The Limitations of Isolation Products

Everything would be so easy if only that 1/16” thick product made of some unidentifiable material could achieve IIC ratings in the low 70’s regardless of the assembly. We could tell customers to install this wonder material, that essentially adds no height to their floor, and they will achieve ratings that previously only several inches of rubber underlayment or a ceiling suspended by wire over 24 inches could achieve. Or if that thin foam strip can be applied to the studs and joists for significant gains in airborne or impact isolation. Life would be so easy and quiet for everyone!

It appears that physics do not apply to some manufacturers or distributors, or at least their marketing leads us to believe this is the case. Alas, the basic physics of sound and how materials relate to each other prevent these wonder products from achieving the ratings claimed by the companies marketing to unsuspecting consumers.

It's unfuriating at times and other times just disappointing to hear from customers that were duped by a competitor, even a competitor with a good reputation, into using incorrect products, or most often, too many products. One of our competitors, a well known company that seems to have a lot of credibility, promotes STC and IIC ratings for their recommended assemblies that reach well into the 70's for walls and ceilings. These assemblies use pretty basic products overall and in ways that were never tested together and were never intended to reach that high of ratings. They're attempting to use the performance gain of one product added to the performance gain of another and another and another.

STC and IIC ratings don't work like that. If Product A improves your STC rating by 15 points in one assembly and Product B improves your STC rating by 10 points in another assembly, using both the products in the same assembly does not improve the assembly by 25 points. It never will. It's just as likely that it will max out at that 15 point increase from Product A or maybe incrementally improve by 2-3 STC points with adding Product B. It's a logarithmic increase and it's just not that simple. There are too many variables to make such outlandish claims.


Without significant decoupling of the ceiling or wall, achieving extremely high levels of isolation will be somewhere between difficult and impossible. There are few exceptions for this, such as a four foot thick concrete wall, but if you had a wall that thick you probably would not be reading this.

We suggest reading the following articles for a better understanding on how sound isolation products work, why certain products work, and how to maximize performance of various products or methods:

Basic Sound Isolation Concepts

Comparing Types of Sound Ratings

Maximizing Rubber Underlayment Performance

Concept of Decoupling

Concept of Damping

Explanation of Flanking

Choosing Your Sound Door Wisely

The Insulation Debate

And if you are still confused, drop us a line. We are happy to help dispel any untruths pushed around the web on various competitor's sites or forums.