Cloud Electronics CX2300 User Manual

CX2300

Active Filter

Installation & User Guide

Cloud Electronics Limited

140 Staniforth Road, Sheffield, S9 3HF England

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web site http://www.cloud.co.uk

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CX2300 I

NSTALLATION AND OPERATION MANUAL

CX2300 Active Filter

Installation and operation manual

Contents

Section Page

1 Introduction ................................................................................................1

2 Active Filters and Crossovers.....................................................................2

2.01 Why use an Active Filter/Crossover ? ........................................2

2.02 What are the optimum crossover frequencies?..........................3

2.03 Why 3 pole filters ?..................................................................... 3

1

3 Installation..................................................................................................4

3.01 Installation notes for the experienced installation engineer........ 4

3.02 Mounting ....................................................................................4

3.03 Audio Connections.....................................................................4

3.04 Schematic Diagram....................................................................5

3.05 Power connections..................................................................... 5

3.06 Plug-in Filter Cards ....................................................................5

4 Operation and Controls ..............................................................................6

4.01 Two Way Operation ...................................................................6

4.02 Do I use the 20Hz high pass filter ? ...........................................6

4.03 The Invert Switch .......................................................................6

4.04 The Mute Switch ........................................................................6

4.05 The Gain Controls...................................................................... 7

5 Circuit Description ...................................................................................... 7

5.01 Schematic diagram ....................................................................7

5.02 The Audio Path ..........................................................................7

5.03 The Power Supply...................................................................... 8

5.04 Signal Connections and EMC ....................................................8

5.05 The benefits of balanced interconnections.................................8

5.06 Using the CX2300 with unbalanced equipment..........................8

5.07 40Hz - the minimum frequency. .................................................8

6 How to change the frequency of the filter card. ..........................................9

6.01 Table of resistor values for the filter card ...................................9

7 Technical Specification.............................................................................11

1 Introduction

The Cloud CX2300 3 Way Stereo Active Crossover has been designed without
compromise to operate with very low levels of noise and distortion as part of a high
quality professional sound system. A high degree of security is provided by using fixed
frequency plug-in filter cards together with a tamper proof cover for the front panel. Once
the unit has been correctly installed, no unauthorised adjustments can be made thus
maintaining system integrity and reliability.

Balanced audio connections are used throughout via Neutrik 3 pin XLR type connectors
with gold plated pins. We suggest that balanced interface connections are used wherever
possible, even for very short interconnections to take advantage of the common mode
rejection and freedom from earth loops when wired correctly.

The control layout is very simple and logical with each frequency band having its own
stereo controls for gain, phase invert and mute. In addition, a 20Hz high pass filter can be
switched in or out of the signal path. All these controls and switches, including the power
switch are protected by the security cover supplied with every unit.

Plug-in fixed frequency filter cards determine the frequency characteristics of the CX2300
and these can be specified from the list detailed in section 6.01. To change the frequency
of any filter card, refer to the component list in section 6.01 which gives details of
resistors which should be fitted to the filter card to achieve a particular frequency.

Experienced installers who are fully conversant with the Active filters and
Crossovers skip to section 3 for installation details.

2 Active Filters and Crossovers

2.01 Why use an Active Filter/Crossover ?

Virtually all high quality speaker systems whether domestic or professional use two or
three drivers to cover the whole of the audio spectrum with each driver specially designed
to reproduce a finite frequency range. In most low to medium power speaker systems, a
single full range power amplifier would be used to feed a passive crossover to filter the
signals to the two or three speakers within the full range enclosure. There are several
disadvantages when using full range amplification and passive filters; any differences in
driver efficiency have to be corrected by adding power resistors which is both wasteful
and reduces driver damping; High order passive filters with good attenuation levels are
expensive and inefficient; Any distortion present in the power amplifier is heard across the
whole audio spectrum.

A well designed fully active system will overcome all of the above problems, the sound
quality will be improved and the system will be much easier to set up. In a typical active
sound system, the bass, middle and treble regions would each have their own speaker
drive units which would be wired directly to separate power amplifiers. The bass amplifier
would be the most powerful, the amplifier used for the mid range would be around half the
power of the bass amplifier and the treble amplifier would be around half to two thirds the
power of that of the mid range amplifier.

The active filter/crossover would be used to separate the two or three frequency bands at
line level immediately before the signal connects to the power amplifiers.

Some active filters have adjustable crossover frequency controls which can be useful
when testing the system to determine the most satisfactory frequency but care must be
taken to ensure that any final setting is within the speaker manufacturers specifications.

CX2300 I

NSTALLATION AND OPERATION MANUAL

Once the crossover frequencies have been determined, an active filter with fixed
frequencies determined by plug-in cards may be preferable for a fixed installation.

2.02 What are the optimum crossover frequencies?

A professional sound system should have a useful response from below 30Hz to above
20kHz but this overall response is a function of the design of the enclosures and the
placement within the building and is beyond the scope of this manual. Wherever possible
refer to the manufacturers specification for details of the crossover frequencies. Where no
specific details are available, there are practical guidelines which can be used to
determine the most suitable crossover frequencies for a particular system.

It is common to find multiples of 38cm and 45cm drivers used in low frequency
enclosures where the upper frequency limit of around 800Hz is dictated by a narrowing of
the dispersion and a loss of definition. The optimum upper limit is around 250Hz.

Where cone drivers are used for mid range purposes, the lower frequency limit should be
no lower than double the resonance of the drive unit and should be compatible with the
upper frequency limit of the bass drivers. The upper limit is again dictated by a narrowing
of the dispersion and loss of definition. For 30cm drive units the upper limit is 1.5kHz and
2kHz for 25cm units.

3

The high frequency section would normally use horn loaded compression drivers and
manufacturers data would have to be used to determine the most suitable crossover
frequency. A higher frequency than that specified by the manufacturer is often chosen to
improve the reliability of the compression driver's diaphragm. A system compressor/limiter
is also often used to prevent clipping of the power amplifiers output waveform which can
cause premature destruction of the diaphragm(s).

If compression drivers with horns are used to handle the high frequencies, it is common
practice to improve the ultra high frequencies by adding horn loaded tweeters to the same
circuit by using passive filters usually at frequencies above 5kHz.

2.03 Why 3 pole filters ?

When designing the CX2300, we were mindful of the requirement that the unit should
sound good. It is generally accepted that odd order filters sound more musical than their
even order counterparts and our own tests confirm this. The use of third order Butterworth
filters gives a high 18dB/octave roll off which relates to a power reduction of 85% per
octave.