Audio refers to the sound we hear from our “naked ears”, but in strict sense, Audio refers to a range of frequencies from 20 Hertz to 20,000 Hertz, this is normally written like this (1) 20 Hz ~ 20 Kilo Hz or simply (2) 20Hz ~ 20KHz. This range of frequencies is called Audio Spectrum, Audio Bandwidth as other called it. Some audio we can hear and some we cannot hear, the below picture is an electrical representation of Audio signal.
The human hearing ability is affected by age, as soon as we age to 50 years old, the spectrum of our ears respond changes (except for some super human ears).
Audio Spectrum
Audio spectrum (sometimes it is called Music Spectrum) range from 20 Hz to 20,000 Hz. A 40 Hz means – the signal is transverse 40 times in 1 seconds. The 40 Hz is called low frequency. The 1,000 Hz is called middle frequency (1 KHz means, the signal will transverse 1000 times in 1 second) and a 15,000 Hz or 15 KHz (15,000 times transverse in one second) is called high frequency.
The 20 Hz (lower end of Audio Spectrum) when used as signal in our Amplifier is rather felt than heard. It is reproduced from the woofer or sub-woofer speakers, we feel the pressure especially when you are in a Disco or Cinema with 5.1 Speaker Systems like the sound of a Thunder or explosion. The 20 KHz is seldom heard from the tweeter speakers, as this is beyond the hearing ability of most human ears (unless you have a “super ear”).
The 1,000Hz or 1 KHz is the middle frequency, this is where our ears are tuned (to some) that our ears can hear this frequency so clear and loud. The 1 KHz is used as a standard frequency for parametric testing of Tone Control and Amplifiers (again, 1 KHz means that the signal will transverse 1000 times in 1 second)
Frequency
The Audio Spectrum is determined by its range of Frequencies and the unit is Hertz or Hz, it means that 1,000 Hertz or 1 KHz, the signal is transverse 1,000 times in 1 sec. Our home is powered by 220Vac, 60 Hz sinewave, the voltage and current is repeatedly transverse 60 times in one second. We cannot hear this 60Hz because there is no speaker in our AC power line.
In telephony, the voice is specific to a range of frequencies from 300Hz to 3400 Hz, this is the range of frequencies when we are chatting or called our love one over the landline Telephone or using our Mobile Phone (Smart Phone). I am not so sure when we are fighting on the phone (for whatsoever reason ), if our voice became so high pitch and a lot of shouting. Anyway, wide-band telephony now offers from 300Hz to 7200 Hz, like those in Wideband DECT Phone.
In the Health section of my website, I mentioned several frequencies that can have DNA hack or DNA fixed by revitalizing the human parts with specific frequency, like the following :
- 321.9 Hz – blood
- 418.3 Hz – bone
- 281 Hz – Intestine
- 319.88 – Kidneys
And to mentioned the Schumann Resonance Frequency of 7.38 Hz which is the frequency to the human body to the universe (well, 7.38 Hz is outside the lower end of the audio spectrum).
A low frequency means that the signal is not so compressed, like the signal you can see on the left side of the figure below. A high frequencies means that the signal is compressed as you can see from the right side of the figure below.
Let’s relate this frequency in our daily life. When we fill a glass with water, at the start we can hear the water sound splashing into the glass as lower frequencies sound (the waveform is not compressed as the representation above and this is low frequencies), and as soon as the glass almost filled with water, the sound increases in frequencies (now the waveform will compressed and this is high frequencies).
God is good! The design of our ears respond only to a range of frequencies (Audio Spectrum), you can imagine if our ears will respond up to 5 GHz, then our world would be very noisy, imagine when your neighbor open the garage, you may hear the signal when he pressed the button on the control. Cellular signal operate in the 800~900 MHz and 1.9 GHz and those signal from the cell site would be very noisy if we can hear them. Thanks God!
Signal Type
The type of signal being used in DIY Amplifier Build (and also in Amplifier Manufacturing) are ; (1) Sinewave and (2) Squarewave. The sinewave represent audio performance and use in measuring the Total Harmonic distortion (THD), the maximum power and Stereo Separation.
While the Squarewave is used for parametric test performance, how amplifier respond measured in slew rate, wideband (20Hz to 20 KHz), how the amplifier reproduce the input signal as compared to the output without degradation and used often in Tone Control Bass, Treble and Mid response.
Audio Frequency, Speakers & Ear
In this digital age, we often listen to music and watch video clip on our Smart Phone (no matter what kind of video clip from Facebook, Instagram or from Youtube or videos that we downloaded into our phone, iPad).
When we play the video, the Audio is process electrically (electrical audio) and then it will be fed into the speaker (sound wave audio) so we can hear it.
The speaker above is called 2 way having only the (a) Woofer speaker (the big speaker) and the (b) Twitter speaker (small speaker). The choose of speaker system is very important to have a hi-fidelity music reproduction.
Let’s see this in DIY Audio Amplifier build perspective. Let see the 3-way passive speakers below, you can see that Speakers system comes with 3 speakers (1) Woofer that reproduce the low frequencies [Thunder, Bass drum, Bass Guitar] , (2) the Mid-range which reproduce the middle frequencies [Voice, Snare Drum] and (3) Tweeter that reproduce high frequencies [ Cymbals, Hi-hat]
It is our ears that perceive the sound coming from the speakers, and our mind inner sense processor of music will determine how good (or how bad) is the music. Different people have different taste of music, some like bass or a music with a lot of bass while other prefer crystal clear music to be heard on the Tweeter speaker, but there are music that love by most people, one of which is the “Hotel California”.
In the real world, the 2 way or 3 way passive speakers have a passive dividing network or passive crossover that divide the audio spectrum into 2 way or 3 way. this RLC circuit is isntalled inside the speaker.
The use of passive crossover is to channel the right frequencies to the right speaker, example is the low frequencies goes into the Woofer and the high frequencies into the Tweeter and the mid frequencies goes into the Midrange speaker. Here is an example of the passive crossover network, please note that I keep on stressing the world “passive” as there is also an active crossover network, and there is also Active Speakers. Well, let’s discuss them next time.
But of course, there is (are) single Speaker that can reproduce the Audio Spectrum – they often called Full Range Driver and they do not need a passive crossover network, example is the Mark Audio Speakers, which generally use in Hi-Fidelity (Hi-Fi) and not in Mobile Disco.
Guys, be careful of our ears, because this is the medium that receive the Audio wave from the speaker and translate into a nerve response. Loosing our ear ability will degrade our enjoyment of hearing our favorite music.
That’s it for now fellows! I hope this post can bring clarification to our Audio Starter Friends and our upcoming friends who would like to have fun in the DIY world of Audio Amplifier Build.
Feel free to comment below, add more explanation make it more clearer to be understand by our friends or link related topic. Kindly support this post. Thank you – Salamat Po!