The way that sounds behave in a room can be broken up into roughly four different frequency zones:

• The first zone is below the frequency that has a wavelength of twice the longest length of the room. In this zone sound behaves very much like changes in static air pressure.
• Above that zone, until the frequency is approximately 11,250(RT60/V)^1/2, wavelengths are comparable to the dimensions of the room, and so room resonances dominate.
• The third region which extends approximately 2 octaves is a transition to the fourth zone.
• In the fourth zone, sounds behave like rays of light bouncing around the room.

Natural Modes

Computer plot of the application of criteria to a room with correct dimensions

Computer plot of the application of criteria to a room with bad dimensions

Typical acoustical absorption of the standard panels developed by Oscar Bonello

The sound wave has reflections at the walls, floor and ceiling of the room. The incident wave then has interference with the reflected one. This action creates standing waves (described at Standing wave) that generate nodes and high pressure zones. The mode spacing is a very important matter especially in small and medium size rooms like recording studios, home theaters, broadcasting studios and concert halls. Some methods were created from 1940 - 1981 to obtain the best mode spacing to avoid sound coloration, but none of them succeed, because the mode spacing is not only a geometric problem  An incorrect mode spacing in a room determinates a bad frequency response from a loudspeaker or a music player

In order to solve this problem, Oscar Bonello, professor at the University of Buenos Aires, created in 1981 the Modal Density concept that solves the problem introducing concepts from Psychoacoustics  This new Bonello’s Criterion as it was named, analyzes the first 48 room modes and plot the numer of modes in each one-third of octave. The curve must increase monotonically (each one-third of octave must have more modes than the preceding one). This Criterion is now the standard method of designing the room dimensions.

Reverberation of the room

After determining the best dimensions of the room, using Modes Density criteria, the next step is finding the correct reverberation time. A good explanation of the theory can be found at Reverberation. The reverberation time depend on the use of the room. Times about 1.5 to 2 seconds are needed for Opera Theaters and Concert Halls. For Broadcasting & Recording studios and Conference rooms, values under one second are frequently used. The recommended Rev Time is always functioning of the volume of the room. Several authors give their recommendations A good approximation for Broadcasting Studios and Conference Rooms is: TR[1khz] = [0,4 log (V+62)] – 0,38 TR in seconds and V=volume of the room in m3  The ideal RT must have the same value at all frequencies from 30 to 12.000 Hz Or at least, is acceptable to have a linear rising from 100% at 500 Hz to 150 % down to 62 Hz

In order to get the calculated RT in a room, several acoustics materials can be uses as described in several books. A valuable simplification of the task was proposed by Oscar Bonello in 1979. It consists of using standard acoustic panels of 1 m2 hanged from the walls of the room. These panels use a combination of three Helmholtz resonators and wooden resonant panel. This system gives a large acoustic absorption at low frequencies (under 500 Hz) and reduces at high frequencies to compensate the typical absorption of people, lateral surfaces, ceilings, etc

Heating, ventilating, and air conditioning is based on the basic principles of thermodynamics, fluid mechanics, and heat transfer, and to inventions and discoveries made by Michael Faraday, Willis Carrier, Reuben Trane, James Joule, William Rankine, Sadi Carnot, and many others. The invention of the components of HVAC systems goes hand-in-hand with the industrial revolution, and new methods of modernization, higher efficiency, and system control are constantly introduced by companies and inventors all over the world.

The three functions of heating, ventilating, and air-conditioning are closely interrelated. All seek to provide thermal comfort, acceptable indoor air quality, and reasonable installation, operation, and maintenance costs. HVAC systems can provide ventilation, reduce air infiltration, and maintain pressure relationships between spaces. How air is delivered to, and removed from spaces is known as room air distribution.^[1]

In modern buildings the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally “size” and select HVAC systems and equipment. For larger buildings where required by law, “building services” designers and engineers, such as mechanical, architectural, or building services engineers analyze, design, and specify the HVAC systems, and specialty mechanical contractors build and commission them. In all buildings, building permits for, and code-compliance inspections of the installations are the norm.

