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3.5: CONSOLE REFLECTIONS
Another area of confusion is around the meaning of the term "near-field". Here's one interpretation:
"In physical acoustics, the near-field is defined as the region of space within a fraction of a wavelength away from a sound source.
According to this definition, the outer boundary of the near-field region varies inversely with frequency. In terms of human localisation,
we will designate the near-field as region of space within 1 m of the centre of the listener's head, and the "far-field" as the region
at distances greater than 1 m".
In this interpretation, only frequencies below 170Hz are a fraction of a wavelength @ 1m (3' 3 ")( wavelength). 1m (3' 3 ")is
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1
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wavelength @ 85Hz
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wavelength @ 34 Hz etc. At high frequency you are lots of wavelengths away from the speakers, e.g.
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30 wavelengths @ 10kHz.
That is mostly to do with understanding how you sense the direction of the source of sounds, which is a complex subject. For the
rest of us, the near-field is a sufficient proximity to the sound source for the room reflections to become negligible. Clearly, the closer
you get to the source, the indirect sound bouncing off all the reflective surfaces in the room will be reduced in proportion to the
direct sound coming straight from the speakers; but it will never be totally eliminated.
The nearest, and therefore the most significant, reflective surface in a near-field monitoring set-up is the working surface of the
console. Its delayed reflection interferes with the direct sound in a particular way to do with the path-length difference between direct
and indirect. If the path from the speaker to your ears via the surface of the desk is 340mm (1' 1 ")longer than the direct path, for
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example, then the indirect sound will arrive one millisecond after the direct. The direct and indirect sounds will, therefore, be in phase
@ 1kHz, and will add or reinforce, but @ 500Hz the two signals will be half a wavelength out of sync, so they will partially cancel.
Partially, because the indirect sound is lower in magnitude than the direct, and so is too weak to cancel totally the direct sound.
This strong, single delay gives rise to "comb filtering", so called because the repetitive peaks and dips in the frequency response
look like a comb. Peaks will appear at multiples of 1kHz and dips at odd multiples of 500Hz. The weaker the reflection, and the
further away the listener is from the "angle of reflection equal to the angle of incidence", the less the effect will be. With careful
placement it can be minimised, one major tip can be to use stands behind the desk, rather than site the monitors on the Meter Bridge
or small platform
4.0: DESIGN FEATURES
4.1: AMPLIFIER STAGES
The input XLR is directly connected to the chassis with a grounding pin on pin 1. Pin 2 is the non-inverting input and pin 3 is the inverting
input. Pins 2 & 3 connect to an electronically balanced, variable gain instrumentation amplifier, which has identical gain and impedance
on each input pin for high CMR (common mode rejection). This circuit also contributes very low noise and distortion, while allowing
infinitely adjustable sensitivity between +4dBu and -10dBu for full output; two-stage RF filtering further reduces interference.
The signal then flows via a mute circuit for switch-on delay or fault conditions, to the variable EQ (section 4.5). Before reaching the
crossover frequency-dividing filters, the signal passes through a complex set of active CL filters (capacitor / inductor), whose purpose
is to add finely tuned emphasis or de-emphasis in various narrow frequency bands, to augment the frequency response shaping built
into the EQ and crossover circuits.
These help create a more neutral system, diminishing the main sources of colouration. To describe something as characterless and
colourless normally wouldn't sound all that attractive; but these are good qualities in a monitor. It means it won't superimpose its own
sound-fingerprint onto the signal, but will let you hear the sounds you are creating, neutrally, naturally.
The crossovers are based on Rauch filters, with additional first order and all-pass sections to arrive at symmetrical acoustic transfer
functions and optimum phase relationships. Finally, the signal passes to the power amplifiers. Two 150W power amps drive The Dual
Concentric™ driver in the Ellipse. A monolithic 30W wide bandwidth amplifier powers the SuperTweeter™ giving ample headroom for
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the minute signal in this very high frequency band.
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