Vivid Enclosures - a closer look...

The way in which these waves interact with their surroundings is not always intuitive and one of the most difficult ideas to grasp is why a wave radiating from a loudspeaker is reflected by a sharp cabinet edge. We're all familiar enough with sound bouncing off a hard surface, that's the echo you hear if you shout at a smooth wall. Imagine putting two flat boards either side of the tweeter. The sound bounces off the walls like ripples in a pond.

But there's no hard surface at the edge of the cabinet, just free space. As the sound moves outwards from the tweeter it forms hemispherical waves with one edge running along the flat cabinet front until it reaches the edge.

Well it turns out that the sudden change from being bounded on one side to being completely free is almost as big a shock as running into a hard surface. Re-radiation from sharp discontinuities is also something that concerns designers of sneaky military aircraft. They aim to create as little radar reflection as possible to avoid detection. The B1 bomber has a radar signature just one percent of that of its less discreet predecessor the B-52. Much of this benefit has been achieved by keeping the surface as smooth as possible.

The problem with these secondary sound waves is that they can now mix with the main sound and cause interference that will create peaks and troughs in the sound as you move around the speaker.

When you place the speaker in a normal room with reflective walls you hear the main sound followed by a sort of average of all the irregular off axis output. Replacing the flat baffle and sharp edge with a single smooth curve means there is no longer a single point at which the sound space changes from half space to full space. In turn this means that there is no interference and a smooth off axis response. A frequently encountered shortcoming of many speaker systems is a jump in the dispersion between the mid-range driver and the tweeter. A typical cone mid-range driver concentrates the sound into an ever tighter beam as the frequency approaches the point at which it crosses over to the tweeter (2-3kHz).

However a tweeter mounted on a flat baffle or, worse still, in free space has a very wide dispersion at the lower end of its range which in turn means an excess of high frequencies reach the listener after reflecting from the walls of the room. At the bass end of the spectrum it's no longer the wave-like nature of sound which is a concern but the sheer movement of the air.

Vivid Audio loudspeakers utilise the vented style of enclosure to improve low frequency distortion performance.

This means introducing a carefully optimised duct which connects the inside of the box to the outside. Sound output from the rear of the bass unit causes the air in this port to move in and out and for a certain band of low frequencies the majority of the system output is from this port. Benefits include reduced cone excursion and hence distortion but only if the air in the port moves smoothly. All too often vented loudspeaker systems have simple lengths of tube with no attention paid to the manner in which these are terminated. As the air moves back and forth through such tubes a distinct chuffing sound may be heard that becomes rapidly more significant as the drive level is increased. The cause of this undesirable distortion is turbulence and it represents a transformation of the desired airflow into useless eddies.

Turbulence occurs whenever there is an abrupt change in the direction of a flowing fluid. You can see it as you swish you hand through water or in the wake of a boat and you can hear it when you hiss through clenched teeth or in the roar of a jet engine. In every case the energy in the smooth stream is being converted into rapidly spinning vortices where it dissipates into waste heat. A quick look at any design where fluid movement is an issue reveals a simple solution - streamlining. Be it plane or a fish, sharp steps are nowhere to be seen. And so the same can be applied to loudspeaker ports.

Vivid Audio loudspeakers feature bass ports with gentle flares at both the outside and inside ends and delivers a bass performance that far surpasses any simple tube. All of these features deserve an equally prestigious cabinet and the curvaceous nature of all the components lead naturally to the final VIVID AUDIO enclosure design. Not a straight line in sight and a result far stiffer than an equivalent square box. Put together all these elements and you have one of the most surprising performances ever put on by a loudspeaker.