22 May 2024

Acoustic Terminology Explained

What’s the difference between sound insulation and sound absorbing products?

Soundproofing, as it is commonly known, is all about creating an acoustic barrier. Sound insulation and soundproofing products are specially designed and manufactured to act as an acoustic barrier in order to reduce the amount of sound leaving or entering a room or workspace.
Sound absorbers are designed to absorb the sound within a room and help reduce sound reverberation or echo. Sound absorbers do not stop the sound leaving the space but will reduce the amount of noise by reducing the reverberation (echo) within the enclosure.
If you want to soundproof a room as fully as possible you almost certainly need to install both types of sound insulating materials.

What is the difference between sound absorption & sound insulation?

There is often confusion between sound insulation and sound absorption. Sound is absorbed when it encounters a material which will convert some or all of it into heat, or which allows it to pass through not to return. For this reason good sound absorbers do not of themselves make good sound insulators. Sound insulators rarely absorb sound. Sound absorbers contribute little to sound insulation. They are treated separately in sound control design.
Sound insulation prevents sound from traveling from one place to another, such as between apartments in a building, or to reduce unwanted external noise inside a concert hall. Heavy materials like concrete are the most effective materials for sound insulation – doubling the mass per unit area of a wall will improve its insulation by about 6dB. It is possible to achieve good insulation over most of the audio frequency range with less mass by instead using a double leaf partition (two independent walls separated by an air gap filed with a sound absorber).

What is soundproofing?

This is a term used when a reduction in the level of noise being heard is being reduced. It is often thought that if something has been soundproofed then the noise being generated has been silenced. This may be the case in some instances but is not always possible so a soundproofed situation may also refer to a noise nuisance that has been reduced in intensity as much as feasible or possible.

What is sound absorption?

Sound absorption is normally required in enclosed spaces such as studios, halls and recreation centers to reduce reverberation (echo) of noise. An un-insulated hall is often unusable for many events due to excess reverberation. This makes speech difficult to comprehend and becomes more of a problem when people are speaking further apart.

What is a sound barrier?

A sound barrier is another way of describing a sound blocker and normally comprises insulation with a high mass which then reduces the amount of noise that can pass through it. A simple door can be described as a noise barrier when it is closed to reduce the sound of noisy kids playing just outside. Sound waves flow like water and air so it is impossible to use a sound barrier such as a fence or screen to stop noise but they are effective when used to reduce noise immediately on the other side of them. From distances farther away the noise reduction will be less efficient.
If you imagine a large stone in the middle of a river, you will see that the water flows quickly around it but leaves a slack area immediately behind the stone. Sound waves act in exactly the same way when presented with a sound barrier that is not complete.

What is sound damping?

Sound damping is normally required to reduce noise from resonating panels. Noise from resonating panels is annoying and addressed by stiffening the panels usually with a vibration damping pad that is glued on.

How small and rapid are the changes of air pressure which cause sound?

When the rapid variations in pressure occur between about 20 and 20,000 times per second (i.e. at a frequency between 20Hz and 20kHz) sound is potentially audible even though the pressure variation can sometimes be as low as only a few tens of millionths of a Pascal. Movements of the ear drum as small as the diameter of a hydrogen atom can be audible! Louder sounds are caused by greater variation in pressure. A sound wave of one Pascal amplitude, for example, will sound quite loud, provided that most of the acoustic energy is in the mid-frequencies (1kHz – 4kHz) where the human ear is most sensitive. It is commonly accepted that the threshold of human hearing for a 1 kHz sound wave is about 20 micro-Pascals.

What makes sound?

Sound is produced when the air is disturbed in some way, for example by a vibrating object. A speaker cone from a high fidelity system serves as a good illustration. It may be possible to see the movement of a bass speaker cone, providing it is producing very low frequency sound. As the cone moves forward the air immediately in front is compressed causing a slight increase in air pressure, it then moves back past its rest position and causes a reduction in the air pressure (rarefaction). The process continues so that a wave of alternating high and low pressure is radiated away from the speaker cone at the speed of sound.

What is a decibel (dB)?

A decibel is one unit on the decibel scale, which is a logarithmic scale. The name means one-tenth of a bel, a bel being an eponymous unit named after Alexander Graham Bell and used to compare power in electrical communication, voltage, or intensity of sound. The abbreviation of bel is B and decibel, dB. 10 dB = 1 B
Eighty-five decibels is the threshold for the possibility of noise-related hearing loss, and this guideline is intended to prevent such hearing loss. This figure suggests that many people who do not currently use ear protection should consider it. The following chart reveals that a great deal of the sound we’re exposed to is above that 85-decibel threshold. Because conditions may vary and distances are not specified, these figures are approximate.

