A. Bonnie Schnitta, owner of Sound
Sense LLC, a full-service acoustic consulting firm and
manufacturer of specialty sound-control products, responds:
Most of the noise from a garage door is structure-borne and
results from the opener motor being rigidly connected to the
joists or ceiling of the garage. Typically, structure-borne
noise from a garage door can range from as little as 5 decibels
(dB) to as much as 20 dB above background noise levels;
regardless of the amount of background noise, any 5 dB noise
increase is considered significant and perceivable. Even a 5 dB
noise-level increase represents more than a 50 percent
energy-level increase, and can travel several stories above or
several rooms adjacent to the garage. The solution is to
decouple the motor from the structure.
To isolate the motor's vibration from the structure the motor
is attached to, our company often installs decoupler clips (see
photos, left). Depending on the horsepower of the motor and the
weight of the garage door, these clips will typically reduce
the vibration to only 2 dB (or less) above background, a level
that's barely perceivable. The ones we use (PAC International,
866/774-2100, www.pac-intl.com) have rubber mounting feet and
can support approximately 36 pounds per clip; they cost about
Depending on the garage-door opener motor, there can also be
significant airborne noise. This can be reduced by enclosing
the motor first with an absorber that has an NRC (noise
reduction coefficient, a simplified rating of a material's
sound-absorbing properties) of .85 or greater, and second with
a barrier that has an STC (sound transmission class, a measure
of how effectively a material prevents sound transmission) of
27 or greater. For the barrier, we prefer a mass-loaded vinyl,
since its flexibility — which inhibits the movement of
the acoustic wave — aids in structure-borne decoupling.
Some mass-loaded vinyls have a higher transmission loss than
standard one-pound loaded vinyl, and are therefore more
effective at reducing airborne garage-door motor noise, which
is typically a low-frequency sound.
Some noise-control products function as both barrier and
absorber, making installation easier and more cost-effective.
For example, my company makes a quilted fiberglass insulation
with a mass-loaded vinyl barrier backing. For more on
sound-control techniques, see "Innovations in Sound Control"