Sound Insulation vs. Sound Absorption

Ranking high on a building owner’s punch list of priorities is good acoustics. With study after study linking acoustics to occupant comfort and performance, this key feature has evolved from a best practice to an essential design requirement.

That said, one often-misunderstood aspect of acoustic performance is the noteworthy difference between soundproofing/insulation and sound absorption.

Sound-insulating materials effectively block or stop sound waves from traveling to adjacent spaces, whereas sound absorption products absorb echoes inside a room, thereby preventing sound from bouncing around the room.

For example, wall systems, acoustic ceiling tiles and acoustic flooring systems can either be insulators or sound absorption materials, or in some cases, both.

Heavier, more massive materials — such as gypsum board or concrete block — are used to block sound, while softer porous materials — like fiberglass or carpeting — work as sound absorbers.

Both types of acoustic “materials have different properties and are used for different purposes, which cannot be interchanged. But due to confusion, both materials are often misused,” cautions National Bureau of Standards researcher Raymond D. Berendt, et al., in Quieting: A Practical Guide to Noise Control.

For example, Brian Atkinson, a consultant with Acoustics By Design, explains that if a sound wave can pass into a porous material such as open-cell foam, then it can also pass through that material, making it a very poor sound blocker.

In some cases, it can actually be challenging to discern exactly how a product will perform, especially when generically billed as “acoustical treatment” or “noise reduction” materials.

To help end-users discern what the product actually does, engineer Sarinne Fox, in her Noise Help blog, recommends looking at the product’s test data.

“If the product specifications include a sound transmission class (STC) number, a transmission loss (TL) curve, or a weighted sound reduction index value, the product was tested as a sound-blocking material,” she explains. “If the specs include a noise reduction coefficient (NRC) or a weighted sound absorption coefficient, the product was tested as a sound-absorbing material.”

Even better are savvy manufacturers who take the time to help specifiers and end-users understand how their products perform through accurate labeling and insightful marketing literature.

In terms of application, before selecting acoustical materials and products, Acoustical Surfaces’ Ted Weidman offers a list of important questions in his blog, “Soundproofing vs. Sound Absorbing — What’s the Difference?”

  • What are the dimensions of and surfaces in the room?
  • What is the room used for and what types of sounds need to be blocked and/or absorbed?
  • Brainstorm some ideas about how to treat the room and where to put product.

Helping designers, building owners and facility managers understand the important distinction between sound insulation and sound absorption is key to selecting the most acoustically appropriate product for a given application. Communicating this essential information will enable you to avoid confusion and optimally support product selection and specification for your clients.