Achieve NRC sound acoustics
The call you fear: The phone rings. It's your client. And it’s not the usual small talk. They just settled into the office you finished for them and they tell you, "The noise in here is unbearable."
Current architectural trends are increasing the number of calls like these. Spaces are larger and more open. Little huddle and quiet rooms where people are supposed to concentrate are decorative at best because they have open tops, demountable glass walls and sliding doors that let noise pass freely.
Despite winning a design award and being exactly what your client asked for and approved, you now have a serious problem – the fact that there's no one thing that will fix it. Do you add absorption over the open office area? That would be difficult because of the existing location of the fire sprinkler heads and lights. Do you focus on the meeting rooms and executive offices? The demountable wall systems are inadequate acoustically and you can't switch the sliding doors for swinging doors with seals because of egress route infringement.
It would be a relief to know that this scenario is hypothetical, but it's not. Here's how to avoid a call like this from your client.
Even if you are not required to comply with an acoustics standard or follow the recommendations of an acoustics consultant, you can rest assured that with a simple design process called Optimized Acoustics you can flex your design imagination and still create an acoustically comfortable and effective environment.
The first step is to understand and appreciate the role of ceilings and walls in your building. Acoustic ceilings (or baffles or islands) are made of lightweight materials and are porous, making them great at sound absorption and terrible at sound blocking. Use ceilings for sound absorption only. Absorption performance is characterized by Noise Reduction Coefficient (NRC) and varies between 0 and 1 – the higher the better. NRC can be categorized as Good 0.70, Better 0.80 and Best 0.90. If a space is normally occupied by people, the NRC of the ceiling should not be less than 0.70. The optimal NRC for less noisy and less sensitive spaces like private offices is 0.70 (Good) while most standards require a minimum NRC 0.90 (Best) in open offices.
Walls and slabs, on the other hand, are massive and nonporous, making them great at sound blocking and terrible at sound absorption. Their capability to block sound is quantified as Sound Transmission Class (STC) and it can be categorized as Good STC 40, Better STC 45 and Best STC 50+. When sound privacy and noise control are expected inside an enclosed room, the wall, whether site built from gypsum board or pre-manufactured and modular, should achieve STC 45. If the walls are not full height from slab to slab, then a vertical plenum barrier over the wall should be used in combination with the ceiling to achieve the same level of performance as the wall. The old days when demising walls stopped at the height of the ceiling, allowing sound to pass up and over the walls through the ceilings, are gone. This no longer complies with the acoustics standards or user expectations.
With these guiding performance metrics established, only specify and install tested products and systems that meet or exceed them.