 Decibels  Sound Source
 0  low threshold of hearing – softest sound you can hear
 10  leaves rustling in the breeze; quiet whisper
 20  average whisper
 20-50  quiet conversation
 40-45  conversation between acts at a theater; hotel lobby conversation
 50  rainfall
 50-65  loudish conversation
 65-70  moderate traffic; hair dryer
 65-90  train
 75-80  factory (medium) – washing machine
 90  heavy traffic – power lawn mower – busy city walk
 90-100  thunder – walkman – tractor
 100  boom box with volume turned high – chain saw – leaf blower
 110  shouting; synphony concert
 115  rock concert
 120  ambulance siren
 130  threshold of pain – loud fireworks – gunshot
 140  airplane takeoff from short distance away
 140-190  space rocket takeoff
 170  shotgun

Acousticians use the dB scale for the following reasons:

  1. Quantities of interest often exhibit such huge ranges of variation that a dB scale is more convenient than a linear scale. For example, sound pressure radiated by a submarine may vary by eight orders of magnitude depending on direction; expression in linear units carries with it the confusion of the location of the decimal point. Decibels values are characteristically between only -999 to +999.
  2. The human ear interprets loudness more easily represented with a logarithmic scale than with a linear scale.

Amplitude measures how forceful the wave is. It is measured in decibels or dBA of sound pressure. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can be about 120 dBA.
Sounds that are 85 dBA or above can permanently damage your ears. The more sound pressure a sound has, the less time it takes to cause damage. For example, a sound at 85 dBA may take as long at 8 hours to cause permanent damage, while a sound at 100 dBA can start damaging hair cells after only 30 minutes of listening.
Frequency is measured in the number of sound vibrations in one second. A healthy ear can hear sounds of very low frequency, 20 Hertz (or 20 cycles per second), to a very high frequency of 20,000 Hertz. The lowest A key on the piano is 27 Hertz. The middle C key on a piano creates a 262 Hertz tone. The highest key on the piano is 4186 Hertz.

Measuring sound reduction – Decibels vs. Percentage reductions

Sound intensities are measured in decibels (dB). Decibels however cannot be expressed in percentages.
There are two reasons why you can never equate decibels to percentages. First, the decibel scale is open-ended like that of the Richter scale used for measuring earthquake intensities. To calculate a percent you need to know the maximum value possible. In both of these scales there is no limiting maximum value. Therefore, you cannot calculate a percentage. Any attempt to do so is just meaningless!
Second, the decibel scale is logarithmic, while the percent scale is linear. Numbers that appear to be similar have vastly differing meanings. They are as different as trying to compare apples to elephants!
A decibel is not a given intensity (loudness) of sound, but rather, it is a ratio of how many times louder (or softer) a sound is than a given reference sound level.
This means that 0 dB is not the absence of sound, but is an arbitrary zero. We define it as the faintest sound that a young sensitive human ear can hear. Furthermore, because the decibel scale is logarithmic, every 10 dB increase in sound intensity is actually a ten-fold increase. Therefore, a sound intensity of 20 dB is not twice as loud as a sound intensity of 10 dB, but is 10 times as loud, and a sound intensity of 30 dB is 100 times as loud as a sound intensity of 10 dB. Similarly, a sound intensity of 50 dB would be 100,000 times as loud (10 x 10 x 10 x 10 x 10). This is how the decibel scale works. It is totally unlike the linear percent scale.
It is a fallacy trying to compare the decibel scale to the percent scale. To illustrate this, let’s wrongly assume that 0 dB is equal to 0 percent hearing loss or sound reduction and that 100 dB equals a 100 percent loss or sound reduction. This would then mean that 50 percent would equal a 50 dB hearing loss, right? Wrong! Not by a long way! A 50 percent hearing loss would equal, believe it or not, only a 3 dB loss! Looking at it the other way, a 50 decibel loss is not just half as loud, like it would be in a percentage scale, but would only be one thousandth of one percent as loud!
So decibels and percentages just do not equate. They are absolutely meaningless!

How are decibel sound levels added?

