority of historic and current loudspeaker designs. Adhering to these criteria results in preservation of the attack component of a musical note and the harmonic and temporal coherence associated with listening live.  The Etude 5 (left) and the Etude High Sensitivity Bipole (EHSB) (right) embody these principles. 

The Etude loudspeakers are designed around the latest generation of wide-band drive units known as balanced mode radiators (BMR). There are numerous published descriptions of how these operate; though in essence they act as a conventional pistonic drive unit at low frequencies and then change to radial bending wave drive units at higher frequencies. The transition from pistonic to bending wave, and the number of bending modes (nodes), are carefully engineered parameters. The balanced mode aspect greatly increases the frequency range of BMR drive units to the extent that one appropriately loaded 120 mm diameter (6.5 inch chassis) BMR drive unit can deliver useful output down to 20 Hz (depending on room dimensions and positioning) all the way to slightly beyond 20 kHz. No other wide-band drive unit can achieve this range in such an even-handed manner. The loudspeaker latterly described is the Curvi-BMR (see Curvi website).

The first Etude loudspeaker was the Etude 1, this was developed in 2010 in collaboration with Christien Ellis of CE Electroacoustics and uses two 85 mm BMR drive units in a 10 litre sealed enclosure. The prototype was reviewed by Paul Messenger in Hi Fi Critic (2010, 4(4), pp. 30-31) where he found that “…the Etude 1’s freedom from crossover effects really pays dividends, delivering an almost electrostatic-like coherence through the midband”. (see legacy material on the Etude 1) 

In parallel with the Etude 1 development, further experiments were conducted with the objective of extending the frequency range beyond 20 kHz, increasing bass output / extension and maximum output level. The second Curvi prototype cabinet was used as a test bed and was fitted with two 85 mm BMR drive units; one firing forward, the other firing upward. These units were loaded by the 2.4 m transmission line and directly driven, though the upper unit was later fitted with a shunt capacitor to limit high frequency output. The bass was augmented using two Jordan JX92S mounted on the rear of the cabinet such that the line was driven about 1/3 along its length. The bass units contribute to output below 100 Hz. The high frequency extension was bolstered above 5 kHz by a ring radiator tweeter. This “Etude X” prototype sounded effortlessly powerful, very smooth and coherent. At low frequencies, the two Jordan bass units were well damped and did not modulate the motion of the two BMR units. Simulations confirmed the latter effect and validated the line sharing – “common time base” concept. The only problem with the prototype was high frequency output from the upper BMR unit blurring of stereo images, this was cured using the shunt capacitor.

These observations led to the design of the Etude 5 prototype back in 2012-13. There have been several key iterations of the design including changing the positions of the bass units and tweeter, rigid circumferential mounting of the BMR array and trial and implementation of high quality passive components in the filters.

The most recent design is the Etude High Sensitivity Bipole (EHSB), developed in collaboration with Danny Baty of Super Natural Audio.  I have been working with Danny, the designer and manufacturer of a 2.3 W single ended triode amplifier, amongst other superb valve audio electronics, for some years now.  He needed a loudspeaker sensitive enough to use with his amplifier.  The EHSB is the result – for the first time, horn-like sensitivity (slightly more than 100 dB/W total output) is combined with the speed and coherence of BMR drive units and truly extended bass (to below 25 Hz), thanks to inverse tapered transmission line loading.