Bozak Audio Lab CS410 Moorish Concert Grand Speakers

Vintage Bozak CS410 Moorish, Concert Grand Speakers - Pair

 Signed by Bozak.

Specs:

• 12"Low Frequency - Variable Density, Multi-Fiber
• 6" Mid Frequency - Metal Alloy  Curvilinear
• 2" High  Frequency - Metal Alloy with .75" Dome

• 16 Hz to 20kHz

• 8 Ohms Nominal, 5 Ohms Minimum

• 94dB @ 2.83VAC (1 Watt), 1 kHz, 1 M

• Minimum 50 Watts
• Maximum 500 Watts

• 400 Hz and 2500 Hz

• 36.75" W x 18.25" D x 50.25" H

• 300 lbs (136.46 KG)

Description (from Stereophile.com)
stereophile. com /historical /1005bozak/ index .html 

The heart of every Bozak speaker is the 5¼" midrange driver, whose magnet structure is the same size and diameter as that of the 12" woofer. Bozak stated that, "based on the laws of physics, [this unit] is so sized that the diameter of the speaker cone does not exceed the wavelengths of the sounds they are designed to reproduce." The cone itself is made of uniform-density aluminum coated with a thin film of latex rubber on each surface. The aluminum is perforated to help bond the rubber coatings and damp the cone. Legend has it that Rudy Bozak worked on the voicing of this drive-unit to minimize the annoyance of LP tracing distortions.
The tweeter is a standard, dual-cone design. The inner aluminum diaphragm handles frequencies above 10kHz, the outer diaphragm the frequencies below 10kHz. Both are coated with rubber and damped with an abutment of foam rubber. Early Concert Grands had a multitweeter array in the shape of an Altec sectional horn; later designs had a line array.
There are a couple of different driver configurations for the Concert Grand. One pair I own places the midrange drivers almost 20" apart on the horizontal plane. I experimented with physically covering one of these to reduce combing artifacts—this made a big improvement in the imaging and increased the seamlessness of the integration with the woofers.
The CG's large (52" H by 36" W by 19" D), massive, particleboard enclosure is designed to be as close to an infinite baffle (a large wall) as possible. In fact, Bozak sold many Concert Grands in kit form where the buyer supplied the enclosure—a wall of the house. (Imagine the wife catching you drilling 14 good-size holes in the living-room wall.) From the mid-'60s through the early '70s, CGs were available in three distinctive cabinet styles—Classic, Contemporary, and Moorish—and were built to a standard of fine furniture at the Bozak factory in Darien, Connecticut. The old-world craftsmanship is a far cry from the robotic look of more modern designs.
The CG's front face, or baffle, is 1.5" thick. The drive-units are mounted to the inside of the baffle with standard wood screws and hooked up with ordinary stranded copper wire. The midrange units are isolated from the woofers and tweeters in a semispherical inner enclosure of plastic, to reduce interference from the backwave. To access the drive-units, you remove the rear of the cabinet by unscrewing 40 large wood screws—no easy task. The enclosures have minimal cross bracing, which gives the cabinets some life when you rap your knuckles on the top and sides—it's as if they're living, breathing things.

Setup
If you live in a walkup apartment, forget about the Concert Grands. If you have a small room, forget about them. If you have neighbors, forget about the CGs. These imposing speakers dominate a room, and should be placed far apart—they need room to breathe. Their bass response is amazing enough that you can also forget about placing them in a room adjacent to a room anyone else is going to use.
It's funny, but the CG looks so "old world" that it's hard to imagine it producing a "modern" sound. Now for the surprise—it's friendly to single-ended-triode (SET) tube amplifiers. I get rock-concert levels with 845s (300Bs for chamber music or jazz), and have found the CGs wonderfully match with 18W, 6BQ5 SET amps to produce a clean, articulate sound. I've had excellent results from a number of such amps, including the EICO HF-81, Stromberg Carlson ASR 433, and Heathkit AA-151. Each served up tight bass and airy highs with three-dimensional images and springwater-like clarity. You'll get more punch as you move up the power curve to 845 and EL34 SET amps, but not better sound.