The HVAC industry is a worldwide enterprise, with career opportunities including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry had been historically regulated by the manufacturers of HVAC equipment, but Regulating and Standards industries such as ASHRAE, SMACNA, ACCA, and AMCA, have been established to support the industry and encourage high standards and achievement.

The International Association of Plumbing and Mechanical Officials (IAPMO) published its first version of the Uniform Mechanical Code (UMC) in 1967. The UMC provides complete requirements for the installation and maintenance of heating, ventilating, cooling and refrigeration systems, while at the same time allowing latitude for innovation and new technologies. The 2006 UMC is supported by the Mechanical Contractors Association of America (MCAA) and Plumbing-Heating-Cooling Contractors National Association (PHCC-NA).

Most recently, the ICC has been established to create international standards that many countries, including the US, Canada, the UK, Australia and many others have been adopting.

Air-conditioning

Air Conditioning and refrigeration are provided through the removal of heat. The definition of cold is the absence of heat and all air conditioning systems work on this basic principle. Heat can be removed through the process of radiation, convection, and conduction using mediums such as water, air, ice, and chemicals referred to as refrigerants. In order to remove heat from something, you simply need to provide a medium that is colder — this is how all air conditioning and refrigeration systems work.

An air conditioning system, or a standalone air conditioner, provides cooling, ventilation, and humidity control for all or part of a house or building. The Freon or other refrigerant provides cooling through a process called the refrigeration cycle. The refrigeration cycle consists of four essential elements to create a cooling effect. A compressor provides compression for the system. This compression causes the cooling vapor to heat up. The compressed vapor is then cooled by heat exchange with the outside air, so that the vapor condenses to a fluid, in the condenser. The fluid is then pumped to the inside of the building, where it enters an evaporator. In this evaporator, small spray nozzles spray the cooling fluid into a chamber, where the pressure drops and the fluid evaporates. Since the evaporation absorbs heat from the surroundings, the surroundings cool off, and thus the evaporator absorbs or adds heat to the system. The vapor is then returned to the compressor. A metering device acts as a restriction in the system at the evaporator to ensure that the heat being absorbed by the system is absorbed at the proper rate.

Central, ‘all-air’ air conditioning systems are often installed in modern residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required. A duct system must be carefully maintained to prevent the growth of pathogenic bacteria in the ducts. An alternative to large ducts to carry the needed air to heat or cool an area is the use of remote fan coils or split systems. These systems, although most often seen in residential applications, are gaining popularity in small commercial buildings. The remote coil is connected to a remote condenser unit using piping instead of ducts.

Dehumidification in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below dew point, moisture is collected at the evaporator. This moisture is collected at the bottom of the evaporator in a condensate pan and removed by piping it to a central drain or onto the ground outside. A dehumidifier is an air-conditioner-like device that controls the humidity of a room or building. They are often employed in basements which have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal air. Conversely, a humidifier increases the humidity of a building.

Air-conditioned buildings often have sealed windows, because open windows would disrupt the attempts of the HVAC system to maintain constant indoor air conditions.

VISIT ISTIQ WEBSITE AT WWW.ISTIQ.NET

1. What is Noise? [top]

The path length and the efficiency of the wall in reflecting sound determine the amplitude of a particular reflection. That efficiency is described as the absorption coefficient (any sound not reflected is absorbed). The coefficient of absorption is a number between 0 and 1, with 1 representing total absorption (an open window) and 0 representing total reflection.

