Do ultrasonic dog deterrents go the distance?
To answer the age-old question: “If a tree falls in a forest and no one is around to hear it, does it make a sound?” the properties of a sound wave should be looked at. To answer the question, it would be helpful to know that sound is essentially vibration. The tree falling would create a disturbance in the air around it during the fall. The result is vibration. When the tree hits the ground, it would also cause vibration. These vibrations would be perceived as sound. All objects have a resonant frequency that is determined by its size, density, and so on. The tree’s size and density, as well as the ground it falls on, would determine the tone of the sound the falling tree makes.
Why are ultrasonic tones influenced to a greater degree by damping?
Damping is defined as an influence on an oscillating system that has the effect of preventing, reducing, or restricting that system. Oscillation can be described as vibration. Vibration is often perceived as sound. Friction, in general, is most normally the cause of damping on vibration. The higher the tone, the more compact the waves, and the more energy is required to move the vibration through the medium. The more energy needed to move the vibration through the medium, the quicker friction acts on the sound’s wave, reducing its energy and amplitude. Decreasing amplitude translates into reducing the volume until there is no sound, the vibration is absorbed by the medium. Ultrasonic dog deterrents emit high-frequency tones. These ultrasonic tones lose their energy faster as the sound wave moves through the atmosphere. As frequency increases, the distance the sound wave can travel decreases.
Diffraction also affects high-frequency sound waves to a greater degree.
Diffraction is the ability of a sound wave to continue around an object as it moves through an environment. If the wavelength of the wave is smaller than the obstacle, no diffraction occurs as the sound wave is too small to move around the object. Ultrasonic dog deterrents use very high-frequency tones that have shorter wavelengths. The sound wave will either be absorbed, reflected, or refraction may occur. Ultrasonic sound waves have very compact, small wavelengths. This translates into more opportunity for the ultrasonic sound wave to be absorbed or reflected, which decreases the distance the sound wave may travel. It might be helpful to visualize waves encountering a bulkhead pier that protrudes into the water horizontally to the incoming waves. The smaller waves are just too small to travel around the bulkhead, so that vibration is either absorbed into the bulkhead or reflected back.
In closing the lower the frequency, the greater the distance a sound wave can travel, and the less likely the sound wave is to be vulnerable to objects in the environment. The Sound Defense K9 Warning Device sounds within dog’s sensitive hearing range. The dogs sensitive hearing range is at a much lower frequency than ultrasonic sound.
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