How is a loudspeaker made

Knowledge: How does a loudspeaker work?

Even non-audiophiles should be aware that sounds come from a loudspeaker. But how does a box actually work, how is it made Audio data in sound events implemented? We explain the individual steps from processing the music signal to vibrating the loudspeaker coil.

Music data becomes electrical impulses

How does a speaker work? You could put it this way: It converts coded audio signals into sound waves - that's why it is also known as a sound transducer. The data can be analog, like on a record, or digital, like CD or MP3. Since no loudspeaker can do anything with digital data, the binary code must first be converted into an analog signal, more precisely into AC voltage being transformed.

This is done through a Digital-to-analog converter (DAC). The DAC is often already integrated in playback devices. External converters are commercially available for analog hi-fi systems and other areas of application.

The current signal has to go to the right transducer

As soon as the audio data is available as current impulses, the processing for the loudspeakers continues. Loudspeakers in the hi-fi and home cinema area are usually designed as multi-channel loudspeakers. This means that two, three or even four sound converters are integrated in one housing. Each transducer is responsible for a specific frequency range. There is also often talk of woofers, mid-range speakers and tweeters. The current pulses present as alternating voltage must now be conducted to the sound transducers assigned to them according to their frequency.

That's what this is for Crossover responsible. Depending on the system, the crossover can be housed inside or outside the loudspeaker housing. It consists of an arrangement of resistors, capacitors and coils. While capacitors transmit higher frequencies, these are cut by coils. The frequency ranges at which the separation takes place differs depending on the loudspeaker.

The amplifier supports the signal

One step is still missing so that the sound transducers can convert the current impulses into sound events: the signal is usually too weak to fire the loudspeakers. For this reason, an amplifier is connected upstream.

The current signal generated from the stored audio data is used as a control signal in a bipolar transistor such as that used in most amplifiers. It regulates the voltage of the current that flows through the amplifier. An amplifier can draw its power from the socket or a battery, for example. How this principle is implemented in each individual case depends on the amplifier. One differentiates between different Amplifier classes. With so-called active loudspeakers, both the amplifier and the crossovers are integrated into the loudspeaker.


The swing begins

After the music data has been converted into analog signals, directed to the right transducers and amplified, a loudspeaker can finally do it Generate sound events. This is always done according to the same principle:

  • A speaker membrane is set in motion.
  • These vibrations change the air pressure in the immediate vicinity.
  • The changes in air pressure travel as sound waves through the room to our ears.
  • The frequency level of the sound event is controlled via the vibration frequency of the loudspeaker membrane.

The diaphragm is usually driven by a moving voice coil and a permanently installed permanent magnet. The process is based on the electrodynamic principle and was first used at the end of the 19th century. The amplified alternating current signal flows through the voice coil and generates a magnetic field. The coil is movable forwards and backwards and usually consists of a conductive wire and a carrier.

The alternating current continuously reverses the polarity of the coil. Since this is located within the magnetic field of the permanent magnet, it is attracted and repelled. The acting force is called Lorentz force designated. The magnet is usually made of ferrite or Neodymium. The frequency of the polarity reversal of the current determines the frequency with which the coil is pushed and repelled - and thus how fast the loudspeaker membrane vibrates.

This animation clearly shows the structure of a loudspeaker:

The speaker membrane pushes the air

The membrane of a loudspeaker is installed in such a way that it follows the movements of the coil exactly. For this it is on the one hand on the voice coil and on the other hand Bead and spider attached. Similar to springs, these elastic components ensure that the membrane always moves back into its starting position.

By vibrating the membrane pushes the air in its environment. These changes in air pressure propagate in space as sound waves. We have already mentioned that other types of transducers are used depending on the frequency range. A decisive reason for this is that sound waves are significantly longer at low frequencies than at medium and high frequencies. Large diaphragms with heavy voice coils are therefore suitable for basses in order to provide a corresponding to push a large volume of air. On the other hand, they would be too sluggish for higher frequencies. Therefore, the diaphragm diameter of midrange and tweeters is significantly smaller.

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Conclusion: In the end it has to vibrate

  • The music data is available either as analog or digital information.
  • They are converted into current pulses.
  • An amplifier increases the strength of the current pulses so that they can drive the speaker membrane.
  • First, the alternating current sets a voice coil in motion, which is located in the magnetic field of a permanent magnet.
  • The speaker membrane is attached to the voice coil. It picks up the frequency of the current impulses, oscillates with it and in this way generates sound waves.