Frequently asked questions

What humans perceive as sound is the propagation of pressure waves through a medium. The speed of sound varies from medium to medium, with denser mediums having faster wave propagation. Different sound frequencies are perceived as different tones. Any undesirable sound is referred to as noise.

Quite simply, noise is any undesirable sound.

Noise reduction is any targeted reduction to sound pressure levels implemented using noise reduction equipment.

Sound is a pressure wave that propagates through a medium (typically air). Like any wave, sound waves have hills and valleys corresponding to areas of high and low pressure. The amplitude of the sound wave (distance from atmospheric pressure to the high or low points on the wave) is the sound pressure and is typically expressed in units of Pascals or pounds per square inch.

Sound power represents the total energy of a sound. It is independent of distance and the acoustics of the surrounding space. You cannot hear sound power; you can only hear sound pressure.

Sound frequency is the number of oscillations of a sound wave in a set period of time. From a human's perspective, these frequencies can be equated to the pitch of a sound. Sound frequency is measured in number of oscillations per second, or Hertz. Humans can hear between 20 Hz and 20,000 Hz, with lower pitched sounds having a lower frequency.

A decibel is a logarithmic measure of sound pressure or sound power levels. It is based on the threshold of human hearing. As a result, 0 dB is the quietist environment a human can perceive. On the other extreme, 130 dB is the loudest sound a human can hear without experiencing immediate physical pain. Since it is a logarithmic scale, every 3 dB increase in sound level requires twice the amount of sound power or sound pressure to produce.

Humans do not hear all frequencies equally. Sound levels in the low frequency end of the spectrum are reduced. In order to account for this, different weightings have been created to give a loudness measurement that takes into account how the human ear actually perceives sound. In North America, the most common of these weightings is the "A" weighting. Values that have been corrected using the "A" weighting system are shown using units of dBA. Values not corrected to account for human hearing are written using units of dB.

A Sabin is a unit of measure of sound absorption. It is calculated by multiplying a material's absorption coefficient by the square footage of the absorptive material.

Sound absorption is the process by which sound waves incident on an absorptive material are converted in whole or in part to heat, reducing the overall noise level.

The absorption coefficient is a ratio of the sound absorbed by a material to the incident sound acting on the material. Absorption coefficients are used in determining how "soft" or "loud" a room is with respect to sound.

Sound pressure levels decrease with the square of the distance. So doubling the distance to a sound source results in a 6 dB decrease in sound levels.

Dynamic insertion loss is the difference in sound levels at a given point before and after the installation of noise reduction equipment while under flow. It is essentially a measure of the amount of noise that the silencer or other equipment is removing. The silencer DILs are specified for each of the standard octave bands and are guaranteed for every piece of noise abatement equipment dB Noise Reduction designs and manufactures.

A noise reduction coefficient (NRC) is a single number that represents an average of the sound absorption coefficients in the 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz octave bands. Detail of its calculation can be found in the ASTM C-423 standard.

Transmission losses are defined as the difference between incident sound power coming into contact with the surface of a material and the sound power emitted by the material its opposite surface. It is essentially the amount of sound lost when travelling through an obstruction. Generally speaking, denser materials have higher transmission losses than lighter materials. Transmission losses are measured in decibels (dB).

A sound transmission class (STC) is a single number that estimates the performance of an acoustic barrier in certain common noise reduction applications. STC numbers are determined based on the ASTM 413 standard.

Breakout noise is undesirable sound that is caused by the transmission of sound through the walls of a duct, building or other enclosure. It can normally be remedied by applying absorptive cladding or erecting acoustical barriers.

Self generated noise is noise typically caused by gas turbulence at the inlet and/or discharge of a silencer, and should be taken into account when selecting a silencer.

The near field is defined as an area close to the noise source where small changes in position can result in large variations in noise level. In this area, the noise is essentially interacting with itself and its surroundings in such a way that the noise field is extremely chaotic and unpredictable.

The far field refers to any location outside of the near field. In this area, the sound level is far more orderly and predictable and drops off at or near the theoretical rate of 6 dB for every doubling in distance (the Inverse Square Law). Noise measurements are typically taken in this area.

Free field is typically used when referring to measured or calculated sound level values. It indicates that the values in question were obtained by assuming that the surroundings of the noise source do not cause any meaningful changes to the noise propagation. In other words, it is assumed that the sound level drops off at the theoretical rate of 6 dB for every doubling of distance (the Inverse Square Law).

When noise arrives by means of flanking, the noise is travelling along, over or around a noise control surface, silencer casing, or other device on its way to the listener.

Technically, pressure drop is defined as the difference between the pressure between any two points in a gas flow. Changes to or increases in surface geometry, flow velocity, surface roughness, path changes, etc. can all cause increases in pressure drop. For practical purposes, pressure drop can be thought of as a measure of the resistance the fluid flow has to overcome. The more resistance the flow has to overcome, the higher the pressure drop. Pressure drop is a pressure and is usually measured in inches or millimeters of water.

A silencer is a passive noise abatement device that is typically placed on the inlet or outlet of a noise producing piece of equipment. It allows the air or other gas to flow freely while providing a reduction in sound levels.

There are government noise regulations that must be complied with in and around the workplace. These regulations stipulate the allowable noise levels for unprotected workers in the workplace, as well as the allowable noise at the perimeter of a property.

Silencers are often required on smaller fans and other types of equipment in addition to large fans. As well as designing and fabricating silencers for fans, dB Noise Reduction also designs and fabricates silencers for steam and natural gas venting (vent or blowdown silencers), for engine exhaust (mufflers), gas turbine intakes and exhausts, and for hazardous gasses and/or particulate-laden gasses.

