Acoustical Isolation vs Acoustical Treatment – How to deal with entry points? (Part 4)

Isolating the entry points of a room can be one of the trickiest parts when constructing an acoustically sensitive room. For this article, the following features door, window, ducking and outlet bays will be referred as entry points. As these entry points require some level of manoeuvrability (e.g. opening of doors), the design of these features demand it to be acoustically sealed when it's put in place. If the features are not done properly, they will be the weakest link of the room acoustically as air provides almost zero transmission loss (TL) (Part 3).

The importance of a door

Essentially, a room cannot function without a door. While most of the features mentioned above are designed to be permanently sealed, doors are designed to be open. This presents a challenge where the doors need to maintain at least the same level of transmission loss to the wall attached to it. Thus, a door design, in this case, would require sufficient mass (part 3) and also a closure system that reliably seals the entire perimeter around the door. Some doors are specially engineered for this very purpose, and it will provide excellent results in this application. However, if you are on a budget, here are some pointers for you to look out for some alternatives with the appropriate mindset.

In general, a hollow door can only provide an STC rating of around 20s and of course a door with a solid inner core (more mass) will have a higher rating (around STC-25, higher but still ineffective). In contrast, metal door performs better than wood doors, but that poses another challenge for reflection (covered in later parts of the blog series). Similar combinations between interior airspace stuffed with absorbent material and partition board can be employed for the fabrication of the door (part 3). As for isolation when the door is closed, we need to ensure that the door is gasketed and airtight. To seal the gap between the door and frame, several materials have been used to provide pleasing results, namely, rubber strips or neoprene foams. In some cases, magnets have been used to DIY between the frame and door to help improve the compression of the door to the insulating materials.

Neoprene tubing, possible material to stick between frames, credits 1001blocks

Windows are important too! 

If you have the luxury to have separate rooms for your recording needs, then a window might be essential. Although in today’s technology standard, it might be cheaper to install a set of camera and screen in both rooms as it can provide higher insulation when done properly, it does not compensate for the human interaction component for artistes to help them calm their nerves down. A window can contribute to making space feels and looks less claustrophobic; it also provides the visual stimulant for the artiste and engineer to communicate. In some cases where an artiste does not wish to be looked when recording, curtains can be hooked up to provide the privacy he or she needed.

Despite that, most of the suggestion I’ve mentioned so far require construction works, and I will not be surprised that some of you have superb craftsmanship to do it yourself. However, building an acoustically sound window is challenging (in my opinion) but here are a few recommendations to help you look out for or build (seriously? If you do please share it with me!) a window. Firstly, plastic can be used in the construction of a window, although it does not provide as much transmission loss rating as glass does. The principle difference is that plastic would require double the thickness to provide the same amount of transmission loss on glass. Hence, the glass may be a better material to start on. Secondly, which is better single-pane or double-pane window?

Single-pane window vs. Double-pane window

The single-pane window is commonly used in household and does not provide good sound insulation. Thus, you might have observed that if you are living near a bus interchange, your flat will probably come with a double-pane window to help insulation the outside noises. The ideology follows similarly to the construction of a wall (part 3), a logical thought process would conclude that more panes (higher density) will offer greater loss. Beside mass law, it is shown that a double-pane window separated by an air gap can provide approximately 30dB of transmission loss. As the window provides a visual cue to both parties on either side of the room, it will not be advisable for you to stuff absorbent materials such as fibre glass to help improve the insulation. Hence, it would be even more important for you to find a good ratio between the partitions thickness (e.g. glass) and the interior airspace. For a simple guideline, a double-pane window with an interior airspace of 0.1m sandwiched between a 0.01m and 0.006m glass panels (total thickness of 0.116m) can provide an STC rating of 42.

Cross-section of a double-pane window, credits Glassdoctor

What about introducing a third pane

If you’re wondering whether does introducing the third pane further improve the STC rating, the short answer is yes but not significant. Through extensive research in 1983 from Quirt, J. D. measuring the difference made between windows (double glazing and triple glazing), the result in the differences are subtle. Although some might argue that a triple-pane window does still increase the insulation, I feel this is a diminished effect, and you can spend it better in other areas. Otherwise, do indulge yourself with it if you can afford.

In the next article, we will look further into treating other entry points such as heating, ventilating and cooling system.