Pitch vs. Loudness: Understanding the Key Differences in Sound
One of the major student misconceptions is the fact that students perceive sound pitch and loudness as being the same. The forum discussion centers on the misconception that sound pitch and loudness are the same, specifically addressing a quote from M. Allen's "Misconceptions in Primary Science." This is not a topic on education or pedagogy, but rather on the physics itself. Let's delve into the fundamental differences between pitch and loudness, two essential characteristics of sound.
Pitch refers to the frequency of a sound wave, which is related to the number of vibrations per second. It is a subjective perception, but it can be measured using units like Hertz (Hz). Frequency is the main determining factor of pitch in a sound wave, with higher frequencies being perceived as higher-pitched sounds and lower frequencies being perceived as lower-pitched sounds. Pitch depends only on frequency.
Pitch is directly related to the frequency of a sound wave.
Frequency and wavelength are connected. They are connected by the formula (definition) c=fλ but the one which cannot vary, once the sound (or any wave) has been generated, is the frequency. One can either say the sound depends on frequency, or on wavelength because the speed of the "wave" for a particular instrument or medium is fixed. So once a wavelength or frequency is established, the other is also known. This means that saying that the pitch depends on wavelength is the same as saying that it depends on frequency.
You can hear a sound under water - say a tone played on a loudspeaker. It will have the same frequency when you take your head out of the water but the speed of sound in water is five times (about 1500m/s) that of of sound in air (about 330m/s. Consequently, the wavelength in water will be proportionately greater (about five times greater). On the other hand, the pitch of your flute (a wind instrument) can change as the speed of sound in the air (inside your flute) can be different in the desert.
Increasing the pitch increase the frequency and decreases the wavelength. It really doesn't matter how it was created or what medium it had gone through. The problem is simple.
Loudness, on the other hand, refers to the amplitude, or intensity, of a sound wave. It is a subjective perception that depends on the individual listener and their hearing abilities. However, loudness is typically measured in decibels (dB) and is related to the amplitude of the sound wave. Loudness is how big the sound. Loudness on the other hand is an empirical measure of the intensity of sound, ergo, the energy of sound waves arriving at a 1m^2 area per second.
Amplitude of a sound wave determines its loudness.
The amplitude of oscillation determines the "energy" in the wave, and thus, the loudness of the sound wave. Now, OP seems to see a conflict, because a high frequency at amplitude X has more energy than a low frequency at amplitude X. But I see that as something separate. It still holds true that loudness is a factor of amplitude. In simple terms, if I increase/decrease the amplitude of a sound, all else being equal, and the sound is in the range of human perception, the sound will be perceived as louder/softer.
The energy of sound waves is proportional to the square of both amplitude and frequency. Now, the exactly relationship may not be the same, i.e. the energy of various vibration frequencies varies predictably with their frequency.. in electronics, in optics... a photon has wavelength, frequency and energy.. it takes many phonons distributed over one square meter in one second to derive the "energy" as you describe it... be careful as to what you call energy... think phonons, like photons... photons are packets of electomagnetic vibrating energy... The pressue on that area...can be describe in different ways if you use the concept of "energy" then you must call it power or watts per square meter.. and then adding time it becomes watt seconds - like KWH killowatthours...
To illustrate the difference, consider a musical instrument. You could certainly use a musical instrument to illustrate the meanings. If these two waves represented sound waves, the pitch and loudness would be the same in both cases. But would they sound exactly the same? The answer is No, because there is one more attribute to sound waves that you are familiar with, and that is tone quality. This is what makes different instruments sound different. A violin and a trumpet can play the same pitch with the same loudness, but we can easily tell them apart, because they have a different tone quality. In fact, the same instrument can create different tone qualities. If you pluck a guitar in different ways, you can get quite different tones. Try it! The technical musical term for this is timbre.
To begin our discussion, we will consider the attributes or characteristics of any kind of wave. The most noticeable aspect of a wave is that it repeats in time. Whether it is a vibrating string on a violin or waves breaking at the shore, something is repeating. Musical notes or tones have a pitch. The pitch of a particular note is often given as a number. For example, the note "A" in the middle of a piano is designated A=440. Now, the question is 440 what? will vibrate or oscillate back and forth and will have a certain pitch. all of the time, so a shorthand has been developed. Each way of writing this gets progressively more compact. Since frequency always refers to some number of oscillations, we do not have to keep writing "oscillations". Also, "per second" is more easily written as /second, and second is abbreviated as sec. What may be more unfamiliar is the designation that "/sec" = "Hz". Hz is an abbreviation of the unit Hertz, named after the physicists Heinrich Hertz.
Once we understand the meaning of a pitch or frequency of 440 Hz, we can ask a related question: how long does 1 oscillation of the vibrating string take? If the string oscillates 440 times in 1 second, then each oscillation will take (1/440) seconds. Another way to look at this is the following: if each oscillation takes (1/440) seconds then 440 oscillations will take 1 second. Again, we have used some shorthand notation. If the period is rather small, we don't want to keep writing lots of zeros after the decimal point, so we use scientific notation, instead. 10-3 seconds corresponds to 1 millisecond and 1 millisecond is abbreviated as 1 msec.
Repetitive sounds can be formed in different ways. common, of course, is from a musical instrument. The individual echoes of the drum off each step are delayed from one another. So, to the drummer the echoes form a repetitive sound which then is heard as a pitch. Besides the pitch of a musical note, perhaps the most noticeable feature in how loud the note is. The loudness of a sound wave is determined from its amplitude. While loudness is only associated with sound waves, all types of waves have an amplitude. Waves on a calm ocean may be less than 1 foot high. Good surfing waves might be 10 feet or more in amplitude.
Several factors can influence how we perceive sound:
- How far are you from the source of the sound?
- Intervening material.
- Depends on what is detecting the wave sound. Ear vs.
Although a wave repeats in time, its motion during on oscillation can be simple or highly complex.
| Feature | Pitch | Loudness |
|---|---|---|
| Physical Property | Frequency (Hz) | Amplitude (dB) |
| Perception | High or Low Tone | Soft or Loud Sound |
| Determining Factor | Vibrations per second | Intensity of sound wave |