Issue 42 summer 24 web - Flipbook - Page 20
Speech intelligibility
for Places of Worship
Traditional places of worship are notorious for poor acoustics degrading the intelligibility of the spoken
word. Ironically, for the hard of hearing we have largely solved the problem with the development and
continuous improvement of Induction loop systems. However, for the majority, with apparently
good hearing, little has been done to improve the intelligibility of sound in these highly reverberant
environments.
Delivering services in the mother tongue of the
congregation arguably increases the need for greater clarity and intelligibility of speech; the Catholic church
switched from Latin to English Mass in the UK back in
1964. Slowly over the decades, we have seen the introduction of reinforced sound in these environments, but
with mixed success. The Classic building for worship is
highly reverberant producing a vibrant cocktail of sound.
Whilst this enriches the sound of music and song it has
a devastating effect on speech and can destroy and
intelligibility.
speaker needs to be very high for those at the back to hear.
This just exacerbates the problem. Reverberation is not
resolved and sound levels are too variable for comfortable
listening.
The issues are multifaced. Some reverberation can be beneficial: the trained orator can take advantage of it defying
the inverse square law and projecting intelligibility speech
to the back of the congregation without deafening those in
proximity. Too much reverberation, however, and the speech
is blurred lacking any clarity regardless of the volume.
Above, Imagine blowing up a balloon with a big red dot on it.
As the balloon gets bigger the red dot stretches and becomes
lighter and lighter in colour as the red pigment is stretched over
the growing surface area of the balloon. Sound emanating from
a conventional speaker is being stretched over an ever growing
sphere, just like the balloon surface.
The surface area of a sphere is proportional to r2 so the power
(loudness of the sound) at the surface of the sphere is reducing
as the square of the radius. At a distance 2r from the speaker
the power has dropped by a factor of 4 at a distance of 3r it
has fallen by a factor of 9 and so on.
Above, Speech taking a direct path to the listener will reach
him first, Speech reflected from different surfaces will reach
him later and later depending on just how far it has travelled.
Hard surfaces such as stone are almost perfect reflectors
providing little of no attention.
Early audio systems used in places for worship comprised
of not much more than a couple of speakers, an amplifier
and a microphone. Raising the volume was the prime objective; everyone could hear the services. Unfortunately,
they could not necessarily decipher what was being said.
Higher volume means everyone can hear, but from a point
source such as conventional speaker the volume falls
according to the inverse square law so the volume at the
A Solution is to use multiple speakers down the length of
the building creating zones. Each speaker covers small
range, so it is not too loud for those close to, but it has
sufficient level for those at the back of the zone to hear.
However, using multiple speakers in this way leads to
more sound blurring. The Problem of reverberation is still
there, and additionally, sound from the first zone spilling
into the next zone will be delayed as a consequence of the
distance between the speakers. It may not be reverberant
sound, but it has the same result-reduced intelligibility.
To overcome this problem a delay is introduced between
zones. Now the system is becoming quite complex! Each
zone needs to be wired to a separate amplifier with a
different (delayed) audio feed.
