Audio Frequency Induction Loop Amplifiers
AudioFrequency
Induction Loop Amplifiers
Incorporating:
Amplifier Type A,i.e. the PDA200/2
Amplifier Type B, i.e. the PDA500/2
Amplifier Type C, i.e. the PDA1000/2
Audio Extension System, i.e. the Outreach Plates
Induction Loop Tester, i.e. the FPRO
Audio Signal Generator, i.e.the FPROSG
Consultants Specification
Approved Document No. DFS1000000 Rev 1
CONTENTS
1Scope of work......
2STANDARDS AND regulations......
3Planning the system......
4Amplifier features / SPECIFICATION......
4.1Rear Panel Components......
4.2Front Panel Components
4.3Supplementary Specification......
5audio extension system
5.1Input Plate Variants......
5.2Output Plate Variants......
6Installation
7Commissioning / Testing......
8maintenance......
9Documentation......
1Scope of work
1.1Todesign, supply, install, test and commissionthe following equipment which shall form part of an audiofrequency induction loop system (AFILS):
1.1.1Induction loop driver, i.e. amplifier.
The amplifier shall provide the following coverage:
Amplifier Type A – provide coverage for areas up to 200m2
Amplifier Type B – provide coverage for areas up to 500m2
Amplifier Type C – provide coverage for areas up to 900m2
1.1.2Audio extension system.
1.1.3Induction loop tester c/w audio signal generator.
1.1.4Spares and accessories includingamplifiers and mounting kits, induction loop cable, audio extension systemplates, induction loop testingequipment and induction loop ancillaries.
2STANDARDS AND regulations
2.1Where applicable, the induction loop amplifier shall comply fully with the following British Standards and/or other nominated rules and regulations. The equipment manufacturer shall confirm compliance with the standards.
2.2The equipment manufacturer shall be approved to BS EN ISO 9001 quality system standard for the design and manufacture of the equipment.The product shall be manufactured in conformance with the requirements of all applicable EU directives.
2.3The amplifier shall be designed to comply with BS 7594 - Code of practice for audio-frequency induction-loop systems (AFILS).
2.4A 400mA Induction Loop Tester, shall be used to test the AFILSin accordancewith BS EN 60118-4 (Magnetic field strength inaudio frequency induction loop systems for hearing aid purposes).
2.5Installation practices shall conformto the current edition of BS 7671 (IEE Wiring Regulations).
3Planning the system
When planning the design of the induction loop system, the Contractorshall carry out a site assessment observing the following best practise:
3.1Area of Coverage
Refer to section 4.3.2 for maximum area of coverage provided by the amplifier.
3.2Loop Cable Selection
Single core, tri-rated, cable with appropriate DC resistance (ideally 0.5 to 1 ohm) shall be used for the induction loop.The thickness (CSA) of the cable for different cable lengths shall be calculated thereby avoiding risks of distortion and overheating. Flat loop cable shall be provided for under carpets and other floor coverings.
3.3Loop Cable Position
The loop shall be installed above (or below) the listener at floor level or ceiling height to attain the optimum field strength in the plane of the loop (the height at which the cable is positioned).Note that the listening plane for seated listeners is conventionally taken as 1.2m above floor level and that for standing listeners as 1.7m above floor level. Where a single plane height is required for design purposes, it shall be taken as being 1.45m above floor level, and the resultant design shall be checked for heights of 1.2m and 1.7m.
Running loops along girders or under floor mesh shall be avoided in order to maintain the strength of the loop field.
3.4Overspill and ‘cross-talk’
The signal generated by the loop will radiate outside as well as inside the loop. If there are other loop systems in close proximity, overspill such as this may lead to ‘cross-talk’ (signals from different loops merging into one). If this is likely to be an issue, special designs of loop shall be implemented to help reduce the magnetic overspill field.
3.5Trial Loops
Trial loops shall be run to evaluate performance and coverage by listening to the signal with a hearing aid or a dedicated loop test receiver. Before installation, the Contractor shall provide evidence that the magnetic field strength of the proposed system meets the required standard.
For compliance with BS EN 60118-4, magnetic field strengthsshall be measuredusing aninduction loop tester, as detailed in section 7.2.
3.6Background Noise & System Noise
Tests shall be performed to ensure that background and system noise levels in the areas designated for loop coverage do notaffect the intelligibility of the system in the covered area.Background noise measurements shall be taken before the system is installed and system noise measurements shall be taken after the system is installed.
For compliance with BS EN 60118-4, noise levels shall be measuredusing aninduction loop tester, as detailed in section 7.2.