8. What is NRC? [top]

NRC is the abbreviation of Noise Reduction Coefficient. It is defined as the average absorption measured at 250, 500, 1000, and 2000 Hz of a certain material

9. What is the difference between insulation & absorption? [top]

If you want to hear the very best effects processors can do, then make sure you have as good a sound-stage as possible. Only a room with good reverberation time, a diffuse sound field and as few acoustic artifacts as possible will demonstrate just how amazing these processors can sound. Determining the amount of each treatment needed and where to place that treatment is the first step to achieve a balanced listening environment.Call ISTIQ Noise Control Sdn. Bhd. Phone No. 03-91727205, or E-Mail us at nonoise@istiq.com

11. How do I get help improving my listening room? [top]

It is generally not possible to give a firm indication of likely costs on this site, as each particular investigation or report will vary in the time it will take, and the resources that are necessary to achieve a successful conclusion. For this reason, it is essential that we provide you with a written quotation in advance. There is no charge for this service, which will usually entail a site visit. Under some circumstances, it may be possible to give either an indicative estimate or even a firm quotation if sufficient information can be obtained prior to a visit.
Our quotes give a clear indication of the extent of the contract and what you can expect to be contained in the final report. If you would like to e-mail ISTIQ Noise Control to discuss your requirements, please click here.

The ASTM test methods have changed every few years and over many years have been changed significantly. Thus, STC results posted before 1999 may not produce the same results today, and this difference becomes wider as one goes back in time (that is the differences in test method from the 1970’s to today are vast).

The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz. These transmission-loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour. Acoustical engineers fit these values to the appropriate TL Curve (or Transmission Loss) to determine an STC rating. The measurement is accurate for speech sounds but less so for amplified music, mechanical equipment noise, transportation noise or any sound with substantial low-frequency energy below 125 Hz. Sometimes, acoustical labs will measure TL at frequencies below the normal STC boundary of 125 Hz, possibly down to 50 Hz or lower, thus giving additional valuable data to evaluate transmission loss at very low frequencies, such as a subwoofer-rich home theater system would produce. Alternatively, Outdoor-Indoor Transmission Class (OITC) is a standard used for indicating the rate of transmission of sound between outdoor and indoor spaces in a structure that considers frequencies down to 80 Hz (Aircraft/Rail/Truck traffic) and is weighted more to lower frequencies.

STC is roughly the decibel reduction in noise a partition can provide, abbreviated ‘dB’. The dB scale is a logarithmic one and the human ear perceives a 10dB reduction in sound as roughly halving the volume - a 40 dB noise subjectively seems half as loud as a 50 dB one. (For more detail on equal-loudness curves see: Fletcher-Munson curves.) If an 80dB sound on one side of a wall/floor/ceiling is reduced to 50dB on the other side, that partition is said to have an STC of 30. This number does not apply across the range of frequencies, since the STC value is A-weighted and derived from a curve-fit of many datapoints. Any partition will have less TL at lower frequencies. For example, a wall with an STC of 30 may provide over 40dB of attenuation at 3000 Hz but only 10dB of attenuation at 125 Hz.

Typical interior walls in homes (2 sheets of 1/2″ drywall on a wood stud frame) have an STC of about 33. When asked to rate their acoustical performance, people often describe these walls as “paper thin”. They offer little in the way of privacy. Adding absorptive insulation (i.e. fiberglass batts) in the wall cavity increases the STC to 36-39, depending on stud and screw spacing. Doubling up the drywall in addition to insulation can yield STC 41-45, provided the wall gaps and pentrations are sealed properly.

Note that doubling the mass of a partition does not double the STC. Doubling the mass (going from two total sheets of drywall to four, for instance) typically adds 5-6 points to the STC. Breaking the vibration paths by decoupling the panels from each other will increase transmission loss much more effectively than simply adding more and more mass to a monolithic wall/floor/ceiling assembly.

Structurally decoupling the drywall panels from each other (by using resilient channels, steel studs, a staggered-stud wall, or a double stud wall) can yield an STC as high as 63 or more for a double stud wall (see table below), with good low-frequency transmission loss as well. Compared to the baseline wall of STC 33, an STC 63 wall will transmit only 1/1000 as much sound energy, seem 88 percent quieter and will render most frequencies inaudible.

