PSI Audio develops unique EXD driver type between cone and dome for even greater midrange performance of the A25-M.

Yverdon-les-Bains, 14th April 2021 – When the market does not offer what you need, you have two options: you can change your requirements, or you can create the required component yourself. PSI Audio chose the latter option when the market did not provide a driver that would suit their needs – so they developed the Extended Dome driver (EXD).

A25-M equipped with all-new EXD driver

PSI Audio developed the EXD driver as an update for the large-format classic A25-M. The three-way monitor speaker was already a point of reference for acoustic precision and faithful reproduction. However, the engineers at PSI Audio found that the midrange driver could be improved, if only there was a driver that would suit the specifications. When the market offered no such component, PSI Audio decided to develop a new driver from scratch, so as not to compromise the quality of the speaker. The result is the EXD driver, an innovative combination of dome and cone constructions that boasts the strengths of both types while eliminating their weaknesses.

Cone drivers: powerful but heavy

When thinking of a speaker, most people will probably imagine a cone type driver as they are most commonly used for lower frequencies and significantly dominate the visual appearance of the respective speakers. Cones can generate a comparatively large bandwidth and still produce a lot of energy in low frequencies. Due to how a cone driver is constructed, it is quite heavy: consisting not only of the membrane, but also of a dust cap, spider and suspension, the overall weight severely impacts inertia and hence diminishes performance for higher frequencies, which require a fast-moving driver. The result is less output with more distortion – not helped by the fact that heavy basket designs restrict airflow and make the membrane even harder to move. For these reasons, cone drivers are generally well-prepared to reproduce lower frequencies, but do not fare too well in higher registers.

Dome drivers: fine but prone to distortion

Probably the most popular choice for high-frequency reproduction are dome type drivers. They are lighter systems – particularly in the sizes used for tweeters – and hence move more freely and easily. In lower registers, however, dome drivers cannot perform quite as well. Their bandwidth is limited and they tend to become unstable in the centre, introducing distortion. When more rigid material is used to counteract this effect, the driver gains weight, thus losing its most precious advantage. Consequently, dome drivers are and will probably continue to be popular for tweeters, but their midrange applicability is very limited.

EXD: the best of both worlds

Setting out to find the ideal mix of cone and dome type drivers, PSI Audio may well be said to have attempted to square the circle – but square it they did. The result is the Extended Dome driver, or EXD for short. This innovative hybrid driver type features a four-inch paper cone infused with latex and graphite as well as a polypropylene dome membrane. Both parts of the driver are directly connected to the voice coil. As a result, the dimensions of the driver and its weight are perfectly balanced with the coil to provide a performance unlike any other driver, with higher SPL and lower distortion figures. There is also no basket behind the membrane, so air can move freely without restrictions. Especially as a midrange driver in between a cone woofer and a dome tweeter, the EXD is the ultimate compound of both types, allowing for a particularly smooth transition between the ways.