Public address design software

The PA system sound level must be sufficiently above the ambient noise level to achieve intelligibility. Ambient noise sources include HVAC systems, aircraft operations, human activity, concession mechanical equipment, TVs, escalators, and people movers.

The PA system components that affect intelligibility include the microphones, headend electronics, and loudspeakers see Figure All of these components are subject to bandwidth distortion, which can diminish intelligibility in the presence of noise. Generally, purely electronic components such as headend electronics and power amplifiers maintain the best one-to-one relationship between input and output. Components introducing the greatest nonlinearity are usually elec- tromechanical transducers such as microphones and loudspeakers.

Professionally prepared Figure Typical PA system signal path. Thus, when specifying equipment, it is important to use high- quality, commercial-grade components for the loudspeaker and microphones. Consumer-grade or home hi-fi components have no place in airport PA systems.

Components within a PA system must be properly matched to ensure that their imped- ance and signal levels are matched to the other components in the system. Proper impedance- matching maximizes power transfer between components. Mismatched impedance makes this power transfer inefficient and will introduce signal loss as the sound signal moves from one mismatched component to the next.

Signal loss then increases the likelihood of a poor signal and distortion at the loudspeaker due to poor signal level and poor gain settings. In modern PA systems, impedance matching is less of a problem because inputs are typically actively balanced. When all components are obtained from one manufacturer, it is more likely that the individual components are properly matched. The PA system should be correctly configured at every stage of its operation. Overdriving inputs with a signal that is too strong can cause output clipping, which will introduce distortion and diminish intelligibility.

Clipping in the digital signal processor DSP can occur when the signal is driven beyond its digital capability to perform the signal processing functions easily. Clipping can also occur when the amplifier is overdriven beyond its maximum capability, causing the signal broadcast through the loudspeaker to no longer match the original input.

This can also cause perma- nent damage to the loudspeakers. For example, when a microphone is abruptly turned off or disconnected, a crunchy, static-like chirp is heard at the loudspeaker; this chirp can cause the loudspeaker cone to break. In airport PA systems, the acoustic signal is the human voice. Two types of microphones are used in airport PA systems: omnidirectional and unidirec- tional.

The unidirectional microphone is most sensitive to sound arriving from one particu- lar direction and is less sensitive at other directions. This gives the unidirectional microphone a higher gain-to-feedback ratio, which maximizes performance and intelligibility.

A cardioid microphone is an example of a unidirectional microphone and has a heart-shaped response about its main axis see Figure This pick-up pattern is the most sensitive at 0 degrees on-axis and is least sensitive at degrees off-axis.

Independent of microphone selection, feedback rejection can also be improved with proper loudspeaker placement at the microphone location. If the design can avoid loudspeakers above the microphone location, omnidirectional microphones can be used. Less microphone technique training is required, because there is no prox- imity effect in omnidirectional microphones. A good push-to-talk microphone has a reliable, high-quality, long-lasting switch.

The button is mounted on the microphone or on the paging station, depending on the type of microphone used. Such microphones are particularly useful to improve intelligibility for live announcements in noisy, reverberant environments e. Handheld microphones are found at wall- or desk-mounted paging stations where the microphones are conveniently located and readily accessible to gate and baggage agents.

Handheld microphones should have a frequency response designed for voice communications. The limiting factors that affect paging microphone performance are microphone sensitivity and frequency response. The microphone output should match the DSP input in level and impedance to maintain good signal quality. Handheld microphones typically have a clip or hook for mounting to the wall station.

One manufacturer offers a microphone with a magnet to hold the microphone on the wall station. Besides serving as the microphone input, the paging stations also have a keypad for access control and routing. The pushbutton on the side of the microphone activates it and engages the PA system.

Figure shows a push-to-talk microphone. Figure Polar response pattern. The desktop and gooseneck microphones also have pushbuttons, typically on the base or paging station, to activate the microphone and engage the PA system. Figure shows a desktop paging microphone.

Photo Credit: J. Lewitz Figure Push-to-talk microphone. Photo Credit: Wikimedia Commons Figure Desktop paging microphone. Headend equipment constitutes the control center where most of the functional aspects of the PA system are established and stored. The main components of the headend electronics are the digital signal processor DSP and the power amplifiers.

This equipment is typically rack mounted in a telecom or server room. In a large airport, the headend may be in a central location, feeding audio signals to audio power amplifiers in satellite equipment rooms to minimize loudspeaker line power loss.

Long loudspeaker lines waste amplifier power and are costly. Typically, loudspeaker line loss should be kept under 0. A 3 dB loss would represent a loss of half the power over the length of the line, so loud- speaker line loss is an important design consideration. Loudspeaker line loss is determined pri- marily by the impedance of the connected loudspeaker load, the length of cable, and the cable size. Line loss can be compensated for by using larger gauge AWG cables, but this is also a cost consideration.

Shortening the loudspeaker lines by remotely locating the amplifiers, if possible, is the most cost-effective strategy. Minimize loudspeaker line power loss. This can be done through specification and layout. An important part of the headend DSP is the processing of the information from the ambient- noise-sensing microphones.

Some systems include ambient-noise-sensing microphones to mea- sure the noise environment in each zone. The DSP in the headend uses that information to temporarily add gain to the loudspeaker input signal when the ambient noise levels increase.

Device latency should be considered in the PA system design and product selection. Excessive audio delay anywhere in the PA system hinders intelligibility, but can be controlled through specification and component selection.

Key operations that relate to speech intelligibility are included here: Pre-amplification During pre-amplification low-level microphone signals to be processed by the DSP are ampli- fied. This stage electronically amplifies a very weak signal for example from a microphone or. Compressors and Limiters The compressor, a component of the DSP, narrows the difference between the softest and loudest sounds passing through the PA system.

The compressor does this by compressing the dynamic range of the audio signal, thereby essentially reducing the volume of loud sounds and amplifying quiet sounds. Large swings or extreme peaks in the PA signal level are detri- mental to intelligibility. If the PA is too loud that can be annoying or distracting, but if it is too soft, the intelligibility would be lost in the ambient noise.

Such issues can be controlled through specification, component design and PA system optimization. A limiter is a compressor with a high compression ratio and a fast attack time. Compression is sometimes built into the paging microphone circuitry.

Equalization EQ Equalization increases or decreases the level of different frequencies in the PA signal. Equal- ization is performed by digital electronic equalizers within the DSP component. In the DSP, the equalizer performs more complex frequency-response adjustments to tailor the frequency response of the PA system to improve sound quality and intelligibility.

Examples of EQ use for speech intelligi- bility would be to emphasize and smooth the frequencies useful for understanding speech or to compensate for frequency-response anomalies in the loudspeakers or room response. Different equalization is necessary for different signal sources and zones such as loudspeaker zones, local announcements, prerecorded announcements, and background music.

Audio Delay In some situations, it is necessary to delay an audio signal in time to synchronize arrival of signals between loudspeakers at different distances from a listener. Sound travels at a fixed rate of speed. Solutions by industry Connected technology for all industries Aviation Banking and finance Cargo and logistics Casinos Commercial real estate Critical infrastructure Data centers Education Healthcare Hotels and restaurants Industrial Maritime Parking Prisons and correctional facilities Public transport Retail Smart cities Stadiums and venues Traffic.

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