Acousta-Wal

Questions and Answers

How do Acousta-wal blocks work?

Simply put, it absorbs sound and then spreads it throughout the block.

Technically speaking, unlike acoustical ceilings Acousta-wal blocks do not operate on the principle of porosity. The basic operating principle is the Helmholtz resonator. That is that every cavity has a frequency to which it is sympathetic (called the resonant frequency). Examples of this would be an opera singer breaking a glass by singing a note at its resonant frequency or a bell ringing at its resonant frequency when it is struck. It is as if the cavity captures and absorbs the sound waves at or near its resonant frequency. These sounds are then dissipated in the structure. The Helmholtz resonator principle is not new, it is used in internal combustion engine mufflers and was used in ancient amphitheatre where bottles where built into the walls to absorb unwanted sound.

What does NRC stand for?

Simply put, Noise Reduction Coefficient.

Technically speaking, NRC stands for Noise Reduction Coefficient. NRC is the average of absorption readings obtained at four frequencies: 250, 500, 1000, and 2000 Hertz (Hz). For example, a reading of .85 at 250Hz means that 85% of the sound striking the Acousta-wal surface at this frequency (250Hz) is absorbed and therefore not reflected back into the room as unwanted noise. It is customary and useful to take readings at 125 and 4000 Hz even though they are not used to calculate NRC. Although NRC is a convenient measure of a product’s acoustical performance, it is something of a “shotgun” approach and should not be depended upon when choosing absorbing materials for a specific application.

Is it structural?

Simply put, yes.

Technically speaking, yes. Acousta-wal blocks are manufactured to meet ASTM C90 or C129. The slots are more than compensated for by the added strength and lateral stability provided by closed tops.

What is the fire rating?

Generally the following results;

15 cm Type I 1 ½ hours
15 cm Type II 2 ½ hours
20 cm Type I 1 ½ hours
20 cm Type II 3 ½ hours

What do the fillers do? Are they for insulation?

Simply put, Absorb high frequency sound and diminish low frequency.

Technically speaking, No they are not for insulation. They absorb high frequency sound without diminishing the low frequency absorption and therefore broaden the response of the units.

Does Acousta-wal cause a maintenance problem?

Simply put, No, in fact they require less maintenance than other systems for sound absorption.

Technically speaking, this is one of the most commonly asked questions. Walls constructed with Acousta-wal blocks actually require much less maintenance than walls faced with other acoustical materials. This is particularly true when Astra-glaze/Acousta-wal glazed acoustical units are used. When dust or dirt settles in the slots, it can be removed easily with a vacuum cleaner; neither the fibrous filler or the individual fibers will be disturbed.

If water gets into the block cavities, how can it be removed?

Simply put, it drains itself.

Technically speaking, because Acousta-wal blocks are laid with the open ends of the slot down and the closed tops of the blocks up, any water, which enters the cavities quickly, drains out.

Will moisture affect the fibrous filler or cause any adverse effects, such as deterioration of the filler or a loss in the acoustical properties?

Simply put, No.

Technically speaking, because fibrous glass is an inorganic material it will not deteriorate, rot or mildew. The sound absorption of Acousta-wal blocks would be adversely affected only if water completely filled the fibrous glass. This is unlikely because the pad must be immersed completely in water and worked like a sponge to reach the saturation limit. The filler can hold no more than 20% of its own weight. Since the filler used in a 20 cm Type II Acousta-wal block cavity weighs only about 6/100 of a pound, the water it could hold, if saturated, would amount to about 1/8 of a cubic inch per cavity and would evaporate to dryness in a relatively short time.

Can the units be painted without disturbing their sound absorption?

Simply put, yes.
Technically speaking, yes. However, if the units are left unpainted, the sound absorption at the high frequencies (above 1000 Hz) would be slightly improved depending upon the surface texture of the unit (porosity). The sound absorption at the low frequencies would be unchanged since the unit’s function on Helmholtz resonator principle.

How many should I use on my job?

The quantity is proportional to absorption required. A rule of thumb to use for mechanical equipment rooms and noisy areas in general. Treat 40% of the combined area of walls, floor and ceiling. In gymnasium/auditoriums with about a 25′ ceiling height, treat approximately 50% of the total wall area with 20 cm Type II or 10 cm Type I Acousta-wal blocks. As a practical matter, the type and purpose of the room often controls the number of Acousta-wal blocks which can be filled into the structure e.g. in school applications Acousta-wal blocks are best used only above door height.

What type of Acousta-wal blocks should I use on my project?

Simply put, either Type I or Type II.

Typically speaking, the type of application controls the choice. In installations where there will be adequate frequency absorption provided by other materials such as an acoustical ceiling, upholstered seats or draperies, Type I would be adequate. In applications where both low and high frequency absorption are desired, e.g. multi-purpose rooms, gymnasiums, and music rooms, Type II units give the best results. In specialized applications such as electrical generating stations, and transformer screens, 20 cm Type I is particularly effective because its peak absorption occurs at the same frequency as the noise generated by these devices. Whenever possible get an octave band analysis of the noise. Then it is relatively simple matter to select the unit giving the greatest absorption (see absorption table) at the frequencies with the highest decibel readings.
Rule of Thumb:

  • Low frequency absorption only - Type I
  • Low and high absorption - Type I
  • Indoors - Type I or Type II
  • Outdoors - Type I

What is the sound transmission loss of Acousta-wal blocks?

Simply put Type I, 15 cm - STC49, Type II, and 15 cm - STC52.

Technically speaking, it is critically important to remember the difference between sound absorption and sound transmission loss. Sound absorption is a measure of the sound absorbed in the same room in which the sound is generated. Sound transmission is a measure of sound transmitted from one room into an adjacent room. Sound transmission loss is measured in decibels. The sound transmission loss of the material at various frequencies to the response of the human ear at the same frequencies.

  • 15 cm ordinary 2 core block - *STC 43
  • 15 cm Type I Acousta-wal - *STC 49
  • 15 cm Type II Acousta-wal - *STC 52
  • *STC stands for sound transmission loss

As you see the above table, Acousta-wal blocks give superior sound transmission loss performance when compared to ordinary hollow concrete masonry units of the same thickness and composition. To insure good sound transmission loss performance; 1. The unslotted side of the units must be painted or parged to seal the porosity of the aggregate, 2. The units must be laid in a full horizontal bed of mortar. This same procedure must also be followed when using ordinary concrete masonry units when good sound transmission loss performance is important.

Does it matter where I put the units in the room?

Simply put, Yes

Technically speaking, in schools and public buildings the units should be kept above door height. The slots must always face the noise source. In an auditorium, sound absorption is most desirable at the rear. When partitioning off an office or a control room from an existing noisy plant area, the slots should face into the office. In addition, to the sound transmission loss provided by the units (when properly installed in a full horizontal bed of mortar), noise which enters the room through the doors, windows or ceiling will then be subject to absorption by Acousta-wal blocks.

Are there any special instructions I should give the Masons regarding the laying up of the units?

Simply put, Yes

Technically speaking, the units should be laid in a full horizontal bed of mortar. They should be laid with the closed tops up. The slots should face toward the noise source (with the exception of partitioning a small office, or from a large noisy plant area). Under no circumstances should the units be laid upside down, that is, in a full horizontal bed of mortar if they are laid upside down. Second, excess mortar would drip into the slots giving an unsightly appearance. Thirdly, if the cavity volume were reduced by more than 5 – 10% due to mortar dripping inside, the acoustical performance of the units would be altered.

What is the delivery time for Acousta-wal blocks?

Simply put, Contact us for immediate response.

Generally speaking, in most cases, two – three weeks.

Top