The ELS 303 utilises the Swift Tweeter and Lightning 130 midrange driver from the ELS 3 with improvements to the cross-over and midrange linearity. Epos has also developed a new 130mm woofer, based upon the same chassis as the Lightning 130 midrange. It can be differentiated by the round dust cap and lack of cone damping material used on the outside. The woofer is coupled to the rest of the speaker in a 2 1/2 way fashion with a high linearity crossover which rolls off at 100Hz. This combines with the low frequency output of the midrange to give added power handling to the bass, while maintaining a very slim 150mm front baffle, which improves imaging at high frequencies.

The cabinet has the same footprint as the ELS3 but the height is 87.5cms, including the plinth but not spikes. This brings the tweeter up to the optimum 81cms listening height to the user, when seated. The midrange section is not ported. The woofer section is braced and sealed off from the midrange section and is tuned with a port to 47Hz, which determines the lower cut-off frequency of 43Hz for the speaker.

Because the ELS 303 is a tall and slim speaker, it needs to be stabilised to prevent it being accidentally knocked over. Epos has designed a PVC foiled MDF plinth, which is attached to the bottom of the cabinet with 6mm bolts. The plinth increases the footprint of the speaker to make it more stable. 6mm spikes are also supplied to help decouple unwanted energy from the cabinet/plinth, when in use, through to the floor.

To enable the user to connect the bass driver separately from the midrange and tweeter, a gold plated bi-wiring terminal is used. Metal links join the upper and lower sections together and can be removed by the user to allow bi-wiring.