Sound Frequencies

     and Music Quality

A sound wave in the air can be visualized as a pressure wave consisting of densely packed and sparse regions. Lower sounds are modulated with finer lines that carry higher frequencies. The precise shape of these lines carries information about the frequency and amplitude of the sound. Frequency is measured in hertz - Hz (cycles per second), and it's one of the most important aspects when dealing with sound.

Hearing transforms sound waves into nerve impulses that the brain can process. Newborns can hear sounds in the frequency range of about 20 Hz to 20,000 Hz, but as they age, their ability to hear higher frequencies diminishes. An adult's hearing ability is typically limited to around 20 Hz to 16,000 Hz. Human hearing is most sensitive in the frequency range of 2 kHz to 5 kHz. Within this range, the human auditory sense can detect and differentiate sounds most effectively, which is crucial for speech communication and music. Additionally, human attention is focused within the range where people can speak or sing, roughly 80 Hz to 1.2 kHz or slightly higher. The frequency range of 7-9 kHz is also important for consonants. Therefore, it can be said that the significant frequency range for a listener is 80-9000 Hz, where the sound needs to be clear and accurate.

In music, notes are used to indicate pitch. The most common musical frequency system is based on eight fundamental notes that form an octave. An octave refers to the frequency range between two similar notes, with one note having a frequency twice that of the other. For instance, the frequency of A4 note is around 440 Hz, while the frequency of A5 note is about 880 Hz. Thus, the A5 note is one octave higher than the A4 note.

Octave Note Frequency (Hz)

0 A0 ~27.5

1 A1 ~55

2 A2 ~110

3 A3 ~220

4 A4 ~440

5 A5 ~880

6 A6 ~1760

7 A7 ~3520

8 A8 ~7040

Notes end around 7000 Hz, but music transmission involves even higher frequencies due to harmonic frequencies. The first three harmonics are the most prominently heard. These harmonics relate to the fundamental frequency as follows: 1st harmonic: Strongest harmonic frequency, twice the fundamental frequency; 2nd harmonic: About three times the fundamental frequency; 3rd harmonic: About four times the fundamental frequency.

String instruments (e.g., violin, cello), brass instruments (e.g., trumpet, cornet), and flutes have the most high-frequency harmonics. High frequencies are also present in percussion instruments struck sharply or with metallic components (cymbals). Presenting various harmonic frequencies in music contributes to its tone. While it might seem that frequencies up to 10,000 Hz are sufficient, the actual sound profile extends up to around 16 kHz. It's a common belief online that if a sound is inaudible, it's worth filtering it out for noise reduction. However, if they exist in the original sound, they should be reproduced. They might induce audible changes in the waveform at lower frequencies, even if the high frequency itself isn't audible. Nevertheless, anything above 20 kHz is likely a significant topic for rodents—though it doesn't enhance music quality. The lowest frequencies are played by instruments such as the double bass (lowest note E0, around 41 Hz, occasionally B0, about 31 Hz); tuba (F1 around 43 Hz or C2 about 65 Hz); organ (can go very low, depending on the organ, down to 16 Hz or even lower), bass drum (around 30 Hz or lower), bass marimba (up to 65 Hz). Of course, electronic instruments or special effects are not limited and can play various frequencies depending on the music creator and performer's choice.

Now, by adding the listener's important frequencies and the essential frequencies in music, we get the following picture for transmitting music through speakers:

The lower significant limit is 20 Hz. In real music, it rarely occurs, and the lower limit is more around 40 Hz. However, for a powerful cinematic experience, it's better if the lowest level is 20 Hz. In the range of 20 - 80 Hz, a human ear cannot judge real sound quality very well. It's important that something is present in this range, but there's no need to chase special quality indicators. Within this range, a person cannot even distinguish sound direction, which allows using a single subwoofer for multiple channels. Despite the foregoing, the sound volume should not be very uneven in this range. Here, room resonances and reflections are more important than the speakers, as well as the speaker's placement in the room.

The range of 80 - 9000 Hz is a quality range, especially its middle part. Here, uniform sound reproduction and low noise levels in terms of harmonics, distortions, and other noise components are important. Investing in rigid membrane and controlled harmonic speakers, fine-tuned passive and active electronics is necessary within this range. As an example, a high-end inductor coil or capacitor costs more in purchasing price than some "test-winning" speakers put together.

The frequency range of 9-16 kHz is crucial for providing tonality to the music. Quality remains important here, but the speakers are small, and the cost doesn't have to be high. The frequency range of 16 - 20 kHz should exist, but even small fluctuations in volume or other aspects that would be very disturbing in the so-called quality range are no longer a concern. In any case, streaming music cuts this information, the typical Bluetooth codec cuts the rest, and processing turns the remaining part into unnecessary noise;). Lately, it seems that many studios preemptively cut this part of the music, and even CD recordings are increasingly omitting this frequency range.

In summary, for a good music experience (in terms of frequencies), you need:

Subwoofer 20/40 - 80 Hz, the selection is broad, and the quality is sufficient. Adequate choices start with prices over 600 EUR and / or

Speaker pair 40/80 - 20,000 Hz, with clean sound mid and high-frequency drivers, a straight sound pressure graph in the essential frequency range, both directly and sideways, and THD 1% or less. Adequate choices start in the price range over 3000 EUR."