Due to their high density, concrete and concrete block walls have good TL values (STC’s in the 40s and 50s for 4-8″ thickness) but their weight, added complexity of construction and poor thermal insulation tend to limit them as viable materials in most residential wall construction, except in temperate climates and hurricane or tornado prone areas. Various Cellulose insulation installation options can result in an STC of 50 or greater. ^[1]

Materials which can improve STC’s in walls include mass-loaded vinyl (MLV) and soundproof drywall, such as QuietRock.

It must be noted that acoustical performance values such as STC are measured in specially constructed acoustical chambers and field conditions such as lack of adequate sealing, outlet boxes, back-to-back electrical boxes, medicine cabinets, flanking paths and structure-borne sound can diminish acoustical performance. The as-built ‘field-STC’ (FSTC) is usually lower than the laboratory-measured STC.

New multifamily dwellings(apartments, condominiums, duplexes, etc.) are required by building code to meet a minimum of STC 50 between units. This is sufficient to block normal speech, but may not adequate for a home theater or loud stereo which can reach 110 dB or more.

In serious cases (for instance, a bedroom adjacent to a home theater room, and an inconsiderate nocturnal neighbor, to boot) a partition to reduce sounds from high-powered home theater or stereo should ideally be STC 70 or greater, and show good attenuation at low frequencies. An STC 70 wall can require detailed design and construction and can be easily compromised by ‘flanking noise‘, sound traveling around the partition through the contiguous frame of the structure, thus reducing the STC significantly. STC 65 to 70 walls are often designed into luxury multifamily units, dedicated home theaters, and high end hotels.

The demanding THX reference standard (a guideline for high-quality audio in movie soundtracks) requires partitions to achieve 50dB of attenuation at 63 Hz. Few walls can meet that, as that requires a wall with an STC of 80 or higher. For all practical purposes, no sound will be heard on the other side of the wall with this level of construction. However, an STC this high is not achievable in simple construction and this level of isolation is only feasible for high-end studios and theaters, where the design and construction can be carefully controlled and the additional cost is justified.

Sound Transmission Class Examples

STC partition ratings taken from: “Noise Control in Buildings: A Practical Guide for Architects and Engineers”; Cyril M. Harris, 1994

Noise health effects

Roadway noise is a major source of exposure

Noise health effects are the health consequences of elevated sound levels. Elevated workplace or other noise can cause hearing impairment, hypertension, ischemic heart disease, annoyance, sleep disturbance, and decreased school performance. Changes in the immune system and birth defects have been attributed to noise exposure, but evidence is limited.^[1] Although some presbycusis may occur naturally with age,^[2] in many developed nations the cumulative impact of noise is sufficient to impair the hearing of a large fraction of the population over the course of a lifetime.^[3][4] Noise exposure has also been known to induce tinnitus, hypertension, vasoconstriction and other cardiovascular impacts.^[5] Beyond these effects, elevated noise levels can create stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors.^[6] The most significant causes are vehicle and aircraft noise, prolonged exposure to loud music, and industrial noise.

Hearing loss

Hearing loss is somewhat inevitable with age. Though older males exposed to significant occupational noise demonstrate significantly reduced hearing sensitivity than their non-exposed peers, differences in hearing sensitivity decrease with time and the two groups are indistinguishable by age 79.^[2] Women exposed to occupational noise do not differ from their peers in hearing sensitivity, though they do hear better than their non-exposed male counterparts. Due to loud music and a generally noisy environment, young people in the United States have a rate of impaired hearing 2.5 times greater than their parents and grandparents, with an estimated 50 million individuals with impaired hearing estimated in 2050.^[3]

The mechanism of hearing loss arises from trauma to stereocilia of the cochlea, the principal fluid filled structure of the inner ear.^{[citation needed]} The pinna combined with the middle ear amplifies sound pressure levels by a factor of twenty, so that extremely high sound pressure levels arrive in the cochlea, even from moderate atmospheric sound stimuli. Underlying pathology to the cochlea are reactive oxygen species, which play a significant role in noise-induced necrosis and apoptosis of the stereocilia.^[7] Exposure to high levels of noise have differing effects within a given population, and the involvement of reactive oxygen species suggests possible avenues to treat or prevent damage to hearing and related cellular structures.^[7]

