Meridian Audio Speaker manual Composite Input 40V Peak HF Driver

The Meridian Papers - 1 Meridian Loudspeakers: The DSP Path page 4

Fig. 3: Considerably less power is needed to deliver the same voltage – and thus the same sound level – from an active system than a pas- sive one.

Digital Audio:

Music to the Ears

➤...Hence the crystal clarity of good digi- tal sound: no detail lost, no noise added.

COMPOSITE INPUT 40V PEAK

HF DRIVER

20V PEAK

PASSIVE CROSSOVER

LF DRIVER

20V PEAK

Paramount among audiophile truths is that music’s electronic journey to our ears should be as short and unadorned as pos- sible; this preserves the fragile nuances of live performance. This is why, for exam- ple, audiophiles have long rejected ana- logue tone controls, correctly seeing them as electrical mazes where musical sub- tleties are lost or rearranged.

Yet the typical purist hi-fi is hardly pure. Rather, it’s a confusion of components with varying reactive properties, tangled together through a rat’s nest of electrical-

COMPOSITE INPUT, ˜1V PEAK

HF POWER

AMPLIFIER

ELECTRONIC

CROSSOVER

LF POWER

AMPLIFIER

HF DRIVER

20V PEAK

LF DRIVER

20V PEAK

ly whimsical cables. Each piece lengthens the path and damages delicate harmonic, phase and other relationships that con- tour music.

The amusing irony is, these boxes and cables are generally assembled for tone control: each piece chosen for how its voice changes the message.

Why not simply replace the whole corrupt chain with one transparent digital link, particularly if the music source is digital already?

At Meridian, that’s exactly what we did. In essence, we decided to convert the sig- nal from a source into digital form as early as possible and at the highest level of quality (if it wasn’t already), then maintain that signal in digital form as long as possible before converting back to analogue (although the part of our hear- ing system from middle ear to brain is actually digital, analogue pressure waves carry the sound from a loudspeaker, through the air, to the ear). So in a com- plete Meridian system, the signal is only converted from digital to analogue imme- diately before it enters the amplifier.

range of loads, and so on. The common method of dealing with these possibili- ties is to give a power amplifier four times the current delivery capacity it needs; and give it and its power supply the ability to handle the strange loads likely to be encountered in use and abuse.

Engineering for the unknown inevitably means over-engineering. But in a prop- erly integrated active system, however, each part of the system, including the amplifiers and power supply, can be designed specifically to provide the power required – no more, no less – and into a known, carefully defined load. This can obviously improve effi- ciency and reduce the need for over- engineering. Thus such a design does not have to be more expensive than a conventional passive approach. It can certainly be more efficient, and more effective.

But there’s more. Imagine we are listen- ing to a piece of music that includes a bass part and cymbals, and that to replay this accurately at a chosen level on a two-way system we want to see a not unrealistic voltage of 20v peak at the terminals of both the tweeter and the woofer. To do this with a passive system, even ignoring losses in the crossover, the driving amplifier needs to develop 40v peak.

For a 8-ohm system, this requires an average power of 100W (by Ohm’s Law, the power is equal to the voltage squared divided by the impedance). In the equivalent active system, with a 1v line level input, a pair of 25W amplifiers will do the same job! (See Fig.3.)

Extend this thinking to a three-way sys- tem, and three 25W amplifiers in an active configuration will do the same job as a 250W amplifier driving a pas- sive system.