Lest my sharing of several guilty pleasures like Buffy fool you into thinking my brain's gone all soft, I've decided to reprint here a short published essay I wrote in response to a comment that was made by a fellow subscriber to The Stream, which is a newsletter from a website called Project Renaissance that features articles, books, and suggestions for increasing brain health, creativity, and intelligence. The site is the result of decades of work in this area by a gentleman named Win Wenger, and we give it a big Asparagus Pee thumbs-up.

The other reader wrote "I have a question about audio feedback, if there is an increase in the amount of energy being used during feedback? There must be. If so, is the relationship between the amount of energy used to increase volume during feedback the same as energy used to increase volume by just turning it up?"

Here's my reply:

The power required to produce a certain increase in sound volume is a simple logarithmic curve, where each doubling of the perceived loudness (yes, perceived by a human - if Werner Heisenberg isn't in the forest when the tree falls, can we be certain that there really was a tree?) requires 10 times the energy in terms of kinetic energy. I'd be really surprised (shocked and sickened, actually) if this didn't apply to feedback squeals as well.

Basically, feedback occurs through the process of escalating reinforcement. A sound is being produced that resonates with the environment in some way, in either the room or the electronics, much the same as a note is produced when you blow across a bottle. Some form of amplification is required to provide the escalation of the resonance, but as long as the amplifier and other elements of the system can provide greater output, the escalation should follow the typical dB power curve, the same as turning up the volume on a non-resonant sound.

Where it gets interesting is when the limitations of the devices or the characteristics of the environment cause the feedback resonance frequency or character to change as the power escalates.

Resonance itself is a strange beast, and another thing entirely. If you can determine the resonance of an object, a space, a device, a person, etc., it's not exactly what I would call feedback, but vibrations can become self-reinforcing due to the correspondence of coinciding wavefronts.

I'm now thinking specifically of a story regarding Nikola Tesla when he was immersed in resonance studies where he invented a mechanical reciprocating device to provide a small hammer blow at regular intervals, calculated the resonant frequency of a large building in New York, and placed the device on the corner of the building. According to this anecdote, it worked so well that the building began to sway and he ended up shattering the device with a sledgehammer and breaking the resonance to prevent it from toppling.

Whether or not this story is true, SELF-reinforcing systems are subject to runaway escalation with very little additional power input because they become chaotic in nature and it takes only 'a minimal change in the input variable' to provide a 'catastrophic change' in the resulting output, by forcing the system to another area of a strange attractor that represents the available states in phase space. This is a lot of scientific-sounding mumbo-jumbo for the last straw on the camel, or Ella Fitzgerald breaking the wine glass on the old 'Is it live or is it Memorex?' commercials.

This is also how lasers work. And metaphorical thinkers can see that this has ramifications for socio-political power, resonance, and feedback as well.

posted by Chris at 10:29 AM Permalink |