Classical: Ear,Ear,Ear

Remember that bit in 2001 when the astronaut floats off after his airline is cut by the robot arm of a spacecraft? We hear his laboured breathing while he's working and then, snip! Nothing... Complete hush as he twitches off into orbit around the sun. Forget all that stuff about outer space and futuristic music. There is no music in outer space: no air, no sound. Nevertheless, as we approach the millennium, space is still music's final frontier.

So why is it that, unlike Captain Kirk, the rest of us have no front ear? The fact that we have only got the two, one on each side of our heads, must be something to do with our need to locate exactly where a sound is coming from. If sound location wasn't important, one front ear would probably suffice. But sounds are three-dimensional, they are located in space and the space in which they exist colours the sound. People sing in the bath because bathrooms usually have hard reflective surfaces - tiles, mirrors, ceramics etc - that cause reverberation and make the singing voice sound wonderfully rich and resonant. Hence the abundance of bathroom Pavarottis. Sitting-rooms, by contrast, have soft furnishings that absorb sound, making voices two-dimensional and flat.

But what has all this got to do with music and why is space the final frontier? Most people think of music in terms of notes and rhythms, harmony and orchestration, maybe even a beautiful tune. Or perhaps strong beats with a heavy bass. Whatever takes your fancy. But other elements are at work. Loudness and softness, for example; timbre too.

We all know what tunes are. They're made of pitches (the notes) and rhythm (the length of notes). We notice how loud the notes in a tune are and what their sounds (timbres) are. And our recognition probably occurs in that order - pitch, rhythm, volume, timbre - because, until the middle of this century, pitch and rhythm (tunes) were the primary building blocks of music - a hierarchy reflected in conventional Western music notation. But in recent times composers have used dynamics and timbre as primary building blocks, often relegating pitch and rhythm to the second division. Today the creation of space, and the location of sound in space, has become as vital a component as melody, harmony and rhythm. Modern composers hurl sounds around the concert hall as if they were attached to the end of a long rope, while rock bands cocoon each carefully crafted sound in a halo of synthetic, studio-generated reverberation.

The idea that space is important in music is not new. In the middle of the 16th century Adriaan Willaert and Giovanni Gabrieli composed for multiple choirs positioned in the detached galleries of St Mark's, Venice. And, at the turn of the last century, Charles Ives was fascinated by the sound of several marching bands arriving on his village green simultaneously, all continuing to play different pieces as they marched round and round. But sound location, and the construction and articulation of space, have become crucial musical ingredients in their own right during the latter half of this century.

For Karlheinz Stockhausen, "Sound in space has become as important as harmony and melody and rhythm and dynamics." In 1955, when he was only 27, he composed Gruppen for three orchestras. The piece involves the idea of multiple speeds. He originally wanted a single orchestra to play several different tempos all at once. This didn't work, so he divided the orchestra into three, placing one section to the front of the audience, one to the left and one to the right. And bingo! Almost by accident, space became a guiding light in 20th-century music. There aren't really any tunes in Gruppen. Well, not the sort that anyone could sing in the bath. But there's lots of other stuff to listen to. The piece is like a rich painting, full of dazzling colour, intricate texture and writhing shapes, inviting you to bathe in glittering complexity as sweeping gestures arc through space, carving out great lumps of orchestral material.

"Every room has a hidden melody," says Alvin Lucier, composer of the classic piece, I Am Sitting In A Room, in which Lucier recites a short text that describes exactly the process used to make the piece. "I am sitting in a room, different from the one you are in now. I am recording the sound of my speaking voice and I am going to play it back into the room again and again..." Which is exactly what he does. It's like a photocopy of a photocopy of a photocopy ad infinitum. The result is a resonant frequency pile-up, as the natural reverberation of the room becomes more and more prominent. The voice slowly transforms into a lilting melody of pure tones generated solely by the physical properties of the room in which the recording was made. Lucier has a stutter and some of his words sound like an early Eighties dance record. RRRRhythm. The stutter adds spice to the emerging melody and the melody smooths the stutter (or, as Lucier puts it, "any irregularities my speech might have").

According to La Monte Young, space is "the original instrument". Resonance as a reinforcing powerhouse provides the energy behind his work, and his work has been, and still is, a major force in 20th-century music. Without him there would be no minimalism, no "Ambient" music, no Velvet Underground - and, without them, no punk! Young is the musical godfather of post- modernity and space is his main currency. Like Alvin Lucier, he is a sorcerer who melts the edges where space and time meet, erasing the lines around our reality.

Since the 1960s Young and his wife, the light-artist Marian Zazeela, have been working on what they call "continuous sound and light environments" or "Dream Houses". Their current work, Dream House: Seven Years of Sound and Light, was installed at 275 Church Street, New York, in 1993 and will run until at least the year 2000. The sound part of the piece comprises a single rich fusion of 35 sine waves stretched across 10 octaves. The frequency of each waveform is carefully calculated using prime number ratios and then specially tuned by Young. As you enter the space, all you hear is a loud, dense drone, like a deranged factory; but then, as you walk around or simply turn your head, individual notes leap out from the background. Tiny harmonies float in their own very specific space; in some parts of the room a great lumpen bass thunders at a frequency so low it's almost a pulsating rhythm. What's happening is that the sine waves are literally sculpting the air, setting up very stable high and low pressure areas in the room. As listeners investigate this material, they generate their own private melodies by moving through space and time. A symphony of spaces for those that have ears to hearn

'Music for Spaces': Mon-Fri 5pm Radio 3