Bookshelf Speakers — Acora Acoustics SRB

The SRB is the granite stand-mount in the SR Series of Acora Acoustics, a company based on Milner Avenue in Scarborough, Ontario. Its designer Valerio Cora spent three months a year in Italy until the age of 18 working in the family stone and machining trade, where his father taught him how to judge and select stone. In 2023 Cora also acquired Audio Research Corporation. The SRB sells for USD 18,750 per pair, and a cheaper quartz twin called QRB shares its layout.

Key specs that matter

The SRB works as a ported two-way design, pairing a 1 inch beryllium dome tweeter and a sandwich paper cone for bass and midrange, which Acora lists at 5.5 inches. Frequency range runs from 43 Hz to 35 kHz, efficiency is 86.5 dB at 1 W and 1 m, and impedance is 8 ohm. The enclosure is 23 cm across, 33 cm high and 28 cm front to back. Each speaker weighs 26.3 kg without a stand, with small differences depending on the stone, and the terminals are Cardas binding posts with rhodium plating over pure copper.

Engineering and use context

Panels are 2 cm slabs of high-polish black granite. Cora uses only black granite across the SR Series because, as he explains, other granite colours all have lower density than black. The rigidity of the slabs lets the cabinet do without internal braces. The front baffle is sloped so that tweeter and woofer stay in phase at the listening position, and the crossover is a modified fourth-order network whose parts were chosen for signal purity and mechanical isolation. The beryllium tweeter carries no diamond coating and, like the woofer, is voiced to Acora's own brief, with no resistor placed in its path. Standard finishes are Nero Assoluto and Mystic Grey. Blue Pearl, Emerald Green Pearl, Black Galaxy and Steel Grey are special order, and Lilac Purple, Mari Blue and Sunset Fire form a limited group of rare stones sold at an upcharge.

Pairing

Acora states a power window of 10 to 150 W. The easy nominal load allows low-output valve amplifiers, while the moderate efficiency makes more headroom sensible in larger rooms. Two stand options exist - the SRS-M in steel and granite at USD 3,125 and the all-granite SRS-G at USD 6,250, the latter weighing 42.3 kg each. Placing the speakers on two BedRock subwoofers instead of stands turns the set into a three-way full-range system.

Alternatives

The Acora QRB keeps the same drivers and cabinet size but uses quartz walls and is lighter.