- Typical reverberation time is between 0.4 and 1 second.
- Absorptive materials will most likely be necessary for the ceiling.
- Even if the reverberation time is optimally controlled, reflections from the walls can be problematic. Parallel reflective surfaces can cause an annoying condition called flutter echo or standing wave. Ideally, at least two non-parallel walls should be treated with acoustically absorptive material. It might not be necessary to completely treat the wall as long as the critical zone (normally from 3'-7') is treated with a material that has an NRC of at least 0.50, ideally at least 0.80.
- Draperies typically provide very little, if any, absorption.
- Beware of potential noise impact to your space from exterior sources and/or excessive HVAC noise. To help protect your design, the NC level should not exceed 25 to 35. When specifying NC, specify an actual rating, such as NC 30, rather than a range, such as NC 25-30. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project's budget when specifying an NC level.
- Awareness of activity in adjacent spaces is typical in most offices. However, if the transmitted speech is intelligible, it becomes far more distracting. Additionally, confidentiality and speech privacy can become a serious concern. Noise transfer is due to the isolation quality of a wall assembly, as well as any potential flanking paths. The isolation quality of an assembly is largely determined by the weakest point of the assembly. Any air-gap can substantially degrade the isolation quality of the assembly. Even if the assembly has a high STC rating, a variety of flanking paths can allow noise transmission and speech to be understood between spaces. Some of the sound paths that can contribute to potential noise transfer are:
- Wall Assembly
- Door Assembly
- Penetrations (outlets)
- Air-Gap between wall and window mullion
- Flanking over the wall/through the ceiling
- Through the ductwork
- If confidentiality or privacy is an issue, you need to be concerned with the isolation quality of the wall. Even if you specify a high STC rating for the wall, it will not allow for privacy if the wall only extends to the ceiling, or just above the ceiling. For optimal confidentiality, the wall must extend to, and seal to, the deck. Remember, the STC rating of a wall only refers to how well a section of that wall performs in a laboratory and does not necessarily indicate how well the system will perform in the field. Specifying an NIC rating can help ensure the desired isolation level.
- Client Expectations: There is a large range of acceptable isolation levels for office spaces. Transmitted noise that would be tolerable for some projects can be very annoying for others. The annoyance potential is based on individual sensitivities, confidentiality issues, and the level of privacy to which the users are accustomed. It is important to understand your client's needs in regard to privacy and confidentiality expectations in order to design a space that is best suited for their individual needs.