Underneath we have listed some of the most frequently asked questions about all our soundproofing products and solutions.
There are two different kinds of noise:
Airbourne Noise – Sounds transmitted between rooms via flanking elements instead of directly through separating elements or along any path other than the direct path.
To reduce the amount of sound heard by the other person you would need to install a barrier or Sound Insulator between the source and you, the thicker and denser the barrier then the better the sound reduction will be.
Impact Noise – This is the transmission of sound via the connection of different Materials to each other i.e. Footsteps on a floor of a house.
To reduce vibration transmission, you need to either stop the sound getting into the floor, out of the ceiling or a combination of both, by adding a Floating Floor or an Acoustic ceiling system.
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 travelling 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).
Flanking noise is more often perceived in flats where noise is transmitted through the fabric of the building. Flanking noise is more often caused by impact noise and often travels through the walls of the building.
This is more of a problem if the walls are of a lightweight construction so it is important the correct density blocks are used in the construction of new flats today.
Normally a minimum 7 kilonewton density block is specified today to reduce flanking noise nuisance and also help comply with the current regulations for noise control in flats and other multi-occupied buildings.
Noise from vibration is often a problem and can be caused by something simple such as a washing machine or a more extreme example such as heavy industrial machinery in a factory. Noise from vibration will generate both flanking noise and airborne noise depending on its location.
This answer would be best discussed with our friendly team of experts please contact us for more information.
Our soundproofing materials are delivered throughout mainland UK, for more information on deliveries visit How to Buy. If you are outside the UK please contact us on 01204 548 400
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.
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.
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.
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.
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.
|low threshold of hearing – softest sound you can hear
|leaves rustling in the breeze; quiet whisper
|conversation between acts at a theatre; hotel lobby conversation
|moderate traffic; hair dryer
|factory (medium) – washing machine
|heavy traffic – power lawn mower – busy city walk
|thunder – walkman – tractor
|boom box with volume turned high – chain saw – leaf blower
|shouting; synphony concert
|threshold of pain – loud fireworks – gunshot
|airplane takeoff from short distance away
|space rocket takeoff
Acousticians use the dB scale for the following reasons:
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.
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.
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.
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. It is best to use soundproofing products in these instances.
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”.
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
Attempts to quiet rooms over the years have created many fallacies. Even today, some companies and builders merchants sell a variety of ‘soundproofing’ materials to unsuspecting contractors and homeowners based on fallacies which have been pervasive for years. A few of these are:
|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”
As you can easily see, if we are trying to make a 30dB improvement, it will not be achieved with egg cartons and vinyl.
We know Soundproofing can be a problematic area but the team at JCW Acoustic Supplies are always on hand to offer technical advice and provide you with free information, including decibel charts and installation guides.
We also have experts who will gladly come and visit your site to offer their vast expertise free of charge!
So please get in touch with your soundproofing issues, we would love to hear from you…
Call – 01204 548 400