So why tone wood for loudspeakers? Here we need to get technical. But just a bit. A loudspeaker radiates sound in two directions –at the listener and into its box. Half goes out, half stays in. Since sound diminishes with distance (a marching band gets quieter as it moves away, for a given playback volume a small room sounds louder than a big one) the loudness inside a speaker’s enclosure is far higher than in your room. This pressure excites the walls of the enclosure. It bounces around like a bunch of billiard balls and attempts to escape through the thin driver diaphragms. All such secondary radiation is distortion by definition. Because it arrives at your ears delayed in time, it causes the equivalent of motion blur. That’s a slight audible smear and fuzziness often mistaken for warmth. When addressed, the result is more clarity.
Some speaker designers reason that a super inert ultra dense box will completely kill off this rear wave by absorption in high mass. They also believe that they suffer no time-delayed resonance or internal reflections. Hence the popularity of massive aluminium, composite, glass, carbon fibre and other ‘heroic’ constructions. The problem we see with such an approach is this. Damp what amounts to exactly half of your driver’s emission and it kills or suffocates something in the direct sound too. Think of what would happen to a violin or guitar if its thin resonant sound panels were damped by rubber mats. Their big freely gushing sound which transmits so easily across distance would dull over, collapse and shrink. The fine harmonic modulations would squash and true tone suffer. That’s the core notion behind the Wave 40 and its name. Rather than capture and damp our rear wave, we want it to dissipate rapidly and freely. We want the entire enclosure to act as one constant energy-shedding mechanism. We want our sound to carry across distance as vibrantly and rich as a musical instrument made of top-quality tone wood. Incidentally the ovoid Wave 40 body doesn’t ‘make’ a sound of its own. It’s not a secondary player in the musical mix. It simply provides an active release mechanism for the rear wave.
You’ll have already noted that we don’t use a sealed alignment. That would trap all internal energies and build up very high box pressure. We also don’t use an otherwise ubiquitous port because its endemic ringing ruins both the impulse response and time-domain behaviour. Our chosen solution is a very short flared line instead. It lets the driver breathe freely. It doesn’t resist the rear wave yet augments the low-frequency reach to what is an impressive ~55Hz for our small cubic volume. This also isn’t a ‘brute force’ alignment which attempts to take a driver lower than it comfortably goes.
If you look at the microscopic structure of wood it is a bit like swiss cheese, full of holes. These tubular cells have an amazing ability to absorb and dissipate mechanical vibrations. There are two main reasons why natural wood is so good at this. The first is the irregularity of the cell structure, each cell is different from the next. In any man made material this does not occur, the cell structures are much more uniform and trying to replicate this irregularity in a material is virtually impossible. Here nature has the upper hand. Why is this important ? The irregularity can cover a much wider area of the bandwidth were as a regular cell structure will be much better at targeting specific frequency bands but will leave anything outside untouched. The second reason is the elasticity of natural wood, vibrational absorption/damping is much moreeffective when the material modulates with the vibration.
Obviously any transducer needs to work with a firm unmovable foundation from which to launch its sound waves. Here our driver couples directly to the stand with a solid vertical wood brace that bolts to its magnet whilst the entire ovoid hull suspends from the same brace. This achieves two contradictory goals. The wavy baffle is of deliberately low mass just like a guitar top yet the driver anchors firmly to the stand which grounds itself to the floor with the high-mass metal plinth. That’s how we get away with a thin deliberately resonant baffle yet still have a properly inert driver.
As would be the case for a guitar or cello, our side walls are composed of denser thicker wood species like Maple, Cherry or Walnut. This creates the necessary structural integrity. Meanwhile the sound activated thinner surfaces face the listener and room’s front wall. These larger oscillating surfaces then become directional contributors to the speaker’s acoustic energy transmission.