Cardiovascular effects

Noise has been associated with important cardiovascular health problems.^[8] In 1999, the World Health Organization concluded that the available evidence showed suggested a weak association between long-term noise exposure above 67-70 dB(A) and hypertension.^[9] More recent studies have suggested that noise levels of 50 dB(A) at night may also increase the risk of myocardial infarction by chronically elevating cortisol production.^[10][11][12]

Fairly typical roadway noise levels are sufficient to constrict arterial blood flow and lead to elevated blood pressure; in this case, it appears that a certain fraction of the population is more susceptible to vasoconstriction. This may result because annoyance from the sound causes elevated adrenaline levels trigger a narrowing of the blood vessels (vasoconstriction), or independently through medical stress reactions. Other effects of high noise levels are increased frequency of headaches, fatigue, stomach ulcers and vertigo.^[13]

The U.S. Environmental Protection Agency authored a pamphlet in 1978 that suggested a correlation between low-birthweight babies (using the World Health Organization definition of less than 2,500 g (~5.5 lb) and high sound levels, and also correlations in abnormally high rates of birth defects, where expectant mothers are exposed to elevated sound levels, such as typical airport environs. Specific birth abnormalities included harelip, cleft palate, and defects in the spine. According to Lester W. Sontag of The Fels Research Institute (as presented in the same EPA study): “There is ample evidence that environment has a role in shaping the physique, behavior and function of animals, including man, from conception and not merely from birth. The fetus is capable of perceiving sounds and responding to them by motor activity and cardiac rate change.” Noise exposure is deemed to be particularly pernicious when it occurs between 15 and 60 days after conception, when major internal organs and the central nervous system are formed. Later developmental effects occur as vasoconstriction in the mother reduces blood flow and hence oxygen and nutrition to the fetus. Low birth weights and noise were also associated with lower levels of certain hormones in the mother, these hormones being thought to affect fetal growth and to be a good indicator of protein production. The difference between the hormone levels of pregnant mothers in noisy versus quiet areas increased as birth approached.

Annoyance

Because some stressful effects depend on qualities of the sound other than its absolute decibel value, the annoyance associated with sound may need to be considered in regard to health effects. For example, noise from airports is typically perceived as more bothersome than noise from traffic of equal volume.^[14]Annoyance effects of noise are minimally affected by demographics, but fear of the noise source and sensitivity to noise both strongly affect the ‘annoyance’ of a noise.^[15] Even sound levels as low as 40 dB(A) (about as loud as a refrigerator or library^[16]) can generate noise complaints^[17] and the lower threshold for noise producing sleep disturbance is 45 dB(A) or lower.^[18] Other factors that affect the ‘annoyance level’ of sound include beliefs about noise prevention and the importance of the noise source, and annoyance at the cause (i.e. non-noise related factors) of the noise.^[19] Evidence regarding the impact of long-term noise versus recent changes in ongoing noise is equivocal on its impact on annoyance.^[19]

Estimates of sound annoyance typically rely on weighting filters, which consider some sound frequencies to be more important than others based on their presumed audibility to the human ear. The older dB(A) weighting filter described above is used widely in the U.S., but underestimates the impact of frequencies around 6000 Hz and at very low frequencies. The newer ITU-R 468 noise weighting filter is used more widely in Europe. The propagation of sound varies between environments; for example, low frequencies typically carry over longer distances. Therefore different filters, such as dB(B) and dB(C), may be recommended for specific situations.

