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Please find below a Glossary of Terms relating to Acoustic Cleaning which we have compiled for the benefit of all those interested in understanding the principles of the science and its associated, often industry-related terminology.


The removal or erosion of material from the surface of a solid due to friction imparted by the movement of another gas, liquid or solid.


The science of sound, including its production, transmission and effects


The state in which two materials are held together by forces existing between the surfaces.


The adherence of one substance on the surface of another.


A technique that combines small or powdered materials into larger particles, sub-clusters and clusters.

Airborne sound

Sound transmitted through air as a medium rather than through solids or the structure of a building

Ambient Noise

The background noise in an area, generally measured without noise of particular interest


A space which is almost totally free of reflection over a wide range of frequencies. An anechoic chamber gives close to free field conditions.

Background level

The normal sound level present in an area.

Bag filter

Process plant containing one or more cloth bags for recovering or removing particles from dust laden gas or air.


A process in which two or more materials are mixed together so the parts are intermingled with one another.


A high temperature water heater used for the generation of steam or cooling of gasses.


The process of making beer, ale or other malt beverages by boiling mashed malt to produce a wort, flavoring with hops, fermenting this mixture with yeast, and drawing off the fermented wort for distribution in barrels or bottles.

Carbon Black

Carbon black is a powdered form of carbon. It is used for its mechanical properties and pigmentation effects in many automotive products as well as rubbers inks and dyes.


A powder made from silica, alumina, lime, iron oxide, and magnesia which solidifies when mixed with water; this is used as an ingredient in mortar, concrete self levelling solutions etc.


Solid materials made by firing of non-metallic minerals, used in the manufacture of such products as tile, plaster refractories or brick.


A process in which a substance of individual particles comes together to form a coherent mass.


The act or process of pressing together substances either through gravity or applied pressure, which can form a denser substance or cohesive product.


The transfer of heat by molecular collision. This process is more efficient in metals and other thermal conductors and poorer when combustion products build up on heat exchange surfaces.


A device designed to regulate the fuel, air, water, steam, or electrical supply to the controlled equipment. It may be automatic, semi-automatic or manual.


The addition of some unwanted substance to a product or intended mixture of products.


Removal of kinetic energy in an oscillating medium by converting it to heat using frictional or viscous forces.


A division of a uniform scale based upon 10 times the logarithm to the base ten of the ratio of sound field intensities being compared

Diffuse sound field

A sound field in which the energy density is the same everywhere and sound waves are likely to be travelling in any direction with equal probability.


Concentration of acoustic energy within a limited location in a room as the result of reflections from concave surfaces.

Free field

A region in which no significant reflection of sound happens

Fundamental frequency

The frequency with which a periodic function reproduces itself.


An enclosed chamber where high temperature reactions or combustion take place.


The process of converting solid or liquid products into a gaseous fuel through heating in the absence or reduced presence of oxygen.


Calcium sulfate dihysrate, CaS04.2H2O, used in wallboard manufacture, and fertilizers.


A sinusoidal component in a complex periodic wave of frequency, which is an integral multiple of the fundamental frequency of the wave.


A substance that absorbs moisture from the air.

Induced draft fan

A fan which pulls a gas or air stream usually used for high temperature gasses. .


The rate of sound energy transmitted in a specified direction through a unit area

Kiln Dust

Dust produced during cement or lime processing.


A covering, usually of insulating material, on pipe or ductsLoudness
The subjective judgement of the intensity of a sound.

Natural frequency

The frequency at which a resiliently mounted mass when set into vibration would vibrate under the influence of gravity alone with no additional forces or constraints.


Solids that reflect light of certain wavelengths, without producing appreciable luminescence these are used in solids and paints to achieve a desired colour.


Chains of molecules formed by the chemical combination of two or more identical combining units called monomers.


Materials suitable for use at high temperatures; usually used for thermal insulating or thermal barriers composed of aluminas, silicas, etc.


The persistence of sound within a space after the source has ceased, due to repeated reflections at the boundaries of the space (walls)

Reverberation time

The time it takes for a reverberant sound of a given frequency to decay by 60dB after the source is cut off.


A means of converting Nox gasses (nitrogen oxides) with the aid of a catalyst into Nitrogen and water. SCR's use ammonia as the reducing agent. This prevents Nox gasses entering the atmosphere where they can combine with cloud moisture to produce the strong inorganic acid – Nitric Acid.

Slag cements

Cements made from blast furnace slag.

Sound Power Level (SPL)

A value equal to 10 times the logarithm to the base 10 of the ratio of total acoustic power emitted by a source to a reference pressure normally 2 x 105 N/m2.

