ASL Underground

For the ultimate in acoustic challenges, ASL provides the ultimate in reliability. Our systems can be configured to meet the unique acoustic demands of even the longest tunnel, to deliver intelligible speech when it matters.

ASL systems provide clear communication in tunnels and offer a wide range of proven products and solutions that deliver supreme levels of reliability in an application where there is no room for compromise on safety. ASL’s high quality audio circuits and digital signal processing provides precise time delays and delivers clear audio. The PAVA systems provide status data for Remote Condition Monitoring, while ASL’s iVENCS Control Systems can monitor and control your assets throughout the tunnel.

ASL keeps travellers informed and safe, even when hundreds of metres underground.

  • Security staff can inform
  • Fire and emergency staff can protect

Tunnel Management

The ASL PAVA equipment provides remote condition Monitoring by pushing system status information to the tunnel’s SCADA monitoring and control system.

Alternatively, ASL’s iVENCS Control System can be used to provide full control and monitoring of all of the tunnel’s assets. iVENCS can provide automated and manually controlled PA and visual display messaging, control the CCTV, answer help points, and enable the management of the tunnel from one or more workstations.

Loudspeaker Audio Delays

ASL’s VIPEDIA-12 router is specifically designed for use in tunnel installations. The router offers equalisation on every output, and can provide up to 60 seconds of configurable audio delay. Delaying the signal to each speaker in turn along the tunnel provides time-alignment of the audio from each of the speakers, by matching of the speed of sound propagation along the tunnel. This provides clear audio, with minimised reverberation effects.

The routers can be connected via fibre optic cables, and can be placed up to 2,000m apart when used with multi-mode fibre, or up to 10,000m apart with single-mode fibre.

Peace of Mind

With more than 25 years experience of designing and developing Public Address and Voice Alarm products for critical infrastructure applications, ASL offers peace of mind. You can rely on ASL solutions to work, and to continue working, throughout the life of the system.

Our PAVA systems will deliver the message to where it needs to be heard, when it needs to be heard. Long, reliable, product life also means lower ownership costs and low whole life costs.

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Major Tunnels


km of Tunnels


Protected Annually


Remote monitoring and configuration makes the operation and maintenance of ASL PAVA systems easy, even for equipment installed in the most remote and hard-to-reach areas.

ASL's powerful DSP Digital Signal Processing provides sophisticated EQ Equalisation Controls, while DANS Dynamic Ambient Noise Sensors and continuous noise compensation technology enables broadcast intelligibility to be optimised to cater for varying real-time ambient noise levels.
ASL also has high power amplifiers to suit the largest of tunnel horns.

EN 54 is a legal requirement for road tunnel audio systems in Europe. All ASL products are designed around the most stringent safety requirements, including EN54.

ASL’s MPS, SAP and VRMS microphones can be connected over IP. This lowers installation costs as existing network infrastructure can be utilized instead of running additional cables.

ASL's iVENCS Control System provides intelligent artificial messaging. The iVENCS GUI can be translated into different languages, and announcements can be stored and played in multiple languages, including text to speech.

ASL’s microphone user interface is also available in a number of languages, and new languages can be added as required.

To secure the PAVA system and to ensure uninterrupted operation: ASL’s solution supports full encryption and authentication of control and audio data, including 2Factor authentication for tools and configuration management.

Sector-Specific Products

ASL combines close liaison with our customers and end users, technological innovation, and the comprehensive knowledge of our experienced team to tailor our products to industry-specific requirements, and to set new standards with our dedicated industry specific products. A few key examples are referenced below.

Dynamic Volume Control

ASL’s DANS01 dynamic ambient noise sensor enables the PA volume level to be automatically adjusted in real time. These sensors are placed along the tunnel, and feed audio from the tunnel back to the ASL router, where the DSP digital signal processor separates any broadcast audio from the ambient noise. Thus, the volume can be controlled in response to ambient noise, even during announcements.

This ensures the PA audio is intelligible, and also at the most comfortable level that can be achieved, even if the noise level varies widely during a broadcast.

High Power Horn Speaker

ASL’s SPHW-100W-480-EN54 100V weatherproof horn loudspeaker is perfect for tunnels.The horn provides an enormous sound pressure level, providing a maximum average SPL of at least 135dB Pmax/1m which enables intelligible voice announcements over a large area using a minimum number of loudspeakers.

Single Box Wall Mount PAVA

Lower installation costs and a considerably smaller footprint than a typical 19″ rack makes ASL’s powerful but compact wall-mount INTEGRA PAVA system ideal for tunnels where there are regular but small equipment rooms, and installation space is at a premium.

The INTEGRA is based on the same powerful DSP router as ASL’s rack mount systems, and can be fitted with amplifiers for up to ten horn loudspeaker positions, with a maximum total power of 2000W RMS, so small size doesn’t mean low feature or low power. 


The iVENCS Control Software is a truly open and intuitive integrated management platform

iVENCS - Integrated Tunnel Control

ASL’s enhanced iVENCS Site Management System provides integrated distributed control

The iVENCS Control System has recently received an entire technology and GUI upgrade, consolidating its place at the forefront of the management of the public in large sites.

iVENCS is a truly open and intuitive integrated management platform which offers robust control, monitoring and incident analysis across all safety, security and communications subsystems. Plus, in addition to the standard subsystems and functions, iVENCS provides the flexibility needed to provide custom integrations with industry-specific  and site-specific equipment.

The award-winning and unique true 3D GUI can show an accurate, fully scaled model of the whole tunnel complex. The model’s pan, tilt, rotate and zoom controls allow the user to move the viewpoint at will, to any part of the 3D model, and with seamless viewing from any position. This avoids other system’s need to split the GUI into multiple small 2D maps and false-3D plans, requiring the operators to switch between many different maps in order to operate the tunnel’s equipment.


Key Features:

  • Award-winning 3D or traditional 2D GUI
  • System schematics and dedicated subsystem controls
  • Consistent and simple to use functionality, for multiple systems
  • Industry and custom site-specific integrations
  • Remote Condition Monitoring
  • Distributed processing with multi-site redundancy
  • Modular system architecture; easily expandable
  • Cross-platform support
  • No ongoing license costs

Tunnel operators need to monitor an ever-increasing number of subsystems, from fire detection to CCTV, PA to information displays, access control to intruder detection, and far more. ASL’s award-winning iVENCS Control System empowers both managers and operators to simultaneously control a multitude of systems. Via the intuitive 3D user interface, staff can keep a constant eye on the public and on the status of equipment around the site, are able to remotely control devices, and be alerted to any faults and devices that are in need of investigation.

iVENCS makes public and staff communications easier to manage, through auto-scheduled announcements, intelligent message builders, multi-lingual messaging, and information displays.


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