“Papa, the old headphones that you used with your laptop have a different jack pin from the ones you use with your new phone,” said Raju to his father.
“What difference, Raju? I do not see any difference. I am using these headphones because they came along with the new phone,” replied his father, fully aware of what Raju wanted to know.
“No papa, I will show you the difference. I have saved your old headphones in my kit box.” Raju wanted to prove his observation. He ran to his room and brought the old headphones.
“See papa, can you see this jack pin that is inserted into the laptop port? It is slightly different from the pin that is on your new headphones. See, there are three rings on the new headphones, whereas, the old ones have only two rings. You can clearly see the difference.”
“Good. Your observation is correct. The jack pin of the headphones that connect to my laptop have two rings and the jack pin of the headphones that connect to my phone have three rings. There are also some jack pins which have only one ring,” said his father.
“What do these rings indicate, papa? Does it indicate new versions or improvements made in the model of headphones? Also, this pin has the number 3.5 mm engraved on it. Why?” Raju was eager to find out more.
“No Raju, it indicates whether the headphones will provide a single channel output or a double channel output. You are aware that the sound outputs differ in the various types of music players. Some are mono (monaural), meaning only one output channel of sound. Stereo may use more than one channel and then transfer these channels to two speakers separately. In old radios and phonograms, there used to be only single channelled speakers. With the advent of sound engineering, today we have musical experiences that are made possible by splitting some specific sound signals separated out into different speakers thereby creating a depth or surround effect. That is why the stereo headphones will have two rings.”
“Then, what is the use of the third ring, papa?” asked Raju.
You will find that most mobile headphones have three rings. Two rings are for hearing and the third one for speaking connects to the mic. The pointed one is usually connected to the left headphone, the next one to the right and the third one to the mic. Headphones of mobile phones have three-ringed jack pins. So that you can pick up calls hands-free. The number 2.5 or 3.5 mm indicates the diameter of the pins.
(Writer is a mechanical engineer and runs a hands-on science activity centre at Margao)