What Loudspeaker Piezor Buzzer and Bleeper is

This post covers what loudspeaker, piezor, buzzer, and bleeper is. These are all output transducers in electrical or electronics engineering.


Loudspeakers are output transducers; they convert an electrical energy to sound energy. They make use of circuit to drive their output such as a 555 astable or an audio amplifier. There are many ranges available, but for many electronic projects, a 300mW miniature loudspeaker is ideal. This type is about 70mm diameter and it is usually available with resistance that is “Impedance” (Z) of 8Ω to 64Ω. If a project requires a 64Ω speaker, adhere to speaker of this impedance to prevent the driving circuit from damage.

Most loudspeakers’ drivers generate an alternating audio signal which DC signal also accompanies it. The DC signal will make the current to flow largely through the speaker due to low resistance (impedance) of the speaker. As a result, it can possibly damage both the speaker and the driving circuit. Connecting a large value electrolytic capacitor in series with the speaker can avoid this damage. By doing so, it blocks DC from the signal but passes only AC audio signals.

Using and connecting Loudspeakers
  • You may connect Loudspeakers in either way round except in stereo circuits.  In stereo circuits, the marking on the speaker’s terminals is a consideration factor.
  • In a situation where by large speakers in cabinet is a need, the correct polarity is also a consideration factor. Because, the cabinet may diverts the high frequency signals to a small speaker usually called “tweeter” because the large main speaker is poor in producing them (the high frequencies).
  • Miniature loudspeakers can also be used as a microphone. For example in intercom system, they are well enough for speech picking.
  • Also, speakers can be connected in parallel or in series. In parallel connection, each speaker draws its signal directly from the source driver thus maintaining its constant impedance, (Z). Meanwhile, in a situation where large impedance speaker is a need, you can connect speakers in series. Because series connection increases the impedance by summing or adding up the impedance of each speaker that are in the series all together. See the effects of Resistors in series and parallel 

Speakers have their resistance called “IMPEDANCE” and the unit is in Ohm ().

In a circuit, you may see speaker symbol as +sp and –sp.

Piezor, Buzzer, and Bleeper

These are output transducers purposely to convert electrical energy into sound. They have internal oscillator that produces the sound which is at about 400Hz for buzzers and about 3KHz for bleepers.

Buzzers have a voltage rating about 6V approximately and 12V buzzers can be used with a 9V supply. They also consume about 25mA current.

Bleepers have wide range voltage such as 3-30V with a low current of about 10mA. Buzzers and bleepers must be connected the right way round, their red lead indicates positive terminal while the other lead negative.

You may also want to read simple single transistor audio amplifier apart from what loudspeaker, piezor, buzzer, and bleeper is.

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