An electrodynamic loudspeaker is a device that converts an electrical signal into sound by moving a coil with current in the magnetic field of a permanent magnet. We use these devices on a daily basis. Even if you are not a big fan of music and do not spend half a day in headphones. TVs, radios in cars, and even telephones are equipped with speakers. This mechanism familiar to us is actually a whole complex of elements, and its device is a real work of engineering art.
In this article, we will take a closer look at the speaker device. Let's discuss what parts this device consists of and how they work.
History
Day start a small digression into the history of the invention of electrodynamics. Loudspeakers of a similar type were used as early as the late 1920s. Bell's phone worked on a similar principle. It involved a membrane that 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 Lorde suggested using his work. His coil moved across the lines of force. a littlelater, two of his colleagues adapted the technology for the consumer market and patented a new design of electrodynamics that is still in use today.
Speaker device
The speaker has a rather complex design and consists of many elements. The speaker diagram (below) shows the key parts that make the speaker function properly.
The acoustic speaker device includes the following components:
- suspension (or edge corrugation);
- diffuser (or membrane);
- cap;
- voice coil;
- core;
- magnetic system;
- diffuser holder;
- flexible leads.
Different speaker models may use different unique design elements. The classic speaker device looks exactly like this.
Let's consider each individual design element in more detail.
Edge 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-damping coating are used as the main material. Corrugations are divided not only by the type of material from which they are made, but also by shape. The most popular subtype is semi-toroidal profiles.
There are a number of requirements for the "collar", the observance of which indicates its high quality. The first requirement is high flexibility. Corrugation resonant frequencyshould be low. The second requirement is that the corrugation must be well fixed and provide only one type of oscillation - parallel. The third requirement is reliability. The "collar" must adequately respond to temperature changes and "normal" wear, retaining its shape for a long time.
To achieve the best balance of sound, 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 cone is a kind of piston that moves in a straight line up and down and maintains the amplitude-frequency characteristic (hereinafter referred to as the frequency response) in a linear form. As the oscillation frequency increases, the diffuser begins to bend. Because of this, so-called standing waves appear, which, in turn, lead to dips and rises in the frequency response graph. To minimize this effect, designers use stiffer cones made from lower density materials. 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 frequencies.
- Diffusers can be rigid. They are made of ceramic or aluminum. Such products provide the lowest level of sound distortion. Rigid cone speakers are much more expensive than their counterparts.
- Soft diffusers are made from polypropylene. Such samples provide the softest and warmest sound due to the absorption of waves by a soft material.
- Semi-rigid diffusers are a compromise. They are made from Kevlar or fiberglass. Distortion provoked by such a cone is higher than hard ones, but lower than soft ones.
Cap
The cap is a synthetic or fabric shell whose main function 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 playing medium frequencies. For the purpose of the most rigid fixing, the caps are made rounded, giving them a slight bend. As you probably already understood, the variety of materials is precisely related to achieving a certain sound. Fabrics with various impregnations, films, cellulose compositions and even metal meshes are used. The latter, in turn, also perform the function of a radiator. Aluminum or metal mesh conducts excess heat away from the coil.
Puck
Sometimes it is also called a "spider". This is a weighty part located between the speaker cone and its body. The purpose of the washer is to maintain a stable resonance for the woofers. This is especially important if there are sudden 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 disk. More modern options look a little different. Some manufacturers deliberately change the shape of the corrugations so as to increase the linearityfrequencies and stabilize the shape of the puck. This design greatly affects the price of the speaker. Washers are made of nylon, coarse calico or copper. The last option, as in the case of the cap, acts as a mini-radiator.
Voice coil and magnet system
So we got to the element, which, in fact, is responsible for sound reproduction. 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 system of a magnet in the form of a ring and a core. Between them, at the time of sound reproduction, the voice coil moves. An important task for designers is to create a uniform magnetic field in a magnetic system. To do this, speaker manufacturers carefully align the poles and equip the core with a copper tip. The current to the voice coil is supplied through the flexible leads of the speaker - an ordinary wire wound over a synthetic thread.
Working principle
We figured out the speaker device, let's move on to the principle of operation. The principle of operation of the speaker is as follows: the current going to the coil causes it to oscillate perpendicularly within the magnetic field. This system drags the diffuser along with it, causing it to oscillate at the frequency of the applied 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 as an electrical signal to the amplifier. This is where the sound comes from.
Frequency range directlydepends on the thickness of the magnetic cores and the size of the speaker. With a larger 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 crackle when you crank up the volume.
Rated electrical resistance
The wire that supplies current to the coil has active and reactive resistance. To determine 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 an impedance level of 2, 4, 6, or 8 ohms. This parameter must be considered when buying an amplifier. It is important to agree on the level of workload.
Frequency range
It has already been said above that most of the electrodynamics reproduces only a 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 the woofers are best at handling the bass. They operate in the range of 25 hertz - 5 kilohertz. High-frequency ones are designed to work with squealing tops (hence the common name - "tweeter"). They work infrequency range 2 kilohertz - 20 kilohertz. Midrange speakers operate in the range of 200 hertz - 7 kilohertz. Engineers are still trying to create a quality full range speaker. Alas, the price of the speaker goes against its quality and does not justify it at all.
A little about mobile speakers
Speakers for a phone differ from "adult" models constructively. It is unrealistic to place such a complex mechanism in a mobile case, so the engineers went to the trick and replaced a number of elements. For example, the coils have become fixed, and a membrane is used instead of a diffuser. Phone speakers are oversimplified, so don't expect high sound quality from them.
The frequency range that such an element can cover is significantly narrowed. In terms of its 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 lack of independence. The capabilities of the device are limited by the software. This is done to protect the design of the speakers. Many people remove this limit manually, and then ask themselves: "Why do the speakers wheeze?"
In an average smartphone, two such elements are installed. One is spoken, 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-fledged stereo system.
