Many
public facilities and even some homes have problems with sound.
These problems may be classed as "too much sound",
"too little sound", "poor-quality sound",
or "uneven sound". Often the owners/occupants of
these facilities do not know what to do about the sound problems.
This can lead to wasting money on the wrong "solutions",
attempted fixes by self-styled experts, or more commonly,
just putting up with the frustration and sub-optimum performance
of the room or building.
Under
the heading of "too much sound" are external and
internal noise sources. External sources can include highway
noise, "boom cars", noisy neighbors (individuals
or businesses), or various kinds of miscellaneous machinery
noise. Short of moving, one may find quieting these noise
sources difficult or unfeasible. Well-constructed new buildings
can incorporate walls having a high sound transmission
coefficient (STC) that will help block external
noise. Some retrofit measures may be applicable for existing
buiuldings, including special windows and doors. Noise sources
such as air conditioners and ventilating fans can be quieted;
this is much less troublesome if the air conditioner is owned
by the person wishing to reduce the noise, as otherwise conflicts
of interest may hamper efforts to mitigate the noise problem.
Internal
noise sources include heating/ventilating/air-conditioning
systems, or occupants of adjoining rooms (especially rooms
beside or above the affected room). As with external noise,
proper initial design goes a long way toward avoiding excess
internal noise. Some retrofit measures can be applied, primarily
through the use of special doors or door seals and carpeted
floors.
Problems
with too little sound are usually found in rooms especially
used for listening, such as classrooms, auditoriums, churches,
theaters, etc. Often these rooms are served by electronic
sound systems, and all too frequently these systems are improperly
designed, installed, or operated. but too little sound can
also be the result of uninformed attempts to rectify other
sound problems by using the wrong kind, quantity, or location
of acoustical treatment. The solution to sound system problems
may well not involve purchase of new equipment, but may involve
adjustment, training, and/or acoustical work.
Poor-quality
sound almost always is associated with electronic sound-system
problems as described in the previous paragraph. Uneven sound
-- a defect in which some people in a room hear good sound
but others don't -- can result from either sound-system problems
or problems in the architectural acoustics of the room.
In
any of these cases, the building owner/occupant is faced with
the choice of whether to involve a professional, and if so,
what kind of professional. It is not necessarily true that
someone who works for the telephone company, a radio or TV
station, or a pro-sound or musical instrument store is qualified
to assist in correcting sound problems. Nor is a person necessarily
qualified by virtue of being responsible for operating the
sound system at a church or theater, or for a musical group.
The combination of public ignorance about the technical aspects
of sound, along with the sizeable egos of many professionals,
leads to a proliferation of poor advice, wasted money, and
frustrated listeners. An experienced consultant who has an
appropriate education can provide trustworthy guidance. Consultants
may specialize in noise control, architecturel acoustics,
and/or sound system design. It is always best to choose a
consultant with all the specialties that may be needed to
solve the specific problem. Usually a consultant will give
a certain amount of free advice before "starting the
clock" on billable time. Many times, this free advice
can at least point the owner in the right direction for solving
the sound problem. If not, then the consultant will provide
a specific proposal for further investigation, with costs
included so that the owner can make an informed decision of
how best to proceed.
Comment
thread:
Our church has a longstanding problem with reflections
from the front balcony wall interfering with the sound
coming directly from the front speakers. This makes
it hard for some people to understand what's said, even
when the sound system is loud enough. Two different
acoustical consultants suggested a product to cover
the balcony face. The church bought the product, but
it was not installed the way the consultants recommended.
Does it really make a difference if the acoustical
board is mounted directly on the wall instead of having
space behind it filled with fiberglass?
Janet Miller
Thanks for your question, Janet . [Rant coming up!]
Unfortunately, this type of problem (consultant recommendations
only being partially followed) is not rare. I have a
book written by an eminent Russian acoustician, in which
he describes various projects on which he consulted
during the Communist years. In other words, the government
paid him for his recommendations, owned the building,
and paid the building managers. Yet in many if not most
cases, acoustical problems remained due to his instructions
not being followed. [Rant finished.]
More to the point of your question: If you need acoustical
absorption to be effective at bass frequencies to avoid
echoes and excessive reverberation, that absorption
must be very thick ( 4" or more), or must be mounted
over an airspace or building fiberglass to achieve a
4" or greater effective thickness. The fiberglass-in-the-airspace
approach is cheaper and almost as effective in many
cases. But if the fiberglass and airspace are omitted,
the bass echoes and boominess will remain.
