Improving speech intelligibility in highly reverberant worship spaces
By: Michael Pettersen
As a vocalist in choral ensembles, I can attest that the natural (or, more accurately, architectural) reverberation found in many houses of worship helps acoustic music to sound fantastic. Traditional sanctuaries with high, soaring ceilings and lots of hard, reflective surfaces lend power to music, especially the pipe organ and choir for which they were designed.
Unfortunately, the very qualities that help cathedral music sound so great stand in direct opposition to clarity of speech. Spoken language loses its intelligibility – the ability to be clearly understood – when the listener hears multiple versions of the same audio “image” reaching the ear at different times. This is important in houses of worship, since the entire point of weekly services is delivery of The Word.
Imagine a group of professional photographers shooting the same subject, all from different angles and distances. Viewed individually, each photo would be perfectly clear, but seeing them all at once on the same screen would be a disaster. The images would interfere with each other, making it very difficult to perceive the subject clearly, resulting in a meaningless visual cacophony.
The same idea applies to sound. As the sound bounces off reflective hard surfaces, it reaches the listener’s ear at slightly different times. Each reflection sounds fine individually but, taken together, they present a confusing audio signal that is literally difficult for the human brain to understand.
There are no quick fixes to intelligibility issues caused by the room itself. Sound system redesign and acoustical treatments are generally required, both of which are expensive. However, there are some simple techniques available to everyone that can improve intelligibility. Doing something as simple as slowing down one’s rate of speech can help. Here are some practical techniques that can help without investing a lot in new equipment.
The microphone is your link to the sound system and, by extension, to the congregation. Poor microphone technique is a major cause of reduced intelligibility, so it pays to learn how to use it effectively.
When the microphone is attached to a lectern or podium, the speech level reaching the sound system changes – often drastically – every time the talker turns their head while speaking. No sound engineer can hope to anticipate these head and body movements. Maintaining a constant distance between microphone and mouth is the key to avoiding this problem, so beware of turning your head too far from side to side.
Lapel microphones, also called lavalier mics, can be similarly problematic. When the talker turns their head, speech level at the mic (and thus, intelligibility) is reduced. To minimize this problem, learn to turn your body, not just your head – keeping your mouth centered over the lapel mic.
Handheld microphones create a different set of challenges. Common problems include cupping the grille and holding the microphone under the nose. While those “techniques” may be common among rock stars and rappers, they are not recommended for clear communication of speech.
Holding the microphone under the nose causes two significant problems – loud plosives (popping “p” sounds) that obscure the following vowel sounds, and breath noises from both the nose and mouth. To address this, hold the mic by its handle, not the grille, and position it at the corner of your mouth. You’ll be surprised at how much more clearly your words are heard.
Headworn microphones are an excellent way to accomplish proper positioning. By placing the mic element at the corner of the mouth, speech level stays consistent regardless of head movement, while unwanted plosives and breath noises are avoided. A headworn microphone also offers total freedom of movement.
Just as sound bouncing off the walls and ceiling creates interfering reverb and echo, using a monitor speaker (typically, a floor wedge) for the preacher hurts intelligibility by sending a slightly delayed version of the sound back through the microphone and back into the congregation. While many people love to hear themselves big and loud, this actually hurts intelligibility. Here are two solutions:
- Try muting the floor monitors during spoken word portions of the service. This should be a simple matter for the sound engineer. It will require a slight adjustment by the preacher, but will pay dividends in improved intelligibility for the congregation.
- A very effective (but slightly more expensive) alternative to a floor monitor is a personal monitor system. Going in-ear allows presenters to monitor at their preferred volume without hurting intelligibility for the congregation.
Sound System Considerations
Of course, the most obvious (and expensive) source of intelligibility problems is the PA system. Any sound system change should consider possible effects on intelligibility. According to Dr. Peter Mapp, a highly respected expert in speech intelligibility issues caused by acoustics and sound systems, here are the top five considerations for intelligibility in house of worship sound systems:
- Direct-to-reverberant ratio. As discussed above, maximizing this ratio is critical for audio clarity.
- Signal-to-noise ratio. In terms of intelligibility, any sound that is not the intended speech – the “signal” – is considered to be ambient “noise.” This would include background music as much as HVAC, fans, audience an environmental noises. For adequate intelligibility, the desired sound – the spoken word – should be at least 20 dB higher than the noise.
- Appropriate frequency response. For intelligibility, the key range is roughly 200 to 6,000 Hz, preferably flat in the 400-4,000 Hz range.
- Freedom from strong late reflections or echoes. This type of problem can be caused by large glass walls, parallel surfaces, domed ceilings, etc.
- System must be free from audible distortion. There are many forms of distortion, from input clipping to hum, buzz, and the like.
To maximize intelligibility on a system level, loudspeakers must concentrate the sound directly on the congregation to avoid unnecessary reflections from walls and ceilings – a difficult task. In recent years, there have been great advances in sound system design that offer unprecedented control of loudspeaker directivity.
Concert-style line array systems have become very popular, especially in churches with contemporary music presentations. These systems have advanced directivity characteristics, enabling designers to create a cohesive sound field that minimizes reflections off the walls and ceiling.
Even more advanced is the “steerable array.” These tall, slender columnar systems use digital signal processing (DSP) to literally steer the sound across the seating area in a precise plane, drastically reducing unwanted reverberation. Steerable arrays are most effective in the speech ranges, making them an excellent choice in traditional churches and cathedrals that employ unamplified music.
Another sound system design that eliminates unwanted reverberation and enhances intelligibility is called the pew-back system. In this approach, small loudspeakers are attached to the backs of each pew, putting the sound just a couple feet away from each listener. The sheer number of speakers and the wiring/power requirements make it an expensive option, but a pew-back system can be one of them most effective ways to promote speech intelligibility, and has the added advantage of keeping the line of sight to the altar area free from distracting speaker arrays.
The problem of poor speech intelligibility in churches can and should be addressed. The good news is that, many times, noticeable improvements can be made at minimal cost. While each sanctuary and sound system is unique, the principles of physics still apply. Smart loudspeaker placement, proper microphone technique, and the judicious use of technology can all produce noticeable improvements in intelligibility.
Here’s my final tip: When new systems are being considered, remember to specify your expectations for intelligibility of the spoken word (measurable via Speech Transmission Index Public Address or STIPA) along with the sound quality of the music and the speech. It’s not enough for The Word to be heard. It should also be understood!
Originally published in the November 2013 issue of Technologies for Worship Magazine
Michael Pettersen is Director of Product Support at Shure Incorporated, where he has worked since 1976. He has presented technical white papers to the National Association of Broadcasters, Acoustical Society of America, National Systems Contractor Association, European Institute of Acoustics, Voice of America, and White House Communications Agency. He is also a contributing author to the 1,550-page “Handbook for Sound Engineers – Third Edition.”