KingRO4Y systemPhoto web2

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 Crossover

The crossover for this system is handled by the Hypex amplifier- the design is fairly similar to the MK II version however the midrange & tweeter having a channel of equalisation each has allowed for a slightly finer tuned and more consistent frequency response and the increased power of the amplifier has allowed for extended bass response of the L26RO4Y.


KingRO4Y MKIII XoverGraph


The sub and midrange are crossed at 215Hz, the sub rolls off with a 3rd order Butterworth slope and the midrange rolls on with a 4th order Linkwitz-Riley resulting with a -6dB point for each driver at 215Hz which can be observed in the measurements section. The sub has a second order 0.7Q high-pass filter set to 17Hz, this is a protect for the driver, so it does not reach excursion limits for sub-sonic frequencies in some recordings.


The crossover configuration between the midrange and tweeter follows the same pattern as the sub to midrange so the midrange rolls of with a 3rd order Butterworth slope and the tweeter rolls on with a 4th order Linkwitz-Riley. The filters are set to 1880Hz however this translates closer to a -6dB point of around 1600Hz in the measurements, this is because of the EQ applied to both drivers. 


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 subwoofer needs a 12L closed box as a minimum to have a nice response. However, the actual enclosure is 15.6L. This is a slight reduction in volume compared to the MK II, a compromise to retain the same outer dimensions while providing a larger housing for the FA503. This compromise works as the reduction in Box volume is rather small and a we are using a more powerful amplifier which compensates for the increased air stiffness of a lower volume enclosure.

The coaxial uses a closed box of 10.4L, which was the smallest possible enclosure on top of the subwoofer and still have an easy build. That gives the midrange excellent working conditions and a nice response.


Measurement results

A sound pressure frequency response measured in an anechoic chamber is shown. All of the measurements are made at 1m at tweeter height. 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.


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