Speech Intelligibility: Clear Communication in Transit Hubs

The Speech Intelligibility Index (SII) is a measure of the intelligibility of speech. The FeONIC® Audio Drive regularly achieves an SII greater than traditional loudspeakers, making it by far the best system to install on transport.

The Speech Intelligibility Index is the amount of speech that is recognised correctly, on a scale of 0 to 1, where 1 is excellent and 0.5 is fair to good. In most PA applications an SII value of 0.5 or above is acceptable and FeONIC® Audio Drives regularly deliver over 0.6 SII without distortion and with a more even distribution of sound than horn speakers.

Immerse people in Sound - don't blast it at them

Intelligible announcements in a transport environment are essential to ensure passenger safety, information and satisfaction. Traditional speaker-based systems don’t live up these requirements, because they lack speech intelligibility which measures the quality of sound on four key measures:

• Speech-signal-to-noise ratio (S/N).  Noise has the effect of masking or obscuring the voice signal. Remarkably, we are able to tolerate a great deal of noise before intelligibility diminishes appreciably but, once it begins to diminish, it diminishes rapidly.
• Reverberation. Most people are familiar with how difficult it can be to understand speech in a reverberant environment such as a railway station or airport. Reverberation is made up of sound reflections that have the effect of smearing or blurring speech, making it less clear and distinct and therefore more difficult to understand.
• Echoes. If echoes arrive much later in time than the first arrival of sound, they can harm intelligibility. In continuous speech, the echo from a previously uttered syllable masks or obscures the sound of subsequent syllables, making speech more difficult to understand. The time delay and level of the echo are key variables in determining the impact of echoes on intelligibility.
• Distortion. If one of the electrical or electro-acoustical components in the sound system is distorting, it is generating a form of noise that masks the original speech signal. Severe amplifier clipping, for example, can make an otherwise perfect speech signal at the input to the amplifier more difficult to understand at the output.

Horn Speakers: Louder isn't Better

Speech is not necessarily intelligible simply because it is audible. Having enough speech level is a necessary, but not sufficient, condition for good intelligibility. Just like adding more light to a blurry text doesn’t make it more legible, adding more sound level to speech that has been blurred by reverberation, echoes or distortion does not make it more intelligible. A loud enough, but overly reverberant, speech signal can be almost completely unintelligible, to which users of many railway stations and airports can easily attest. FeONIC® Transport's Audio Drive technology overcomes these problems, providing superior levels of speech intelligibility.

Voice Alarms : Avoid Annoying Irrelevant Messages and Habituation

Voice alarms are a good example of the importance of speech intelligibility. Voice alarm systems are meant to inform and instruct building occupants in the event of an emergency and their use is based on strong evidence that people often ignore normal audible and visual alarms but will obey a voice command. Note that normal alarms have extremely limited information content (on or off), whereas voice can be used to deliver a wide range of potentially life-saving information. Crucially, this can be precisely targeted where it is needed rather than broadcast.

However, for a voice alarm system to be effective, it must be targeted and intelligible. Habituation can occur when messages are constantly broadcast to everyone in a location leading to people filtering out and ignoring messages.
FeONIC’s Audio Drive technology can be placed just where the messages are needed. On panels, escalators, doors, platforms etc. And is much more intelligible than traditional speaker systems – potentially saving lives.