If there are two uncorrelated sound sources in a room – for example a radio producing an average sound level of 62.0 dB, and a television producing a sound level of 73.0 dB – then the total decibel sound level is a logarithmic sum i.e.
Combined sound level = 10 x lg ( 10^(62/10) + 10^(73/10) )= 73.3 dB
Note: for two different sounds, the combined level cannot be more than 3 dB above the higher of the two sound levels. However, if the sounds are phase related (“correlated”) there can be up to a 6dB increase in SPL.

How does the ear work?

The eardrum is connected by three small jointed bones in the air-filled middle ear to the oval window of the inner ear or cochlea, a fluid- filled spiral shell about one and a half inches in length. Over 10,000 hair cells on the basilar membrane along the cochlea convert minuscule movements to nerve impulses, which are transmitted by the auditory nerve to the hearing centre of the brain.
The basilar membrane is wider at its apex than at its base near the oval window; the cochlea tapers towards its apex. Groups of the delicate hair sensors on the membrane, which vary in stiffness along its length, respond to different frequencies transmitted down the spiral. The hair sensors are one of the few cell types in the body which do not regenerate. They can therefore be irreparably damaged by large noise doses.

At what level does sound become unsafe?

It is strongly recommended that unprotected exposure to sound pressure levels above 100dB is avoided. Hearing protection should be used when exposed to levels above 85dB (about the sound level of a lawn mower when you are pushing it over a grassy surface), and especially when prolonged exposure (more than a fraction of an hour) is expected. Damage to hearing from loud noise is cumulative and is irreversible. Exposure to high noise levels is also one of the main causes of tinnitus.
Health hazards also result from extended exposure to vibration. An example is “white finger” disease, which is found amongst workers who frequently use hand-held machinery such as heavy drills or chain saws.

What is the sound absorption coefficient?

The absorption coefficient of a material is ideally the fraction of the randomly incident sound power which is absorbed, or otherwise not reflected. It is standard practice to measure the coefficient at the preferred octave frequencies over the range of at least 125Hz – 4kHz.
It can be determined on small material samples with an “impedance tube” or on large samples in a laboratory “reverberation room”.

What is sound insulation and how is it measured?

Sound insulation is a measure of the sound stopped by a barrier such as a partition wall. We can measure the sound reduction index in a laboratory transmission suite. This consists of two adjacent reverberant rooms, the difference between the level of the sound in the source room and the receiver room is measured, and the properties of the receiver room are taken into account by calculation.
The measurement method depends on the particular situation. There are standards for the measurement of the insulation of materials in the laboratory, and for a number of different field circumstances.
Usually test procedures generate a loud and consistent broadband spectrum of steady noise on one side of a partition or specimen of the material under test, and then measure the amount of this sound that passes through that material. The ratio of the incident sound to the transmitted sound is the “noise reduction”, usually expressed as 10 times the logarithm of this ratio. If the noise reduction is also corrected for the amount of sound absorption to be found in the receiving room, 10 times the logarithm of the corrected ratio is called the “transmission loss. This is performed for 1/3 octave bands of noise from 100 to 4000 Hz.

Modern myths about soundproofing

Attempts to quiet rooms over the years have created many fallacies. Even today, some companies and builders merchants sell a variety of materials to unsuspecting contractors and homeowners based on fallacies which have been pervasive for years. A few of these are:

 Fallacy  What they said  What it actually does
 Fill the wall with egg cartons  “Will improve loss by 10dB”  No measurable effect
 Put acoustic insulation in wall  “Will fix everything”  Typically 3 – 4dB improvement
 Put mass loaded vinyl under drywall  “Will improve loss by 27dB”  Actually 3 – 9dB
 Add another layer of drywall  “Will stop the bass sounds”  Actually 2 – 3dB per layer
 Use foam as a barrier  “Regarded as a great barrier”  Actually <2dB

As you can easily see, if we are trying to make a 30dB improvement, it will not be achieved with egg cartons and vinyl.

Soundproofing vs Sound Absorption

To assist customers who are not sure whether they need soundproofing materials or sound absorbing materials, the short definitions below will help provide a brief outline. If you want to soundproof a room as fully as possible, you will almost always need to install both types of sound insulating materials.


Soundproofing is all about creating an acoustic barrier. Soundproofing products are specially designed and manufactured to perform as an acoustic barrier by reducing the amount of sound entering or leaving a room.

Sound Absorbers

Sound absorbers are designed to absorb the sound within a room and help to reduce the amount of reverberation or echo within the space.
If you want to soundproof a room as fully as possible, you will almost always need to install both types of sound insulating materials.

