The Last Loudspeaker System

By Stig Erik Tangen
15 Dec 1997

Introduction

These speakers were build for a good friend of mine, who of various reasons is unable to either design or build speakers himself. I'm not too happy with the carpentry part myself, so I decided to find a nice looking finished box I could use. After having heard my own speakers, he also wanted to have some kind of Focal tweeter and at least one Seas Excel mid/woofer. The total project cost should not exceed 7500 NOK (about 1000+ US$). The last thing limited me to using only one mid/woofer. Available finished enclosures also pointed in this direction.

The sonic goal was to build a speaker as true to the input signal as possible; a true monitor. To achieve this, the frequency response must be very flat, the phase response and dispersion well behaved and the distorsion low, especially in the midrange. Those are not impossible goals. What is impossible within the previously discussed limitations is subsonic bass extension, realistic dynamics at low frequencies and the ability to play very loud. A single 17 cm mid/woofer simply can't do that.

The box
I chose to use a box made for the German company Intertechnik for their «MS 3 mk II» speaker. This box is build of 22 mm MDF and painted white. It has precut holes for a 17 cm mid/woofer, a 104 mm diameter tweeter, reflex port and terminal cup. The net volume is about 15 liters. It also has slightly cut-off edges which, in theory at least, reduces diffraction problems. It also comes with a detachable grille.

The selected box was actually quite good, so I did very few mods on it. Of obvious reasons, I cut the tweeter hole larger to fit the big Focal tweeter. Further I covered all inner surfaces, including the plastic reflex tube with bituminous damping sheets to reduce cabinet wall resonances. This also doubled the total weight. I did not use the terminal cup, as I put a plastic box on the rear side to house the crossover and put a Speakon 4-pole connector in the plastic box. The terminal hole were covered first by a piece of 16 mm MDF.

The box volume was acoustically damped with fiberglass. All surfaces was covered with one 5 cm layer, sufficient to kill all standing wave modes and reflections within the box.

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