Insight - How Headphones with Microphone works

When the internet computing era was catching pace, it was speculated that people might get distant from their loved ones and will immerse themselves in the computer mania. However, the manner in which internet has brought people close is quite amazing. Now important meetings don’t require one to travel long distances. They can be scheduled through video conferencing, just with a click of the mouse. The medical experts at New York City can directly involve themselves in an operation conducted at Nairobi. Several more applications are there that display tremendous ways in which internet based audio-video solutions have got people all over the world closer to each other.

All these things might seem magic to a computer illiterate, but this is something that computer savvy people use every day. A webcam gets a video feed of over loved ones right to our desktop while a speaker and a mic are needed to have a voice interactive session to go along with video, or just as voice chat. Now what if both these functionalities could be combined into one lightweight gear which can be easily worn over our heads and used without any quirks? That’s right; we will explore one such gadget in this insight, a headphone with mic.

Fig. 1: Image of a Headphone with Mic

Structure

Fig. 2: Image of a Conventional Headset Microphone

The image above shows a conventional headset microphone that has a semi-circular band which is curled around the head. At the ends of the band are the headphones, among which the left one has an extended support boom through which a microphone is attached. The headset can be plugged into the computer with the help of two jacks, one for microphone and the other for headphone. Here, the jacks are 3.5mm ones which are most common but even USB based devices have been invented which are exclusively used with computers. This also facilitates the headset to be separately used as headphones and/or microphones by plugging-in only one jack. The headphone jack has a light green colored jacket while the microphone jack has a light blue plastic jacket. The wires of both the jacks merge into a hub which controls the volume and acts as a switch for the headset as well. USB based devices do not require a sound card like the conventional ones as they process digital music which requires no Digital to Analog conversion at the computer. This leads to slightly better sound quality compared to the former type of devices.

The earphones of the headset are structurally connected by a flexible plastic head band. This headset features an ergonomic design where the band is intentionally curved near the headphone part so that it can fit around the ear of the user comfortably. The structure is made of plastic that not only makes the set, economic but also fairly light-weight. Thus, they can be worn for hours at length and still the ears would not feel heavy.

Headphones and Wiring

Image Showing A Closer Look of Headphone Structure

Fig. 3: A closer Look at the Headphone Structure

The earlier insights have detailed about the structure of the headphone and its working. The headphones here too follow the conventional structure. However, the part that bears the boom for microphone has a slight difference as an extra cable for it is attached into it.

Fig. 4: Inner Dynamics of Speaker Section of Microphone

The left section of the headset houses the microphone and one half of the speaker set. When the speaker section of the headphone is opened, the wiring coming from the headphone jack can be seen soldered to the driver of the speaker section. The wire coming from the microphone jack doesn’t form any connections to the internal circuitry. The copper wire in a thin plastic covering in the image above is that of the microphone. Instead, the wiring from the jack of the microphone simply extends to the microphone

Fig. 5: A Look into the Right Part of Headset

Right part of the Headset merely houses the headphone circuitry and is not having any extra wire for microphone. A single wire which connects the left and right headphones is placed in the groove of the plastic band.

Microphone

Fig. 6: Headset Microphone Dynamics

A microphone boom emerges from the left section of the headset. The boom terminates to a plastic casing under which a unidirectional microphone is placed. The unidirectional microphone collects maximum amount of signal directly from the user’s vocals and minimal ambient noise is captured. Microphone used for this purpose is a condenser microphone which is small in size and has less power requirements.

Ball Socket Joint Connecting Headset and Boom

Fig. 7: Ball Socket Joint that Connects Boom to Headset

The boom is connected to the headset through a ball socket joint. This type of joint is named after the shoulder or hip joint which makes their movement around the axis of the linkage. It can be adjusted so as to place the microphone at a close and comfortable distance from the user.

Image Showing Wire Configuration Inside Condensor Microphone

Fig. 8: Wire Configuration of Condensor Microphone

The two wires that emerge from the condenser microphone combine to form a single and comparatively thicker wire. This combination is covered by a thin plastic sheath that keeps the structure together, thus forming a shielded twisted pair. The combination occurs in the boom which can be a stainless steel or a flexible plastic structure depending on the manufacturer.

Volume Control Mechanism

Image Showcasing Positioning of A Potentiometer Used For Controlling Volume In A Headset

Fig. 9: Potentiometer in Headset for Volume Control

In order to switch the headset On and Off, a slider switch is provided on the hub placed midway between the connecting jacks and headphone section. Also, a potentiometer is there to serve as a rotary volume control feature for the headset.

The electric signal that comes to the headphones is an AC. Just like resistance is defined for DC networks, impedance is defined for AC networks. Headphones can be high impedance headphones or low impedance headphones. Higher impedance headphones have a higher obstruction to the current and thus require a good sound driver (amplifier) and power while low impedance devices do not require such additional circuitry. A few manufacturers often advertise using laser tuned drivers instead of conventional acoustic measurement based design for their headphones. The laser tuning process is precisely frequency oriented and claims to reduce sound distortion due to moving internal parts to a minimum. High end headphones are used by professional sound mixers and audiophiles who need a distortion-free high quality output. While headphones with lower impedances require less power and delivering outputs to such headphones is quite easier. That is why the headphones used in portable devices such as laptop or mp3 players have low impedance.

Ideally, the audio signal that comes from the computer directly reaches the headphones, providing limited solutions on the hardware to control the volume. In a headset, however, an optional feature of volume control through a potentiometer is used which is put in series with the headphones.

To lower down the volume, the user rotates the potentiometer dial. When the potentiometer is set to a higher value, impedance of the circuit increases. This reduces the power of the signal reaching the headphones which, after transduction, gives a lower output. A vice versa procedure is adopted to get a higher volume output.

Connecting Jacks

The Ideal 3.5mm Audio Jacks Used For Headphone and Microphone

Fig. 10: Standard 3.5 mm Audio Jacks for Microphone and Headphone

Standard 3.5 mm audio jacks are used in a computer headset. Separate connecting jacks for microphone and headphones are provided in the headset. Usually, both have their symbols engraved on the jacks.

A headset, thus, is a balanced combination of two transducers: microphone and headphones. Previous insights did reveal that how closely structures of these two are related and how exactly opposite these two are in their working. However, there is no interdependency between these two except for the fact that boom rests on one of the headphones. Headsets have successfully migrated to wireless configurations also, but the working still remains the same.