This page contains some extended explanations about the Parlé ceiling microphone calculator, in particular the Room Acoustics setting, details about the sample recordings and access to the recordings. In particular it discusses the role of Noise Floor and RT60 as a constraint in the placement of mics.
Room Acoustics setting
The Room Acoustics setting in the Parlé ceiling microphone calculator is intended to allow the user to estimate the quality of the acoustical environment in which the microphone(s) will be installed, which will inform the calculator recommendations for placing the mics.
Five preset settings are offered for Room Acoustics: Poor, Fair, Good, Great, and Perfect. When the Room Acoustics setting is changed, it affects the maximum distance that a person is allowed to be from a microphone.
- In a room that is judged to have Perfect acoustics, microphones may be spaced further apart (since it is assumed that talkers can be further from the microphone and still sound acceptable).
- In a room that is judged to have Poor acoustics, microphones must be spaced closer together (since it is assumed that talkers must be closer to the microphone to sound acceptable).
Noise Floor, NC, and RT60
The two primary factors that affect the subjective assessment of acoustic quality in a room are Noise Floor and Reverberation Time.
Noise Floor is a measure of how loud the background noise in the room is when it is at rest, measured in A-weighted decibels (dbA). The louder the Noise Floor, the closer a talker will have to be to a microphone to be understood.
The Noise Criteria (NC) rating of a room compares the room's octave-band measured noise floor response curve against a standardized set of response curves to yield an NC-rating for the room. The NC-rating is a generalized method of explaining what applications a room may be suitable for, based on the noise profile.
Reverberation Time is a measure of how reverberant a room is, described as a time value called RT60. RT60 is a measurement of how many milliseconds it takes for the reverberant field energy of a room to decay by 60dB after an impulse sound (like a clap). RT60 can be given as a single average value encompassing the whole audio spectrum, or RT60 can be reported on a per octave response curve where the reverb times are indicated based on the frequency of the audio signal. The higher the reverb time, the closer a talker will have to be to a microphone to be understood.
Recommended room values
Below is a table that roughly outlines what Biamp recommends as the desired Noise Floor and Reverb Time of each of the five preset Room Acoustics settings. The last three columns of the table show the maximum mic-to-talker distance for each of the Parlé microphones. The Parlé Processing block in Tesira software includes 5 presets to tailor the processing for the specific conditions of the room.
When Biamp Launch is used to automate the room configuration process with TesiraFORTÉ X or Devio SCX processors the Room Acoustics settings are determined and applied based on the system's actual measurements of the room. The Parlé ceiling microphone calculator should still be used to inform your placement of the mics prior to installation.
Room Acoustics setting
Reverb Time (RT60)
|Max. Mic-to-Talker Distance|
|Poor||more than 50 dBA||more than 1000 ms||1.5 meters (5 feet)||1.8 meters (6 feet)||1 meter (3.3 feet)|
|Fair||43-50 dBA||500-1000 ms||2 meters (6.5 feet)||2.3 meters (7.5 feet)||1.3 meters (4.3 feet)|
|Good||35-43 dBA||400-500 ms||2.4 meters (8 feet)||3 meters (10 feet)||1.7 meters (5.6 feet)|
|Great||30-35 dBA||300-400 ms||3 meters (10 feet)||3.8 meters (12.5 feet)||2.1 meters (6.9 feet)|
|Perfect||less than 30 dBA||less than 300 ms||4 meters (13 feet)||5 meters (16.3 feet)||2.5 meters (8.2 feet)|
Improving a room
In designing a conference room for audio and video we are really creating a recording or broadcast studio environment, tucked into an office or education space. It is desirable to manage the room's acoustics with that in mind.
In a room with a high noise floor the fixes are typically mechanical in nature. High noise floor is caused by unwanted sound in the room, caused either by something in the room (HVAC vent airflow noise, computer or projector fan noise, refrigerator motors, etc.) or something external to the room (HVAC system noise, elevator motor noise, subway or highway traffic noise, airplane noise, outdoor wind noise, human speech or occupancy noise intruding into the space, etc.) Resolution to noise floor problems often involve working with other building specialists to find ways to reduce or eliminate the noise source or the path of acoustic intrusion.
The NC-rating of the room will improve when the noise floor is reduced. When a lower NC rating is required reducing the ambient noise in the room is the first item on the agenda.
In a room with excessive RT60 values a per octave analysis is critical. This will reveal what frequencies are most problematic and can inform choices of materials or products that will be needed to reduce the reverberance in the frequency ranges of interest. You want to focus resources on the frequencies which are troublesome to prevent putting a generic "sound deadening" or "acoustic treatment" solution in place only to find it missed the problem.
Rooms that have many hard reflective surfaces are notorious for high RT60 times. Parallel reflective surfaces make bad things even worse, allowing sound to flutter between them. An architectural acoustician can be called in to evaluate the room or solutions can be trialed to see if the desired results are obtained. For low frequency energy bass traps may be beneficial, for mid-range and high-frequency sounds acoustic panels of different thicknesses, heights, and widths may be needed. The thickness of the panel affects the frequency range it can be effective in, with lower frequencies requiring thicker panels to be effective. Acoustic diffusers are also useful, these act to passively disperse acoustic energy bouncing off them to minimize reflection hot spots.
Sample recordings of Parlé mics
Biamp has created some sample recordings with the Parlé Beamtracking™ microphone in various acoustical spaces. These recordings are intended to demonstrate what the Parlé might sound like from different distances, in spaces that have differing reverberation and noise levels. Each recording has been normalized to provide a stable listening volume, therefore a recording at 1 meter will be a similar volume to a recording at 5 meters.
Note that speech quality and speech intelligibility are heavily affected by the noise level and reverb time of the space. As noise levels and reverb times increase, the maximum distance that a talker can be located from the mic (and still be understood) will decrease. For most cases, Biamp doesn't recommend locating a microphone further than 5 meters (16 feet) from a talker, even in spaces with superior acoustics. In spaces with more typical acoustics, limiting distances to 3 meters (10 feet) is a good rule of thumb.
Each recording is available either unfiltered (i.e., what it sounds like directly out of the microphone) or phone-filtered (i.e., what it sounds like after going through the typical filtering that a phone system would apply to it)
- Related Standards:
- NTi - (NC) Noise Curves and Criteria for evaluating a room (p. 14)
- Cisco TelePresence - Room Readiness