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In buildings, it is important to prevent noise from spreading between enclosed rooms. Conversations between doctors and patients in the medical examination room, or between lawyers and clients in the office should be confidential. People in adjacent rooms should not be able to hear the private information being exchanged.

Room separation sound is applicable to closed rooms adjacent to the same floor level. Construction methods for internal partitions that provide the required level of noise isolation between rooms are well known. A number of comprehensive studies have been conducted on the noise isolation performance of partitions.

Noise isolation between vertically adjacent rooms is also important. For example, energetic students in a classroom upstairs in a school building should not disturb their concentrating peers in the library below them. In these cases, the floor structure is the main architectural element that controls the amount of noise transmission between rooms. In buildings with ceilings, the combination of floor and ceiling components determines the overall sound insulation performance between rooms.

Compared with partitions, there is much less information and test data on the noise isolation performance of floor and ceiling components. The information that does exist mainly applies to multi-family residential buildings with wood frames/floors and gypsum board ceilings. For non-residential buildings with concrete structure floors and suspended sound-absorbing panel ceilings, information and test results are limited.

In the absence of test results, architects and acousticians followed some general "rules of thumb." One of them is to achieve greater vertical noise isolation-the sound-absorbing ceiling suspended under the concrete slab should:

• Made of a certain material, such as wet felt mineral fiber;

• Have a certain minimum weight, such as 5 kg/m2 (1 psf); and

• Obtained a minimum ceiling attenuation (CAC) rating of 35.

The test conducted for this article used a consistent reference concrete floor slab and three suspended sound-absorbing panel ceilings of different material types, weights and acoustic properties to study the potential impact of sound-absorbing ceilings on the sound insulation performance of the entire floor ceiling assembly.

Most acoustic standards, guidelines, and rating systems have minimum requirements for noise isolation between enclosed rooms. They are usually expressed as Sound Transmission Class (STC) ratings for interior partitions, doors, windows, and floor and ceiling components.

The guidelines for the design and construction of healthcare facilities developed by the Facility Guidelines Association (FGI) require floor and ceiling components between hospital wards to achieve a minimum STC 50 rating (see Table 1.2-6 in the 2018 Hospital Volume).

American National Standards Institute/American Acoustic Society (ANSI/ASA) S12.60, acoustic performance standards, design requirements and school guidelines, requires floor and ceiling components between classrooms to reach the minimum STC 50 rating (see Table 4 2010 edition).

The General Services Administration/Public Building Services (GSA/PBS) P100 facility standard for federal office buildings requires floor and ceiling components between offices to achieve a noise isolation level (NIC) rating of 50 (see section 3.5.3.4 in the 2018 edition).

NIC is similar to STC in that both measure the noise isolation performance of building elements or assemblies. STC is measured in the laboratory and used as a reference during the design process. NIC conducts on-site measurement after construction is completed.

Since STC 50 has been used for floor and ceiling components in the acoustic standards of healthcare, education, and office buildings, the research in this article also uses STC 50 as the target reference standard.

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