For decades, the pioneering innovations developed at Bowers & Wilkins Steyning Research Establishment have influenced the way speakers are designed and built all over the world.
We asked our Senior Development Engineer John Dibb to discuss the challenges faced developing CI 800.
What challenges were presented incorporating technology from 800 Series Diamond into a custom installation range?
The main challenge stems from the need to fit systems into around 100mm (3.9in) depth walls and around 200mm (7.8in) in-ceiling cavities.
Whilst high-frequency and midrange drive units do not present a depth problem, specialised shallow bass drivers are necessary for in-wall applications, and considerable development is needed to ensure that they match the performance of their deeper box-speaker counterparts.
It is also essential to supply a rear enclosure, fitted within the wall or ceiling, to define the working volume of the system. For the in-wall case, this has to have a relatively thin wall construction, in order not to eat up valuable cavity space, and a great deal of time has been spent optimizing materials and internal bracing to get the stiffest possible structure.
The finish and dimensional accuracy needed on baffles used on in-wall/ceiling systems precludes the use of more traditional materials such as wood or MDF. It took some time to find the ideal material, one that would give us the precision, strength and acoustic properties required. Ultimately, the material which best suited our needs was a highly glass-filled thermoset resin.
What are the advantages of in-wall and in-ceiling design?
There are two real advantages in mounting a speaker flush with a wall or ceiling. Firstly, there are no discontinuities, such as the corners on conventional cabinets, so the diffraction effects caused by these edges are no longer present,
and there is none of the typical back reflection from walls behind the speaker. Secondly, a speaker mounted on a large surface operates more efficiently in the low frequencies, giving a different characteristic to a box speaker in free
air. This effect can be exploited in a correctly designed bass driver, to give greater headroom with lower distortion.
And how do you meet the challenge of any drawbacks?
There are two drawbacks with in-wall systems. Firstly, the wall structure in which they will be used is uncertain. It might be masonry, which is excellent, or it might be a lightweight timber/ plasterboard construction, which itself will vibrate to colour and distort the sound. To alleviate this problem, we try to reduce to a minimum any vibration reaching the wall, by isolating drivers from the baffle.
Secondly, there is a practical limit to the volume available in a rear enclosure, which can restrict the low frequency extension of the system. This we counter with specially developed back boxes.
The major disadvantage with ceiling placement, is that the listener is, more often than not, a long way off the axis. With freestanding and in-wall speakers, the position of listeners relative to the speaker is relatively well defined, typically varying only a few degrees off the forward axis. In stark contrast, someone listening to a ceiling speaker might typically
be 60 degrees off axis, where the response of drivers is markedly altered. To counteract this our ceiling systems have the drivers recessed into the ceiling, angled at 30 – 45 degrees.
What different challenges do you face designing an in-ceiling as opposed to an in-wall loudspeaker?
With CI you need to ensure that the dispersion of sound is as wide as possible, and experience has shown that a coaxial driver arrangement does this best. Previous systems have also used mechanical rotation of the high-frequency
unit and variable driver equalization to optimizeresponses at different angles. Any change in the position of a driver will, however, introducesmall changes in performance, so for a purist design such as the CCM8.5, any variation in driver positions were ruled out. The drivers were optimized for wide and even dispersion, to give the minimum variation within a defined listening window. Some flexibility is available however, in that the entire baffle can be rotated with no effect on performance, allowing the centre of the window to be aimed at the listening position.
For more on our custom installation series, contact your nearest retailer.