Tuesday, January 5, 2010

Psychoacoustics and why people daydream during speeches

So you are at a church service or speaking engagement and watching the guest speaker (or pastor) but the sound seems to come from someplace other than his / her lips? If you closed your eyes and tried to guess where the sound was coming from, you might open your eyes to be staring at the speakers, or even worse, a wall! This kind of issue can be confusing and somewhat tiring for the brain to process, as your eyes are telling you one thing, and your ears another.

As this kind of acoustical phenomenon is tiring to process for the brain, it is also just plain tiring. Often people attending a church service, or speaking engagement, will wonder off into daydreaming or even drowsiness. Not because the person giving the speech is delivering horrible content, but because it is simply too difficult to listen. I recently read a great article on Pro Sound Web, that pointed out this issue of yawning, and daydreaming in church services.

From here I would like to delve into the realm of Psychoacoustics. Psychoacoustics is the study of how sounds are perceived and processed by the human mind. Many venues are plagued with issues relating to psychoacoustics, such as the issue mentioned earlier.

Our brain has many ways of filtering sounds, and processing what is coming into our ears. If we did not have these filters, we would not be able to have a conversation in a restaurant, localize sounds, or be able to decipher the intensity sounds. The less our brain has to process sounds the better we are able to absorb important information, or enjoy our sonic experiences.

One psychoacoustic effect that I would like to focus on is the “Haas Effect” also known as the Precedence Effect, or the Law of the First Wave Front. This effect is responsible

for the ability of listeners with two ears to accurately localize sounds coming from around them.

When two identical sounds originate from two sound sources at different distances, the sound created from the closest location is heard first. The listener perceives that this sound is from that location alone and all later arriving sounds are suppressed, even if the later arriving sound is louder. This could be called “involuntary sensory inhibition”

The Haas Effect occurs when the arrival times of the two sound sources are within 30-40 mili seconds. Any sounds arriving later than 40 mili seconds are perceived as delays or echoes.

So imagine a person on a stage, speaking, is 10 feet behind the main speakers. Obviously you would hear the sound from the speakers first as opposed to hearing the persons actual voice. You would hear the persons actual voice 8.9 mili seconds later than when you heard the main speakers. According to the Haas Effect, your mind would disregard the persons actual voice and perceive that the persons voice is coming from the main speakers.

The Haas Effect often happens because of reflections of sounds as well. Imagine if you’re in the back of a venue and the sound that arrives first is from a reflection off of the back wall. You would perceive that the persons voice is coming from behind you, which could be quite confusing, and would require your brain to work a little more, causing you to daydream as you’re looking at the guest speaker and his voice is coming from behind you.

Many of these issues can be dealt with by proper speaker placement, acoustical treatment of reflections, and time aligning speakers. But the sad case is that many local sound contractors do not understand some of these basic acoustic concepts that are critical to creating an accurate listening environment.

If you have any questions, don’t hesitate to send me an email. Capsicum Pro Audio & Visual would love to help in creating a better listening experience for your audience.

Noah Waldron

Capsicum Pro Audio & Visual



1 comment:

  1. Interesting Noah! I had always wondered why this happened! Great Blog BTW, proud of you! :)