There are many options available for most applications, each with their own advantages and disadvantages. Most of the time the physical arrangement of the equipment being silenced will also determine or limit the silencer selections available. The frequencies to be silenced and the composition and velocity of the flow will also play a role. Please contact us to discuss your specific situation.

Reactive sound reduction devices are devices that are especially effective at reducing low frequency sound, although they can be designed to target different frequency ranges. They consist of a number of plates and/or tuned perforated pipes. This type of silencer is designed around the principles of Helmholtz resonators and expansion chambers. They essentially work by reflecting the sound around indefinitely until much of its energy is lost.

Absorptive silencers are the most common silencers and contain an acoustically absorptive material, usually fiberglass or mineral wool. This material is contained behind perforated metal and removes energy from the sound waves as they propagate through the unit. This type of system reduces sound levels across a broad range of frequencies and can be configured to provide maximum sound level reduction in a specific frequency range.

Yes! In fact, combining reactive and absorptive sound reduction methods works extremely well to create a device that is excellent at reducing both low and mid-to-high frequencies.

Complying with government regulations usually determines how loud something can be. These regulations often stipulate what level of noise a worker can be exposed to without proper hearing protection, or what noise level is permitted at the perimeter of your property, for example. Typically, most companies strive to meet 85 dBA within the workplace.

A silencer's size is based on several criteria that (with the exception of connection size) all influence each other. These criteria are:

• Connection size required - The most cost effective way to make a silencer is to have the dimensions of the silencer match the size of its inlet/outlet connections.
• Flow velocity - Typically in order for a traditional silencer to function properly, the flow velocity inside the silencer passage should not exceed 6000 feet per minute. This means that for typical applications, the flow entering the silencer should not be higher than 4000 feet per minute. Higher flow velocities result in larger pressure drops and more wear on the equipment.
• Desired pressure drop - If a very small pressure drop is required, the cross-sectional area of the silencer will have to increase to allow for a lower flow velocity.
• Desired sound level reduction - Increasing the length of a silencer increases its overall noise reduction capability. However, the longer a silencer is, the higher its pressure drop.

This really depends on what your particular application is and what sort of environment your silencer will be operated in. We would be happy to discuss your specific needs and show you various options.

While choosing a silencer from a catalog can sometimes yield the desired results, in order to get a properly designed silencer with consistent guaranteed results and as low a pressure drop as possible, a custom designed piece of equipment is the best choice.

In order to have a silencer sized, you will need to supply the following information:

• The noise characteristics of your equipment (noise level at each of the eight octave bands). This is usually available from the equipment manufacturer but can also be measured on site.
• The amount of reduction desired or the noise target at a specific location relative to the noise source (ie: 85 dBA at 3 feet directly in front of silencer inlet).
• Maximum allowable pressure drop.
• The flow properties (flow rate, density, temperature, etc.).
• Available space and geometry/orientation of connections.
• Size and type of connections and hole pattern required (if any).
• Material and finish of silencer (if desired).

The typical connection types offered include ANSI flanges, plate flanges, angle flanges, blow pipe flanges and slip fit connections. If you require another connection type, it can certainly be arranged. Please contact us.

Yes we will. Aside from ANSI and blow pipe flanges which already have standard hole patterns, we will custom drill any other type of flange to match your needs.

Silencers require very little maintenance. Generally, an annual inspection to ensure that the paint or other protective exterior coating is still intact is all that is required, touching up where necessary. For flows where particulate is present and may accumulate, the inside of the silencer should be checked and cleaned periodically if required. Special access doors can be added to accommodate this.

A silencer running under normal conditions and with a clean airstream should last between 10 and 20 years of continuous operation. With a dirty airstream, the silencer life will be shortened.

dB Noise Reduction puts quality and customer satisfaction first. We excel in custom design and fabrication, and strive to build long-lasting relationships with our clients. Our competitive pricing, warranty and commitment to service give our customers the peace of mind that they expect and deserve. Please contact us to see what we can do for you.

Yes, dB Noise Reduction has installations crews allowing us to provide a complete noise reduction system for all of your noise control needs.

We are currently able to design and construct a wide range of noise solutions, from silencers, mufflers, and vent silencers to expansion joints, acoustical panels and even acoustical buildings. We are able to fabricate silencers up to 120" in diameter and up to 50 feet long as a single piece. We are able to make silencers out of a wide range of materials including mild steel, galvanized steel, stainless steel, aluminum and fiberglass reinforced plastic (FRP).

dB Noise Reduction's manufacturing facilities are 100% AWS/CWB certified.

All of our fabrication is done at our two manufacturing facilities by a dedicated fabrication company.

We can offer any sprayed paint system that you may require as well as sandblasting.

Our two top priorities at dB Noise Reduction are quality and customer satisfaction. We routinely follow customers' quality control procedures and specifications above and beyond our own.

Yes, we provide ground shipping to anywhere in North America and containerized ship transportation to the rest of the world. However, if you require a different shipping method, we can almost always accommodate you.

On small orders, complete turnaround time for a custom-designed unit is less than four weeks, often two to three. For larger custom-designed orders, six to eight weeks is typical.

We do on-site installations anywhere in North America.

Absolutely! If there is thought to be any issue with either pressure drop or noise reduction, dB Noise Reduction will review and/or test your equipment to verify it is operating properly, and modify it or replace it if necessary.

Our standard warranty covers any defects or imperfections in materials, fabrication or performance during normal operation for a period of 18 months after shipment or 12 months after installation, whichever is sooner.