The Battle For Better Hearing

It is a common misnomer that adding audio to a room will make others in the room hear “better”. While the sound pressure level (SPL) is increased, it does not necessarily make the audio more intelligible especially the human voice and a live microphone. In the past few years, companies have invested heavily in research and development to make the learning environment audibly better. Often times, the nemesis of an intelligible environment are feedback and reverberation. I want to touch on a few items of focus that will make the audio learning experience more enjoyable and give you a few challenges/techniques for improving intelligibility within your room.

Facts About Human Speech

• First, here are a few important facts about human speech that are important to know when putting live sound in a room.
• Frequency range of an adult is between 512 Mhz to 2.48 kHz. Obviously, the frequency range will change depending on gender.
• Human speech is a modulated signal with a fundamental frequency in the range of 100 to 400 Hz.
• Intelligibility is imparted by consonants, which average from 10 to 100 ms in duration, and may be as much as 27 dB lower in amplitude than vowels
• The loudness of an adult human voice is about 70 dB SPL at 3 feet.

Feedback

As any sound engineer will attest, feedback is one of the greatest deterrents to intelligible audio. Feedback is when an audio loop exists between the microphone and loudspeaker. When the loop occurs, you will hear a screeching noise through the amplified speaker system. The noise could occur at almost any frequency, but with a human voice it will most likely occur in the frequency range of the human voice (see above). There are many ways to eliminate feedback, but the most common would be to “notch out” the bad frequency by using and equalizer. When a frequency is notched out its level is decreased so that the feedback will not happen. When using an amplified sound system in a room, fighting feedback without out an equalizer, will force the user to decrease the audio level of the room.

Reverberation

The term “reverberation” refers to sound that is continuously reflected within a large space for an extended period of time. Reverberation time greater than 0.60 seconds is typically too long for a learning environment and will lead to muddled syllables and unclear speech. This problem is common in large rooms with tall ceiling heights (greater than 10ft), and many hard surfaces on walls, floor, and ceiling. Another negative effect of excess reverberation is that it amplifies unwanted noise from intrusive sources. This is why underground concrete subway stations are so much louder than elevated outdoor stops for light rails systems.

Eric Wolfram is the Lead Acoustical Engineer and noise control consultant for Riedel & Associates, an acoustical consulting firm based in Milwaukee Wisconsin. In a 2009 article he shares some excellent points regarding reverberation and why the classroom acoustical environment is critical to student learning and academic performance.

A Solution

Though it may be difficult to solve all feedback and reverberation issues, there are ways to improve a room’s intelligibility. If you application is having complaints about poor intelligibility, refer to this table for a possible solution (ProAV Magazine, August 2005)