Brüel Acoustics
Per aumentare la riservatezza in banche, ospedali, sale
d'attesa di studi medici e di studi legali, abbiamo sviluppato un
dispositivo per migliorare l'ergonomia degli ambienti di vita e di
lavoro chiamato AntiTell tipo 45BA.
Questo sistema
di mascheramento sonoro è costituito da un generatore di rumore agente a livello
psico-acustico posto in una piccola sfera di 11 cm di diametro priva di
emissioni elettromagnetiche.
Il generatore ha uno spettro di rumore simile
alla voce umana, cosicché maschera il parlato e riduce l'intelligibilità
nell'ambiente trattato senza modificare la sensazione del rumore di fondo e
senza produrre rumore inutile.
Il livello di emissione dell'AntiTell, una
volta regolato, introduce nell'ambiente il cosiddetto "profumo di
rumore" fino a ridurre l'indice RASTI sotto il 40%.
The AntiTell is a small noise generator which constantly
produces a very low noise level.
When there is a normal level of activity in
the room it can hardly be heard. If the normal noise level momentarily goes down
the AntiTell generator takes over and reduces the
intelligibility of speech thereby maintaining privacy for those people
talking.
The frequency spectrum from the AntiTell generator
consists mainly of those frequencies important for speech comprehension. The
generator does not produce any low or very high frequencies as these frequencies
are not important for understanding speech signals.
The sketch in Fig. 1 shows a typical installation in a bank. Here, the AntiTell works to make it difficult for the people waiting (W) and the people being served at other tellers (0) to hear the conversation between the bank clerk and the customer presently being served (P). The X indicates the position on the ceiling where the AntiTell should be attached.
As the bank: if the noise level in the doctors waiting room goes very low (
down to 25 - 30 dB A) people waiting with good hearing could easily hear what
the doctor is discussing with his/her patient, even when the door is tightly
closed.
By placing the AntiTell is the postion marked X privacy is
maintained.
The AntiTell works best if the rooms already
have the same acoustical treatment.
If the rooms are acoustically hard and
have a long reverberation time, the noise from the generator will spread across
all the rooms, which makes it difficult to direct the masking sound to the
strategically correct areas.
As shown in Fig. 2, the AntiTell is a small sphere with a
diameter of 11 cm and contains an electronic generator and a small loudspeaker.
The noise level can be controlled from the outside with the use of a
screwdriver.
The power supply is 6 V DC and is only a few mW so a very thin
cable is sufficient.
The AntiTell should not be seen. Some people could
believe the AntiTell to be part of a surveillance system or a smoke detector.
In all banks, hospitals, waiting rooms and offices the acoustics must be controlled and in many places acoustic ceilings have already been installed. The AntiTell sphere should be installed over the sound absorbing board.
In rooms with acoustic ceilings separated from the building structure, the AntitTell can be easly intalled in the space between the acoustic material and the ceiling (Fig. 3)
A good and economical method is to install absorption cones on the ceilings of the rooms. The AntiTell can then be hidden inside the cones (Fig. 4)
Within the AntiTell sphere there is still plenty of room for further installations i. e. fire alarm, temperature or humidity sensors, or sensors for radioactivity etc.
For larger places the system should be optimized by making careful
measurements of the Speach Transmission Index (STI) or the Rapid STI known as
RASTI.
The measurements should be made before and after the
installation of the AntiTell.
® Web masters Mario
& Paolo Mattia - updated on February 2001, Web Master
On line from 1995 November 10