Model 2b


The Pietra Model 2 series uses a nonstandard 3rd-order crossover to mitigate two problems inherent to 2-way loudspeakers: directivity mismatch caused by large ratio of woofer-to-tweeter cone radiating area, and acoustic center offset of the midwoofer. The target transfer function for the crossover was derived via numerical maximization of the width of the vertical and horizontal listening windows. Detailed cabinet diffraction and radiation analysis (pictured below) was performed with the MFS algorithm developed by Pietra [J. Audio Eng. Soc., 61 (2013) 356].



Model 2a/b radiation pattern at 2050 Hz crossover frequency


The Model 2b features a Beryllium dome tweeter. The high strength-to-weight ratio of Beryllium produces a flat sound presure up to 40kHz. This exotic tweeter is paired with a very-high-excursion midwoofer. The midwoofer uses powerful neodymium ring magnets -- which are nearly a factor of 10 stronger than ferrite magnets -- to enable the use of an underhung voice-coil. The underhung design ensures the magnetic flux seen by the voice coil is constant over the excursion range, thereby reducing nonlinear distortion. This remarkable midwoofer, however, has a very deep acoustic center which, as mentioned above, motivated the design of the nonstandard 3rd-order filter. Like all Pietra enclosures are fabricated from slabs of solid granite by a master craftsman.

Specifications

midwoofer diaphragm diameter 14cm
tweeter diaphragm diameter 2.7cm
sensitivity 86dB @ 2.83V, 1m
minimum impedance 3.4 Ohms @ 130Hz
crossover frequency 2080Hz
weight 50kg
dimensions 251cm x 33cm x 34cm

$6400 USD      Sales