Image source soundscreen.com.au.
I have recently been trawling several websites of manufacturers of acoustic insulation for internal walls.
I noticed that practically all such websites carefully select what information to post and do not publish some of it. Why so?
What is normally posted on manufacturers’ websites is a brief introduction into how sound pressure level is measured and a brief comparison of a typical interior wall construction consisting of stud and plasterboard and the same construction with mineral wool batt insulation. Also, the sound insulation performance is not shown of the batt packaging.
The diagrams show how sound transmission is reduced. However, without special knowledge about the scale of sound power one can misinterpret such diagrams and come to inaccurate conclusions. One may believe that this is enough to enjoy the privacy of a bedroom and later may be quite surprised with what they can hear.
Another thing that is worth noting is that manufacturers often used word “screen” for their acoustic products. It seems to be a very clever and careful choice too as it is more open to interpretation and implies a certain degree of permeability.
What is important to know?
Human hearing is most sensitive in the range of 0 dB (that is when we do not register any sound) to 140 dB (that is louder than jet engine with airburner 100 m away). Normal human voice at 2 m is taken to be 60 dB, while very soft whisper at the same distance is 20 dB.
While a typical noninsulated timber stud and 10 mm plasterboard wall will make loud voices of 80 dB sound like 48dB, an insulated wall will turn 80 dB into 38 dB. However, sound perception is largely psychological. So the foreground sound needs to be just 5 dB higher than the background noise to draw our attention and be intrusive. And to be inaudible a sound has to be a whole 10 dB lower than the background sound. Therefore, if we expect peace and quiet in a strict sense, a basic insulated construction is not enough.
In addition, to stop sound of certain frequencies different materials are required. Density of material plays a great role so the best sound stopper is a thick concrete wall.
What do you need to ask your designer?
If you have particular requirements regarding sound insulation, it is important to bring it up talking to your designer in the beginning of design stage. Then designer will be able to specify suitable construction type and think about location of openings. It is the openings that compromise sound insulation qualities of a wall and a small power point can be a source of that intrusive noise.
One of the biggest concern is the noise from bathroom. If you do not want to hear any sounds you may want to discuss with your designer the location of the bathroom and its door. As you already know, the door will compromise any insulation, especially if it is a pocket door. If you must have the bathroom next to your living areas you may consider special door seal.