The SEAS KingRO4Y is a 3-way loudspeaker kit, using a 26 cm aluminium cone subwoofer and an 18 cm midrange coaxial. The coaxial unit uses a magnesium/aluminium-alloy cone for both the midrange and dome tweeter. All are housed in a compact closed box enclosure and powered by the Hypex Fusion FA.503 or FA.253 DSP amplifier.

The design goal for this kit is to get a true fullrange loudspeaker system in a compact enclosure with outstanding performance.


The Drive Units
To achieve the design goals of this kit we chose to start with a coaxial unit in order to save some baffle space and get all of the benefits of sound quality from a coaxial. Since the chosen midrange coaxial can easily play down to 150Hz, it was possible to use a high quality subwoofer with excellent low-frequency extension to take care of the lower frequencies.

C18EN002/A - The coaxial unit uses a lacquered magnesium/aluminium-alloy cone and dome, and are integrated to form a single acoustic source. A benefit of the coaxial arrangement is that the off-axis response is equal in all directions. That makes the sound imaging very stable with a large sweet spot. It uses a Neodymium magnet system for optimum air-flow, minimal back wave reflection and a healthy sensitivity.

L26RO4Y - This subwoofer driver is the perfect solution for good bass in a small enclosure. With its high power handling and low Q and Fs it can handle a large amount of EQ in the low end. Since it also has a smooth response high up in frequency it can be used all the way to a midrange unit, thus eliminating the need for a dedicated mid-woofer in this loudspeaker kit.


The Amplifier and DSP

We chose to use a three channel plate amplifier with DSP capabilities which is of high quality, easily available and provided ample power for the speaker system. The choice lands on the Fusion FA.503 DSP amplifier from Hypex. It delivers 2x500 W into 4 ohm & 1x100W into 4 ohm, and has a large filter bank for crossover and EQ.  Three channels of amplification mean that there is available DSP for each individual driver. 

Detailed info and datasheet on the DSP-amplifier can be found on Hypex' website,


The Enclosure Design

One of the design goals of this system is to make the enclosure as small as possible. Since the target group is the DIY enthusiasts the design also required reasonable simplicity.


The Measurement results

Anechoic chamber frequency response. All of the measurements are made at 1m at tweeter height:

KingRO4Y MKIII XoverGraph

Sound pressure frequency response measured in an anechoic chamber is shown. The below figure shows the off-axis measurement at 0°, 15°, 30°, 45° and 60° using "Preset 1" in the provided DSP setup file.

KingRO4Y MKIII OffAxisGraph

The next figure shows the on-axis response of the different presets provided in the DSP setup file.

KingRO4Y MKIII PresetsGraph


Listening Room and Placement

High quality stands should be used to bring the tweeter approximately to ear level or slightly above. Even in the best listening room, it is important to determine the positions where the loudspeakers will perform optimally. Placing the cabinets too close to the walls or corners will result in more powerful bass but may also cause response irregularities in the bass/midrange area. Some experimentation is recommended in order to find cabinet positions that result in a good tonal balance and freedom from coloration.

As can be seen from the off-axis response plot above, the smoothest listening angle is around 15°- this should be taken into account when placing the speakers in-situ. 

After finding a good placement of the speaker, then there are almost endless possibilities to fine tune the sound balance with the Hypex DSP. Please see the Application Note for details.