Spray Drying

The production of a solid product by the atomization of a liquid solution into a heated vessel which evaporates the liquid. The dry particles fall to the bottom of the vessel.

White Noise

Noise of a statistically random nature having equal energy at every frequency between set limits.

Wood Pulp

Wood which has been broken down, to a fine powdered substance called pulp through mechanical or chemical processes.

What is Acoustic Cleaning?

Acoustic Cleaning is the use of high energy - low frequency sound waves which eliminate particulate build up and maintain material flow throughout a wide range of "dry processing" industries and applications.

What is Sound?

Sound may be best described as the rapid passage of pressure fluctuations through bonded material by means of a vibrating source and transmission medium.

What happens to changes in frequency?

We have selected a range of key fundamental frequencies between 60 and 420 Hz for a very particular reason. At the 420 Hz frequency the wavelengths are much shorter than at the 60 Hz frequency level. Therefore where high intensity, short distance material debonding is required (for example at the discharge of a silo) we would employ a suitable higher frequency Audiosonic™ Acoustic Cleaner. The opposite is true for say large silos; here to prevent material build up of a sidewall a suitable low frequency Audiosonic™ Acoustic Cleaner is employed to provide long-distance debonding power.

How do Audiosonic™ Acoustic Cleaners work?

Particles with different masses and clusters of particles are all hit by the alternating sound waves as the particles have different masses they travel slightly different distances, when this is repeated between 60 and 420 times per second the particles start travelling out of phase with each other and break apart.

How is this "sounding" activated?

The sounding is created when normal plant compressed air enters the Wave Generator this forces a diaphragm which acts a little like a reed to allow pulses of air into the horn section. The frequency of the sound is then dependant on the size and shape of the horn section.

Does the shape of the Bell Section matter?

Very much so, imagine a church bell and why it is shaped in the manner it is. This is for two reasons, firstly to provide as pure a tone (or fundamental frequency) as possible and secondly to cover an effective range. Could you imagine a square, straight-sided bell sounding properly - no of course not and that is why all our bell sections are precision spun in this exponential round bell shape.

What is the key difference between Audiosonic™ Acoustic Cleaners and vibrators?

Vibrators by their very nature and location have to first pass all their vibrations through the wall of the vessel. This results firstly in severe loss of power and secondly the damaging transmission of vibration through the vessel which can result in metal fracture. With Audiosonic™ Acoustic Cleaners - 100% of the debonding power goes into the material without any risk of damage to any structure or material of construction.

What is the key difference between Audiosonic™ Acoustic Cleaners and Air Cannons?

Air Cannons employ a unidirectional "blast" of high-pressure air to try and remove blockages that have already built up. That is why you always see groups of Air Cannons on any part of an application. Audiosonic™ Acoustic Cleaners prevent the build up from occurring in the first place. Sound waves travel in a 360° radius at a speed of 344 metres per second, therefore a single Audiosonic™ Acoustic Cleaner can be much more effective.

What is the relationship between frequency and dB?

Both are very important, the frequency provides the correct number of debonding pressure fluctuations and the dB provides the necessary energy to successfully complete the job.

Will Audiosonic Acoustic Cleaners damage my equipment?

Primasonics® Audiosonic™ Acoustic Cleaners are designed by tuning the wave generator and shape of the horn so that sound is reflected from solid surfaces rather than passing into them this helps in three ways, equipment is not vibrated and damaged, sound is increased inside the vessel where cleaning is required and as the sound is contained in the vessel this reduces noise nuisance.

What are the compressed air requirements?

The Audiosonic Acoustic Cleaners operate using normal plant compressed air provided three important factors exist.

  • Compressed air piping up to the cleaner - 25 mm diameter
  • Compressed air pressure - 4.8 - 6.2 bar/70 - 90 psi/ 480 - 620 kPa
  • Compressed air volume* - 21.25 l/s 45 SCFM @ 5.5 bar/80psi

* - but remember the Audiosonic™ Acoustic Cleaner is only "sounded" for a few seconds over usually between every 3 - 30 minute period depending on the application.

Acoustic Cleaning Technical Advice – WHAT NOT TO DO!

The Primasonics® Wave Generator and Aerospace Grade Titanium Diaphragm are precision made items and their correct assembly and use are essential to the correct operation of the Audiosonic™ Acoustic Cleaners.

Each Wave Generator is carefully inspected and assembled in a particular way and is attached to its Audiosonic™ Acoustic Cleaner and fully tested prior to storage and despatch as per our strict ISO Standards. When tested and approved a Primasonics® sticker is placed on the side of the Wave Generator across the area where the body, special gasket and lid join. This sticker is dated and signed and this seal should not be broken by the client otherwise the warranty is invalidated.

