Room Acoustics vs Soundproofing

Room Acoustics vs soundproofing

Are they the same?

When we discuss sound related constructions, most people have this problem. Some people think avoiding incoming sounds to the room is acoustics. Sometimes people think placing a bulk of sponges or acoustical foams will stop the incoming sounds or sound leakages to the outside of the room. Room acoustics and Soundproofing are totally different concepts. Since we are dealing with the sound, the materials that will be used in both applications can be the same. Let’s sort out these misunderstood concepts first.

What is soundproofing and what is room acoustics?

Soundproofing is the concept of isolating a room from the sound. After soundproofing, the room will not receive sound from the outside and leak any sound within the room to the outside. 

After you soundproof a room, you’ll get an artificial sound vibe within the room due to reflections on the surfaces of the room. These uncontrolled reflections will create serious impacts to the sound propagation and hearing. The science of fixing these internal reflection issues is called Room acoustics.

Do you have to always soundproof your room? 

The direct answer is “NO”. You don’t have to always soundproof your room if you don’t care about sound leakages and external sounds. If you soundproof your space, lot’s of things to consider. Existing noise levels, Ventilation, Light conditions, Budget etc.. In simple words, If you soundproof your room, you have to put extra effort to fix the hygiene in the room. 

Why is it important to always correct room acoustics?

As we mentioned, we are living in artificial buildings most of the time. There will be many materials in a building whether it’s soundproofed or not. Tiled floors, Wooden floors, Plaster walls, Brick walls, Furniture, Concrete are only a few materials we find in our daily life. Each material has their own reflection behavior. Therefore it’s a must to correct acoustics in any room, space, hall, theater or any other construction. 

You can easily identify a properly treated acoustical space. It’s pleasant, comfortable, calm and easy to communicate.

When we talk about acoustics in a music studio, the same scenario is applicable. The studio should be soundproofed for recording purposes and avoid neighbor complaints. Also, acoustics should be corrected not only for communicating, but also for listening to music with loudspeakers.

You may have heard about the frequency range of human hearing. It’s from 20Hz to 20,000Hz. The speciality of a studio is that we have to consider the acoustics of each frequency within this range. Now you have an overall idea about soundproofing and room acoustics. Let’s find out more technical details.

Sound damping vs absorption

Sound damping is a term related to soundproofing most of the time. We must try to damp all the sounds arriving from both the outside and inside. Special structural constructions are used to damp sounds.

Room in a room concept is a very popular concept in sound damping. According to this concept, if we create 2 walls and create a vacuum between these 2 walls will damp the sound completely (Removing the medium allows sound to travel).

Unfortunately, creating a vacuum is not very easy. Therefore structural engineers are using multiple walls with sandwiched walls and air gaps. Changing the medium will change the direction of sounds and reduce the energy at each layer (Refraction). 

In the modern world, rockwool or mineral wool is the most popular sound damping material used for sandwiched walls. 

Sound Transmission Class vs Absorption coefficient

If we discussed we are using sound damping materials to absorb sound. When we observe some absorption materials, they are not effective uniformly within the 20Hz to 20,000Hz range. Thin materials like acoustic foam absorb only high frequencies. Increasing the thickness will improve the lower frequency absorption. Different densities of the same material exhibit different performances at different frequencies.

Therefore the performance of materials is always interpreted as a Transmission Loss (TL) for a standard set of frequencies. In simple words, Transmission Loss is the reduction of Sound Pressure Level for each standard frequency due to the absorption material.

https://www.trustile.com/technical-information/understanding-stc-ratings

It’s not practical to check sound transmission for each frequency when we are selecting materials. Therefore, acousticians introduced a standard term as Sound Transmission Class (STC). STC value is an average representation of sound transmission loss for each frequency. Higher the STC, better in performance of isolating sound.

Absorption coefficient also interprets a similar concept with STC but in a different perspective.

As we discussed soundproofing or isolating, there are always 3 domains.

1. Domain before hitting the material
2. Domain within the material
3. Domain after the material

Therefore STC is always about these 3 domains.

Absorption coefficient is related to room acoustics. Room acoustics always consider only 2 domains.

1. Domain within the room
2. Domain within the absorption material

That’s because we are no longer worried about the sound outside the room. The only concern is about reflections within the room.

Therefore the absorption coefficient is defined as a ratio of absorbed energy at hitting the material and energy before hitting the material. As the Sound Transmission Loss, the Absorption coefficient is also measured for the same set of standard frequencies.

https://www.acoustic.ua/st/web_absorption_data_eng.pdf

If the absorption coefficient getting closer to 1 interprets that the material is absorbing a higher amount of energy for that frequency. As the STC represents Transmission losses for all frequencies, Noise Reduction Coefficient (NRC) represents the average absorption coefficient.

Reverberation time

Reverberation time is the most important thing in an acoustical treatment. In general, reverberation time is the duration it takes to end all audible reflections within a room after the source stopped generating the sound. Usually it’s measured in standard measurement called RT60. RT60 is the time it takes to drop the sound pressure level of reflections by 60dB after the source stopped producing the sound.

RT60 also measured at a set of standard frequencies as we previously did. There are recommended RT60 values for different venues to maintain the vibe. We have to maintain the RT60 for each frequency at the given range.

We can calculate the RT60 of a room before the treatment and after the suggested treatments with absorption coefficients of each material, room dimensions and dimensions of components in the room using Sabine’s equation. That’s the way of predicting required absorption panel counts.

Factors to consider when placing panels

When you are placing absorption panels, it’s really important to have an idea about the sound application of the room. If your room is just used for communicating, gathering or any non music or movie related application, you can easily fix the acoustics. 

When it comes to music related venues like a studio, concert hall, movie theater the job becomes complicated with low frequency management and room modes. Room modes are a set of frequencies that will boost or cancel within your room due to its dimensions. You’ll require some special attention in correcting lower frequency range with bass absorption panels, corner traps, helmholtz resonators etc. Finally you must achieve approximately flat frequency response and a good reverberation after the treatment.

Summary

As a summary, soundproofing and room acoustics are totally different concepts but using the same absorption concepts. It’s not always required to soundproof your room, but it’s a must to correct acoustics. 

Sound Transmission Class is the parameter you should check when you are looking for soundproofing materials and Absorption coefficient for Acoustics treatments. Treatment for acoustics is dependent on the application of the room and the operational frequency range of the room. You must try to achieve a suitable reverberation time and frequency response after a proper acoustical treatment.