The three different types of transducers are subwoofers, compression drivers, and tweeters. They all feature the combination of a voicecoil, magnet, cone or diaphragm, and a frame or structure. Loudspeakers have a power rating (in watts) which indicates their maximum power capacity, to help users avoid overpowering them. Thanks to the efforts of the Audio Engineering Society (AES) and the loudspeaker industry group ALMA, power-handling specifications became more trustworthy, although adoption of the EIA-426-B standard is far from universal. Around the mid 1990s trapezoidal-shaped enclosures became popular as this shape allowed many of them to be easily arrayed together.