PRODUCTS

The production of bass ? good bass that is ? involves a driver being able to move relatively large volumes of air with accuracy and precision. This process involves high forces, not only the voice coil pushing the diaphragm back and forth, but also pressure changes inside the cabinet acting on the whole diaphragm surface. In order to withstand these forces without deformation, a stiff, strong cone is required and our paper/Kevlar? cone is one way we realise this.

The advantages and disadvantages of stiff diaphragms are discussed in the article on aluminium diaphragms. Although not a suitable material for tweeter diaphragms, paper/Kevlar? is equally suitable for bass drivers and there are instances where aluminium is difficult to implement.

Paper pulp has been used as a cone material from the early days of moving coil drivers. Because of that, it is often thought of as old technology and not very exciting. But the laws of physics do not change and paper continues to have very desirable properties. It can be made to be extremely stiff by the application of resins and the fact that it is a bulky material helps in this respect too. One of the difficulties with aluminium is in making a large diameter cone that is not too heavy to maintain a reasonable sensitivity. Make the metal thin enough and it will tend to split when formed. Paper then comes into its own.

If paper pulp has a deficiency in bass drivers, it is that a cone can buckle close to the neck if subjected to a powerful impulsive signal ? a kick drum and bass for example. This is especially a problem with high power applications such as studio monitor and musical instrument speakers and it was in those applications that Kevlar? fibres were first added to the paper mix. They add tensile strength as opposed to stiffness. That means the fibres are extremely difficult to break in tension. It is this property that makes Kevlar? an excellent material for bulletproof vests ? it can dissipate impulsive energy. Likewise, in a cone, the fibres help dissipate the impulsive forces throughout the cone, away from the most vulnerable part, the neck.

One might reasonably ask why Kevlar? does not form 100% of the mix. The reason is the structure of the fibre. It is a monofilament and therefore smooth. The more 'hairy' nature of paper fibres is far better at binding the cone together. Typically, Kevlar? fibres form between ten and twenty percent of the total.

Some of our powered subwoofers use a cone that has a paper/ Kevlar? base, on top of which is bonded an aluminium layer. Here, the aluminium is applied only from the outer edge of the cone to just under the dust cap. There is no danger of the neck splitting during forming and the cone visually matches the bass drivers used in the associated main speaker series.

echnical Specifications : ASW750

Description Active closed-box subwoofer system
Dimensions Height: 437mm (17.2 in) not including feet
Width: 396mm (15.6 in)
Depth: 479mm (18.9 in) including grille and controls
Net Weight 32kg (70 lb)
Freq. Response ?3dB 20Hz ? 31/110Hz adjustable (EQ at A)
Freq. Range -6dB at 15Hz and 40/140Hz adjustable (EQ at A)
Drive Units Unit 1: f300mm (12 in) paper/Kevlar? cone long-throw
Unit 2:
Unit 3:
Finish Cabinet: Real wood veneers of Maple, Cherrywood, Rosenut, Walnut or Black Ash
Sub Woofer Amplifier Description: Class D
Power Output: 1000W
Input Impedance: 33k ohms
Signal Noise: >90dB
Functions: Volume level
Low-pass filter frequency
Low-pass filter bypass
Bass roll-off alignment
Auto sense on/standby
Phase switch
Inputs: Line In (RCA Phono)
Outputs: Line Out (RCA Phono) high-passed
Link Out (RCA Phono)
Low Pass Filter Active 2nd -order, variable cut-off frequency
High Pass Filter Active 3rd -order ?6dB at 80Hz