B&W 808

Commentary

A professional studio monitor speaker jointly developed by Nakamichi and B & W.

The development of the 808 began in October 1981 when President Nimro Nakamichi asked B & W President John Bowe's to co-develop it. After that, based on the specifications presented by Nakamichi, two engineers conducted repeated technical negotiations and Mr. Bowers conducted hearing coordination in the trial listening room. The development took three years.

In the specifications presented by Nakamichi, there were 3 specific things written.
First, the flat frequency characteristics should be used to eliminate the colorization in the same way as in 801F to achieve an ultra-low distortion rate. Second, the efficiency should be twice that of 801F to obtain 91 db at 1W input power. Finally, the maximum sound pressure obtained in the listening room should be on the order of 120 db (125 db at peak).
The background to these requirements was the judgment that the monitoring capability of digital recording would become an essential requirement for pro-monitor speakers in the future, and that it would be necessary to support not only classical music but also all music sources.
To achieve these specifications, the B & W project team began with the design and manufacture of driver units with low distortion even at high sound pressure levels. The Nakamichi advice on total integration. The results are reflected in the Quarter-wave Transmission Line system for medium-to-high-range enclosures, the shape of the enclosure, and sound creation. In addition, B & W's expertise is fully utilized, including vibration analysis using a laser interferometer and the adoption of a computer-based crossover network using numerical optimization technology information.

The low range is equipped with BT 300 which is a 30 cm cone type woofer.
This unit has a parallel drive of 300 mm diameter developed based on the 801F unit.
The voice coil uses Kapton bobbin with excellent heat resistance, Bextrene (ベクストレン) for corn, and PVA (polyvinyl alcohol) coating for damping material.
The magnet reaches 9 kg in total for 2 woofers.

Two 10 cm cone mid-range MT-100 are installed in the mid-range.
The cone is made of Kevlar, an aromatic polyamide fiber with excellent transient characteristics and linearity. The same polyamide fiberglass used for thermal insulation of spacecraft is impregnated with PVA by a special processing method patented by B & W to improve airtightness.
Like the woofer unit, the voice coil uses Kapton as a base to improve heat resistance.
The 808 achieves ideal results for sound localization and sound field reproduction by placing two mid-range tracks in-line and placing a tweeter between them at an appropriate distance.

A 3.2 cm domed tweeter (TX-32) is mounted in the high range.
The diaphragm uses the same polyester single fiber woven diaphragm as 801F, and in 808, heat-resistant processing around voice coil and new approach to magnetic circuit are carried out.
In the tweeter, thin wire is used for the voice coil to enable ultra-high-frequency reproduction. However, this may cause disconnection due to temperature rise at the time of large input. Therefore, in the 808, magnetic fluid is sealed in the gap between the magnet and the voice coil to keep the temperature rise of the voice coil within a safe range of 100 ℃. In addition, in order to obtain high efficiency, the Reverse Magnet System is adopted so that all the magnetic flux of the external magnet converges in the gap. A ring magnet that repels leakage flux is added so that the magnetic force of the newly developed ceramic magnet is concentrated in the gap as much as possible.

The network section employs a numerical optimization design technique using B & W's unique computer.
The crossover points are 400 Hz and 3 kHz, and the slope is equipped with a fourth order Butterworth filter to obtain a steep attenuation characteristic of 24dB/oct. and to cut unnecessary bands. At the same time, symmetrical on-axis characteristics are achieved.
High-quality parts are used for the network assuming large input power, and all capacitors are polyester type to realize low distortion and good frequency characteristics.
The network section is mounted on separate boards for low-band, mid-band, and high-band. The three boards are installed separately to eliminate mutual interference. In addition, all connections are directly connected to the cable without using any plugs or connectors to further reduce sound quality. We also select and use the largest diameter internal wiring material.
Phase correction between units is done by electronic circuits in the crossover network, and an all-pass network is combined with the high-pass filter circuits of tweeters and mid-range units to provide appropriate phase conversion at the crossover point.

A level control is provided for the middle and high frequencies, each of which can be controlled by ± 1.5 db.

The enclosure is made of high-density particle board for greater rigidity and is integrated externally but completely separated into two internal enclosures : a woofer enclosure and a mid-range / tweeter enclosure.
The mid-range / tweeter enclosure uses an acoustic load system called the Quarter-wave Transmission Line System. In this system, an inclined reinforcing plate is installed inside the enclosure to form a tapered space at the rear of the unit. The reinforcing plate prevents the occurrence of standing waves and effectively attenuates rear waves, contributing to the improvement of transparency of middle and high sound. The name of the system is derived from the fact that the length of the tapered space is equal to 1/4 of the wavelength of the lowest sound (80 Hz at 808) at which this effect occurs.
The woofer enclosure is designed as a 220 liter bass reflex, and the tuning frequency of the duct is 22 Hz. Internal reinforcement based on computer analysis reduces the surface vibration (squeal) of the enclosure by more than 60 dB below the level of the direct signal.

It is equipped with B & W's original electronic circuit configuration protection circuit APOC (Audio Powered Overload Circuit).
The Woofer unit does not use this APOC because of its huge power handling, but the Tweeter and Mid-Range units each use their own APOC, which works independently.

Equipped with input terminal for multi-amplifier, 2-way and 3-way multi-amplifier drive is possible.
There are 2 variations of exterior finish, black and walnut.

Model Rating

Method	3-way, 5-speaker, Quater-wave Transmission Line Method / Bass-ref Method, Floor Type
Unit	For low band : 30 cm cone type (BT-300) x2 For Medium Range : 10 cm Cone Type (MT-100) x2 For High Range : 3.2 cm Dome Type (TX-32)
Frequency characteristic	30 Hz ~ 20 kH z ± 2 dB (2m front, free field)
Impedance	8 Ω
Output sound pressure level	91dB/W/m(1kHz)
Maximum input level	Mid-range : No upper limit due to built-in APOC system. Low frequency : 200W with continuous sine wave input of 400 Hz or less
Crossover frequency	400 Hz, 3 kHz
External dimensions	Width 653x Height 1,050x Depth 510 mm With Grill : Depth 542 mm With Caster Pedestal : Height 1,122 mm
Weight	78kg