Sound – The Sounds of Silence?

Today’s blog will let you actually hear some of the qualities of sound that are important to successful ultrasonic cleaning.  Since we humans can not actually hear ultrasound by definition, the sounds you hear will be “translated” into a sound range that we can hear.  A good starting tone is 1,000 Hz.  Sounds at 1,000 Hz are audible by most people who do not have an acute hearing deficiency.

Previous blogs have explored amplitude and frequency and variations that we can add to enhance ultrasonic cleaning as schematic representations of these sounds on an X-Y plot.  Actually hearing the variations as sound should be interesting.  The links in today’s blog are to mp-3 files that should play with Windows Media Player or any program capable of playing mp-3 files.  They can also be downloaded and saved as mp-3 files.

For starters, let’s talk about amplitude and simple variations of amplitude.  Sound amplitude is what we call “loudness.”  Loudness is usually measured in decibels.

Sound – Amplitude

In the following clip, the amplitude of a 1,000 Hz tone is varied from one amplitude to a lower amplitude and back again to the starting amplitude.  Note that the musical note or “pitch” does not change, only the loudness.

Sound wave illustration showing X-Y and density

Hear It!

In the next clip, the amplitude of the 1,000 Hz tone varies at a constant rate of about 2 cycles per second.  Notice that the frequency of the tone does not change, only the amplitude.

Amplitude Modulation

In the next clip, the degree of amplitude modulation is reduced from a starting maximum modulation to no modulation which produces a steady tone.  The degree of modulation is then gradually returned to what it was at the beginning of the clip.

Varying the Manitude of Amplitude Modulation

In today’s final clip, the modulation rate is changed from relatively slow to quite fast and is then returned again to the slow rate of the start.  The base 1,000 Hz tone and amount of modulation remains the same but the frequency of the modulation changes.

Varying the Frequency of Amplitude Modulation

As you can see, there are quite a few things that can be done by just changing amplitude in special ways.  And, yes, this is what AM radio is all about – sort of.  The sound source, music or whatever, controls the amplitude of signal which is broadcast at a constant frequency.  The radio station frequency (1240 for example) is the base frequency much like that 1,000 Hz tone used in the above clips.  The radio receiver senses and decodes the variations in amplitude of the tone to reproduce the sound that created them.  The static we often hear in AM radio broadcasts is caused by signals other than those produced by the radio transmitting station (lightning or whatever) that create changes in the amplitude of the signal.  An upcoming blog will allow the reader to hear what variations in frequency sound like.

–  FJF  –


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