Preventing mechanical vibration from the bass cabinet reaching the tweeter leads to a much cleaner, sweeter high frequency performance. For the 800 Series, we’ve adopted a new synthetic gel to cushion the tweeter better than ever before. Not only that, we’ve also isolated the tweeter assembly from the tube and mounting behind, which reduces external interference to virtually nil. Imagine driving a car where the engine is rigidly mounted to the bodywork. Now try to imagine actually liking the experience. Difficult, isn't it? Isaac Newton (who gave his name to a force, approximately equal to the weight of an apple) reasoned that every action has an equal and opposite reaction. So it is that when a driver diaphragm vibrates, there is a reaction on the chassis, which has the potential to transmit this vibration through to the enclosure walls, giving us cabinet coloration.
Mounting the driver compliantly greatly reduces the degree of transmission of this vibration. The softer the material used for isolation, the more effective it is. Bowers & Wilkins make extensive use of a gel material, which is similar to that used in mobile phones to isolate the microphone from handling vibration. It can be made much softer than rubber without losing dimensional stability. Decoupling can be extremely useful in conjunction with stiff enclosures. The stiff walls resist deformation under internal pressures at lower frequencies, but any tendency to ring at higher frequencies is prevented because the exciting force is decoupled. That's why you should always be careful in judging an enclosure's quality by knocking the walls (I know, we all do it). The driver will not "hit" the enclosure in the same way if it is decoupled. Try hitting the enclosure with the fleshy part of your hand instead of the knuckles. That will give you more of an indication.
The combination of stiff enclosure and decoupling is exemplified in the midrange and tweeter head assembly of the Flowport™ 800 Diamond and 802 Diamond speakers. The head is made from an extremely hard resin called Marlan® (a registered trademark of Polylac Holland Bv). Both drivers are decoupled from their enclosure and the enclosures are decoupled from each other and the bass cabinet below using gel components.
Find out what Bowers & Wilkins customers and audio enthusiasts are talking about on our blogs, and read in-depth articles in the Sound Lab.
Production Notes: ‘Saving the Tapes’April 26,2015
Will Gregory in conversationApril 21,2015