AES British Section techincal visits - July 2007
Technical visit: ATC loudspeakers
www.atc.gb.netFounded 33 years ago in West London, Loudspeaker Technology Limited - better known as ATC - has grown into one of the UK's most respected suppliers of loudspeakers to the professional and high-quality domestic markets. In the mid-1980s it moved to rural Gloucestershire, to a site just off the A419 between Cirencester and Stroud, where it currently occupies three buildings over 13,000 sq ft, with planning permission in place to allow further expansion if necessary. We were given a guided tour of the facility by Operations Director Bob Polley, with company founder Billy Woodman in attendance to answer the more technical questions and chat individually with the AES members attending. As it was the summer holiday season, we were able to move around the factory without inconveniencing too many of the workers.
Originally a manufacturer of PA drivers, ATC is notable today for the broadness of its business base which encompasses broadcast, studio, domestic hi-fi and concert halls. That this small, specialist UK company should win the contract to 'rescue' the initially poor reproduced sound in the Walt Disney Concert Hall, Los Angeles is a testament to both its diversity and its reputation.
We began our tour where the voice coils are manufactured - one of the most skilled operations in the whole assembly process. As far as possible ATC uses local suppliers and does as much of the critical engineering as possible on-site. This includes flattening the wire for the edge-wound voice coils, using a deceptively simple machine with two hardened steel rollers which has already been operating for most of the life of the company. Wire thicknesses of 3.5 to 7.5 thou are used across the range of ATC products, in voice coils of 1.75", 3" and 4" diameters. As the magnet gaps are very narrow, tight tolerances are vital. Aluminium formers are used for the professional products and kapton formers for the domestic range. Wet epoxy resin is used to bond the voice coils and also acts as a lubricant during winding. Maximum production capacity is 2000 coils per month.
Voice coil winding
All voice coils are overwound slightly so that they can be brought back to the correct resistance at the following stage by the unwinding of a few turns. As Billy Woodman says, "All the problems of making loudspeakers revolve around methods of manufacture," so these have been meticulously developed and carefully controlled. After adjustment, the voice coils complete with their hardened tool steel former are baked in an oven at 200C. This former is only removed towards the end of the driver's assembly, when the diaphragm, surround and suspension have all been glued in place. ATC's trademark soft dome midrange driver is hand-doped using a brush because consistent results are difficult to achieve using a machine. All ATC drivers use an underhung voice coil (short coil, long gap) and many are equipped with ATC's proprietary Super Linear Magnet Material which, as a result of its low electrical conductivity, suppresses the formation of eddy currents within the magnet structure. The result is a claimed 12-15dB reduction in third harmonic distortion.
Assembled cones
After driver assembly an initial test is conducted in an adjacent booth to check for correct function. No measurement is performed at this stage as listening suffices to identify faulty drivers that should not proceed to final assembly. At this stage full electronic inspection takes place ensuring +/- .5dB matching. In addition to manufacturing new drivers, ATC also undertakes to service any product it has ever made.
Drive unit assembly
The next building houses the warehouse of finished cabinets and a small cabinet-machining shop for special projects. Cabinets for ATC's standard range of products are manufactured externally.
Assembled bass units
Building three houses cabinet assembly and electronics assembly for ATC's active speakers and line of audio separates components. New items are currently being added to this range, driven principally by ATC's growing market in China, Korea and Japan. This building also features a fully isolated listening room in which we were able to sample the final product, both before and after enjoying a fine lunch in a marquee outside.
Listening room
The visit was well attended by AES members, all of whom expressed thanks to Billy and Bob for an absorbing insight into ATC's activities.
ATC founder Billy Woodman (left)