We have an exciting opportunity for a Field Service Technician to join our team. B.L.Acoustics Ltd operate within multiple areas of the audio industry but primarily within the Public Address & Voice Alarm sector.

We are looking for an enthusiastic and well-organised individual who has an aptitude for fault finding, diagnosing and resolving technical problems. You will deal directly with customers and attend a variety of different sites across the UK. This is a full-time position (Monday to Friday) and requires work to be carried out outside the company‘s core hours. This includes night or weekend work, allowing the applicant to earn substantially more than their basic wage.

The successful applicant will receive on-the-job training on the various systems we maintain. An interest in audio systems or similar electronic systems would be preferred, and experience from other industries in communications and electronics will be considered.

Area of Responsibility & Key Activities

– Service and maintenance of PAVA systems

– Reactive maintenance of PAVA systems

– System upgrade works and system programming

– Providing visit/fault reports

– Basic acoustic measurement and analysis

– System installation

– Out of hours working and call out cover on a rota basis

Education level and/or relevant experience(s)

– Relevant engineering qualification would be preferred but not required

– Full UK driving license

– Good IT skills

Personal qualities (general and technical)

– Strong fault-finding skills

– Able to lead from the front with a visible ‘can do’ attitude.

– Self-motivated and able to work without full supervision

– Strong numeracy and literacy skills

– Personal drive and determination to achieve success.

– Must have a confident and professional manner in front of customers.

To apply, please click here: https://www.linkedin.com/jobs/view/2644825883

As incumbent maintainers and installers of the PAVA Systems at the ICC Birmingham, BL Acoustics were engaged to further upgrade the Voice Alarm systems for the newly refurbished Symphony Hall.

The specification required high-performance Music Routing for the Performance Spaces and Bars by utilising the existing sound systems where possible.

Music was routed via the Bosch Voice Alarm system using Symetrix AV Processing Controllers.

For the main Performance Space, we installed four HK Audio VORTIS 2 EN54 rated Loudspeakers providing a powerful & superb quality sound in combination with the Bosch Praesideo Voice Alarm Amplification.

Fourteen music inputs were distributed throughout Symphony Hall providing a great deal of plug and play flexibility with the Symetrix System routing any input to any output.

Input panels were constructed using the single gang MK Edge Brushed stainless panels as the standard. We would implement the use of two types of panels; one would have a single XLR input and the other a 3.5mm mini jack input.

Flexible Control

The Symetrix ARC-3 Control Panel provided simple control of each input panel/music source to multiple zones throughout the Symphony Hall Foyers and Performance Spaces.

Design Verification & Modelling

The expansion included the fitting of new bars in each of the lobby areas on Levels 3, 4, 5 and 5A, a new performance space and 2 hospitality rooms on level 5A.

As part of the project, we were commissioned to design and install voice alarm coverage to the acoustically unique space, specifically the performance area with its high open ceilings and full length glass exterior wall which presented significant challenges to intelligibility. Being integrated with the Voice Alarm system, the project specification necessitated the use of EN54 approved loudspeakers only.

Before we could commence physical works, Computer Simulated Modelling of the prime areas for new coverage needed to be carried out to give evidence of design and to plan the equipment and cabling requirements. A computer model (Catt Acoustic 9) was used to create the three-dimensional environment which was then compared in performance to the specified requirements.


The specification gave a target of band ‘G’ 0.48 STI or better for 80% of the area exceeding 85dBA.


Our model implemented surfaces that were approximated to the surface types used in the building. These would provide prolonged activity for sound in terms of reverberation. We distributed the reflective and absorptive surfaces accordingly and checked the reverberation levels were in line with what would be expected for the space.

               The Model

Our Catt model was a complete model of all areas. This enabled us to model a large number of options, should they be required. The model was run several times to see the most optimum position and direction of the speakers.


               Proposed System Performance

As stated in the specification, the system was expected to meet band G in 80% of the spaces. The most acoustically challenging space, as afore mentioned, was the performance area. Here, we specified 4 high power cabinet speakers capable of delivering the sound pressure levels and performance required to give clear coverage across the atrium.

For the Hard of Hearing

The Performance Space on Level 4 was fitted with a large 16m x 12m Seven Segment Induction Loop powered by UNIVOX Audio Systems. This was installed beneath the oak floor so as to be undetectable. An audio feed was provided to the loop from the PAVA rack BL Acoustics were installing in Hall 2. This would enable both audios from the Performance Space systems and from the Emergency PAVA to be transmitted onto the loop.


The installation exceeded the clients’ expectations and offered a massive cost saving by utilising much of the already existing amplification and loudspeakers.

B L Acoustics are proud to add another notch to our belt, having successfully completed the replacement of the public address and voice alarm systems at the (formerly named) Arena Birmingham. The old systems were replaced with Bosch Praesideo EN54 compliant systems communicating via a site-wide optical network installed and designed by BLA.

Utilita Arena Birmingham is an indoor arena and sporting venue with a capacity for 15,800 people. Each year (excluding lockdown), the venue hosts over 100 live events and welcomes half a million visitors through its doors. In 2018 the venue underwent a major renovation with remodelling of the concourse areas and public realm.

A site maintenance visit highlighted several issues with the site’s PAVA system. The main issue was the lack of audibility in certain areas during an evacuation, particularly the main concourse area. The audibility problems were caused by a combination of high noise levels from the smoke extract fans and unsuitability of the loudspeakers installed as part of the renovation project

B L Acoustics have been maintaining the systems at the ever-developing site for many years which helped us to acquire substantial site-specific information which proved to be valuable throughout the complex installation. This benefit enabled us to recognise that maintenance visits before 2019 continued to report existing and new issues across the system with some components beyond their recommended life.

Our Proposal

A solution was designed for the problem areas and modelled using acoustic modelling software. More suitable loudspeakers and an improved layout was proposed and installed to produce much improved audibility even when the smoke extract was running. The increased power requirements of the new loudspeaker layout design had an effect on the rest of the system as higher power loudspeakers require more amplification, and more amplification requires higher capacity battery support. 

Our proposal offered replacement equipment which would have the capacity to support the improved loudspeaker coverage throughout the building.  This would include the installation of a new high integrity fibre cable network between each of the equipment locations.  As well as changing the loudspeaker layout in the concourse areas, each voice alarm loudspeaker across the site was upgraded to new EN54 variants.

During the operation of the aforementioned fans, the SPL level would need to be a substantial level, which would be too high for normal PA announcements.  The system includes for ambient noise sensing in the concourse areas to allow the full potential of the system to be used when the fans are operational but keeps PA announcements at a comfortable level during normal operation.

One of the major priorities our client expressed was that the systems could remain in full use throughout the replacement process. The venue is an extremely busy one, meaning that downtime of the system would have been unacceptable and hazardous to life safety.

System Replacement

The completed project was a result of thirty days/nights of work, involving multiple phases of installation, commencing with the fitting of a new resilient loop in fire-rated cable across the site. To ensure the site remained operational throughout the installation process, temporary audio and control links were fitted between the new and existing systems so that both systems could operate concurrently while circuits were switched over from the old system to the new.

Microphone Panels

The old system had both emergency fireman’s microphone and paging microphone units located in various positions throughout the site. B L Acoustics provided replacement units and in the case of the fireman’s microphone provided re-engineered panels which were custom-built to fit their location.


Choosing loudspeaker types was critical to the project with tight specifications to provide key criteria:
– EN54 Compliance
– Acoustic Performance
– Aesthetics
– Programme Windows
All loudspeakers were replaced to meet the latest EN54 standards; compact Bosch ceiling loudspeakers were utilised in most areas.

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.