ISO 23351 Class A: What It Actually Means When You're Buying an Office Pod

Q: Which Alcove series carries ISO 23351 Class A?

Atom Series is Alcove's ISO 23351 Class A certified series: 30 dB speech level reduction with reverberation time under 0.4 seconds. Aura Series carries ISO 23351-1:2020 certification with greater than 29 dB speech level reduction, independently tested. Element Series carries STC 30 dB certification with full UL compliance. If Class A is a stated requirement in your specification, Atom is the series to evaluate.

Jun 23
5 min read

Updated: Jul 30

When you’re evaluating office pods, acoustic specs come up fast. STC ratings, dB reductions, ISO certifications — vendors use these terms confidently, and they can be hard to compare without a frame of reference. ISO 23351 is the one that matters most. Here’s what it actually measures, what the ratings mean in practice, and what to look for when a vendor claims compliance.

What is ISO 23351-1:2020?

ISO 23351-1:2020 is an international standard developed specifically to measure the acoustic performance of furniture and freestanding rooms, including office pods and phone booths. It was published by the International Organization for Standardization (ISO) and replaced older, less rigorous measurement methods that were not built with pod-sized enclosures in mind.

The standard measures one thing above all: speech level reduction. That is, how much a pod reduces the intelligibility of speech heard from outside. This is distinct from measuring raw sound blocking (which older standards like STC do), because it reflects the real-world experience of private conversation more accurately.

What does ISO 23351 Class A mean?

ISO 23351 classifies pods into performance tiers based on their speech level reduction score. Class A is the highest.

Class	Speech Level Reduction	Reverberation Time
Class A	30 dB or more	Under 0.4 seconds
Class B	25 dB or more	Under 0.5 seconds
Class C	15 dB or more	Under 0.5 seconds
Class D	10 dB or more	No requirement

Class A certification requires both a minimum 30 dB speech level reduction and a reverberation time under 0.4 seconds. Reverberation time matters because a pod that blocks sound from escaping but creates an echo-heavy interior is not a good acoustic environment, either for the person working in it or for call quality.

A pod can claim ISO 23351 compliance without being Class A. When reviewing vendor specs, check which class is certified, not just whether the standard appears on the sheet.

How does ISO 23351 differ from STC?

STC (Sound Transmission Class) is a U.S. standard that measures how much a partition or wall reduces airborne sound between two spaces. It’s a legitimate and widely used metric, but it was designed for walls and floors, not for freestanding enclosures with doors, ventilation systems, and gaps.

ISO 23351 was designed specifically for freestanding furniture-scale enclosures. It accounts for the full enclosure: panels, glass, ventilation openings, and door seals. For office pods, ISO 23351 is the more complete and meaningful standard. STC 30 and ISO 23351 Class A both indicate strong acoustic performance, but they are measuring different things under different conditions.

If a vendor lists only STC, that’s not a red flag. But if you’re comparing pods at a specification level, ISO 23351 gives you a more directly comparable number.

What to look for when a vendor claims ISO 23351 compliance?

Three things worth confirming:

Which class? Class A (30 dB or more) is the highest. A pod certified to Class B or C still meets the standard but performs at a lower level. Some vendors list “ISO 23351 certified” without specifying the class.
Independent certification or in-house testing? Third-party, independently verified certification carries more weight than internal testing results. Look for documentation that specifies the testing body.
Does the rating apply to the full pod? The rating should reflect the pod as shipped and assembled, including the door, glass panels, and ventilation. Panel-only ratings or partial assessments are less meaningful.

Which Alcove pods are ISO 23351 certified?

Atom Series carries ISO 23351 Class A certification: 30 dB speech level reduction with reverberation time under 0.4 seconds. It is Alcove’s highest acoustic specification and the standard we hold the flagship series to.

Aura Series carries ISO 23351-1:2020 certification with greater than 29 dB speech level reduction. Aura adds precision human-factors engineering on top of that acoustic foundation: CRI 92 lighting, balanced-pressure ventilation, and auto air-refresh. It is the series for organizations that hold the quality of the environment inside the pod to the same standard as the acoustic spec.

Element Series carries STC 30 dB certification with full UL compliance. Element delivers the acoustic performance most offices need, at a price that reflects the product directly.

The bottom line

ISO 23351 is the right standard to reach for when you’re evaluating office pods at a serious specification level. Class A is the highest tier. When a vendor lists it, confirm the class, confirm independent verification, and confirm it applies to the full assembled product.

If you’re building a specification for a hybrid office deployment and want to compare Alcove’s series on acoustic performance, certification, and price, the Office Pod Certification Guide is a good place to start.

Frequently Asked Questions

Does ISO 23351 certification expire?

ISO 23351 certification is issued based on testing conducted at a point in time. If a manufacturer changes materials, panel construction, door seals, or ventilation components after certification, the original test results no longer apply to the new configuration. When evaluating a certified pod, it is worth confirming that the certification reflects the current product specification, not an earlier version of the enclosure.

What is the difference between ISO 23351 Class A and Class B?

Class A requires 30 dB or more of speech level reduction with a reverberation time under 0.4 seconds. Class B requires 25 dB or more with reverberation time under 0.5 seconds. In practical terms, Class A provides a meaningfully higher level of speech privacy. For open-plan offices where confidentiality matters, or where pods are used for calls with sensitive business content, Class A is the specification worth holding vendors to.

Can a pod claim ISO 23351 compliance without being independently tested?

Technically, a vendor can reference the standard without independent certification. ISO 23351 compliance claims should be backed by testing conducted at an accredited third-party acoustics laboratory, with a certificate number that can be verified. If a vendor lists the standard but cannot provide documentation or a verifiable certificate, treat it as an unverified claim.

If a pod is STC 30, does it meet ISO 23351 Class A?

Not necessarily. STC 30 and ISO 23351 Class A are different measurements under different methodologies. STC measures partition sound reduction and was designed for walls and floors. ISO 23351 measures speech level reduction across the full assembled enclosure, including ventilation and door gaps. A pod can achieve STC 30 and not meet ISO 23351 Class A, because the two tests are not equivalent. If ISO 23351 Class A is your procurement requirement, request the ISO certification directly.

Which Alcove series carries ISO 23351 Class A?

Atom Series is Alcove's ISO 23351 Class A certified series: 30 dB speech level reduction with reverberation time under 0.4 seconds. Aura Series carries ISO 23351-1:2020 certification with greater than 29 dB speech level reduction, independently tested. Element Series carries STC 30 dB certification with full UL compliance. If Class A is a stated requirement in your specification, Atom is the series to evaluate.