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16 August 2022
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Formula Sound identified a need for a unit to assist audio system managers in public places to comply with Fire Officer’s requirements. This was so as to avoid panic when a fire alarm activates, the programme level in the venue should be reduced and not cut altogether, and that a mic override should provide one guaranteed microphone input to the system. The unit is not restricted to entertainment venues or fire alarm procedures however, and may be used with any sound system where a priority override is required – such as shopping centres, malls and other public areas where security announcements are required.

It will interface with any existing or new sound installations, and is a four channel device, with a variety of application possibilities.

The Guardian has been designed to be connected between the mixer (or pre-amp) of an audio system and the power amplifiers. The unit may be connected to 4 channels of audio, normally 2 stereo pairs. The priority input (e.g. DJ microphone) may be at mic or line level (as selected by internal switch), with phantom power now available on the Mk3 version.

The control input is connected to the fire alarm or whatever triggering method has been decided. When the unit is triggered, the programme level in all four channels will be attenuated and the priority input automatically mixed into all four outputs. Eight controls are provided - 2 controls to set the initial sound level of channels 1-2 and 3-4; 2 controls to set the priority attenuation level of channels 1-2 and 3-4; 2 controls to adjust the priority input level into channels 1-2 and 3-4; 2 controls to set a separate dim level for channels 1-2 and 3-4, independently for each stereo channel (useful for use with window and door sensors to temporarily dim the output level when open windows or doors could pollute the outdoors). These are only accessible by removing the security front panel. Test and reset buttons, operational through the small holes in the front panel, are provided for initial setting up and testing.

Two modes of reset, auto and manual are determined by the reset button. This is a latching push-button, the position of which sets the reset mode. If left in the out position reset will be manual. That is to say when the control signal is removed the unit will not reset until the reset button is depressed. If the button is left in the depressed position the unit will automatically reset when the control signal is removed. When the unit is reset the programme will fade slowly back to the original volume. Balanced inputs and output are provided which may be strapped unbalanced with no signal loss and optional output transformers may be fitted.

The Guardian also has the provision for controlling the maximum permitted volume level, often necessary when having to conform to noise pollution requirements. The unit monitors the level in channels 1 and 2 and if this combined level exceeds an internally set threshold a limit warning lamp illuminates. If the level is reduced no action is taken. If the lamp is illuminated continuously for 6 seconds the limit will be activated. This turns the programme level down to the attenuated level (as set by the attenuation controls) for approximately 10 seconds, and has a 10 second fadeback time. The unit will keep returning to the attenuated level until the operating level is reduced to below the threshold. Limit may be disabled by adjusting the internal threshold preset to a sufficiently high level. Peak limiting, relative to this, is also provided at a much faster speed, to protect from transients. The limiting threshold and peak threshold each have a preset control under the front panel. LED indicators of PEAK, LIMIT and PRIORITY are on the front panel and an output socket is provided on the rear for remote indicators.

Technical Specification:

Connectors: Audio inputs and outputs 3-pin XLR.
Priority control input and remote indicators output 6 way screw-terminal connector.
Visual indicators: Power, limit warning, peak warning, priority override.
Parallel remote output will drive solid state relays for external sign switching.
Audio path: Unity gain, 20Hz-30kHz ±0.5dB.
Distortion <0.015% THD at 1kHz +20dBu.
Input impedance >30k ohms, max. input level +22dBu. Output impedance 100 ohms, max. output before clipping +22dBu into 600 ohms.
Priority input: Mic/line internally selectable balanced low impedance mic, gain 15dB-70dB. Phantom power internally selectable. Priority input socket is connected directly to priority output socket until the unit is triggered by the control input, then it is connected to all channels as set by the level control presets, and disconnected from the priority output socket.
Control input: 15-24V DC applied to or from trigger (voltage mode), Isolated switch contacts, NO or NC (switch mode)
Noise Limiter: Level sense taken from channels 1 and 2.
Limit threshold adjustable from –20dBu to +22dBu. Jumper allows faster action if required. Peak threshold limiter adjustable relative to standard limit threshold (fast-acting limiter for peak protection).
Attenuation: Adjustable override, 0 to -60dB on ch 1+2, 3+4. Adjustable dim, 0 to -11dB on ch 1+2, 3+4.
Power: 110-115V or 200-240V AC (switchable), IEC connector.
Dimensions: 1U 19 inch rack mounting x 206mm deep.
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FORMULA SOUND GUARDIAN CX4 Mk3 Stock code: 42-665
Ordered on demand, cancellations may incur charges, available in 2‑3 working days. Need it sooner? Call us