One of the world leaders in Mass Notification Systems, Acoustic Technology Inc. (ATI), has announced the installation of a new emergency public address (PA) system at the Ohio River Bridge East End Crossing Tunnel.
The tunnel is part of the Ohio River Bridges Project that connects Louisville, Kentucky, with Southern Indiana. The tunnel’s new system uses IP (internet protocol) communication to provide safety, evacuation messaging, and emergency services radio re-broadcast systems in the event of an emergency. During emergencies, this system will initially allow for intelligible live PA with the option of adding prerecorded messages at a later date. ATI worked with Canam Technology Inc. (CTI) to jointly provide the tunnels integrated Emergency Alert system. CTI has already developed extensive expertise in tunnel radio for major tunnels, with rebroadcast radio systems for AM, FM, VHF, UHF, 800-MHz and digital in-vehicle equipment.
Achieving reasonable and effective speech intelligibility in a tunnel presents a clear challenge to the design of an adequate PA system. A tunnel environment is highly susceptible to ambient noise and echo, which can significantly affect the performance of a PA system. Ideally, PA speakers should have a wide bandwidth of 125Hz to 8kHz sound wave frequency, and sufficient speaker power to provide sound levels 15dB above the complex tunnel background noise. This performance level is considered to be the minimum required for adequate speech transmission according to NFPA 72.
For this project, ATI designed an innovative acoustic system, the first of its kind in the USA, that uses directional loudspeakers to maximize direct sound to motorists in the tunnel. System equipment includes:
10 outdoor speaker units (OSU);
One speaker inside the tunnel control building to provide an interface to the radio rebroadcast system, allowing system operators to override the radio channels of motorists in the tunnel;
Five speakers in the northbound and southbound tunnels;
Two speakers in each of the cross passageways;
Six central control units (CCU);
A main CCU inside the tunnel control building to control the OSUs;
Five CCUs in several offsite locations to provide redundant and additional monitoring of ATI’s Emergency Notification System.
The speakers project sound longitudinally down the tunnel. Each speaker can provide up to 400 watts of acoustic power in order to overcome the traffic and ventilation noises. Speakers are positioned along the centerline of the tunnel and aimed opposite to the traffic direction. During the system commissioning, power for each individual speaker was adjusted to reach maximum intelligibility. The system testing indicated a great deal of success in providing excellent intelligibility and acoustic balance to compensate for the noisy and reverberant environment of the tunnel.