History of Dogs and Ultrasonic Sound
Although a dogs most powerful sense is that of smell, their ability to hear comes in as their second strongest sense. A dog is able to hear at a much higher frequency than we can, meaning your dog can hear many different noises we would never be able to hear.
Thousands of years ago before dogs became the domesticated creatures we know today, their ancestors, like wolves, used their ability to hear such high frequencies for hunting purposes. Small animals like mice and rats made up a very large portion of a wolfs diet. These kinds of animals make very high-pitched sounds like squealing. These sounds would allow a wolf to locate the animals location much easier so they were able to prey on the small animal and have a meal to eat.
Surprisingly, it is believed that the dogs we know today have lost some of their ability to hear as well as their wolf ancestors. Although dogs still need to use their sense of hearing on a day-to-day basis, they do not need to rely on their ability to hear the high-pitched frequencies of small vermin while they are hunting for food.
Reporting the frequency range for hearing in dogs and other species is not a straightforward task – the “how” of determining hearing frequency ranges must first be explained. Testing in animals differs from the method commonly used with humans of voluntarily reporting if a sound is heard. When determining the frequency range in animals, an investigator usually must first train the animal to respond to a presented sound stimulus by selecting between two actions using rewards. Often this response is to try to drink or eat from one of two dispensers when a sound is heard. The sounds are randomly presented from one side or the other, and the subject must select the right dispenser (on the same side as the stimulus) to get the reward; otherwise no food or drink is dispensed. This is done with the animal hungry or thirsty to motivate responding. Stimuli are different pure tones at varied frequencies (units of Hertz [Hz] – or kilohertz [kHz]) and at different loudness intensities (units of decibels [dB] – a logarithmic measure). The investigator then plots the responses on an audiogram, a graph of the softest intensity at which the subject was able to detect a specific. The plot of responses is a bowl-shaped curve, steeper on the high frequency end. A series of five typical audiograms for different dogs (Canis canis) is shown in the figure below. 
(right click to see it more clearly) These audiograms are from a book compiling thousands of published references into a single difficult to find source (Fay, 1988). This particular audiogram compiles data on the dog from two published sources: one reporting an average from 11 dogs of unspecified breeds (Lipman & Grassi, 1942) and one reporting results from single dogs of four breeds (Heffner, 1983). Frequency is displayed on a logarithmic scale from 10 Hz to 100,000 Hz (100 kHz), while stimulus intensity is displayed (in dB sound pressure level) from -30 to 80 dB. Curve 1 was from the Lipman study, while curve 2 (Poodle), curve 3 (Dachshund), curve 4 (Saint Bernard) and curve 5 (Chihuahua) were from the Heffner study. In general, dogs had slightly greater sound sensitivity (detected lower intensity sounds) than humans, and cats had greater sensitivity than dogs, indicated by how low on the y-axis points were located.
From the figure it can be seen that choosing the frequencies for reporting the frequency range for dogs is hard – presumably lower frequencies could have been detected if a loud enough stimulus was used, and likewise for high frequencies. Nevertheless, the following table reports the approximate hearing range for different species with an attempt to apply the same cut-off criteria to all, using data from Fay (1988) and Warfield (1973). Since different experimental methods were used in these different studies, too much value should not be placed on comparing species.
It can be seen that the lowest intensity detected differs between the two studies; I place greater reliance on the Heffner study because it is more current and because he is a widely published and respected audiology researcher. It can also be seen that the greatest sensitivity (i.e. the frequencies that can be detected at the lowest intensities) is in the frequency range of 4-10 kHz. One dog (the Poodle) heard a tone at the low frequency of 40 Hz, but an intensity of 59 dB was required for it to be detected; most of the other dogs didnt respond until the stimulus frequency reached 62.5 Hz. Three dogs (the Poodle, Saint Bernard, and Chihuahua) heard a tone at the highest frequency of 46 kHz, requiring intensities of 64-73 dB. On the other hand, the Poodle heard a 4 kHz tone when it was -4 dB (since dB are logarithmic units based on a ratio of the stimulus intensity compared to a standard intensity, any stimulus smaller than the standard results in a ratio less than one, and the logarithm of a number smaller than one is a negative number; therefore a -4 dB stimulus intensity is a VERY soft one!) and an 8 kHz tone when it was -3.5 dB. There was no systemic relation seen among the four breeds between high frequency hearing sensitivity and head size, body weight, or tympanic membrane area.
Do plug in rodent repellers affect dogs?
However, dogs are able to hear sounds that are as high as 45-67 KHz, which means that they are able to hear the ultrasonic sound from these rodent repellents. … However, the good news is that the sound will not harm your dog or cause any lasting damage – it may simply cause short term distress.
Sound Experiment – Dog Whistle
Having a dog’s level of hearing would open up a whole new spectrum of sounds that humans don’t currently hear and change the way we think about music.
To make this piano would require adding another 28 keys to the right-hand-side of the keyboard. But to match the full extent of a dog’s hearing, we’d need to add 52 keys.
People like to talk to one another. We use a relatively limited range of sounds and frequencies.
However, dogs use their hearing not to chatter, but to listen for prey and check for danger. Their hearing is tuned to high-pitched rustlings and squeaks.
This makes a whole lot of sense when you think of how your dog can hear a treat bag being opened from the next room. Of course, this is an oversimplification of why dogs and people hear differently, but it gives an idea of why the 2 species differ.1