Sound absorption and diffusion explained
For worship service assembly, sound absorption, sound reflection, and dispersal (diffusion) are necessary in some combination depending on the church’s goals. A healthy balance must be sought, avoiding extremes that are likely to create an acoustic profile inhibiting the church’s inspiring message transmission.
In general, churches are built with high reverberating qualities. As a result, interior design choices are frequently made in part with an eye on reducing reverberations. Interior materials’ sound absorption and diffusion properties must be extensive enough to eliminate potentially disturbing echoes while also ensuring guests occupying the farthest corners of a worshipping area can still hear everything clearly.
Sound absorption is typically the goal in spaces used for most contemporary worship services, recreation assemblies, education, and administration. The average noise reduction coefficient (NRC) for these spaces should be around 0.8, depending on the size and design of the area. Ceiling absorption is more effective in large spaces, and wall absorption is more effective in small rooms. Reverberation time (or echo) is calculated as 0.05 (room volume) divided by the sound absorption capacities of the room.
Diffusion in sound dispersal promotes uniform distribution of continuous sound and improves the sense of ‘liveness,’ which is very important in performing arts. Objects and surface irregularities accomplish this. In the design of these spaces, subtle, non-parallel surfaces eliminate echo and distortion for clear speaking. Specific materials will be specified to redirect and diffuse inspiring music. Sound dispersion can be boosted through strategic acoustic wall placement and the use of appropriate acoustic materials.
Generally, spaces used for speech require 3.4 m2 (120 sf) per audience seat, while spaces used for music require 7.65 m2 (270 sf) per audience seat. If a particular space will be used for both (as worshipping areas in churches often are), the architect will seek a comfortable balance between the two.
To get a better handle on cumulative acoustical effects, church architects will use a Ray diagram. These sketches track both direct and reflected sound paths and help determine whether annoying and distorting echoes are likely to be experienced inside an enclosed space. If a reflected sound path is more than 10.4 m (34 ft) longer than the sound’s direct path, this will create a noticeable and undesirable echo for those inside the church auditorium.
Acoustical factors for architects to consider
From an acoustic perspective, many spaces are designed to make it easy for occupants to have intimate conversations, which means high levels of sound absorption are required. In lecture halls, sound diffusion is critical since people sitting in the back must hear the lecturer. In concert venues, sound reverberation is encouraged because it enhances the impact of live music.
In seeking the ideal balance between all three essential qualities—reverberation, diffusion, and absorption—churches strive to be all things to their communities. The most acoustically beautiful church would be conducive to music, lecturing, and one-on-one conversation, thus catering to none specifically but to all simultaneously. A special effort will usually be required to boost a church’s capacity to absorb and diffuse sound since a potential lack of reverberation is seldom the issue.
Ideally, absorption and diffusion levels would be increased by wall and ceiling construction types and by adding appropriate interior features to worship and gathering spaces inside a church. If this proves inadequate, installing commercially produced absorption and diffusion panels might be necessary, which can be applied to walls at strategically chosen spots.
In churches, effective sound management can be further complicated by controlling unwanted and intrusive sounds. For example, when church services are at capacity with worshippers or guests, they can be quickly filled with the sounds of whispered conversations, coughing, footsteps going up and down aisles, people shuffling around in pews, and the noises of restless children. If there are roads or commercial areas outside, traffic sounds can also penetrate church walls. A church’s HVAC system can add a significant amount of background noise if wintertime or summertime services require them to be kept on full-time. All this sound is distracting and unwanted; it can interfere with a listener’s ability to hear words spoken from the pulpit.
It must also be acknowledged that church members, the pastor, and church administrators have opinions about how a church should look and about the emotions it should evoke. Stray too far from those tradition-shaped expectations in search of improved acoustics, and the congregation is likely to react negatively. This means church architects will not have a green light when adding sound-absorbing or diffusing features to their building plans but will be restricted to design choices staying within certain traditional bounds.
There is another added complication. In the modern day, churches have embraced the principles of multipurpose design and construction. This means a room, hall, or gathering area used for one purpose in 2021, might be used for something else entirely by 2026. In some cases, a room, hall, or gathering area might be designated as multipurpose from the outset, meaning churches plan to use them for different types of activities right from day one.
The acoustic ramifications of multipurpose may be minor or significant, depending on the range of activities that might take place in a particular location. In some cases, churches might have to add acoustic panels or sound diffusers once the area has been repurposed. They might even have to add more reflective surfaces if more reverberation is needed to increase sound amplification.
Ultimately, each church construction or remodeling project is unique. No two churches or church campuses are built exactly alike, and no two congregations are precisely alike, either. On each new project, a church architect’s job is to create a blueprint with a detailed and customized acoustic profile, which has been tailored as precisely as possible to fit that church community’s current and anticipated future needs.