What types of sound are there?

There are two fundamental ways in which sound moves around the rooms and spaces in which you hear them:

  • Airborne Sound
  • Impact Sound
What is airborne sound & how to insulate against it?

Airborne sound is sound waves moving around within a space, such as a room. This sound bounces off walls and floors causing vibrations within those surfaces which will then transmit (re-radiate) to the other sides of the room (receiver space). Often the windows, doors, poorly fitted sockets or any cracks in a wall will drastically reduce its insulation of airborne sound. To reduce the amount or loudness of this sound you need to insulate it with the use of proper soundproofing materials on your walls, floors or ceilings.

What is impact sound & how to reduce it?

Impact sound starts with an incident like a door slamming or heavy footsteps which then creates vibrations directly through the walls and floors of a building, and the sound travels from one room to another. Impact sound can travel through a concrete floor; from one room to another even if the wall in between is a good airborne sound insulator. To reduce the amount or loudness of this sound you need to stop it at its source with proper soundproofing materials on your walls, floors or ceilings.

Nuisance noise within a room and how to reduce it

As well as unwanted noise coming from a separate room, noise from within one large room can also be a nuisance. Large open rooms can often become prone to echoes of noise incidents like people speaking loudly. In an open plan office or any kind of performance hall, this can be a real problem for individuals working or concentrating. Rooms that are prone to echoes (or sound reverberation) are typically large and have wall surfaces that absorb very little of the sound, therefore bouncing it back across a room. To reduce the amount or loudness of this sound you need to absorb it with proper soundproofing materials on your floors or ceilings.

How to Control Noise

Before considering soundproofing a building it is worth considering the quality and methods of construction of the building.
There are two main ways to reduce and control noise.

  • Increasing Mass – the more mass (weight and density) a floor or wall has the less sound will make it vibrate. As a general rule of thumb doubling the mass will give a 5 decibel reduction in the sound transmitted.
  • Additional Layers – adding several layers to the construction of a wall or floor can greatly improve the control of noise. Each layer will be made of soundproofing materials, slightly separated to reduce airborne and impact noise transfer.

22 March 2021

Acceptable noise (dBA)


 The above images extracted from : http://www.benjaminjaffe.net

dB(A) - the A weighted noise or sound measurement - is

  • its adaption to how the human ear responses to sound - the human hearing, and
  • the possibility to measure noise with "low cost" instruments

Maximum acceptable Equivalent Sound Level - Leq - at some locations:

 The above sound level extracted from: https://www.engineeringtoolbox.com/decibel-dba-levels

Caution:  Please be alert not to subject your hearing with a noise level of more than 85 dB(A) each day, doing so will increase the risk factor for hearing damage.

17 November 2020

Soundproof vs Acoustic treatment, is it the same?

This is a very common question, many will says that it is very easy to sound proof a wall, just add acoustic foam to cover the whole walls and that it. My friend, doing this does not make your room sound proof or the wall soundproof. all it does it, it just modify the sound reflect onto the wall i.e. it absorbed the sound. Acoustic foam is usually used for acoustic treatment.  Acoustic treatment is a method to control the echoes and reverberations inside the room. Whereas soundproof is about isolating the room from outside noise coming into or noise from inside going out of the room.   

Let us discuss some basic acoustic for us to get an idea and a better understanding of these confusing subject.

    Extracted from: https://auralex.com/alpha-dst-roominator-kit/

Acoustic treatment:

(the following statement is extracted from Acoustic 101(Auralex) by Eric T. Smith, page 6, 7 . 2014).

    One of the single biggest concepts to understand and appreciate is that (Auralex) acoustic foam, one of our core products, is not going to "soundproof" your room. It is an extremely effective absorber of ambient, reflected sound and helps make rooms "sound better." Acoustic foam does contribute some sound isolating properties (mostly high frequencies), but is not sufficient by itself to keep sound in or out of a room. 

    Thicker acoustic foam is better at absorbing low frequency sounds. Controlling reflected sound within a room is extremely important in producing good sounding recordings. 

Image extracted from : https://all.biz/tr-en/bondex-30mm-g278659

Sound Proof:

(the following statement is extracted from Acoustic 101(Auralex) by Eric T. Smith, page 6 . 2014).

• When sound strikes a surface, some of it is absorbed, some of it is reflected and some of it is transmitted through the surface. Dense surfaces, for the most part, will isolate sound well, but reflect sound back into the room. Porous surfaces, for the most part, will absorb sound well, but will not isolate.

