I notice that Morgan Jones, in his article on the Arpeggio full-range single driver speaker, uses a Zobel network to flatten the impedance curve at high freqs, particularly for use with SET amps. He also adds bass shelf correction. However, other full- range designs omit these., including , apparently, your Pipette and the big Voxatives. What’s your take on impedance correction for SET amps?
My take is that it depends on the speaker and the amplifier.
Most amps use feedback to increase the damping factor, and most speakers are designed to work with high-damping amps. Our speakers are designed to work with zero-feedback low-damping amps.
PB described the effect of voice-coil inductance at high frequencies. An RC Zobel will also make the high treble independent of damping factor. Many drivers, including the one used in the Pipette, have a conductive flux ring to reduce the inductance, making the difference small.
Low-frequency Zobels to do the same are theoretically possible but impractical - the necessary inductors and capacitors are huge and costly.
Baffle step correctors (shelving filters) are commonly used at speaker level when the cabinet is narrow and/or when the single driver has a rising mid-frequency rise. They work by attenuating the response above the upper bass/lower midrange - reducing the efficiency at those frequencies. A better option when using low-power amps is to do the attenuating at line level, before the power amp input. Efficiency is not reduced. We used to offer an adjustable passive filter called the "Fix" to do this, but sales were very few and it was discontinued more than a decade ago. It would be interesting to try it with the Pipette ...
