From figure 1 we can see that:
1) There is no distinct boundary between two neighbouring ranges and overlap is obvious.
2) The low, medium, high frequency ranges can be roughly divided at 500Hz and 4000Hz.
2. Mental feeling of different frequency range
Sounds of different frequency range give different mental feelings.
1) Low, lower part : Refers to sound with frequency lower than 50Hz. Sound in this range is merely audible to human ear. It gives a feeling of heavy, oppressive, strong and shaking. The sound is more felt than heard. Properly enhancing the wave amplitude in this range can make the low and deep sound of some instruments like cello, bass drum, and organ more audible. But excessive enhancement can make the sound or music unclear.
2) Low, medium part: Refers to sound in the frequency range 50Hz to 150Hz. Sounds in this range make you feel grand, strong and spacious.
3) Low, higher part: Refers to sound in the frequency range 150Hz to 500Hz, which includes the fundamental tone in rhythm department. This sound is sturdy and full. Adjusting the sound in this range can make it become thick or thin.
In some cases of application, if the speaker or amplifier cannot play the sound with low frequency well, the sound will become thin and weak. On the other hand, if the low frequency sound is raised too much, the sound will become not clear.
4) Medium frequency: Refers to sound in the frequency range 300Hz to 4000Hz. The beginning part of this range is clear and transparent, while the ending part (4000Hz) is getting screamy.
5) Medium, lower and medium part: Refers to sound in the frequency range 500Hz~2000Hz, which includes lower harmonic wave of most instruments. This sound is bright and clear.
If you try to reduce the frequency by 1kHz for a melody, you will make the playing effect like the singer is singing this song from far away. However, if you try to get the frequency higher, it will result in the effect that it is played from telephone.
Moreover, if raise the frequency with the range of 500Hz~2000Hz, the playing effect will become pretty loud as it is played by amplifier. While raise the frequency up to 1kHz~2kHz, the sound will become noise as it is created by striking the metal. Even raised higher, the sound with this range will cause hearing tiredness.
6) Medium, higher part: Refers to sound in the frequency range 2kHz~4kHz. Sounds in this range are extremely strong and give us the feeling of hard as metal. If properly adjust the frequency in this range, you can improve the clearness of sound. Note that do not raise the frequency too much as it will cause the hearing tiredness.
Since the medium frequency contains abundant fundamental tones or overtones, the processing of medium frequency is crucial to amplifier system design. In general, the too strong medium frequency leads to the not vivid sound, while the too weak medium frequency may result in the un-clearness of sound.
7) High, lower part: Refers to sound in the frequency range 4kHz~8kHz. Adjusting the frequency of this range can create hard or soft music. For string instruments or woodwind instruments, you can raise its frequency to obtain rich sound. While minishing the frequency amplitude can obtain monotonic and plain sound. If enlarge the amplitude too much, the sound will become thin and the background noise will be increased.
8) High, medium part: Refers to sound whose frequency exceeds 8kHz. The sound or music in this range is exquisite. So if raise the frequency to this range, you can create exquisite music.
9) High, higher part: Refers to sound whose frequency exceeds 10kHz. Most human being cannot hear this sound clearly. But this range of sound can highlight the whole sound, and make it more abundant and colourful.
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