Noise Control Treatment Design
NCE develops optimal noise control designs based on comprehensive
sound and vibration analyses, see airborne noise
analysis section. Custom designs are provided for each specific ship
program. Common treatments include vibration isolators, acoustical
insulation, damping, floating floors, HVAC linings, enclosures and
silencers. Each treatment is selected for a specific purpose - to
control noise contributions from a specific source that are transmitted
via a specific path, and each has its own cost benefit tradeoff.
Understanding when to apply specific treatments is critical to
minimizing impacts to non-acoustic factors such as weight, space, and
The following is a brief description of each of the noise control treatments listed above:
- Vibration Isolation: Structureborne noise emitted
from machinery is one of the predominant sources of noise. An effective
way to reduce structureborne noise is to resiliently mount the offending
machinery, in particular for diesel engines/generators, air compressors
and refrigeration compressors. There are numerous types and styles of
vibration isolators. NCE can advise on the most cost-effective isolators
for your specific application.
In all cases, the vibration isolation system needs to be properly
designed and implemented, or vibration can actually get worse. NCE
works with clients to properly design these systems for machinery of all
sizes and functions. NCE selects vibration isolators, reviews proper
equipment mounting points, isolator characteristics, and performs
six-degree-of-freedom (6DOF) "natural frequency" calculations. Lastly,
during sea trials NCE will measure the transmission loss (TL) or
attenuation of the isolation system to check for proper performance.
- Acoustical Insulation: This usually consists of fiberglass or
mineral wool for U.S. Coast Guard inspected vessels. For non-inspected
vessels foam-based products and other types of materials may be used.
Acoustic insulation is most commonly used on the boundaries of the
engine room or machinery space. It may also be used on auxiliary
machinery spaces or any space with elevated sound levels. Some
insulation types have multiple layers with limp mass (or barrier
material) sandwiched in the middle of two layers of a base material,
- Damping: This treatment has two general forms: tile and
spray-on. The tile products are typically installed to the middle of
un-stiffened steel plating. The spray-on products are used throughout a
treated area. Damping treatments convert vibration within a ship's
structure into small amounts of heat and thereby dissipates the
structural vibration. This treatment has some technical and regulatory
limitations which NCE can help you to understand and work with.
- Floating Floors/Rooms: These treatments have many
forms. The common design is to cover the steel floor with a resilient
material upon which another non-structural, but load-bearing floor is
placed. This floor usually floats on a layer of continuous or discrete
resilient material. A finish flooring material (usually carpet or
poured floors) is installed over the non-structural floor. Floating
floors are good for reducing noise for a selected group of compartments
as the treatment must be used in each compartment where noise reduction
A floating room is a compartment where the walls (usually joiner panels)
are located on top of a floating floor. In these cases, the entire
room's boundaries are all isolated from the ship structure which
provides one of the highest levels of shipboard sound reduction.
- HVAC Silencers: Reducing sound from noisy HVAC systems
is accomplished with either HVAC silencers usually located near the fan.
Another noise reduction approach for HVAC systems is to internally line
the ducts for a certain length past the fan. NCE can compute shipboard
HVAC system noise and then evaluate the effectiveness of silencers or
- Exhaust Silencers: This treatment is used to reduce
the sound emitted to the exterior of the ship. They are needed to
reduce noise to the ship's working deck and bridge wings or even to
shores-side areas. Exhaust silencers are usually selected by the ship
designer or engine vendor. Silencers have various grades such as
"Critical Grade" and "Hospital Grade". Usually, the better the grade,
the higher the sound attenuation, the higher the cost and larger and
heavier the silencer. NCE can determine the best silencer option for
Once any of the above treatments have been selected, NCE can provide
material specifications, areas of coverage, installation guidelines,
potential vendors and noise reduction estimates. Further, NCE will work
with the ship designer to minimize the adverse impacts on cost, weight,
space and operation of the vessel.
While NCE will recommend treatments by vendor and model, NCE does
not sell or represent any noise control material vendors. NCE gains no
financial benefit from any noise control treatment recommendations.
Thus, NCE can work independently with our clients to identify the best
solution from both acoustic and non-acoustic perspectives.