When young children are exposed to speech interference levels of noise on a regular basis (the actual volume of which varies depending on distance and loudness of the speaker), there may develop speech or reading difficulties, because auditory processing functions are compromised.^{[citation needed]} In particular the writing learning impairment known as dysgraphia is commonly associated with environmental stressors in the classroom.^{[citation needed]}

Regulations

Environmental noise regulations usually specify a maximum outdoor noise level of 60 to 65 dB(A), while occupational safety organizations recommend that the maximum exposure to noise is 40 hours per week at 85 to 90 dB(A). For every additional 3 dB(A), the maximum exposure time is reduced by a factor 2, e.g. 20 hours per week at 88 dB(A). Sometimes, a factor of two per additional 5 dB(A) is used. However, these occupational regulations are acknowledged by the health literature as inadequate to protect against hearing loss and other health effects

References

1. ^ Passchier-Vermeer W, Passchier WF (2000). “Noise exposure and public health”. Environ. Health Perspect. 108 Suppl 1: 123–31. PMID 10698728. 
2. ^ ^{a b} Rosenhall U, Pedersen K, Svanborg A (1990). “Presbycusis and noise-induced hearing loss”. Ear Hear 11 (4): 257–63. PMID 2210099. 
3. ^ ^{a b} Schmid, RE. “Aging nation faces growing hearing loss“, CBS News, 2007-02-18. Retrieved on 2007-02-18. 
4. ^ Senate Public Works Committee, Noise Pollution and Abatement Act of 1972, S. Rep. No. 1160, 92nd Cong. 2nd session
5. ^ Noise: Health Effects and Controls. University of California, Berkeley. Retrieved on 2007-12-22.
6. ^ Kryter, Karl D. (1994). The handbook of hearing and the effects of noise: physiology, psychology, and public health. Boston: Academic Press. ISBN 0-12-427455-2. 
7. ^ ^{a b} Henderson D, Bielefeld EC, Harris KC, Hu BH (2006). “The role of oxidative stress in noise-induced hearing loss”. Ear Hear 27 (1): 1–19. doi:10.1097/01.aud.0000191942.36672.f3. PMID 16446561. 
8. ^ Ising H, Babisch W, Kruppa B (1999). “Noise-Induced Endocrine Effects and Cardiovascular Risk“. Noise Health 1 (4): 37–48. PMID 12689488. 
9. ^ Berglund, B; Lindvall T, Schwela D, Goh KT (1999). World Health Organization: Guidelines for Community Noise. World Health Organization.
10. ^ Maschke C (2003). “Stress Hormone Changes in Persons exposed to Simulated Night Noise“. Noise Health 5 (17): 35–45. PMID 12537833. Retrieved on 2007-12-22. 
11. ^ Franssen EA, van Wiechen CM, Nagelkerke NJ, Lebret E (2004). “Aircraft noise around a large international airport and its impact on general health and medication use”. Occup Environ Med 61 (5): 405–13. PMID 15090660. 
12. ^ Lercher P, Hörtnagl J, Kofler WW (1993). “Work noise annoyance and blood pressure: combined effects with stressful working conditions”. Int Arch Occup Environ Health 65 (1): 23–8. PMID 8354571. 
13. ^ Noise: A Health Problem United States Environmental Protection Agency, Office of Noise Abatement and Control, Washington, DC 20460, August, 1978
14. ^ Miedema and Oudshoorn 2001 cited in Hypertension and exposure to noise near airports. Medscape.
15. ^ Miedema HME, Vos H. “Demographic and attitudinal factors that modify annoyance from transportation noise”. Journal of the Acoustical Society of America 105 (6): 3336–44. doi:10.1121/1.424662. 
16. ^ [1.pdf Noise Facts and Figures!] (PDF). Chiltern District Council. Retrieved on 2007-12-13.
17. ^ Gelfand, Stanley A. Essentials of Audiology. New York: Thieme Medical Publishers. ISBN 1-58890-017-7. 
18. ^ Walker, JR; Fahy, Frank (1998). Fundamentals of noise and vibration. London: E & FN Spon. ISBN 0419227008. 
19. ^ ^{a b} Field, JM (1993). “Effect of personal and situational variables upon noise annoyance in residential areas”. Journal of the Acoustical Society of America 93 (5): 2753–63. doi:10.1121/1.405851. Retrieved on 2007-12-13. 

Introduction

Generator Sets in general, produce an overall noise level in the range of 100 to 115 dB(A), depending on the rating and manufacturer. The higher the rating; the higher the noise level produces by the genset.

