When “Or Equivalent” Is Not Equal: Protecting Acoustic Performance in Your Specifications

“Or equivalent” appears in countless specifications. It is intended to keep projects flexible and costs manageable. In many projects, it does exactly that.

In acoustics, however, those two words can be the difference between a space that meets its STC and IIC targets and a space that generates complaints. Many proposed “equivalents” fall short when you look at how they function in real-world scenarios.

Not sure how vulnerable your current specifications are? Request a free acoustic analysis and our team can review your project with you.

 

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Why “Or Equivalent” Ends Up In Specifications In The First Place

“Or equivalent” remains common in specifications because real-world project pressures often require keeping product options open.

Why “or equivalent” is used:

• Owner, agency, or government procurement rules that discourage single-source specifications
• A desire for pricing competition and perceived cost savings
• Concerns about long lead times or potential supply chain delays
• Internal policies that push against the appearance of “closed” specifications

These constraints are real and affect every stage of project delivery. The issue is not the intent. The issue is what happens later if “equivalent” is not clearly defined and consistently enforced.

“What you intend when you write ‘or equivalent’ vs. what often happens in the field.”

 

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From Specification to Submittal: What Really Happens To Your Acoustic Assemblies

Specifications describe the ideal. Bid day and submittals reveal the reality.

The Bid-Day Reality

An acoustic specification may name a Soundproof Cow product or another manufacturer’s component, followed by “or approved equal.” Once the project goes out to bid, purchasing teams or sourcing companies look for opportunities to improve the numbers. Teams may be instructed to “match performance at a lower cost,” which triggers substitution requests.

When this happens, it becomes essential to verify that any replacement aligns with the project requirements. A product can meet a single data point on paper and still perform very differently when installed in a wall, floor, or ceiling.

Competing products are often positioned as “equivalent” based on:

• A single NRC table or a single STC number
• Generic “sound control” marketing language
• Similar thickness or R-value without any assembly-level test data from recognized third-party laboratories

Where Performance Gets Lost

Substitutions often arrive through channels that make them easy to overlook:

• A single line on a submittal
• A product data sheet with limited acoustic detail

Architects, engineers, and designers are reviewing extensive submittal packages under significant schedule pressure. Unless someone is evaluating STC and IIC references, ASTM standards, and assembly details, it is easy for a non-equivalent option to slip through unnoticed.

 

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Why Acoustics Is Less Forgiving Than Other Divisions

Acoustic systems differ from many other building assemblies because performance depends on how materials interact, not how they behave individually.

STC and IIC ratings are established through laboratory tests of products conducted by accredited third-party labs. These ratings cannot be inferred from a single product property.

Changing the insulation type, density, fastener pattern, underlayment, or decoupling method can alter the assembly rating, even when materials have the same thickness or R-value. NRC is valuable for interior absorption, but it does not indicate how well a system blocks sound transmission between rooms.

Achieving the planned acoustic performance requires all components to function together. Substituting critical elements can degrade the results of the entire system.

Common Substitution Mistakes

Examples of substitutions that frequently undermine performance include:

• Replacing high-density mineral wool or acoustic batts with lightweight thermal batts marketed as “sound control” without assembly-level STC data
• Swapping a tested resilient underlayment for a generic sound mat that reports only a single IIC number from a different material
• Trading engineered isolation clips or channels for lower-cost hardware without recognized third-party acoustic documentation
• Ignoring UL design details or screw patterns that were part of the originally tested construction

 

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What “Equivalent” Should Actually Mean In An Acoustic Specification

Most proposed “equivalents” do not qualify. A true equivalent must be evaluated at the assembly level.

Match the Assembly Performance, Not Just the Bullet Points

At a minimum, a proposed equal should:

• Demonstrate that it is intended for use in an acoustic assembly known to achieve comparable STC and IIC performance under recognized ASTM standards
• Reference appropriate standards such as ASTM E90/E413 (airborne), ASTM E492 and, where applicable, ASTM E2179 (impact), and ASTM C423 (absorption, when relevant)

Match the Critical Material and Installation Details

An equivalent should also include:

• Comparable thickness and density where these properties influence performance
• Construction details that align with the original assembly, including stud spacing, gypsum layers, and flooring stack-up
• Installation details that match the tested assembly, including underlayment placement, clip layout, and fastener schedules

 

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When “Or Equivalent” Does Not Perform as Expected (and When it Does)

Scenario 1 – The Lightweight Batt That Looked Close Enough

Original specification: High-density mineral cotton in a wall between units
Substitution: Lightweight thermal batts described as “acoustic,” same thickness, lower cost, no product-level STC data
Outcome: After move-in, residents reported clear transmission of voices and TV noise
Takeaway: Matching thickness or R-value does not guarantee soundproofing equivalence

Scenario 2 – The Impact-Noise Swap to “Save the Schedule”

Original specification: A tested resilient underlayment system over concrete with a documented IIC product rating
Substitution: A generic roll material providing a single IIC number from a different product line; approved because it was immediately available
Outcome: Significant footfall noise and low-frequency impact complaints; remediation was invasive and costly
Takeaway: Urgency does not justify accepting a substitution that lacks supporting test documentation

Scenario 3 – A True Equivalent That Actually Worked

Alternative: Matched the original product’s density, thickness, and installation requirements
Review: Evaluated and approved by the design team
Outcome: The project met its acoustic performance targets, and the team had documentation on file to justify the decision
Takeaway: True equivalents are possible, but only when evaluated against the full assembly

 

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How Soundproof Cow Helps You Protect Your Specifications

We support projects by helping design teams maintain the acoustic integrity of their materials.

We work at the assembly level

Our guidance is tied to industry-standard products and materials with known acoustic performance based on standardized testing methods. We help you connect that information to your project’s STC and IIC goals so decisions are grounded in real performance expectations.

We support you through the specification and submittal process by providing:

• Assistance in deciding what the right products and materials systems are during specification development
• Support in evaluating whether proposed substitutions align with the acoustic intent when they involve our products
• Identification of  missing documentation, mismatched material systems, or unrealistic “soundproofing” claims

We help reduce the urge to substitute by providing:

• Clear conversations about lead times and availability to prevent last-minute changes
• Guidance for contractors on installation details that must align with the tested materials  and the manufacturer’s installation instructions

Need help defending a sound-rated assembly on a current project? Send us the spec section and we will walk through it with you.

 

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Checklist – Protecting Acoustic Performance On Your Next Project

During Design and Specification

• Tie acoustic requirements (STC/IIC) to specific, tested materials
• Specify products that appear in assemblies with credible acoustic test data from recognized third-party labs
• If “or equivalent” must remain, define it clearly:
  – Performance at or above target
  – Comparable material properties and construction details

During Construction and Submittals

• Require clear documentation for substitutions to compare density, weight, and installation requirements
• Confirm proposed substitutions align with the construction and function of the intended assembly
• Be cautious of vague marketing terms that lack measurable acoustic specifications
• Consult your acoustical engineer or Soundproof Cow’s technical team when substitutions affect sound-rated projects.

 

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Not Sure How Stringent Your Specification Needs To Be?

Not every product requires a closed specification, but acoustic assemblies rarely benefit from flexibility. A small amount of discipline early in the process can prevent major post-occupancy problems.

If you are wondering:

• “Can I safely leave ‘or equivalent’ here?”
• “Is this alternative actually equivalent?”
• “What should my minimum acceptable requirements be?”

We are available to review your specification and help strengthen it where necessary.

Send us your current acoustic spec section and we will help you stress-test it.