How to create an acoustic “slice of paradise” on the high seas.

Noise is a subjective experience: It has distinctive effects on individuals based on their sensitivities to sound. The physiological effects of noise vary from person to person.  For example, a hearing-impaired person may be susceptible to further harm when exposed to excessive noise levels. 

Recently, a SoundSense client with a hearing problem asked if the noise from his yacht could potentially harm his hearing.  After a quick reading with a spectrum analyzer and an interview, we realized that the noise levels were, indeed, hazardous to his existing condition.

As we discussed potential solutions, the client revealed that he owned multiple yachts. On this particular vessel, though, the noise also seemed to affect his wife as well, causing her to become slightly seasick. “Noise” is defined as unwanted sound. Interestingly enough, its etymological origin is the Latin word for “nausea.” This semantic correlation is imperative in yacht design, as certain untreated structures can result in vibrations, which can cause seasickness. The noise level and type of sound also can cause secondary health concerns that affect one’s overall well-being. Understanding some of the easy fixes to many of these problems can provide a better yachting experience, or a little slice of paradise.

As with any application, there first must be a focus on acoustic separation or isolation to prevent intrusive noises from entering the yacht. This also reduces the amount of sound emanating from room-to-room and from floor-to-floor. At a minimum, the noise levels should be brought to below 70 dB(A) from the engine room. Living areas should have much lower noise levels, particularly for sleeping areas.

Once acoustic separation is sufficiently addressed, relative to the client’s acoustic needs, each room must be reviewed for acoustic decay time and wave-interaction patterns. Correcting the acoustic environment will provide the perfect aural setting for each space, depending on its intended use. The right acoustic treatment will prevent unwanted sounds from becoming amplified, will make a small room feel larger, will project cleaner tones from an audio system, will allow for appropriate speaker placement (not where theory mandates), and will make the surround-sound system “surround” the listener in the truest sense.

Most noise and vibration sources originate externally and internally and include:
• Hydrodynamics of the hull and its appendages: rudders, stabilizer fins, hull surface and interruptions’
• Propeller hydrodynamics, including prop wash and cavitation;
• Flow-induced noise and vibrations, or vortex shedding from the mast or keel;
•  Main engine(s) and transmission(s);  
• Heating, ventilation and air-conditioning motors, fans and ductwork;
• Hydraulic system pumps, motors, valves, piping, and other components;
• Propulsion system components, including main driveshaft and bearings;
• Other ship systems and machinery,   such as generators, deck equipment, filtration systems, etc.

For most of these acoustic problems, it is recommended that acoustic treatment begin at the shipyard when the yacht is being manufactured, as the acoustic treatment should ideally be incorporated into the design of the yacht. Fortunately, many of the solutions can be applied easily after delivery to ensure a better yachting experience. An important consideration to keep in mind is that any noise-control solution must not affect the yacht’s speed capability or fuel efficiency adversely.

Acoustic Separation or Isolation
The acoustic isolation or separation needed between areas that require a level of quietude—such as a spa, music room, stateroom or salon, or from the engine room or between the home theater and adjoining rooms—are critical for the enjoyment of the yacht. While extraneous noise in a house or an apartment may be disruptive, noise from an adjacent room—such as footfall noise—can ruin a movie or a music-listening session.

On a yacht, intrusive engine-room noise frequently disturbs the listening and viewing experience. In fact, engine-room noise can potentially corrupt the quality of the audio system. Since it’s easy to solve such acoustic issues, we’ve outlined the basics of engine-noise reduction below.

To start, the yacht’s hull and the engine room areas must be treated. Engines and pumps, for example, transmit low-frequency sound, which often couples into any surrounding structure and resonates throughout the yacht.

The following commercially available products and/or solutions can be used to eliminate this “structure-borne” noise:
• Spray dB Damp to minimize metal structural resonance;
• Wrap ducts that exit to the floor, above or below, with absorptive material;
• Utilize proper flexible ducts or hose connections;
•  Install proper machine base deflection springs (review for mechanical specs and springs by a qualified engineer is necessary for proper load and deflection);
• Install decoupler clips with resilient channels and a “class A” fire-rated composite barrier and absorber on the critical perimeter walls and ceiling of the mechanical room to inhibit machinery low-frequency noises from coupling into the walls and ceiling. The ATI, which is a light material that blocks and absorbs sound, can be used as an alternative. A recent application using the ATI produced a significant weight savings, while achieving a 10 dB reduction.
• Attach pipes and conduits to Kendorf, which is then connected to the wall with acoustic wall studs. No pipes or similar conduits should be rigidly connected to the walls or ceiling;
• Minimize the transmission noise from floor to floor—especially from in the engine-room area—by placing an acoustic carpet underlayment on the floor. SoundSense’s Vibramat, for example, has a high transmission loss in the lower frequencies with damping qualities.

In addition, extraneous noise that emanates from the yacht’s heating or cooling systems, or from the vessel’s plumbing pipes, can be equally as disturbing during a movie-watching or music-enjoyment session, and even more disruptive to sleep. These types of noises can be eliminated in the following areas.

HVAC/Fan Noise (Projector and Exhaust)    
Replacing a noisy fan with more silent version is the easiest solution. However, active noise cancellation is another alternative. Active noise cancellation emits a reverse phase signal into the environment at frequencies matching the noise of disturbance, effectively absorbing its energy and canceling its sound.

Plumbing Noise
Any pipe with a long drop, or is installed in a wall adjacent to a cabin or stateroom, should also be acoustically addressed. Pipes should be secured to the structure only with flexible acoustic connectors. Also, the sound of running water through PVC pipes should be addressed in acoustically sensitive rooms such as bedrooms, media rooms, dining rooms, massage rooms, etc.

In-Wall and In-Ceiling Speakers
Any recessed speaker must have an acoustic enclosure. The enclosure should be manufactured with a material that prohibits the sound from transferring to another room without distorting the acoustic wave of the speaker.   
Acoustic Leakage
All recessed lighting, electrical outlets, light switches, etc., are major conduits for sound to transmit. However, even smaller voids in the acoustic configuration can lead to a significant acoustic degradation. To illustrate the severity and ramification of acoustic leakage, consider this: A hole that enters a wall by one square inch can result in more than a 10 dB efficacy reduction. Thus, caulking edges, junctures and cracks is essential for creating an acoustically enclosed room.  

Acoustics Throughout the Yacht
Every enclosed space exhibits reverberation, which is sound persistence due to repeated boundary reflections after the source of sound, has stopped. Additionally, the acoustic waves after bouncing off the reflective surfaces can make the room uncomfortable. These are some of the effects:

• Excessive reverberation causes overlapping syllables and tones, which reduce the intelligibility of speech and music;
• High, or long, reverberation times can elevate sound levels, creating a noisy room;
• The reflection of acoustic waves off of surfaces within the space can strike another wave in opposite phase, causing a standing wave. A standing wave is nature's version of noise cancelation, which can negatively affect the environment's audio systems.

Mathematically locating and applying acoustic materials--absorbers, reflectors and diffusors-- at various locations within the boundaries of the room. Many designers can solve excessive reverberation with fabric-wrapped, compressed fiberglass or acoustic diffusors. When doing so, it's important to remember that there are new and innovative ways to achieve an acoustically correct environment.

With every yacht, and every space within the yacht, there's always a personal aesthetic assigned to the design. We all have our own personal vision for how to transform a room into a little slice of paradise--and this vision should always include sound. Sound is a pressure wave not only heard, but also felt.

By providing an acoustically perfect environment, the room will not only sound great, but will feel great as well. Our passion is to provide our clientele with a slice of paradise through perfect acoustics.