Acoustic features of vehicles

Acoustic features of vehicles

(digital annunciators, amplifiers, microphones)

Digital annunciators

Our company produces independent and built-in annunciators. Electro acoustic on-board information systems (hereinafter EPIS) contain multiple digital annunciators that are also able to control radio and radiomodem vehicle communications. They are usually designed to control all acoustic outputs and inputs used in public transportation vehicles including controlling radio communication with the dispatching and command receivers for the vision impaired. From the point of view of the user, digital annunciators integrate (can integrate) in one device:

Basic functions:

  • Multiple independent digital annunciator of stops and other predefined announcements for passengers inside as well as outside the vehicle,
  • generator of service reports of the state of the vehicle, the radio network or service information for the driver,
  • acoustic switchboard allowing the driver to make announcements for passengers inside as well as outside the vehicle.

Additional functions:

  • radio communication adapter for phonic radio stations that are additionally enriched by a digital selective choice function,
  • radio modem for state report data transfers used for communication with the dispatching (mainly for the purpose of informing about the position of the vehicle and identifying the vehicle),
  • dispatching radio used to inform passengers about the present state of the public transportation network,
  • other telematic and memory functions (see. the description of the EPIS 2.45).

Independent digital annunciators are assembled according to the German recommendation VÔV 04.06.2. To ensure acoustic comfort of passengers these annunciators provide sufficient acoustic performance allowing them to support 2 x 8 speakers inside or outside the vehicle and 2 speakers for the driver (valid for bidirectional trams).

The modern coding method of the commonly known M-PEG format used for these annunciators is modified to support the needs of public transportation companies and it is based on sound coding methods that are used to achieve CD-ROM quality. In comparison with other methods, it does not contain any interference, the quality of sound is significantly higher and it places significantly lower demands on digital annunciator memory while achieving a frequency range higher than 10 kHz.

Note.: Vehicle speakers are usually not able to transmit any frequency higher than 10 kHz, therefore it is not necessary to use HiFi quality.

Produced types of independent annunciators :

Digital annunciators integrated (built in) in on-board computers, position surveillance units and checking systems:

Additional appliances related to vehicle sound systems

Additional appliances related to vehicle sound systems include the following:

  • Outer speakers including speaker holders – their description can be found on the web page describing speakers. They are also designed to be placed on the roof in accordance with the supposed direction of sound.
  • Driver microphones – their description can be found on another web page
  • Volume regulators – immediate regulation of volume of driver receiver speakers.
  • Noise microphones – scan the level of sound inside a vehicle on the basis of which volume of announcements for passengers inside vehicles is set. This method has been gradually replaced by announcement double volume – day volume and night volume set internally by digital potentiometers of output amplifiers according to commands sent from on-board computers.
  • Optron separators – separate switch voltage +24V from unit inputs. Now they are produced for a different purpose.
  • Adapters for bidirectional traffic cabins – see below

Adding sound to bidirectional trams – using cabin A adapters

The picture below shows a solution of adding sound to the space outside and around a bidirectional tram using one source of acoustic signal. Our company produces two types of adapters designed for this purpose:

  • cabin B adapter –  collects information about the state of chosen buttons including a command from the vision impaired, it also collects GPS signal and amplifies the signal sent from the cabin B to the microphone of the driver,
  • cabin  A adapter – provides outer sound depending on whether the door is open and it also controls announcements for the vision impaired, collects buttons, throws switches etc.. This adapter also transmits video signal to the cabin B terminal.
Pic. no.1: Arrangement of REXT-8D outer roof speakers controlled using the cabin A adaptor of a bidirectional tram.

Pic. no.1: Arrangement of REXT-8D outer roof speakers controlled using the cabin A adaptor of a bidirectional tram.

Rules for adding sound to the outside of a bidirectional tram:

  • Addition of sound to the correct side of a tram is executed based on which side of the tram has its door opened or loosened (right or left side of the tram). If a tram arrives to a terminus where there are platforms on both side of the tracks and both its left side doors and its right side doors are open it is possible to add sound all around the tram.
  •  Adding sound to announcements for the vision impaired is a bit more complicated. The area where these announcements can be heard without difficulties is determined based on the condition that a vision impaired person enters the vehicle through its first set of doors situated behind the driver in the direction of the tram and on the side where doors are open. This means that the conditions of the driving direction and opened/loosened doors must be observed for the area of announcements for the vision impaired to be assessed correctly.

Cabin A adapter i.e. the cabin where a digital annunciator is situated solves the above described conditions of the announcement area. In our case, it can be an independent EPIS 2.45  or a digital annunciator embedded in an  EPIS 4.0x  on-board computer.