PAVA System Variations

There are many different manufacturers of Public Address and Voice Alarm systems and consequently many different designs.

Deciding on the type of system best used in any particular environment can be determined either by the client or by B.L. Acoustics.

The type of system wanted can have dramatic consequences on the cost of both the system itself and the installation.

Great care must be taken when making these decisions.

B.L. Acoustics has the advantage of understanding and choosing from many different system manufacturers to offer the best solution.

 Here are just a few designs detailing their advantages.

Centralised System

Figure 1 shows a typical Voice Alarm System which uses a high frequency tone to monitor the presence of equipment. The tone, which is a high enough frequency not to be heard is fed through the loudspeaker lines to the end of line modules, these then report back to the fault monitoring panel to confirm they are still intact.

Likewise the Fire Interface, Fireman’s Microphone and the Security Microphone generate the same high frequency signal which is detected by the Audio Routing Matrix and then reported to the fault monitoring panel.

This is an extremely reliable system but loudspeaker lines cannot be spurred off and cable installation can be expensive if required over large sites as all the lines arrive at and originate from a single source i.e. the equipment rack.

De-Centralised System

The system detailed below in Figure 2 works on an entirely different principal in that it is comprised of multiple stations which are linked together in a ring, each of which provides amplification to their own respective area.

Each station is networked via a single cable enabling information to travel in both directions.

If the link were to become detached at a single point, the information would communicate from the other direction upholding the system integrity.

Microphones and interfaces can be integrated at any station.

This system has a high degree of integrity and provides an ideal solution for larger buildings or sites with multiple buildings and avoids the huge cost of loudspeaker cabling to a central source.

In addition to the two main concepts shown above, there are many different ways in which the systems internal functions can operate.

These also have a bearing on the overall costs and abilities of the systems.

The Programmable Audio Routing Matrix

The programmable audio routing matrix allows any mic or line level inputs to address any configuration of the outputs, predetermined by the programming of the processor.

The buttons on the microphone or contacts from the Fire Panel will simply initiate the programmed route for the audio to take.

Each input can be programmed with a priority level.

This system is very flexible but is generally more costly.

Output Relay Selection

Output Relay Selection is a simple and low cost alternative used for Public Address systems.

This cannot be used for Voice Alarm.

The inputs can sometimes be prioritized providing a hierarchy structure to the building.

Inputs are switched using either dry contacts or low voltage and the zone selection, once set, cannot be easily reconfigured.

Input Output Mixer Modules

This type of mixer can be programmed using internal hard wired settings such as removal link configurations.

This enables a fairly flexible but low-cost solution for Voice Alarm Systems.

However, each module can only be programmed with one configuration. Reconfiguration of the programme can be difficult and may require lengthy site visits from qualified engineers.

Programmable Input Output Mixer Modules

This system is similar to the system shown above but has the added advantage of being programmable.

This provides for less service time if the programme were to require change, although would still require an engineer to attend site.

Surveillance Variations for Monitored Systems

Differences in the type of monitoring used can affect the cost of the loudspeakers and the installation.

In addition it will determine the flexibility of the loudspeaker cabling routes.

Monitored Tone

This type of monitoring uses either a high 20kHz or low 30Hz frequency which cannot be heard over the loudspeakers.

The signal is sent via the amplifier down the line and received by the end-of-line monitor.

When the monitor receives the signal it generates its very own signal and sends it back down the line to the amplifier.

The signal that is sent back is recognized by a detection unit and reports OK.

If the signal path is broken or shorted against anything, the end-of-line monitor will report a different type of signal which the detection unit can recognize as a particular type of fault.

The surveillance signal can either be continuous or pulsed but pulsed is a preferred option because the amplifiers need to be active to send the signal through, and if they are only active for brief periods then the amplifiers are more energy efficient.

This type of monitoring does not require capacitors fitted to loudspeakers but does require an earth return wire.

The loudspeaker cables do not need to return back to the central equipment and cannot be spurred off into other circuits.

Faults on individual loudspeakers are not always detected although this is not normally a problem if the system is regularly maintained.

Residual Current Detection

Residual current monitoring relies on a current window set by the detection unit and a current generated by the end-of-line module. If anything should change on the line causing fluctuations in the current then a fault will be detected.

The advantage of this system is that it will detect faulty loudspeakers but the disadvantage is that many non-serious anomalies can be detected giving rise to unnecessary call outs and therefore cost.

Impedance Monitoring

This system again uses a high frequency signal fed via the amplifier and the detection unit monitors the impedance measure from the loudspeakers and cables.

A window is set on the detection unit and if the measured impedance moves outside of that window a fault is detected.

This system has the advantage of not requiring end-of-line modules and the loudspeaker circuits can be spurred.

The disadvantage is that in order to reduce the amount of unnecessarily reported faults, the window quite often needs to be set such that faults that do occur are not detected until there are several other faults also.

Direct Current ( DC ) Monitoring

A DC voltage is injected onto the loudspeaker line and at the end of each line a fixed restive value is added to total the amount that the detection unit is expecting to see.  The system will detect line failures reliably but will not detect loudspeaker failures.

The advantage of this system is that a number of spurs can be used — typically a maximum of eight.

The disadvantage is that the system requires capacitors to be fitted to each loudspeaker, this can add a slight cost to the loudspeakers and can cause problems when using noise masking systems, as the capacitors also act as a filter at certain frequencies.

Frequency Doubling

This is a very reliable system but is not commonly used.

A 20kHz signal is fed via the amplifier to a unit at the end of the line which then converts the signal into a much higher frequency and sends it back to be detected by the detection unit.

This system cannot be used with spurred circuits.

To know what system would suit the requirements of your business, B L Acoustics can provide non-obligatory quotes.