An electrodynamic loudspeaker is a device that converts an electrical signal into a sound signal by moving a coil with a current in a magnetic field of a permanent magnet. We come across these devices every day. Even if you are not a big fan of music and do not spend half a day on headphones. The speakers are equipped with televisions, radios in cars and even telephones. This mechanism that is familiar to us is actually a whole complex of elements, and its device is a real work of engineering.
In this article, we will take a closer look at the speaker device. We will discuss what constituent parts this device consists of and how they work.
History
The day began a small excursion into the history of the invention of electrodynamics. Loudspeakers of a similar type were used back in the late 1920s. Bell's phone worked on a similar principle. A membrane was used in it, which moved in the magnetic field of a permanent magnet. These speakers had many serious flaws: frequency distortion, sound loss. To solve the problems associated with classic loudspeakers, Oliver Lorge suggested using his own ideas. His coil moved across the lines of force. A little later, two of his colleagues adapted the technology for the consumer market and patented a new design of electrodynamics, which is still in use today.
Speaker device
The speaker has a rather complicated design and consists of many elements. The speaker device diagram (see below) shows the key details that make the speaker function correctly.
The acoustic speaker device includes the following components:
- suspension (or edge corrugation);
- diffuser (or membrane);
- cap;
- voice coil
- core;
- magnetic system;
- diffuser holder;
- flexible conclusions.
Different speaker models may use different unique structural elements. The classic speaker device looks exactly like that.
Consider each individual structural elements in more detail.
Corrugation
This element is also called a “collar”. This is a plastic or rubber edging that describes the electrodynamic mechanism over the entire area. Sometimes, natural fabrics with a special, vibration-weakening coating are used as the main material. Corrugations are divided not only by the type of material from which they are made, but also in shape. The most popular subtype is one and a half toroidal profiles.
A number of requirements are presented to the “collar”, compliance with which indicates its high quality. The first requirement is high flexibility. The resonant frequency of the corrugation should be low. The second requirement is that the corrugation must be well fixed and provide only one type of vibration - parallel. The third requirement is reliability. The "collar" must adequately respond to temperature changes and "normal" wear, maintaining its shape for a long time.
To achieve the best sound balance, rubber corrugations are used in low-frequency speakers, and paper ones in high-frequency speakers.
Diffuser
The main radiating object in electrodynamics is a diffuser. The speaker diffuser is a kind of piston that moves in a straight line up and down and supports the amplitude-frequency response (hereinafter AFC) in a linear form. With increasing oscillation frequency, the diffuser begins to bend. Because of this, the so-called standing waves appear, which, in turn, lead to dips and rises on the frequency response graph. To minimize this effect, designers use stiffer diffusers made of materials of lower density. If the speaker size is 12 inches, then the frequency range in it will vary within 1 kilohertz for low frequencies, 3 kilohertz for medium and 16 kilohertz for high.
- Diffusers can be stiff. They are made of ceramic or aluminum. Such products provide the lowest level of sound distortion. Speakers with hard diffusers are much more expensive than analogs.
- Soft diffusers are made of polypropylene. Such samples provide the most soft and warm sound due to the absorption of waves by soft material.
- Semi-rigid diffusers are a compromise. They are made from Kevlar or fiberglass. The distortion caused by such a diffuser is higher than that of hard ones, but lower than that of soft ones.
Cap
The cap is a shell made of synthetics or fabric, the main function of which is to protect the speakers from dust. In addition, the cap plays an important role in the formation of a certain sound. In particular, when reproducing medium frequencies. In order to fix the most rigidly, the caps are rounded in shape, giving them a slight bend. As you probably already understood, the variety of materials is precisely related to achieving a certain sound. The fabric is used with various impregnations, films, cellulose compositions and even metal meshes. The latter, in turn, also perform the function of a radiator. Aluminum or metal mesh removes excess heat from the coil.
