Direct Radiating and Horn Loudspeaker


An electro-acoustic transducer, or loudspeaker, is a device that transforms electrical signals into sound signals. In sound reproduction, loudspeakers are devices that transform electrical energy into acoustic signal energy and broadcast it in a room or open air. The term "signal energy" refers to electrical energy that has a defined form, such as speech, music, or other audible signals (about 20 to 20,000 hertz).


1. Electro acoustic efficiency is close to 100%.

2. Over the entire audible range, the acoustic output is frequency independent.

3. The output is free of harmonics and inter-modulation distortion.

4. The input signal is accurately replicated.

5. It can emit a non-directional radiation pattern.

6. It must be compact and provide the necessary acoustic output.


There are mainly three different types of loudspeakers.

They are namely:

1. Dynamic cone-type moving coil loudspeaker.

2. Horn-type moving coil loudspeaker.

3. Electrostatic type loudspeaker.


It is based on the fact that when a current-carrying conductor is put in a magnetic field, the conductor induces a force.

Construction: Figure 1 shows the structural features of a direct radiator speaker, a dynamic speaker, and a moving coil speaker.

Permanent magnets: A soft iron frame that creates a piece of the pole and a powerful permanent magnet make up the magnetic structure. It's utilized in the annular air gap to provide a high flux density.

Figure: Electromagnetic Loud Speaker

Voice coil (or) speech coil: The coil is wound around a cylindrical shape that is retained in the magnetic structure's annular air gap.

Spider: The voice coil is kept centered by the spring action of the corrugated spider mount.

Diaphragm (cone): It's a paper cone connected to the voice coil that compresses and expands the air in front of the speaker in alternating directions. The corrugations provide appropriate movement flexibility. Similarly, corrugated paper usually known as a spider is used to place the coil end of the cone so that it may easily travel in the gap.

Baffle: A large flat board with a hole in the center through which a cone may operate is the most basic type of baffle.

Dust cap: It keeps dust out of the space between the voice coil and the magnet.

Operation: The voice coil conducts a voice frequency electrical current. A force is created between the coil and the permanent magnet when a positive current is supplied through it, which pushes the coil axially away from the pole structure. It is lightly regulated by the spring action of a corrugated spider structure, which keeps the spool centered. When the current is reversed, the magnetic force is reversed as well, pulling the coil back towards the pole structure.

The air in front of the cone is compressed as the cone moves forward, due to a rarefaction that fits behind it. When the cone travels backward, the procedure is reversed. If all that's left is the cone, the compressed air in front of it can travel back to the cone's edge, where the pressure is low. This maintains normal air pressure in front of the cone. The amount of noise produced is much decreased in this situation. Because the gap between consecutive compression and the then rarefaction is considerable, the loss in sound production is particularly high at low frequencies.

With the use of a blocker, this impact can be minimized. Backward-moving baffles restrict sound waves from entering the cone from the front. As a result, baffles boost low-frequency radiation. Low-frequency radiation is improved by a wider blocking region.

Figure: Frequency Response Characteristics

The figure illustrates the frequency response curve. The magnetic field force, coil size, and effectiveness of the acoustical coupling of the cone all influence the voice coil's ac load impedance measured at the terminals.

The typical range of values is 1 to 300 Ω, with 4, 8, and 16 Ω speakers being the most frequent. The power rating varies between a few milliwatts and several hundred watts. Portable receivers employ lower-power speakers, whereas outdoor auditoriums employ higher-power speakers.


This can be used in all audio systems


1. It's small and inexpensive.

2. Improved audio range responsiveness.


1. Low-frequency efficiency is poor.

2. Directivity pattern with a narrow range of possibilities.

3. The ability to handle a large amount of energy is limited.


At low frequencies, attaching a properly designed horn to a tiny piston line sound source can improve sound production. The speaker's cone is utilized to increase the coupling efficiency between the coil motion and the surrounding air. When the output from a speaker unit is fed into the throat of an acoustical horn, the efficiency increases. The horn functions as both an impedance transformer and a radiator. The construction of a horn-type loudspeaker is explained in the figure.

Figure: Horn Type Loud Speaker


A moving coil made up of a former one and a thin aluminum ribbon is coiled into the annular air gap of a hefty permanent pot magnet. The movement of the edge has been designed. With the horn baffle, this driver unit is utilized. The construction of the driver unit is similar to that of a cone-type speaker, with the exception that the cone is not there. Because an unfurled horn might be as long as 2 meters and 1 meter across the mouth, the horn construction is filled back on itself to save physical space.


Horn acts as an impedance matching device, connecting a high-impedance diaphragm to low-impedance air. A high pass filter is an exponential horn. When the speaker's output is channeled into a horn's throat, the efficiency increases. A longhorn with a smaller taper and a wider area is needed for effective reproduction. These devices can handle more than 100 watts of power with an input impedance of 8 to 16 Ω. The efficiency of horn-loaded loudspeakers is considerably better than that of cone-type loudspeakers.


1. The main application is: it can be used in Announcement systems.






From a few milliwatts to several hundred watts, power handling capability varies.

More than 100 watts of power may be handled by the device.



Cone loudspeakers are less efficient at low frequencies.

Horn-type speakers are more efficient at low frequencies.


Not so

The horn acts as an acoustic transformer, converting low-amplitude diaphragm pressure vibrations into high-amplitude low-pressure vibrations.


The size of the diaphragm is larger.

The size of the diaphragm is small.


This speaker has a low sound impact.

This speaker has a powerful and effective sound impact.


It necessitates the use of an impedance matching circuit external to the system.

It's an impedance matching circuit in and of itself.


To cover different octaves of the sound spectrum, several loudspeakers are necessary.

For many octaves of the sound spectrum, one loudspeaker is sufficient.

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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