B&W P4

 Floor-standing loudspeaker system

The P4 is the smallest speaker in the P Series, in order to achieve sufficient bass extension the design engineers at B&W came up with a unique solution.

The key difference, which is not visible from the outside, is the internal cabinet construction. A folded tapered duct has been used, which is selectively damped to give bass reinforcement similar to a reflex enclosure, without the danger of pipe resonances that would otherwise arise in the tall narrow enclosure. 

 Technical highlights

Kevlar®: B&W developed and patented the method of using Kevlar® for loudspeaker cones to reduce unwanted standing waves. DuPont originally created Kevlar® for use in bulletproof vests. 

 "The P4 is a two unit loudspeaker using a Kevlar coned bass/midrange driver crossing over at around 3,5 kHz to a new variant of B&W's long established light metal dome tweeter. This version, no wider than a matchbox, clearly demonstrates the size reduction that is possible through the incorporation of Neodymium in the magnet material without sacrificing the high flux density around the voice-coil which is required to maintain sensitivity and a fast response to transient sounds. In this application the only advantage of the reduced diameter is to enable closer proximity to the main unit, which can be an aid to cohesive integration. To this end the new unit is fitted with a bevelled escutcheon recessed into the front panel.

The 168mm outside diameter bass/midrange unit is of familiar B&W construction on a very open die-cast alloy chassis. This provides a very rigid mounting for the large ceramic magnet assembly, together with a firm seating in the recess provided in the baffle. The woven Kevlar cone is 120mm in diameter and is quite mildly tapered; it is fitted with a 30mm diameter voice-coil of 3.8 ohms DC resistance, centred in the magnet gap with the usual concentric bellows. The outer suspension is a convex rubber moulding providing a reasonably long throw and a sample unit showed a free-air resonance at 40Hz. ...

 The crossover filter components are fixed to a printed circuit board behind the input terminal panel which is recessed into the lower rear wall of the cabinet. Outwardly this displays four large gold-plated terminals with 4mm centres, each accessing one half of the filter for bi-wiring or bi-amplification; these are normally paralleled with the links provided. The bass/midrange section consists of only a single iron-dust cored inductor of I .75mFl; the treble section is a capacitor/inductor 'T' with a 1.5 ohms resistor to equalise the sensitivities of the two units."

Gramophone

Specifications

Systems:  2-way, 4 th order tapered-line

Drive Units: 

High Frequency :  1 x 25 mm metal dome

Bass/Midrange Frequency :  1 x 165 mm woven kevlar cone

Freqqueny Response:  50 Hz - 20 kHz ±2 dB on reference axis

Frequency Range (-6 dB Frequencies):  37 Hz - 22 kHz

Dispersion (20 Hz - 10 kHz):

Horizontal :  ±2 dB over 60° arc

Vertical :  ±2 dB 10° arc

Sensitivity:  88 dB spl (2,83 V at 1m)

Crossover Frequency:  3,5 kHz

Nominal Impedance:  8 Ω  (minimum 3,7 Ω)

Power Handling:  30 W - 100 W into 8 Ω

Dimensions (H x W x D):  810 x 200 x 256 mm

Weight:  13,5 kg net

Finish:  Black Ash, Rosenut, Cherrywood

Grille:  Black Cloth