Understanding the science of sound
In this three-part video series, you’ll gain a deeper understanding of acoustics, sound transmission, and how to control sound in buildings.
Welcome to Maxxon's "Science of Sound" video series. This three-part series guides you through the essentials of acoustics, sound transmission, and sound control in buildings.
Acoustics is the science of sound, and understanding this science is key to developing and specifying sound control solutions for residential, multifamily, and commercial construction. Whether your goal is to meet or exceed international building codes or increase sound control for greater resident and tenant comfort, Maxxon is your trusted source for acoustical education and industry-leading products based on the science of sound.
Maxxon takes acoustics very seriously in our product development process. Maxxon’s headquarters features a state-of-the-art acoustics lab with the world’s largest floor-ceiling sound chamber. Our research and development team includes a dedicated Lead Scientist of Acoustics. These resources fuel our product innovation process, contribute to acoustical research that advances the construction industry, and seek to elevate the acoustical knowledge of professionals who serve the built environment.
The Basics of Acoustics
Sound travels in waves like ripples in water. When these waves reach a person’s ears, a signal is sent to the brain that's processed and perceived as sound. Sound is perceived in two ways: level and frequency. Level refers to the sound’s intensity, or loudness, and is commonly measured in decibels (dB) ranging from zero to 140 decibels. In this video, you’ll hear clear examples of how changes in decibels are perceived by the ear.
The second way sound is perceived is based on frequency — how high or low the sounds are in pitch. Frequency is measured in Hertz (Hz). Humans can hear sounds ranging from 20 Hertz to 20,000 Hertz, although most people lose the highest frequencies in adulthood. Some dogs can hear sounds as high as 65,000 Hertz. This video demonstrates how changes in Hertz are perceived.
For architectural acoustics, it's important to consider the range of wavelengths of each frequency. The highest perceived frequencies have wavelengths that are less than one inch. The lowest perceived frequencies have wavelengths of over 30 feet. Low frequency sounds won't be blocked by thin, lightweight material that might easily block high frequency sounds. To achieve the desired building acoustics, it’s important to understand low frequency sounds and how to control them.
Measuring Sound Transmission
Two types of sound are transmitted through residential and commercial buildings: airborne sound and structureborne sound. This video provides examples of these sounds, and how their transmission is measured.
Airborne sounds travel through the air and can be transmitted through walls and floors. They include sounds from voices, televisions, noisy pets, and similar sources. Airborne sounds are quantified using a rating known as Sound Transmission Class or STC. To measure STC, noise is emitted from a loudspeaker in one room — a source room — into a receiver room, then the sound levels from the receiver room are subtracted from the sound levels in the source room. The STC rating standard uses frequencies ranging from 125 - 4,000 Hertz.
Structureborne sounds are created by direct contact with the floor. These include footsteps, chair scrapes, and dropped items which transmit through the building structure and radiate as sound. Structureborne sound is quantified with a rating known as Impact Insulation Class or IIC. For the IIC measurement, a standardized tapping machine is used to impact the floor. The intensity of the resulting sound waves transmitted through the floor are measured in the room below using the frequencies from 100 to 3,150 Hertz. The IIC rating is only used for floor and ceiling assemblies. It’s not applicable to walls.
To achieve a single number that determines an STC or IIC rating, test results are measured across 16 frequency bands and plotted on a curve. This curve is then compared to a standardized curve to determine the single number value. Because some building types, such as multifamily properties, require minimum STC and IIC values, it’s essential to check sound codes early in the design process. It’s also important to understand that STC and IIC ratings are lab measurements. Both are performed under highly controlled circumstances and measure only the performance of the assembly being tested.
Measuring actual buildings is more complex because it’s impossible to isolate the interactions between walls, floors, and ceilings. However, tests taken in buildings — also called field tests — are sometimes required by code. To distinguish field tests from lab tests, the letter A for “apparent” is used in front of the STC and IIC acronyms. Ratings referenced as ASTC and AIIC indicate field tests. The industry previously used FSTC and FIIC to identify field tests, so you may also see them referenced this way.
After gaining an understanding of sound transmission and how it’s measured, you’re ready to watch our final video which explains how to control sound transmission through design and construction.
Controlling Sound Transmission
There are four primary ways to minimize sound transfer in buildings:
- Increase the mass (weight) of a floor-ceiling assembly since mass is efficient in blocking airborne sound transmission.
- Design for airspace which can reduce structureborne sound and help minimize airborne sounds.
- Add absorption to buffer sound and minimize sound transmission.
- Create structural breaks that minimize structureborne sound transmission by reducing vibration transfer.
To increase mass for a standard, wood-frame, floor-ceiling assembly, adding 3/4 inch of Maxxon® Gyp-Crete® will triple the total weight of the assembly and increase the STC by up to 10 points, thus lowering airborne sound transmission.
However, adding mass is less effective at blocking structureborne sound transmission. A common way to reduce structureborne sound is to design for airspace, which helps minimize both airborne and structureborne sounds. In this video you’ll find examples for reducing sound transmission in mass timber — a challenging construction type for sound control.
To add absorption, insulation in the ceiling cavity acts as a sound absorption barrier which can increase the STC and IIC ratings by eight to 10 points.
When it comes to structural breaks, using a Maxxon® Acousti-Mat® is an efficient way to minimize structureborne sound transfer by creating a structural break. Our entangled mesh sound mats reduce vibration transfer by creating a completely isolated floor. In this video, you’ll see sound test results that illustrate how even small structural breaks make a big difference in the IIC performance of a wood framed assembly.
To ensure these sound control elements work effectively, it’s important to avoid flanking paths and preserve resilient channels. This video identifies common mistakes that compromise the integrity of acoustical isolation systems and hinder the control of airborne and structureborne sound transmission.
Our video series is designed to expand your knowledge of acoustics, sound transmission, and sound control in buildings. To support you in the design and construction process, Maxxon also offers the following resources.
Fire & Sound Manual
Access the full listing of sound tests and Maxxon UL Fire Ratings by construction type.