3.7Effects of Metal
Large amounts of metal can affect the strength of the loop field therefore, before installation, evidence shall be provided that the loop design has taken into account the effect of metal within the structure of the building(s).
For compliance with BS EN 60118-4, metal compensation shall be measuredusing aninduction loop tester, as detailed in section 7.2.
4Amplifier features / SPECIFICATION
4.1Rear Panel Components
The amplifier shall incorporate the following components, as a minimum:
4.1.1IEC 230Vac Mains Connector c/w On/Of ToggleSwitch
A singleIEC-320 type fused power lead shall also be supplied.
4.1.2Mains Fuse
Theamplifier shall feature an IEC (EN60127 part 2) compliant mains fuse, as detailed below:
- Amplifier TypeA: 2A T 20mm anti-surge ceramic HRC type
- Amplifier TypeB: 3.15A T 20mm anti-surge ceramic HRC type
- Amplifier TypeC: 5A T 20mm anti-surge ceramic HRC type
4.1.3Cooling Fan(provided onAmplifier TypesBConly)
A thermostatically controlled fan shall operate automaticallywhen the temperature ofthe amplifier’s internalheat sink reaches approx.56oC.
4.1.4Induction Loop Connectors
Four-way, heavy duty, binding posts shall accept bare wire ends, 4mm plugs or spade terminals as required.
4.1.5Mic. Input
A single input shall accept standard three-pin male XLR type connectors.Optional 12V phantom power shall be available via Input Mode Select Switch 2.
- Mic. input impedance: 1k ohm + or – input to ground
- Mic. sensitivity: 1 to 8mV balanced
- Mic. phantom power: 12V switchable (on/off)
4.1.6Mic./Line Input
A single input shall accept standard three-pin male XLR typeconnectors. Shall be switchable between Mic. orLine operation via Input Mode SelectSwitch 3.Optional 12V phantom power shall be available via Input Mode Select Switch 1.
- Mic. input impedance: 1k ohm + or – input to ground
- Mic. sensitivity: 1 to 8mV balanced
- Mic. phantom power: 12V switchable (on/off)
- Line input impedance: 1k ohm+ or – input to ground
- Line sensitivity: 200mV to 2.5V RMS balanced or unbalanced
- Line phantom power: 12V switchable (on/off)
4.1.7Audio Extension System Input
A single, four-way Weidmuller connector. Plug type BL5. 08/4.
- Input impedance: >10k ohm
- Sensitivity: 315mV to 6V RMS balanced
- Power: 16 to 21Vdcshall be available via the amplifier’s connector. A self-resetting fuse shall protect this output from accidental overload
4.1.8Input Mode Select Switch
A single, four-way DIP switch, shall allow the Mic./Lineinput to be configuredfor either Mic. or Line operation and for optional 12Vphantom power to be switched to the inputs. The switch shall have the following configuration:
SW / OFF (Up) / ON (Down) / XLR Input1 / 12V phantom OFF / 12V phantom ON / Mic./Line
2 / 12V phantom OFF / 12V phantom ON / Mic.
3 / Line operation / Mic. operation / Mic./Line
4 / Switch 4 shall have no function
4.2FrontPanel Components
The amplifiershall incorporate the following components, as a minimum:
4.2.1Model Number Label
Shall indicate the modelnumber of theamplifier.
4.2.2Loop Drive Control
A single level control shall be used to adjust the strength of the magnetic field generated by the inductionloop.
4.2.3Metal Compensation Control
A single level control shall be used to help counteract the frequency dependent absorption by metal in the proximity of the installation.
When turned fully anti-clockwise shall have no effect on the signal. When turned clockwise shall impart a rising 3dB/octave characteristic to the frequency response of the amplifier over a bandwidth of approx. 100Hz to 10kHz.
4.2.43.5mm Loop Output Monitoring Socket
Shall allow the loop current/audio signal that is present in the induction loop to be monitored using a pair of 32 ohm headphones.
4.2.5Input Signal Level Controls
Three separate level controls shall be used to adjust the sensitivity ofthe three input signals, i.e. Mic. Level,Mic./Line Level and Audio Extension System Level.
4.2.6Power Indicator
A single LED shall illuminate steady green when the amplifier is powered up.Shall flash green when in shutdown mode.
4.2.7Loop Strength (Drive) Meter
Shall provide a visual indication of the current being driven into theinduction loop.
