Common Soundproofing Materials-Part 3: Absorbers
1) Building insulation rolls
Building insulation works as an excellent absorber of sound at the noise source. The denser and thicker mineral products are considered superior. You can improve the performance by providing an air space all over the soundproofing area and also by making use of insulating materials having a lining – making sure that the lining faces the source of sound. Building insulation is more effective when soundproofing is near about the audible frequency of human voice. The thickness of roll insulation of 3 1/2 inches (just below 9 centimeters) is perhaps most economical.
This is same as in the case of for building insulation rolls.
3) Rigid fiberglass ceiling board and sheets.
Here too, if the board is thicker the effect will also be more. Perhaps the most economical fiberglass board thickness is about 2 inches (5 cm). The performance of fiber glass boards having facings is lesser when compared to fiber glass boards that do not have facings.
4) Form board for roofs
Two to 3 kg density fiberglass form board of 1 inch thickness can be handled easily and works very well.
5) Ceiling boards
Perforated fissured and painted mineral ceiling board can be handled easily and it works fairly well at thickness of about 2 cm. Cast mineral ceiling board with rough texture gives the best soundproofing effect. Note: Ceiling boards of wood fiber do not function particularly well. Foam sheets/tiles and ceiling boards from soundproof foam and foam sheets or tiles of thickness one or 2 inches work well as absorbers and perform almost equally well as the mineral ceiling boards, and can be handled more easily without doubt. As for barrier qualities mineral ceiling board probably is better.
6) Wall panels
General principles are similar to ceiling boards.
7) Floor coverings
Carpets are good sound proofers only when used in the form of absorbers. Much of their efficiency is due to lessening impact noise. Carpets are used mostly to minimize noise from footsteps on timber floors and also to dampen some airborne noise. You get dedicated underlays which can be laid below carpets. You must obtain clear performance data on sound transmission and also on performance on impact noise.
Bricks are better sound absorbers than sound barriers. Comparatively brick is a bad sound absorber. The notion that brick homes are very quiet is usually because the older homes were built with double bricks providing air gaps between the two layers of bricks which contribute considerably to the general soundproofing effectiveness.
There are doubts whether plywood, glass and drywall are barriers or absorbers. They are discussed as barriers in the next part. The many proprietary laminates as absorbers are not really worth the investment. Also the result will be better if you buy a pair of them as un-cemented and assemble them with a gap of few inches of airspace between and secured using a resilient fixing. The small air gap between them appears to add to their soundproofing performance considerably. Cellulose spray on is also a good absorber but it is not assured what you can expect or what the thickness will be. If used correctly, it may be a very good material for cavities on the roof and as acoustic and thermal insulation. It may be sprayed straight onto the bottom of tiles, roof board or shingles.