A ‘sound machine', a computer-controlled `ensemble' hangs high above in the Klankkaatser, at one focus point (of the ellipsoid). The sound machine contains a fan which transmits varied wind thrusts to five bamboo flutes, so that those flutes play composed music. These live sounds are reverberated by means of the entire hollow inner wall and connect to the other focus point, at ear level, inside your head. The Klankkaatser has an effect on the senses. It relates to those sensations which arise by intensifying sensual experiences and by connecting these experiences. The public is also confronted in the Klankkaatser with an individual manner of looking and listening, and the perception of how people look and listen.

The Eckoo is powerful, quick and flexible. It can be installed independently in exhibitions to resonate and can be utilized for live playing. Using a computer the compositions can vary within certain borders, with sufficient recognizable parts for frequent visits.

The Eckoo evolved from the overview exhibition in 2002, Primal sound, in which all parts were transmitted by computer; it was, as it were, one huge musical instrument. For that exhibition new sound groups had been devised: flute clusters, pan flutes and basses. For those parts Hans van Koolwijk thereafter designed a console. He did this in collaboration with Hans van Eck, whose name became part of the title Eckoo (Eck & Koolwijk).

The console has many bolts and knobs. When placement of the Eckoo is broad and flat, it can fill large spaces with sounds, which for the visitor seems to come from all directions. 

The fans built specifically for these flutes allow for subtle nuances in sound to occur. The long, relatively narrow flutes are easy `overblown', creating a beautiful range of harmonics. The computer-controlled composition is created to make it seem like these variations happen accidentally. These bass flutes form the basis of the exhibition; they specify the atmosphere upon entry, a blanket of warm sounds.

During a demonstration of his musical instruments, Hans van Koolwijk posed the question to the most inquisitive child in the class: what were the small pieces of lead doing in the flutes? These lead knobs alter the sound waves in the flutes, resulting in a change of tone.

It went too far to explain the theory of harmonics or about nodes and antinodes in wavelengths. But this led Van Koolwijk to his next idea: 'Imagine that you are just as big as the lead nodes and that you can stand inside the flute. That you can change the tone with your own body; how would that feel? ‘This idea developed into this enormous upright ‘flute’, the Oer-Oorsprong. Inside this object you feel the violent ultrasounds, 'sound as matter'.

This test form appears on the scale of a large half egg, with two focus points. The one focus point, with the flutes, can be found in the scale and the second one is positioned at the front. Flute sounds reflect from the first focus point by means of the bent partition to the second one. Because the flutes are reverberated by means of each point on the scale, the reverberating sound comes from all sides and arrives at that second point. As a result, there is no perception of direction; sound simply exists, concentrated in a globule. 

A bass box is an electric air pump which pumps exact wind gusts into flutes, producing rhythmic, percussion-like sounds. The bamboo flutes are capable of easily being `overblown' and are sensitive to fast, small alterations in pressure. Between two airtight chambers in a firm transportation box, the pump is in the shape of a large bass loudspeaker. This builds up a high-speed pressure in the left and right chamber and as a result the flutes, which are connected to those chambers, suctioning successively in and out. The fast `panting' creates nuanced harmonics in the flutes. Since the flute sounds are fairly soft, they are amplified.

The glissando machine can be relentless and sound very loud, almost more than 100 dB. That is dangerous to the ears, so it is better not listen for too long. But this loudness seems worse than it is, because it prickles uncomfortably in your ears. The sound waves from all the flutes move through the space. The crashing of the drifting waves will rapidly create new forms: the alternating tones. These are fundamentally different in character than the ordinary tones, because they do not come from the flutes, but they arise everywhere in the space where those flutes sound. They arise therefore also in the ears of the public, and in this way seem threatening.

The loud glissandi in this work arise by plastic tongues which are found on `saxophone mouthpieces’. Such a `mouthpiece' has been carefully formed into a curve, and as a result the reeds will tremble faster with increasing wind pressure. In this way such a flexible tongue movement is directly related to the wind pressure and the pitches glide easily.

The invisible movement of wind has been visualised in a flowing, lazy rolling dancing of banners. This is accompanied in sound by wind tickers which, depending on the wind strength, their different tempi on the sound pipes swell from piano to fortissimo.