Natural Science Forum / Physics / Acoustics / January 2004

Dividing a space into three parts with hard surface partitions is not going
to significantly reduce the reverberation time in the three new spaces
compared to the original.  To reduce the RT, you need to increase the ratio
of sound absorption to volume significantly by adding sound absorption.
Adding sound absorption will also reduce general sound levels, which seems
to be your other expressed objective.

However, you say this is an open office area.  The objective in such spaces
is usually to reduce the level of understandable speech reaching those who
are distracted by it.  When it is desired to preserve the open plan, this is
usually done with a combination of a highly absorptive ceiling that reflects
very little sound, partial height barriers at least 1.5 m high to block the
direct path, and the addition of masking sound.  You do not necessarily want
to reduce the overall sound level in the space, but reduce the level of the
understandable speech that you do not want to understand.  The masking sound
then helps mask that remaining distant speech without being so loud that it
interferes with hearing those nearby that you want to hear.

If its sound reduction that you are after then you need to establish
what the areas are to be used for and what sound reduction you need.
Then the calculation will be the Lab measured sound reduction index for the
glass partitions less the effects of the flanking conditions.
Glass is NOT a good absorber so it will not reduce the overall sound
levels just by being within the area concerened. Indeed it may well have the
reverse effect and increase the level of reflected sound present.
As a "divider" glass is also pretty bad,,unless the glass is double glazing
and that
each side is of differing glass types.
Avoid both side being toughened or Both sides being laminated. Also avoid
both sides being the same thickness.
The most cost effective combination is 6.0mm toughened and 6.4mm laminate
with a void space of 50-60mm.
This has a Sound Reduction index of 42dB Rw.
The Room to Room rating however would be in the region of 35dB R'w with
typical office flanking conditions and an "imperforate" mineral fibre
ceiling.
If you have a standard perforated steel tile ceiling this could easily drop
to 25dB R'w !!
For speech privacy you really need to aim for 40dB R'w and this is very hard
to
acheive with glass partitions under normal flanking conditions.
Most offices nowaday are lucky to acheive 30dB R'w so don't be put off by
the
low numbers !!.

Lee Roth

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