Sound pressure refers to the physical magnitude, and loudness refers to the magnitude perceived by humans. The interaction between frequency and sound pressure is related to auditory characteristics, and understanding this will help you create a better acoustic environment.
Physically, sound has sound pressure and frequency. Sound pressure is the pressure per unit area of a sound, and it can be said to be the loudness of a sound in a physical sense. Loudness, on the other hand, refers to the loudness of a sound as perceived by the human senses. When we often say that a sound is soft or loud, we are referring to loudness. However, the volume or perceived loudness of a sound can sound different depending on the relationship between sound pressure and frequency.
When two sound sources at the same distance produce sounds of different loudness, people usually think that the sound source with the louder volume has a higher sound pressure level. However, this is not always the case. When a person hears a sound, the ciliated cells of the cochlea respond, and this response is transmitted to the brain to recognize the sound. However, these ciliated cells respond differently to different frequencies, so they are sensitive to some frequencies and insensitive to others. As a result, humans can perceive the loudness of sounds differently depending on both frequency and sound pressure.
Human hearing also changes with age. Young children can hear a wider range of frequencies, but as they get older, their hearing deteriorates in the high frequency range. This is related to the degeneration of the hair cells, and especially after the 20s, high frequency hearing loss gradually occurs. These changes in hearing also affect daily life, such as listening to music and communicating.
The human ear has an irregular frequency response. For example, it is more sensitive to sounds in the 1,000-5,000 Hz range than to other frequency bands. However, it is less sensitive to frequencies below and above this range. It is also known that humans cannot hear sounds below about 16 Hz or above 20,000 Hz. The equal loudness curve is a typical example of the characteristics of human hearing.
The equal loudness curve shows that even if two sounds have the same sound pressure, the loudness of the sounds is perceived differently depending on the frequency. In acoustics, the equal loudness curve is a graph of the sound pressure at different frequencies that is perceived to be the same magnitude as a pure tone of 1,000 Hz. For example, according to this curve, the perceived loudness of a pure tone at 1,000 Hz with a sound pressure of 30 dB is said to be the same as the perceived loudness of a pure tone at 125 Hz with a sound pressure of 40 dB and a pure tone at 4,000 Hz with a sound pressure of 25 dB. If the sound pressure of the three pure tones above is all 30 dB, the 4,000 Hz pure tone will sound the loudest.
Because of this hearing characteristic, when you are listening to one sound, you may not be able to hear another sound well. If there is a lot of noise around you, you may have experienced not being able to hear the voice of the person you are talking to. In this case, one sound (the other person’s voice) is being masked by another sound (the noise around them). The simplest example of masking is when pure tone A is present, but pure tone B cannot be heard within a certain frequency range. The range of sounds that cannot be heard due to masking can vary depending on the sound pressure and frequency of the two sounds. In general, the masking range increases as the sound pressure of the masked sound increases. Also, the closer the two sounds are in frequency, the more likely they are to be masked.
This auditory phenomenon plays an important role in several real-world applications. For example, technology is sometimes used to boost the high-frequency band in noisy public places to make speech more intelligible. In addition, masking effects can be used in music production to emphasize the sound of a particular instrument or to reduce background noise. In addition, hearing aids designed to compensate for hearing loss take into account the user’s hearing sensitivity in a particular frequency band.
An understanding of acoustics also influences the design and placement of acoustic devices. For example, the placement of loudspeakers is determined by the acoustic characteristics of the room and the position of the audience. This is done to optimize acoustic reflection and absorption in specific frequency bands, resulting in clearer and more balanced sound.
In addition, acoustic design is very important in places such as movie theaters and concert halls. In such spaces, the placement of loudspeakers and sound absorbers, as well as the structural design, is made to ensure that all audience members experience optimal sound. Sound designers strive to minimize variations in sound depending on the position of the audience and to ensure that sound is delivered evenly across all frequency bands.
Overall, the complex interaction between the physical properties of sound and human hearing has a significant impact on the quality and understanding of the sounds we experience on a daily basis. Based on this knowledge, we can create a better sound environment and develop sound technology. The development of acoustics will bring about innovative changes not only in the transmission of sound, but also in the fields of music and art. The study and understanding of acoustics will continue to grow in importance.
