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The Boulder
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3 way active monitor with coaxial midrange-tweeter.

The next active professional monitor following on from the The Rock, is the new Boulder. This shares some of the same interesting material and designs such as a Baltic Birch plywood cabinet but this time 18mm instead of 12mm as used in The Rock. A Corian front baffle is used again like The Rock and bonded to an internal wooden baffle, but the Boulder uses a huge 30mm slab of Corian instead of The Rocks 12mm and with large radius edges to reduce reflection. Like The Rock, this new model will boost true fidelity, fast, accurate detailed sound but with extended bass response, even more detailed mid range and higher SPL's for larger rooms.

Two 180mm (7'' ) woofers are used, the same woofer model as in The Rock, this will increase low frequency extension and achieve higher SPL's. Each woofer has a 0.2mm aluminium foil chemically bonded to a rigid pulp fibre cone. This reduces harmonic anomalies and permits +/- 15mm of woofer travel producing accurate low bass frequencies. The use of Aluminium bound to a pulp fibre cone insures that the woofer cone will remain symmetrical at all frequencies, producing a long life for the woofer element and full accuracy of the driver through its life. Something few other materials can claim.

Key features

  • 3-way active monitor
  • 4 x bespoke true class A/B 100 watt E.A.R. discrete amplifiers, one per driver
  • Closed cabinet design
  • 30mm Corian front baffle
  • Coaxial 5'' midrange and 50kHz folded ribbon tweeter
  • 2 x 180mm (7'') woofers
  • 368mm deep x 256 mm wide x 549mm high
  • 23kg each
  • Balanced XLR input
  • 18mm grey Baltic birch 9 ply plywood cabinet
  • Brutally honest
  • HF EQ Shelf @ 10kHz +/- 2.5dB
  • Mid Cut/Boost +/- 2.5dB
  • Frequency response 40Hz-30kHz +/- 1dB
  • Frequency response 33Hz-38kHz +/- 3dB

The Boulder Manual



Tweeter Tweeter

A new dual coaxial Midrange & Tweeter is employed, another unique feature of The Boulder. This new unit is a unique combination of a flat aluminium honeycomb midrange ring radiator and a concentrically arranged folded ribbon tweeter. This design realizes the vision of an acoustic point source! This facilitates an optimized acoustic power response and results in a homogeneous and very wide sound dispersion angle which provides for a new kind of relaxed but very precise reproduction.

Comparison between the 3D radiation patterns of a conventionally designed midrange-tweeter combination (left) and of the Boulder's coaxial midrange-tweeter system at the crossover frequency.

The ultra lightweight honeycomb diaphragm provides a reduced stray magnetic field combined with a strong neodymium drive. The system is driven by a 78mm moving coil. High efficiency is achieved using coppered aluminium flat wire, edgewise-wound, on a ventilated capton bobbin. The resulting unit will deal with frequencies from 450Hz to 50kHz.

The amplifier is a bespoke design by Tim de Paravicini whose company Esoteric Audio Research is regarded as one of the worlds best amplifier designers. Due to the modular design of The Rock amplifier, The Boulder uses the same amplifier modules from the Rock but it employs a total of four amplifier cards per cabinet, one for each woofer, one for the mid and one for the tweeter. A design is a true discrete bi-polar low feedback amplifier with custom wound transformers and dedicated LF, Mid, HF sections with overload/clip protection, will results in very fast and clean, and astoundingly accurate reproduction.


The Boulder Frequency Response
Boulder Full Range Boulder Low End
Boulder HF & MID Switches
These two graphs show the performance of the HF 10kHz EQ Shelf switch, Flat and cut and boost of 2.5dB. The other shows the performance of the MID cut/boost switch.
Frequency Response and HF Boost & Cut Response Frequency Response and MF Boost & Cut Response
Download the Boulder manual  
· Unity Audio Ltd, Unit 3, Hall Farm, Little Walden, Essex, CB10 1XA · +44 (0)1799 520786