Once the noise sources are identified and measured, the goal is to reduce the amount of sound energy emitted by the source, divert the sound path away from the receiver, or protect the receiver from the sound energy reaching him or her. The key factor is to find a solution that is both effective and economical.
Sometimes noise issues are simply occurring because of equipment that is in need of repair or replacement, improper machinery maintenance, poor operating procedures, or bad equipment location. Sometimes the ability to just relocate a piece of machinery can have a big effect on the amount of noise that reaches the receiver, and can be as much as 6dB for every doubling of distance. If these issues have been explored and corrected but the noise problems have not been satisfactorily resolved, then the addition of sound control products is needed.
Room Treatment – The presence of hard reflective surfaces in the workplace such as concrete walls and metal ceilings will result in the build up of sound levels in the reverberant field. By controlling the reflected sound with the use of acoustically absorbent materials applied to the walls and ceiling surfaces, or hung from the ceiling as baffles, this will reduce the sound levels by several decibels. Quilted fiberglass absorber panels and baffles are ideal for industrial environments. If a work area is in close proximity to nearby office spaces it may be necessary to add additional mass and decouple common walls and ceilings with the use of flexible mass loaded vinyl noise barrier and resilient isolation clips. This increases the STC, (Sound Transmission Class), of the partitions and disrupts the sound path. It may also be necessary to replace existing common doors and windows with acoustically rated models or adding acoustic door seal kits.
Vibration Control – Vibration control eliminates or reduces vibration at the source. Airborne noise is produced by any solid vibrating machinery component which pushes and pulls against the air causing pressure changes that radiate in all directions. Through the use of vibration isolators, the vibrating member is disassociated from the force causing it to vibrate by interposing a compressed “springy” material such as ribbed neoprene between the two. Vibrations Isolators are selected by determining the weight to be supported, the deflection required, and the lowest frequency of the unit to be isolated. Any hard connections to the equipment such as conduit or pipe can transmit noise and vibration through the adjoining surfaces they are mounted to and must be decoupled with the use of acoustic isolation hangers. This is also true of HVAC equipment and ductwork. Some machinery such as punch presses may also need to be decoupled from the floor with properly rated isolation pads.
Surface Damping – Metal or plastic parts are frequently set into vibration by multiple impacts with chutes or conveyors. This free vibration can be attenuated with the application of damping materials to reduce resonance. These materials are available in peel and stick sheets, or are sometimes troweled, painted, or sprayed on. When choosing a damping material, the affects of temperature, humidity, and chemical exposure must be taken into consideration.
Acoustic Barriers – An acoustic barrier is piece of solid material of sufficient mass placed between the receiver and the noise source. Acoustic barriers function by deflecting the flow of sound energy away from the worker. They are most effective when the worker is close to the noise source. The farther away the worker is from the noise source, the less sound reduction will be achieved. To minimize the addition of unwanted reflections, the machine side of the barrier should be lined with an acoustical absorbent material such as fiberglass. Barrier Septum Composite Panels make ideal acoustic barriers because they combine a mass loaded vinyl barrier sandwiched between two layers of fiberglass and covered in a quilted vinyl facing that is oil resistant and cleanable.
Machinery Enclosures – Sometimes it is necessary to partially or completely enclose a piece of machinery with an acoustic enclosure. Soft enclosures constructed with acoustical barrier backed composite panels typically achieve noise reductions in the 10 to 15 dBA range. These panels are fabricated with a 1 or 2 pound per square foot reinforced mass loaded vinyl barrier bonded to a 1” or 2” fiberglass absorber covered in a quilted vinyl facing. For higher attenuation, hard enclosures constructed of fiberglass filled modular steel panels are used
Partial enclosures are created by wrapping a barrier around a machine with its top open. A partial enclosure can be effective by reducing noise to workers nearby, but the noise escapes through the top and contributes to the overall reverberant sound in the workroom. Also, reflections from the ceiling can contribute to the reflected-path levels. These spill-over effects can be mitigated by covering the inside of the enclosure with an acoustically absorbent material, and hanging acoustic ceiling baffles over the openings to reduce the escaping noise. Total enclosures achieve the most noise reduction but require additional attention to things like heat build up, personnel access, and material handing. Acoustic enclosures can be equipped with ventilation blowers with HVAC silencers on the intake and exhaust vents to reduce heat and prevent noise from escaping through the openings. Tunnels fabricated with the same material as the enclosure can be added to accommodate the movement of material in and out of the enclosure.
HVAC Noise – HVAC silencers are used to attenuate airborne noise through commercial HVAC ductwork systems, building openings, sound enclosures, ventilating fans, and plenum equipment. They are installed inline with the existing ductwork or over existing openings and attenuate sound through the use of fiberglass filled baffles tuned to specific frequency ranges. The installation of HVAC silencers is frequently necessary to attenuate noise escaping to surrounding areas and to meet with local municipal codes.
Hearing Protection – Sometimes it is impractical or cost prohibitive to shield a worker from loud noise. In this case hearing protection is necessary to protect the worker’s health and to comply with OSHA regulations. Today’s modern hearing protection products are equipped with modern technology such as noise cancellation and impulse suppression, and allow for communication between workers.