Brüel Acoustics
Your Solution to Speech Privacy:
The AntiTell system is an easy to install electronic device wich generates a
complex and adaptable Pseudo-Random Acoustical signal.
The signal consists
mainly of frequencies of importance for speech comprehension and is mixed with
the natural background noise in places where privacy or confidentiality of
conversation is essential as: hospitals, banks, offices, doctors waiting rooms,
post offices, libraries, reception areas, etc.
It is common knowledge that if we wish to concentrate on a certain work
requiring full attention we like to have soft (radio) music in the
backgraund.
If the music is changed to speech, wich can be understand, this
background music is disturbing. But if the speech is drowned by other noises
like noise from trafic or office machines then the speech in not at all
disturbing.
It is therefore important for the concentration that the intelligibility of
speech is very low.
If you ask a person who has worked to background low
level music, what music was played, he will normally not know, so it is the
masking effect which is important.
The frequency spectrum of the noise
radiating from the AntiTellis just formed in such a way that it has the maximum
negative effect on speech intelligibility using the lowest average noise
level.
Normally in rooms where several people are gathered, there is a
natural noise level from activity in the room and from outside, i.e.traffic.
This "natural" noise usually makes it impossible to understand a
conversation occuring between people furùler than 1-2 m (3 -6 feet) away.
You
can hear that the people are talking to each other but you cannot understand
what is being talked about.
However, sometimes the natural noise level will
be very low and under these circumstances a person with good hearing will hear
and comprehend a conversation some distance away (sometimes up to 20 m).
To
prevent this situation the AntiTell has been developed.
The Antitell is a small noise generator which constantly produces a
very low level noise.
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.l 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.
Fig.2 is a sketch of a doctors waiting room.
If the noise level in the
waiting room goes very low( down to 25-30 dB A) people in the waiting room 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.3, 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 6V 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, i.e. AcoustiCone.