A typical design of Acoustic treatment for genset  room normally will reduce the noise level down to 75 to 85 dB(A) measured at 1 meter away from the genset house. However, the noise can be designed to achieve better if the requirement call for it.

In Malaysia, the Department of Environment (DOE) guidelines on the Acoustic Treatment is to control the noise level to 65 dB(A) during daytime and 55 dB(A) during nighttime, measured at the boundary of premises.

Control At Source

The best way to treat noise is always to do it at the source and for Generator Sets, there are three major noise sources produce by the gensets: -

• Noise emitted by the Radiator Fan
• Noise emitted by the Exhaust System
• Noise emitted by mechanical engine itself

Acoustic Equipment for Noise Control treatment in the generator sets room mainly consists of the following: -

• Fan Discharge Silencers
• Intake Silencers
• Exhaust Silencers
• Acoustic Doors

Except for the door, the rest of the equipment are in static condition where there is no moving part in the inside or outside of the Acoustic Equipment. 

FAN DISCHARGE SILENCERS

The silencer is normally installed in front of the radiator fan in order to control the noise emitted by the fan. How much noise to be reduced will depend on the length of the silencer; the longer the silencer, the better the attenuation and thus, more noise will be reduced. However, it will increase the pressure drop across the silencer.

The width and height of the silencer will depend on the airflow of the fan. Higher airflow require the size of the silencer to be bigger.

Discharge Silencers should be not be installed too close to the fan to avoid noise regenerated by the fan blades. Flexible coupling should be used between the silencers and adjoining radiator where there is a possibility of vibration transmission.

INTAKE SILENCERS

Since the generator sets required air ventilation for cooling and combustion purposes, an opening at the generator set house is required. However, this will let the noise escape out from the room. Intake Silencers, consequently is used to serve these ends.

It is highly recommended that the Intake Silencers are not to be installed with the same side with the Discharge Silencer. This is to prevent the “short circuit” of the ventilation.  

Intake Silencer is normally position at the high level of the room.

EXHAUST SILENCERS & SYSTEM

Exhaust system of the generator set produce the highest noise level of all the three sources. The noise level for the exhaust is typically around 110 - 115 dB(A).

When designing an exhaust system there are a number of factors that should be considered to maximize the design in terms of performance and cost. A few of the items that should be taken into consideration include: -

Acoustic Environment into which exhaust is discharging

• Engine Rating, i.e. - exhaust flow
• allowable engine back pressure
• engine exhaust outlet noise level

Engine Exhaust Outlet Design, i.e. single or dual outlets

• Exhaust Piping Arrangement within engine room
• Exhaust Piping Support, Anchoring, and Guiding
• Exhaust Stack Height
• Configuration of Exhaust Silencers, i.e. single or dual inlet

ISTIQ Exhaust Silencers come in standard, stock silencers for general-purpose applications and custom models to fit most OEM engines. These include: -

Model IXP - Multi-Chamber Reactive Type Attenuation - 30 dB     Model IXS - Straight Through Absorptive Type Attenuation - 20 dB

Model IXC - Supercritical or Combination Attenuation - 35 dB

ACOUSTIC DOORS

The requirement of Acoustic Door to be incorporated at the generator set room is obviously to prevent the noise from transmitting through the doorways.

ISTIQ Acoustic Doors used for generator sets are all steel doors utilising the absorptive edge principle. They are used to contain the noise within noisy areas or to prevent noise transmission to sensitive areas.

DUCT SILENCER

Whenever ventilation is required in the enclosed compartment and at the same time noise is to be controlled, installing duct silencers or attenuator are the best way to solve the problem. The silencers permit air to flow through while reduce the noise by absorbing it.

In selecting a silencer, a balance between noise attenuations and pressure drop need to be considered carefully. By using internally developed software, ISTIQ Noise Control can help to make the right choice quickly and most importantly, accurately.

