Those of us who work in education have probably at some point said “It’s OK I’ll use my teacher voice”, but what we probably don’t realise is how this impacts those around us. When we speak louder, our voice becomes less clear, and in addition, our mouths become harder to read. In a large space this is also totally impractical. Here’s a quick math lesson:
When we speak, our voice becomes attenuated (loses volume) by 6dB for every doubling of distance after 1 m. So, if we speak at 60dB, then at 2m we are heard at 54dB and then at 4m, 48dB and at 8m, 42dB. Once we reach 16m we are only at 36dB which is just above background noise (on average). This diagram explains this is an easier to visualise way:
To be able to distinguish speech clearly, we need a signal to noise ratio (SNR) of +10. This means that the decibel difference between the voice and the background noise, needs to be at least positive 10dB (the voice being 10dB louder than the background noise).
So, let’s think about the average classroom where the background noise is on average 50dB, (and in reality probably not below 40dB, this is with students in it talking and working). If you are talking at 60dB in this environment then your voice can only be clearly distinguished in the first meter of the room that you are talking in. The reality is that even if we are speaking loudly or in a classroom which has a low background noise, those at the back of the room (no matter how hard we try) are going to have a hard time listening and understanding speech due to the distances involved.
Speaking loudly in a meeting, in class, in a large space does increase the SNR, but it also distorts the voice, and it also makes lips harder to read, as we mentioned at the start. However, at the same time, it also doesn’t travel as far as you think. In our school auditorium, which is about 75ft (~23m), even shouting at 85db (this is very loud) would see our voice reach the back of this space at around 55dB (which is close to the volume of average conversational speech). Speaking loudly at 75dB, would see us at 45dB (which is just below conversational speech) in a space which has a lot of background noise and reverberation. The voice might be audible, but remember that clarity and comprehension are affected.
How do we overcome this? The answer is simple: we can use microphones! Yes, we might hate the sound of our own voice, but it means that everyone can hear equally, and equitably, and in addition, it means that person speaking doesn’t have to strain their voice. In addition, the use of microphones means that assistive listening systems can be used to make listening further equitable.
So, next time you’re tempted to say “I’ll use my teacher voice”, please take a moment and think about those who have hearing loss, auditory processing disorders, and those who can hear just fine (everyone can benefit from the use of a microphone). Whether you think there is a lot of background noise (or not), please accept the offer of a microphone!
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