Washer
Sometimes it is also called a "spider." This is a weighty part located between the speaker cone and its body. The goals of the puck include maintaining a stable resonance for the woofers. This is especially important if there are sharp changes in temperature in the room. The washer fixes the position of the coil and the entire moving system, and also closes the magnetic gap, preventing dust from entering it. Classic washers are a round corrugated disc. More modern options look a little different. Some manufacturers intentionally change the shape of the corrugations so that to increase the linearity of frequencies and stabilize the shape of the washer. This design greatly affects the price of the speaker. Washers are made of nylon, calico or copper. The latter option, as in the case with the cap, serves as a mini-radiator.
Voice coil and magnetic system
So we got to the element, which, in fact, is responsible for the reproduction of sound. The magnetic system is located in a small gap of the magnetic circuit and, together with the coil, converts electrical energy. The magnetic system itself is a magnet system in the form of a ring and core. Between them at the moment of sound reproduction the voice coil moves. An important task of designers is to create a uniform magnetic field in a magnetic system. To do this, speaker manufacturers thoroughly align the poles and equip the core with a copper tip. Current flows into the voice coil through the flexible leads of the speaker — an ordinary wire wound over a synthetic thread.
Principle of operation
We figured out the speaker device, go to the principle of work. The principle of operation of the speaker is as follows: the current flowing to the coil makes it make perpendicular vibrations within the magnetic field. This system carries the diffuser along, forcing it to oscillate with the frequency of the supplied current, and creates discharged waves. The diffuser begins to oscillate and creates sound waves that can be perceived by the human ear. They are transmitted in the form of an electrical signal to an amplifier. Hence the sound appears.
The range of reproduced frequencies directly depends on the thickness of the magnetic cores and the size of the speaker. With a larger magnitude of the magnetic circuit, the gap in the magnetic system increases, and with it the effective part of the coil increases. That is why compact speakers can not cope with low frequencies in the range of 16-250 hertz. Their minimum frequency threshold starts at 300 Hertz and ends at 12,000 Hertz. That's why the speakers wheeze when you twist the sound to the maximum.
Rated electrical resistance
The wire supplying current to the coil has an active and reactive resistance. To find out the level of the latter, engineers measure it at a frequency of 1000 hertz and add the active resistance of the voice coil to the resulting value. Most speakers have a resistance level of 2, 4, 6, or 8 ohms. This parameter must be considered when buying an amplifier. It is important to agree on the load level.
Frequency range
It has already been said above that most of the electrodynamics reproduces only part of the frequencies that a person can perceive. It is impossible to make a universal speaker capable of reproducing the entire range from 16 hertz to 20 kilohertz, so the frequencies were divided into three groups: low, medium and high. After that, the designers began to create speakers separately for each frequency. This means that subwoofers do best with bass. They operate on a range of 25 hertz - 5 kilohertz. High-frequency ones are designed to work with screeching tops (hence the common name is "tweeter"). They operate in the frequency range of 2 kilohertz - 20 kilohertz. Mid-range speakers operate in the range of 200 hertz - 7 kilohertz. Engineers are still trying to create a high-quality broadband speaker. Alas, the price of the speaker is contrary to its quality and does not justify it at all.
A bit about mobile speakers
The speakers for the phone are structurally different from the "adult" models. To place such a complex mechanism in a mobile case is unrealistic, so the engineers went to the trick and replaced a number of elements. For example, the coils become stationary, and instead of a diffuser, a membrane is used. The speakers for the phone are greatly simplified, so you should not expect high sound quality from them.
The frequency range that such an element can cover is significantly narrowed. In terms of sound, it is closer to high-frequency devices, since there is no additional space in the phone case for installing thick magnetic cores.
The speaker device in a mobile phone differs not only in size, but also in the absence of independence. Device capabilities are limited by software. This is to protect the speaker design. Many people remove this limit manually, and then ask the question: "Why do the speakers wheeze?"
In an average smartphone, two such elements are installed. One is conversational, the other is musical. Sometimes they are combined to achieve a stereo effect. One way or another, you can achieve depth and richness in sound only with a full stereo system.