A five LED bar graph type metershall monitor the true output current rather than from a linelevel derived signal. The calibration is as follows:
- Amplifier Type A: 1st LED - 1.4A, 2nd LED - 1.9A, 3rd LED - 2.7A, 4th LED - 3.8A, 5th LED - 5.4A
- Amplifier Type B: 1st LED - 1.9A, 2nd LED - 2.7A, 3rd LED - 3.9A, 4th LED - 5.5A, 5th LED - 7.7A
- Amplifier Type C: 1st LED - 2.4A, 2nd LED - 3.4A, 3rd LED - 4.8A, 4th LED - 6.7A, 5th LED - 9.5A
4.2.8Compression Indicators
A two LED display shall provide a visual indication of the amplifier’s signal compressor activity.
The first LED (LOW) indicates the beginning of compression whilst the second LED (HIGH) indicates very high compression levels have been reached.
Compressor Attack Time: approx. 5mS. Compressor Release Time: approx. 2.2 sec.
4.3Supplementary Specification
4.3.1Power
230Vac Mains supply.
Amplifier Type A <150VA; Amplifier Type B <225VA; Amplifier Type C <300VA.
4.3.2Coverage
The table below gives the amplifier’s maximum area of coverage for a 400mA/m field strength ± 1dB.
Model / Area of CoverageSquare / Rectangular
(2:1 aspect ratio)
Amplifier Type A / 200m2 (14m x 14m) / 240m2
Amplifier Type B / 500m2 (22m x 22m) / 600m2
Amplifier Type C / 900m2 (30m x 30m) / 1100m2
4.3.3Performance
Frequency response: 50Hz to 6.3kHz ± 3dB.
Total harmonic distortion: Less than 0.5%.
Signal-to-noise ratio: Better than –65dB any input.
4.3.4S/C Protection
In short–circuit condition, the amplifier shall disconnectthe amplifier’s output drive from the rest of circuitryand the single Power indicatorshall flash.
At maximum current output, the S/C protection will activate when the amplifier detects the following load:
- Amplifier Type A: 0.2 ohm
- Amplifier Type B: 0.3 ohm
- Amplifier Type C: 0.42 ohm
4.3.5Dimensions & Weight
Dimensions (including controls) = 80mm (H) x 380mm (W) x 220mm (D).
Weight: Amplifier Type A = 3.74kg, Amplifier Type B = 3.46kg; Amplifier Type C = 4.54kg.
4.3.6Loop Specification
Type: Current mode.
Loop connector: Four-way binding posts.
Cable type: Single core, tri-rated, cable with appropriate DC resistance (ideally 0.5 to 1 ohm).
Recommended loop impedance: 0.5 to 1 ohm @ 1kHz. Will drive higher impedance loops with reduced area of coverage.
Loop drive current @ 1 ohm:
- Amplifier Type A = 4.7 amps
- Amplifier Type B = 6.3 amps
- Amplifier Type C = 10.5 amps
Undistorted max. loop drive current (measured over 5mS integration time):
- Amplifier Type A = 6.6 amps @ 1 ohm, 9.2 amps @ 0.5 ohm
- Amplifier Type B = 9 amps @ 1 ohm, 14 amps @ 0.5 ohm
- Amplifier Type C = 14.8 amps @ 1 ohm, 25 amps @ 0.5 ohm
5audio extension system
In addition to the amplifier’s two XLR inputs (Mic. and Mic./Line Input), multiple microphoneand/or line level inputs shall be connected to the amplifier via arange of specially designed wall, ceiling or desk mounted single gang plates.
Several different audio extension system plates shall be available covering the most common variants of audioconnectors. Total cable lengths shall be up to 100m usingstandard two-pair audio cable such as Belden 8723. Afour-way audio extension system connector shall be included in the amplifier’s accessory pack.
Audio extension system plates shall be mountable on 25mm surface back boxes, and shall be located at any convenient point on the installation, overcoming the need for excessively long microphone or audio leads.
5.1InputPlate Variants
The followinginput plates for the audio extension system shall be provided, as a minimum:
5.1.1Omni-Directional Plated Microphone
A self-contained omni-directional electretmicrophone complete with onboard mic.to line level converter. Typical coverage upto 25m2 (ambient) or 2.5m2 (direct speech)when located at ceiling height of 2.5 to 3m.
5.1.2Dual Phono Line Level Plate
Shall accept stereo phono line-level signals(typically from a stereo source such as a TV,CD or DVD). Shall include an on-board stereoline to mono converter.
5.1.33.5mm Jack Microphone Plate
Shall accept unbalanced electret microphoneswith 3.5mm mono jack plugs. Shall include anonboard mic. to line level converter, highgain pre-amplifier and 11V phantompower.
5.1.46.35mm (1/4”) Jack Microphone Plate
Shall accept balanced or unbalanced electretmicrophones with 6.35mm (1/4”) jackplugs. Shall include an on-board mic. to linelevel converter, high gain pre-amplifierand 11V phantom power.