• The best way to stop sound transmission through a building structure is to isolate the sound source from the structure before the structure has a chance to vibrate.

• Walls need to be isolated from ceilings and floors, usually by means of dense, pliable rubber.

• The main ways to minimize sound transmission from one space to another are adding mass and decoupling.

• Limp mass is most often better than rigid mass (actually, a combination of the two is really what you are after).

• Every object, every construction material has a resonant frequency at which it is virtually an open window to sound — kind of like a tuning fork that “sings” at its particular resonant frequency.

• Different materials have different resonant frequencies.

• Trapped air (a.k.a., air spaces and air gaps) is a very good decoupler.

• Airtight construction is a key concept. Sound, like air and water, will get through any small gap. (Sound can leak through openings as small as 1/32” – in some cases even smaller.)

• Sound bounces back and forth between hard, parallel surfaces.

Soundproofing is not an easy Job and it is recommended to refer the job to professional team or acoustic consultant who has experience building soundproof structure. It should by no mean attempted by DIY or laymen as there are many areas if not done properly can cause sound to leak through gaps or flanking path or faulty structure which may cost more to amend then to build. In addition, there are measurement (acoustic report) need to be carried out before and after the job is done. 

Reference :

Acoustic 101, Practical Guidelines For Constructing Accurate Acoustical Spaces by Eric T. Smith Edited by Jeff D. Szymanski, PE July 2004 Version 3.0


27 May 2020

Build an Online Radio

For those who are planning or about to plan to start an online radio, the above info will get you run at no time. Call the number or whatapps +60162798533 (Ts.C. G. Simon, Senior Broadcast Engineer) . We will help you get started and assist you in whatever question you may have regarding online radio.

27 June 2017

Guide to Mixing by Soundcraft

The Soundcraft Guide to Mixing

A great introduction to "how to use a mixer for live music production", for novices, or to get tips, or as an educational aid for Media Colleges and Schools. 
Even though the last update was in Jun 29, 2014 but the information provided in most of the videos are still relevant for beginners or armature or even for the experience sound engineer. 

20 January 2015

Handy dB Reference Chart

I have enclosed herewith one of the notes from the Seminar I did years ago in Sound Reinforcement System. I Thought this might be handy for those who wants to know how much power increase in relation to dB increase.

23 June 2014

Simple Tools

At present day, most of us involve in audio reproduction will certainly encounters problem with managing the audio for reproduction or processing. For instant, one of the most common fault is to do with ground loops which caused buzz, hum or hissing. A simple thing like cable defect, mismatch audio input level, improper cable conversion form balanced to unbalance, improper audio splitter can more or less introduce undesirable audio i/o which can degrade the quality of the audio.   

An example of such tools are: Rolls BUZZ OFF HE18, Rolls Cable Detect CT1 PRO, Behringer ULTRA-DI20, behringer CT100, Henry Engineering PatchBox II, galaxy Pro JIB/S 4 Way Splitter.

Hence, the following simple solution can somehow improve the audio ( i.e. removes buzz, hum caused by ground loop, matches level, detect faulty cables, convert high level to low level and so on and so forth).  I will discussed each one of these tools later. So in the meantime, stay tune.

30 December 2013

Newly installed Broadcast Conty

We have successfully completed the job of installing the above On-Air Studio on the 8 Jan 2014. This on-Air Studio is ready for use. Notice the mixer is embedded into the table and look more tidy without all the cables laying around/on the tabletop.

The conty is equipped with the latest professional broadcast equipment from branded name such as AKG, Allen & Heath, Warfadale, Behringer, HP workstation, Presonus, Dell workstation, Arrakis System ( Radio Assist Application ) and so on.

 Partially completed broadcast conty (refer below), just few days before Christmas ( on the 23 Dec 2013 ).
As seen above, the student are trying out the soon to be completed broadcast equipment.

08 October 2013

Radio Online Streaming Part 3

Steps 3:

WINAMP STANDARD (to download go to http://www.winamp.com/media-player/all ) Once you have successfully downloaded the application and you may run the setup program as shown graphically below:

A ) Go to www.winamp.com/media-player/all and
Click the “ FREE DOWNLOAD” to download the

 B) click OK.

C) Click “Next”

D) Click “ I Agree”

E) By default the destination folder of the
Winamp shall be located at c:\Program
Files\Winamp…you can change the location
but not necessarily, it best to leave as it is.
Click “ Next” to proceed.