DIRECTIONAL SIRENS LTD MANUFACTURER OF DIRECTIONAL emergency vehicle SIRENS
THE QUADRASONIC DIRECTIONAL SIREN SYSTEM - PATENTS PENDING
There are situations where it is beneficial for people to be able to detect the direction a sound signal or signals are coming from. Examples of such situations include locating the direction of approaching emergency vehicles, locating the position of emergency exits and fire exits in buildings, and exits from modes of transport including trains, airplanes and boats. Sound signals can be used for guiding people through enclosed or open spaces such as industrial complexes in emergency situations and where vision is obscured by smoke fumes or flames or when a person is visually impaired or blind.
Existing emergency and fire exit signage consists of visual information. This is of limited use in situations where the sign is out of line of sight of the observer or where vision is impaired by smoke, fumes or flames. Visual signage is of limited use to people with visual impairments and is of no use to people who are blind.
It is known that it is difficult to detect the direction of approaching emergency vehicles by listening to the sounds emitted by sirens currently in use. This is in part due to the use of a single frequency or a small number of frequencies or swept frequencies and a narrow sound beam. The single and swept frequencies do not convey enough information in a suitable time frame for the listener to readily ascertain the direction these signals are coming from.
The current sirens employ higher frequencies typically between 650Hz and 1600Hz which tend to transmit a narrower beam than lower frequencies. The narrow higher frequency sound beams that the current sirens produce tend to bounce off buildings and other objects. They are reflected without significant noticeable audible attenuation of amplitude or modification of their original frequency. The reflected sound beam is hard to distinguish from the original beam. The current sirens often employ swept frequencies which are continually rising and falling. It is difficult for the human psychoacoustic system to gain directional or other information from such swept signals as there is little time for the auditory system to identify and quantify a particular frequency before that frequency changes by small increments to another frequency. Humans are more adept at perceiving individual frequencies especially if they have other individual frequencies to relate to rather that a single frequency or swept frequencies being heard in isolation or simply repeated.
In many cases it can appear to pedestrians and motorists that the sound is coming from another direction from where it is being transmittedby the emergency vehicle. This occurs when the beam is reflected off a surface in another position to the origin of the sound.
This often results in confusion amongst motorists who become unsure of whether to take avoiding action or not. The short rise time of the sound wave currently used in the Yelp siren often causes a panic reaction in listeners such as motorists and pedestrians. The yelp siren is believed to cause hearing damage to emergency vehicle drivers.
Motorists are often unsure whether the siren sounds currently used are coming from the left, the right, from front or behind. This problem is particularly prevalent at junctions and crossroads.
There is sometimes confusion about the term directional. The word directional is often applied to microphones which can be unidirectional meaning that they will pick up sounds from one general direction only or omnidirectional in which they can pick up sounds from all directions. Microphones can be engineered to pick up sounds from specified directions and angles.The sound signals emitted by current sirens are generally unidirectional over a narrow angle and can be likened to the narrow beam emitted by a spotlight in a theatre. The term omnidirectional can be likened to the all around illumination of light bulbs typically used for illuminating a room.
It can be seen that when an emergency vehicle is approaching a crossroads and projecting a narrow directional beam forwards in the direction it is traveling, vehicles approaching the crossroads at an angle to the direction of travel of the emergency vehicle will have difficulty hearing the siren which projects the sound mainly straight ahead.
This difficulty results in thousands of serious accidents, injuries and fatalities involving emergency service vehicles and ordinary motorists throughout the world.
The social, personal and financial costs of these accidents is enormous and would be significantly reduced if sirens on emergency vehicles enabled motorists to ascertain the direction of approach of emergency vehicles and motorists could then take appropriate action to allow the emergency vehicles to proceed unhindered.
Such sirens that produce this beneficial effect we will designate as ‘directional’ and are the subject of this invention.
A further limitation of sirens currently used is that they typically emit harsh sounds which in themselves directly creates panic amongst motorists. This is in part because the shape of the sound wave has a very steep rise time i.e. it goes from no sound to maximum sound in a very short period of time.
Furthermore the shape of the sound waves can be very sharp shaped waveforms which consist of a steep rise and a sharp point. Alternatively a narrow rectangular wave is used which has an almost vertical rise time going from zero to maximum output in an extremely short time. The listener’s psychoacoustic system has difficulty dealing with these sounds.
The currently used sirens such as Yelp consist of repeated intense sound waves which creates tension and stress in the listener. When motorists hear a siren, the stress induced by the sound of the siren generally has two results, the motorists either panic and take inappropriate action, or they freeze and take no action. In either case, the emergency vehicle is hindered in its progress.
High noise levels inside the cab of emergency vehicles when sirens are on causes impaired concentration for the emergency vehicle driver and severely limits the efficacy of verbal and radio communications, putting personnel and the public at higher risk.
Many emergency vehicle drivers suffer significant hearing loss after exposure to current sirens.
Human hearing is better adapted to sinusoidal waves such as music and speech which have a more gradual initial rise time which then steepens in the middle section and flattens towards the top and degenerates in a similar manner.
Current sirens often use high pitch signals which as well as tending to reflect off surfaces also reflects off vehicles and fail to adequately penetrate the body shell, windscreens or side windows. There is a lack of attenuation on reflection which causes these sounds to be transmitted and reflected over a long distance particularly in urban situations where there are buildings or walls on both sides of the road.
Motorists often experience hearing sirens in adjacent roads to where they are driving even though these sirens are of no relevance to them. Motorists will hear many more sirens during the course of their driving than they are required to take avoiding action in response to those sirens. Over time motorist become relatively immune to reacting to the sounds of sirens and do not react until they see the typically blue flashing lights associated with emergency vehicles. In these situations the current sirens have failed as advanced warning devices.
Modern vehicles are well sealed against external sounds and the power of modern entertainment systems can overwhelm the motorists’ perception of approaching sirens.
Some components in motor vehicles create sounds similar to white noise. White noise tends to mask other noises and reduces the listeners’ perception of external sounds. White noise emitters are fitted in open plan offices for the specific purpose of reducing the perceived sounds in the office enabling easier conversation between people at close quarters. In a vehicle, sounds similar to white noise are produced by the fans and air flow in the air conditioning, climate control and heating systems, thereby further damping down perception of external sounds.
Current sirens are often mounted on the roof of emergency vehicles. In the case of vehicles such as ambulances and fire engines the main part of the sound beam is projected high over the roofs of other vehicles particularly cars and motorcycles.
Alternatively the sirens are mounted within the engine compartment with no direct access to the external environment. This inhibits the sound signal being properly projected towards any traffic which might be obstructing the emergency vehicle. Sirens within the engine compartment are sometimes mounted facing to the side or pointing towards the road surface. Similar to a light beam these mounting positions severely inhibits projection of the sound signals in the desired direction.
The Quadrasonic™ Siren System (patents pending) solves these problems.