Introduction

ISTIQ Duct Silencers are designed to efficiently reduce noise by generator sets, air handling systems, compressor, blower system and all situations requiring air intake and outlet for these equipments to operate.

A duct silencer should always positioned in the plant room and if possible as close to the noise source as possible. Normally for a single equipment, two units of duct silencers - intake and discharge is required to effectively reduce the noise to a desired level.

Construction

ISTIQ Duct Silencers consist of a galvanised sheet metal case containing two side panels and one or more splitters. Normal low pressure silencers uses Pittsburgh  seams with attached angle frames step welded to the case. Duct sealer is then used to seal to ensure that the silencer is airtight. For high pressure system, the silencer has fully welded seams. The angle frame are protected by a paint finish.

Inside the splitters, rockwool or fibre glass is used as sound absorptive infill and is held in the splitters inside a perforated galvanised steel skin. Different  acoustic infill is used depending on the application to ensure excellent performance and its effectiveness.

For heavier industrial or marine application, enhanced construction and corrosion resistance are required.  ISTIQ Engineers will be glad to discuss and advice your specific needs regarding the design of the structural, aerodynamic and corrosion protection requirement.

Features

ISTIQ Duct Silencers are available in two different models, which basically have two different thicknesses of splitters - 200 mm and 300 mm. The thicker the splitter the better performance at lower frequencies. Each of the models have six length sizes from  900 to 3000 mm. The cross sectional  area has no limited size. The performance or the insertion loss of each model is shown in the table 1.

ISTIQ Duct Silencers will be supplied in sections whenever the silencer dimension exceeded 2100W x 2100H x 2100mmL. This will make the transportation and installation easier. The assembly of sectionalized silencers to be done at site.

SELECTION GUIDELINES

The right selection of silencer should gives the essential attenuation at a permissible amount of pressure drop of a given air requirement. The selection method therefore can be simplified as follows :-

• Establish the noise target. Noise target could be in noise overall value or in NC criteria as recommended in Table 1.
• Obtain the noise level of the source,
• Calculate the difference of the level between the noise target and the noise source. Should there is any distance involve or any condition which noise will reduce naturally, it should be considered.
• Match up the difference of the level with the insertion loss of ISTIQ silencer and select the model as shown in Table 2.
• The silencer can be sized up by knowing the airflow requirement and the allowable pressure drop across the silencer by using the formulae below :

                Pressure Drop   = kv²

                where v                = Air Flow in m³/s

                                                   Width x Height in m²

                And k as listed in Table 3.

For detailed procedures of calculating the required attenuation, ISTIQ Engineers will be glad to help.

Established in 1995, we have grown to become one of the leading company in Industrial and Building Acoustics. Our services ranges from products supply, designing, fabricating and installation of an assigned acoustic projects.

ISTIQ Noise Control is highly specialized and well recognized in applications involving Generator Sets, Blowers, Compressors, Press Machine and HVAC systems. All of our works in controlling the noise on these applications either meet or exceed the requirement set by the Malaysian Department of Environment (DOE) and Department of Safety and Health (DOSH).

When it comes to building music rooms, studios, lecture hall or auditorium, our skill and workmanship are at our best. We take pride in building them and we must admit that we are proud of our achievement. Almost all of our customers express their satisfaction to us; one way or the other.

Apart from this, we also provides services in Noise Measurement and obtaining approval from DOE.

In 1997, ISTIQ Fabrication, our subsidiary company was established to make headway in fabricating our Acoustic Products. Among its job are to acquire and implement the latest manufacturing technology while maintaining the cost effectiveness. But, above all, to ensure that ISTIQ products are of their highest standard and quality to meet the demanding requirement locally as well as from various part of the world.

ISTIQ products are widely used throughout Malaysia and Singapore. We had stride far reaching Hong Kong, Taiwan, Maldives and Angola. We are proud to gain recognition from customers such as Matsushita, Shell, HAWLETT PACKARD, Petronas, Volvo, Tractors and SIEMENS. Our commitment to providing our customers with premier service and support is second to none.