DO NOT – tamper with the Wave Generator by removing the bolts and opening it up. Firstly it will damage the special gasket and secondly the special assembly procedure would then not be adhered to.

DO NOT – screw in anything such as a threaded pipe into the exhaust part on top of the lid of the Wave Generator as shown on the left below. This outlet has a critical design dimension and exit air restriction will result in both damage to the Wave Generator/Titanium Diaphragm and non-performance of the Audiosonic™ Acoustic Cleaner. This outlet should either be left open or if necessary a special Primasonics® filter attached as shown on the right below.

Acoustic Cleaning Technical Advice

Instructions for adjusting the Timer Model 1078 (PSI Ref: ASA111 and 112)

  1. Please have both the timer and instruction leaflet in front of you.
  2. Setting the correct on/off function. This refers to switches no 4 and 5 on the bank of 8 switches. Both these switches 4 and 5 should be in the down position.
  3. Set the duration of activating the solenoid to operate the acoustic cleaner. This refers to switches 1, 2 and 3 and also the small blue pot on the bottom left-hand side of the timer. Let's say we are going to set a duration sounding at 10 seconds. If you look at the leaflet under "t'on" look at that column, third one down, you will see on the left-hand column of the figures that this is used to set the duration of between 5 seconds and 100 seconds. In this case switch 1 should be down, switch 2 up and switch 3 down. This gives the general "duration" time range and to fine tune this we adjust the pot on the bottom left of the timer. This pot rotates through 270º, turning clockwise increases the length of sounding, turning it anti-clockwise decreases the length of sounding, therefore the pot should be turned until the sounding of 10 seconds is obtained and the duration of sounding the acoustic cleaner is therefore set.
  4. Now we move on to setting the interval between soundings of the acoustic cleaner and this involves switches 6, 7 and 8 and also the small blue pot at the bottom right of the timer. Let's say we are setting the interval period for 7 minutes. This is the fourth line down on the "t'off" switches. You can see this ranges from 0.5 minutes up to 10 minutes therefore switch 6 down, switch 7 up and switch 8 up. This gives the general interval "time range". Then we adjust the small blue pot at the bottom right-hand side until we reach an interval period of 7 minutes.

Instructions for adjusting the Timer Model TEC 22 (PSI Ref: ASA119)

  1. Please have both the timer and instruction leaflet in front of you.
  2. Setting the correct on/off function. This refers to the two rotary switches set on the front control panel of the timer.
  3. Set the duration of activating the solenoid to operate the acoustic cleaner. This refers to rotary switch on left-hand side with the units in seconds. Turn the rotary switch so that the arrow is pointing at the number of seconds you were advised to sound the Primasonics® cleaner for.
  4. Now we move on to setting the interval between soundings of the acoustic cleaner and this involves the rotary switch on the right of the control panel with units in minutes. Turn the rotary switch so that the arrow is pointing at the number of minutes you were advised to have the Primasonics® cleaner off for. The operation of the unit can be tested at any point by pressing and holding down the button marked TEST.

Acoustic Cleaning Technical Advice

One of the most important installation aspects to get right is the provision of the correct compressed air piping, air volume & pressure. Failure to provide the Primasonics® systems stipulated requirements is by far the major reason for the poor performance of our Audiosonic™ Acoustic Cleaners. The compressed air metal piping up to the point of connection onto the Primasonics®; must have a diameter not less than 25 mm - 1".

Acoustic Cleaners require a volume of 21.25 l/s 45 SCFM @ 5.5 bar/80psi and a pressure of 480-620Kpa (4-8 – 6.2bar) 70-90psi for optimum performance. When using the PAS 60 model there is a minimum air requirement of 5.8 bar. The pressure reading should be made while the horn is operating and the gauge situated near the cleaner, downstream of any accessories that may cause a pressure drop. Plant air is satisfactory; instrument air may be used, but is not required.

We recommend the installation of an entrainment separator positioned upstream of other accessories, as dirt and water can greatly reduce the sound pressure level. Pressure drop can vary widely amongst various separators, and should be weighed carefully against available air supply.

A permanently installed pressure gauge is also beneficial. At the very least, a plugged-off tee should be installed to facilitate easy pressure checks. A shut-off valve (straight through type) and a pipe union installed upstream of other components will permit easy addition of other accessories in the future, and are essential when servicing the diaphragm. It is important to use a ball valve, or another straight through design with full size port to avoid creating a pressure drop.

The inlet adapter is 3/4" [20 mm] to encourage the use of 1" [25 mm] pipe (or larger if desired) from the main air supply to the horn. This is very important to bear in mind, even though the adapter has a 5 mm orifice.

The outlet or back pressure exhaust is ¼" BSP.