ANSI S12.2: American National Standard Criteria for Evaluating Room Noise serves as the basis, with slight adjustments based on other publications. The values above come from a variety of sources around the internet and in published books. Kitchens, Shopping, Common Spaces, Dining Halls, Living Rooms, Classrooms, Lecture Halls, Conference RoomsĬorridors, Open Offices, Bathrooms, Toilet Rooms, Reception, Theaters, Concert Halls, Recording Studiosīedrooms, Libraries, Religious Prayer Rooms This table covers a majority of the space types that an architect may be interested in. The table below provides acceptable sound levels for various room types. Table of Acceptable Room / Space Sound Levels

We expect that many acoustic experts will be pushing manufacturers toward the Blanaced Noise Criterion (NCB) and RC Mark II since these two criteria take into account the high frequencies that create a hiss and the low frequencies that can create uncomfortable vibrations. Our experience is that most HVAC equipment manufacturers are using the standard Noise Criteria (NC).

However, they may be part of a discussion about whether a certain piece of HVAC equipment can be placed in the ceiling of a space or in an adjacent room. In general, architects will not be selecting whether to use one criteria or another. Some of the other criteria include eNC and PNC. Of course, there are other noise criteria that have been developed, however they haven’t caught on like those mentioned above. NR Curves are depicted in the graphic below. NR curves were developed by the International Organization for Standardization (ISO.) Each curve depicts the acceptable dB levels across a range of frequencies between 31.5 Hz and 8,000 Hz (8 kHz). Noise Rating curves have been the international standard for indicating acceptable sound levels within a space. Background noise can be thought of as the general hum of the room or building. The criteria and ratings below take help identify acceptable background noise levels caused by HVAC equipment, refrigerators, computer fans, etc. In addition, acceptable dB levels vary with the frequency of the sound due to the varying sensitivity of the human ear across frequencies. Keep in mind that we need to provide acceptable dB levels across a range of frequencies to account for all the different kinds of sounds in our environment. Concert halls tend to need the quietest levels to allow people to hear the intricacies of the different instruments. A classroom will need to be quieter than a residential living room since the speech needs to reach people further away. The main goal for acoustic design in a space is to keep the background noise levels low enough that normal speech (or other special sound, like music) is easily understood. Since humans detect frequencies differently, sound criteria are measured with curves across a range of frequencies. For instance, a 40 dB sound at 1000 Hz frequency would seem louder than a 50 dB sound at 80 Hz frequency – even though the sound pressure is higher in the 80Hz sound, our ears are not as sensitive to it as they are to the 1000 Hz frequency. Outside of that general range, we aren’t concerned about whether the sound levels are very high or low (for architecture, at least).īefore you can begin to understand the various rating criteria, it is important to understand that humans detect varying frequencies differently because the human ear is less sensitive to very high and very low frequencies.

They can easily detect a 5 dB change in sound level under most conditions.ĭecibel A : dB(A) is simply a filter that adjusts decibels for the frequency range that the human ear is capable of hearing, which is in the range of 1 kHz to 4 kHz. Humans can just barely detect a 3 dB sound level difference. As a general rule of thumb, an increase of 10 dB means the sound is perceived to be twice as loud – however this can vary based on the type of sound and the listening conditions. Keep in mind that sound pressure increases on a logarithmic scale. There are different measurements for different conditions, so let’s take a look at them.ĭecibels : The decibel is used in acoustics as the standard unit of sound pressure level, or the loudness of a sound. Unfortunately, it isn’t as simple as saying the sound in a bedroom should be 30 dB or lower.

Measuring Sound Levelsīefore you can determine the appropriate sound level for your space, we need to discuss the various ways of measuring sound. Be sure to check our article Architectural Acoustics - Controlling Sound, which talks about design methods for controlling sound. Part of that is to control sound sources. This article discusses acceptable sound levels within a room.

Table of Acceptable Room / Space Sound Levels.

So Which Noise Criteria Should be Used?.

Decibel ratings chart