Seas Loki MKIV Active Coaxial Kit - Pair

Seas Loki MKIV Active Coaxial Kit - Pair

Price shown includes a 10% discount on drivers, miniDSP, and accessories.

Flatpack, Assembled, & Finished cabinets now available from Denton Woodworkers!

Named after the Norse god Loki, a shape shifter which corresponds well to how versatile this loudspeaker is. The Loki consist of an 7" coaxial driver. The woofer is made with a TPX cone and the tweeter is a 1" soft dome.

WHY LOKI?

Loki is the result of many years of fine tuning and improvements. It's always been highly regarded as a versatile speaker that works well in almost any placement and setup. Currently in the Mk III version, this compact loudspeaker has proven as a good example on the benefits of our coaxial technology. The common acoustic centre of the woofer and tweeter makes it easy to marry the phase of the two drivers and avoid the common lobing issues. This results in a very large sweetspot and an astonishing soundstage. Whether it's used for stereo or in a home theatre this loudspeaker always delivers a true high-fidelity experience.

Seas Loki MKIV Application Notes (pdf)

As an active design, each speaker requires 2 channels of amplification. A stereo pair requires 4 channels of amplificaiton. Also available in a passive design here.

Each LOKI MKIV Kit Includes:

• (2) Seas Prestige T18REX/XFC (H1353) 7" Coaxial Driver
• (1) miniDSP 2x4 HD USB DAC and Digital Signal Processor
• Madisound will pre-load the 3 crossover configuation files onto the miniDSP for you!

The parts list below is what a typical build of this kit will require. If you are starting from scratch you should consider purchasing the optional accessories package. If you already have stock on some parts, review the parts list to make certain you have what you need.

Optional Accessories Package Includes:

• (2) 2FLARE - Precision Flared Port Tubes - front or rear port
• (2) TD-CUP - gold plated dual binding post input cup
• (8ft) Supra Classic 1.6 - tinned oxygen free copper internal speaker wire
• (.2lb) Acousta-Stuff - fluff & fill behind coax driver
• (1yd) Wool Felt - cut & line internal walls
• (2) QC110B Quick Connects - for - tweeter tab
• (2) QC110R - for + tweeter tab
• (6) QC205B - for + woofer & input cup tabs
• (6) QC205R - for - woofer & input cup tabs
• (12) OXSOCKET8X1 - mount driver to baffle
• (8) OXSOCKET6x3/4 - mount port flare to cabinet
• (8) OX6OVAL3/4 - mount input cup to cabinet
• (6ft) Foam Tape - airtight seal of driver and port flare to baffle

Also consider the miniDSP remote from the drop down menu. That make the use of these speakers very convenient. 

Enclosure, Tuning, & Stuffing

The Loki uses a 0.44 cf vented cabinet to give it a nice roll-off with a good bass foundation. See application notes linked above for cabinet details. Although not critical in a compact enclosure, adding bracing to stiffen the cabinet is a good tip for the advanced builder to take the loudspeaker just a little bit further.

After thorough measurements and extensive listening, we found the optimal tuning frequency and amount of damping material. The cabinet is filled with .45lbs of polyester foam. The dampingmaterial is distributed evenly in the box but kept away from the port opening to allow freemovement of air. This to ensure that the airflow noise stays as low as possible. It's also recommended to line the walls with felt. The port diameter is 2" and the length is 6.5" mm with both the inner and outer flares attached. This results in a tuning of 45 Hz, providing a smooth low frequency roll-off.

Finished cabinet dimensions: 8" wide x 15" tall x 11" deep

Coaxial Drive Unit

The clear PP/TPX based cone matches ideally with the adaptive rubber surround, resulting in an outstandingly smooth frequency response from the woofer. The coaxially arranged pre-coated fabric dome high frequency unit has a low resonance frequency and integrates with the cone driver to a point source. The cone of the woofer acts as a horn loading for the tweeter, and the chassis of the dome unit represents the throat of this horn. An extremely stiff and stable injection moulded metal basket keeps the critical components in perfect alignment, while large windows in the basket both above and below the spider reduce sound reflection, air flow noise and cavity resonance to a minimum.

Crossover

This update for the Loki uses a MiniDSP 2x4 HD unit - the crossover has been made using the MiniDSP software and is aimed to work well as a kit with adjustable modes or serve as a starting point for hobbyists who wish to take their own measurements and adjust this kit for their listening environment.

The crossover included in the kit utilises symmetrical 4th order Linkwitz-Riley roll-offs centred around 1.9kHz, a low crossover point has been chosen to utilise directivity of the tweeter in the upper mid frequencies, providing the body of the vocal range more power, off-axis. A fourth order has been used because of the low crossover point which means less strain on the tweeter below resonance and excellent phase alignment over the narrow crossover bandwidth that this order of filter provides.

The design choices of the crossover have made for a smooth overall power response, this is bolstered by the use of EQ points to tackle resonances in the woofer’s response. The woofer has 4 EQ peaks balancing resonances in its response and a high-shelf EQ point which is used to tackle baffle step caused by the cabinet and cone break-up in the high frequency response of the woofer. The tweeter required very minimal EQ, only having one high-shelf EQ point applied to give lift inthe 10kHz+ region, balancing with the resonance in its natural roll-on.

Measurment 

Measurements are taken on tweeter axis at 1m in free field. The measurements here have been offset to 0dB as the system is digital. The following figure shows the responses for the full system as well as woofer and tweeter independently, the black line is the full system with the tweeter running inverted polarity. The deep and symmetrical notch, when the tweeter is connected with inverse polarity, shows that the drivers are in-phase across the whole crossover region.

In the next figure we can observe the off-axis response of the Loki system with the MiniDSP crossover. Here we can see that even 60 degrees off axis there is a smooth decay of around 3dB between 1kHz and 10kHz then limited by tweeter directivity beyond this. The High shelving added in the tweeters EQ stage here has made a marked improvement upon the passive crossovers power response smoothness off-axis. There are still some of the on-axis resonances inherent to coaxial drivers however these become smoother off axis and an ideal listening position between 15 and 30 degrees can be estimated from this figure.


The next figure shows the 2nd and 3rd order harmonic distortion with an output of 96dB at 1kHz. The overall distortion is low and without any large peaks. This makes the reproduced music very clean and without colouration.

The following figure shows the three MiniDSP crossover configurations included with this kit measured at 30 degrees off-axis, this is around the recommended listening angle for the Loki system so should give a fair indication of the power response at listening position. There are two alternative settings included with the MiniDSP kit which are meant for use as room correction effects, a low frequency boost and a high frequency cut for brighter rooms. These are meant as starting positions and a quick guide to adjusting these presets can be found in the application notes.