Home » Audio/Visual, TECHNOLOGY » Special Section: Audio: Speech intelligibility

Special Section: Audio: Speech intelligibility

By Dan James

Faith comes by hearing – but what if they can’t hear you?

The most important criteria for a church sound reinforcement system are that it is loud enough and that it is intelligible. When your congregation is straining to understand what is being said – even unconsciously – it interferes with learning and one’s ability to ponder your sermon. Your congregation also becomes fatigued, which can lead to frustration and disinterest.

Designing a sound system that is loud enough is pretty straightforward, but designing a system that is intelligible requires implementation of several principles, along with proper operation. Intelligibility is a principle that is often not understood, and thus overlooked. Make sure your sound engineer understands intelligibility and will implement all the criteria required. There is a complete and more technical commentary on intelligibility on www.clearsoundcorp.com that your operator and sound engineer can review.

Hardest to correct
Room environment with its acoustics, the location of the presenter, and the presenter are criteria affecting intelligibility, whether there is a sound reinforcement system or not. If there is sound reinforcement, the system components – including microphone choice and placement, speaker choice and implementation, and audio processors such as mixers, equalizers and compressor limiters – all affect intelligibility.

The correct lighting, setting, appropriate lectern and presentation aids will help you, the presenter, be comfortable and confident. You are best understood if the people can see you well. Body language, especially facial expressions, is a part of the whole in communication.

Room acoustics affect intelligibility more than most things, yet the one hardest to correct. When the sound that is being reinforced bounces off walls, floors and ceilings, the initial sound ends up traveling at different distances reaching people’s ears at different time intervals destroying intelligibility. So what will work?

  • Avoid hard reflective surfaces (including empty pews) and odd- or round-shaped rooms.
  • Rooms that are rectangular in shape, where the presentation is on the short-width end, work well.
  • The thicker the carpet the more sound it will absorb.
  • Walls and ceilings that are broken up architecturally or have acoustic absorption panels will help reduce the reverberant sound, making the room more intelligible.

Intelligibility issues
Few microphones are designed specifically for intelligibility. Look for a microphone that is designed specifically for intelligible speech. It limits the frequency response to just the vocal range and does not boost intelligibility-busting frequencies so the voice sounds natural and intelligible. The microphone should be placed close enough so the voice can be reinforced adequately without producing feedback, yet far enough away so that mouth noises, “P” popping and bass boost are not a problem. This is usually about 6 inches with the microphone aimed directly at the mouth. An adequate pop filter will also help.

We had some intelligibility issues in a church where the microphone was emphasizing the bass and high frequencies. When the pastor was speaking, it sounded muffled because of too much bass, and it was distracting to hear the mouth noises. The congregation was frustrated because the volume seemed plenty loud, but the people often could not understand what was being said. There were also issues with the connection, which made the microphone pop once in a while.

We replaced the microphone with an Intelligibility MI-90 gooseneck microphone and a locking connector, and for years now the congregation can easily understand what is said without the distraction of the mouth noises. Often, the problem was that the operator was boosting the bass and treble on the mixer. Educating the operator took care of most of the problem, but the microphone replacement made speech intelligibility even better. With the microphone eliminating the problem frequencies, it ensured that even if later someone changed the frequencies on the mixer, he or she cannot boost frequencies that are not there.

The lure of the sizzle
We are so used to hearing ourselves with the bass and treble boosted on the sound system that when it is corrected, we think the sound seems thin and we wonder where the sizzle is. Remember, it is more important that people understand what you are saying than for the sound to be bigger than life. Be patient and soon your congregation will get used to it, and then realize how natural and personal the system sounds, and how pleasant it is to be able to understand every word.

I have seen this same problem with televised services. Most televisions will not reproduce the accented bass unless they are equipped with a surround sound system – but almost all TVs will reproduce the mouth noises, which are annoying. I was able to talk to a seasoned engineer at one of the largest international televised services about how the services were not as intelligible as they could be, because on TVs with surround sound systems the bass was interfering with intelligibility, and the mouth noises were so loud they not only affected the intelligibility, they were annoying. They have not corrected the situation; I assume because they are so used to hearing the accented bass and sizzle of the “big production.”

Choosing a speaker system
In choosing a speaker system look for one that provides intelligibility by providing sufficient sound pressure levels (so it is loud enough), low distortion (so the sound is clear), control of the projected sound (so echo is reduced), and a flat frequency response (so frequencies that improve intelligibility are not missing, and frequencies that reduce intelligibility are not increased). A distributed ceiling system is often a good choice. Many times you will be using the sound reinforcement for music also. If so, make sure the frequency response is extended, but still maintains a flat response. Speakers like the Clear Sound Corp. “Intelligibility Series” are a good choice for this. Now with an intelligible speaker system, ensure the speakers are placed so that the projected sound covers only the congregation and not onto walls, floors, ceilings or open vacant areas.

Audio processors
The easiest to fix and the most common intelligibility buster are the equalizer knobs on the mixer. Any sound below 80 hertz is not in the vocal range and will interfere with intelligibility. Engage the high-pass filter if available and turn down the low-frequency knob without making the voice sound too thin and unnatural. Consonances are in the mid-frequency range and are the key to intelligibility. Boosting the mid-frequencies a little provides an edge to intelligibility. Attenuate the high frequency to avoid too much sibilance. Too much “sss” in the letter “s” and mouth noises are distracting.

If you are only reinforcing voice, the main system equalizer can be equalized specifically for the voice, but if you are reinforcing music also, equalize the system to a flat response. Then the mixer can be used to individually equalize the instruments, singers and speakers.

Effects such as reverb, delay, etc. can destroy intelligibility and should never be used for the spoken word; however, a compressor limiter can be used to improve intelligibility by keeping the volume at the correct level.

Imagine offering an environment that will enable the congregation to effortlessly understand every word that is said, allowing them to ponder and learn without being fatigued.

Dan James is the CEO of Audio Systems Group, Chicago, IL, manufacturer of Clear Sound products and the patented Summit Lecterns. [www.clearsound.us]

Share

Leave a Reply