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Noise is defined as unwanted sound and it is usually just a nuisance but at times it can be a real headache. It invades privacy and causes disruption, when all everyone wants is a little peace and quiet.

Movable walls are designed to divide areas of a room and control the level of the noise or sound travelling from one area to another thereby reducing the nuisance, creating an agreeable environment.

When considering noise control it is important to appreciate the difference between sound absorption and sound insulation.

Sound Absorption refers to the attenuation of the reverberant noise within the same room and therefore it mostly falls outside the scope of a movable wall system. However when a sound wave hits a movable wall some of its energy will be reflected and some absorbed.

Sound Insulation, (also known as sound reduction) is the prevention of noise being transmitted from one area to another, by erecting a partition wall, for example. The ability of a partition wall to resist the passage of sound energy through it is largely determined by its mass, but structural isolation of the two surfaces and sound absorbency of the cavities in the construction are other factors which enhance the overall performance.

An Alco Beldan NW100 movable wall combines these 3 factors by: Using dense cladding boards to add to the mass. Careful detailing of the internal components to isolate the boards from the inner steel frame and slabs of mineral wool infill within the cavity to increase the sound absorbency. Attention to detail is all important and that is why even the cavities of the seal carriers at top and bottom of the panel are filled with mineral wool.

The sound insulation level of a movable wall is graded by its Sound Reduction Index (SRI). This is usually derived from the results of laboratory tests and is expressed in terms of 'Rw dB', being a single figure based on a weighting system defined in IS0 140-3 En20 140-3

Since the results of laboratory tests are obtained in perfect conditions where there is no flanking sound leakage, they cannot be replicated on site where flanking leakage is always present at various levels. The normal loss between laboratory and site performance is 3 to 8dB, depending upon how much care has been taken to eliminate sound transmission paths. No movable wall nor partitioning contractor can guarantee any particular 'on site' performance because flanking transmission is beyond their control.

Naturally each manufacturer will try to show their product provides the best performance acoustically, but the only way each product can be compared equally is by a laboratory test result. Recently the testing method has been altered to take into account a wider range of frequencies and hence test results obtained prior to 1995 are invalid. The latest test procedures provide test results at frequencies from 0 through to 5,000hz and the average figure is expressed in terms of Rw. The relevant standard is now IS0 140-3 En20 140-3, 1995 in which results are expressed as Rw values only.

The performance scale is logarithmic which means it is quite easy to achieve acoustic improvement at the lower end of the scale but very difficult to achieve significant improvement at the higher end. Its similar to squeezing water from a saturated sponge and partly explains why it is more expensive to raise the acoustic performance by 2dB from 52dB up to 54dB than it is to raise it from 41dB to 43dB. An increase in insulation of 10dB will correspond to a halving of the perceived loudness of the noise.

The perception of noise is subjective, some people have more acute hearing than others do, and therefore we must understand exactly what level of insulation the client is expecting from the movable wall. In most cases the client's expectation of noise reduction levels cannot be achieved using panels rated lower than Rw 48dB, when flanking transmission losses of 3-8dB are taken into consideration.

Acoustic insulation is expensive and it is tempting to try to make savings, but this will be false economy if the resulting noise level is still a nuisance.

Don't take risks. We can advise you and provide practical 'on site' results based on our experience.

ACOUSTIC CHARACTERISTICS
To achieve the optimum audible condition in a room, it is necessary to consider reverberation times. In general, a concert hall needs acoustically 'live' conditions, whereas a seminar room needs reduced levels of reverberation for intelligible speech.

Alco Beldan NW100 movable wall panels can be faced with special acoustic slotted boards which can improve the acoustic characteristics of a room by increasing the sound absorption levels.

To determine the correct level of sound reduction for any particular circumstance is a complicated process, and for an accurate appraisal, it is better to obtain the advice of an Acoustic Consultant. However, it is possible to obtain a reasonably accurate prediction of expected performance by comparing the results obtained by other methods of dividing rooms, and by using information from various sources, the table shown below may help to identify the required level of noise reduction.

SELECTION OF COMPARATIVE SOUND INSULATION VALUES FOR COMMON WALL AND STUD PARTITION CONSTRUCTION

Effect of sound insulation 25dB Normal speech over heard easily 30dB Loud speech heard clearly 35dB Loud speech distinguishable 40dB Normal speech not distinguishable 45dB Loud speech heard but not distinguishable 50dB Loud speech heard faintly but not distinguishable 55dB Shouting or loud speech heard only with difficulty

Recommended sound insulation levels Laboratory test (Rw dB) Type of room to be divided Minimum Ideal Primary school classroom 41 41 General Office 44 48 Village Hall 46 52 Meeting room 48 53 College study room 48 53 School Hall / Conference room with Audio-visual 52 55 Worship Area / Sunday School / Creche 52 55 5 star Hotel Function Suite 55 58 Lecture Theatre 55 58 Disco / Wedding Reception 58 65

PERFORATED BOARDS Alco Beldan acoustic perforated boards offer you the ideal combination of acoustically absorbent facings with sound insulation on movable walls. Since all acoustic boards are made to order, you can match your acoustician’s requirements as to the area of perforations. We can also manufacture the boards specifically to your design.

SLOTTED BOARDS The Alco Beldan acoustic slotted board is a further possibility. Acoustic requirements, facing board finishes and the stability of the slotted board are all decisive in making the right choice. We are always ready to help you with advice.

TECHNICAL INFORMATION

Acoustic Boards:		– DIN EN 20354 with test certificate
MDF-Boards:		– 6 / 8 / 10 mm
Grid:		– 16
Hole Size:		– 8 / 10 mm
Thickness:		– 22 / 32 mm
Perforated area:		– up to 31% of total board area
Construction of board:		– MDF-sheet
Peripheral frame:		– 2 x non-woven fabric – Black Mineral wool
Max. board size:		– 1280 x 3000 mm
Surface finish:		– Laminates – Wood veneers – Paint or varnish

TEST CERTIFICATES FOR ACOUSTIC PERFORATED BOARDS Test reports are available for 6 different standard types. Our in-house test laboratory enables us to develop special one-off versions to your own specifications.
TEST CERTIFICATES FOR ACOUSTIC SLOTTED BOARDS Test reports are available for various slot widths and thicknesses of absorption material.

* Our movable wall panels are primarily made at our own factory in the Midlands under licence to our associate company in Germany, Franz Nusing GmbH. All test certificates illustrated have been issued from a German test laboratory.