ES-28N

All good things go by three“ is a proverb we often use in Germany if something happens the third time. The new ES-28N is the third model in the current EPOS line-up, and on top of it, it’s a 3-way loudspeaker made by a designer who is well known for doing 2-way systems even with bigger woofers. So what did change his mind? 

Experience! It’s just that a 2-way system is not working so well in a configuration with two woofers. OK, there is the typical D’Appolito configuration with a woofer above or below a tweeter, but as the tweeter should be sitting around one meter, the speaker would end up as a huge tower. Mounting the woofers below the tweeter would need a so called 2.5-way configuration. In such a configuration, one of the two woofers stops working in the lower midband, and the second woofer covers the rest of the midband to connect to the tweeter. That sounds like a good idea, but unfortunately, the main radiation axis for those two woofers would be tilted downwards, so it is difficult to manage the mid-frequency energy properly. So why not make it 3-way? OK, that’s what we did. 

Similar to ES-14N, the cabinet of ES-28N is slightly tilted to get better time alignment for the drivers. The two woofers sit in a Bass reflex compartment, carefully braced for low cabinet colouration. For the same reason, the whole cabinet is made from a sandwich construction with a layer of high-damping glue beside two MDF panels. The front plate is 50mm thick and made from two 10mm sandwich panels and a separate chambered MDF panel of 30mm. The midrange has its own compartment with a triangular backside to avoid reflections. The remaining part behind the tweeter takes the crossover, so the components are isolated from high sound pressure levels. The port tube opening is located on the bottom. That allows an eight-centimetre diameter port in a length that gives the lowest possible output of resonances from the cabinet and the highest maximum output of low frequencies. In addition, the port is equipped with pressure-equalizing holes in the middle to avoid the tube resonance of the port itself. The opening in the socket is big enough, so even in cases where the cabinet is standing on the floor without spikes, the bass performance is not compromised. 

The 30cm long port tube output reached its maximum at the tuning frequency of the cabinet/driver combination, 30Hz. The graph shows the difference between a standard port and a version with the pressure-compensated EPOS design, which removes the double-sided open tube resonance by almost 10 dB. Thanks to the correct position in the design, the cabinet’s standing wave modes do not escape through the port tube.

Impedance:

The response curve shows a falling character toward low frequencies from about 300Hz, the corner frequency of the so-called baffle step. The ES-28N is voiced slightly differently from classic designs, taking into account that the woofers are close to the floor. Together with a low tuning of 30Hz, a very deep and tight bottom end results. The impedance is compensated in the midband for better working with tube amplifiers.

Distortion:

The distortion curves, measured at 86dB SPL show an average level of below 0.2% between 100Hz and 10kHz. 

The two 7“ woofers share the magnet system and basket with ES-14N but use a straight cone instead of a curved cone. A straight cone is the best solution for the bottom end. A large inverted dustup makes the cone even stiffer for fast and powerful bass. The magnet uses aluminium demodulation rings to stabilise the inductance of the voice coil, so there is no modulation of the crossover, low harmonic distortion, and low intermodulation. The coil is 36mm in diameter and 18mm long. The coil former is made from non-conductive Epoxy/Glassfiber material to avoid Eddy Current. 

The midrange is based on the design of the ES-7N woofer – Mica-filled polypropylene cone material made with injection moulding. A low hysteresis rubber surround and a Nomex high-temperature capable spider ensure the suspension is linear with good control of higher excursions. The 30mm voice coil with glass fibre/Epoxy former works in a magnet system with an impedance control ring to minimise distortion and intermodulation. A double magnet compensates the stray field and increases the force of the coil. 

The tweeter is identical to the tweeter of the ES-14N and ES-7N, giving the new model the same top-end quality. It’s a 28mm voice coil on an Aluminum alloy, ceramic-coated dome with a powerful Ferrite magnet and optimized inter-cavity airflow. The tweeter does not use Ferrofluid in the gap for stable temperature and low compression.