5.1.56.35mm (1/4”) Jack Line Level Plate
Shall accept 6.35mm (1/4”) jack feeds fromaudio equipment such as stage, or mixing desks, etc.
5.1.6XLR 3 Pin Microphone Plate
Shall accept balanced or unbalancedmicrophones with standard 3 pin maleXLR connectors. Shall include an on-boardmic. to line level converter, high gainpre-amplifier and 11V phantom power.
5.1.7XLR 3 Pin Line Level Plate
Shall accept standard 3 pin male XLRfeeds from audio equipment such asstage, or mixing desks, etc.
5.2OutputPlate Variants
The following output plates for the audio extension system shall be provided, as a minimum:
5.2.1XLR 3 Pin Balanced Line Output Plate
Shall provide an adjustable balanced lineoutput (+12dB max.) on a standard 3pin male XLR connector. Typicallyused to connect tothird-party audio equipment such asconventional amplifiers.
5.2.2‘AFILS Active’ Plate
Shall include two ultra-bright LEDs in atranslucent diffuser overprinted withthe AFILS ‘ear’ symbol. The LEDs shall illuminate when the audio extension system is powered to indicate thatan AFILS system is installed.
6Installation
The equipment shall be installed by a suitably skilled and technically competent person. The specialist AFILSContractor shall:
6.1Install the equipment in accordance with BS 7594, BS 7671 and BS EN 60118-4.
6.2Install the amplifier as a free-standing unit on a shelf, tabletop or desk, or,alternatively, wall or rack mounted using an optional 19” rack mounting kit or wall-mounting kit.
6.3Ensure the amplifier is not located in areas with high ambient temperatures or high levels of humidity, moisture or dust. In all cases the amplifiershall be operated in a cool environment, away from sources of heat and shall never be covered with any object that could impede the flow of cooling air.
6.4Ensure adequate access space is provided around all AFILS equipment that is likely to need routine maintenance.
6.5Install loop cable in rigid plastic tube.
6.6Follow good audio practice to ensure all necessary equipotential and supplementary earth bonding conductors and connections to each component or item of equipment.Arrangements for earthing shall be in accordance with the manufacturer’srecommendations.
6.7Wire and connect to all items of equipment in accordance with the manufacturers’ recommendations.
6.8Ensure all cables are clearly identified. The locations of cables and joints shall be accurately recorded for future reference.
6.9Co-ordinate with other relevant contactors to ensure that all appropriate audio signals and cabling/connection points are connected to the induction loop system for system integration.
6.10Provide signs in accordance with BS 7594 to indicate areas where an AFILS is installed.
7Commissioning/Testing
7.1The current standard BS EN 60118-4 recommends that the achievable magnetic field strength of an AFILS over a ‘covered area’ shall be 400mA RMS per metre.An induction loop tester shall be used to set up and test the AFILS for compliance tothis standard.
7.2Theinduction loop tester shall have the following features, as a minimum:
- magnetic field strength measurement, 400mA/m at 0dB, range -22dB to +8dB
- background noise measurement, range -42dB to -32dB
- metal compensation measurement
- frequency responsemeasurement (shall detect 100Hz, 1kHz and 5kHz)
- a digital LCD with contrast controls and battery life indication
- two ‘soft’ buttons whichshall change their functions to suit the menu options being accessed
- auto power-off feature
- 3.5mm jack socket,shall allow audible monitoring using 32 ohm headphones
- powered by a 9V PP3 battery (supplied)
- full set of user instructions, test and calibration certificates
7.3In addition, an audio signal generator shall be available with the following features, as a minimum:
- transmit tones to test magnetic field strength, frequency response and metalcompensation, plus music and voice tracks to assist with subjective testing
- a digital LCD with contrast controls and battery life indication
- two ‘soft’ buttons which shall change their functions to suit the menu options being accessed
- auto power-off feature
- 3.5mm jack socket; for balanced line level audio output
- powered by a 9V PP3 battery (supplied)
8maintenance
8.1Periodic inspection and maintenance of the system shall be carried out inaccordance with national, regional or local standards. In the UK the relevant standard is BS 7594.
8.2The corrective works shall be carried out by a competent person with specialised knowledge of AFILS design, adequate access to spares and sufficient information regarding the system. This is normally a third-party AFILS maintenance organization.
9Documentation
9.1On completion of the system, a complete set of documents, as detailed in BS 7594, shall be provided to the user including the following:
- Operating and maintenance instructions
- ‘As fitted’ drawings showing the position of all AFILS equipment and loop cables
- Certificates of design, installation and commissioning
- Log book to record periodic testing of the system
Consultants SpecificationApproved Document No. DFS1000000Page 1 of 10