Any speaker, in fact, is an oscillatory system. Based on this, almost all calculations of the parameters of such sound emitters are made. One of the most important characteristics of modern speakers is the quality factor. This parameter indicates, first of all, the quality of devices of this variety.
What a feature
So, the quality factor of the speaker - what is this indicator? Focusing on this characteristic, one can first of all determine how the oscillatory movements of sound emitters are damped. It is believed that this indicator should not be too large for the heads.
If the quality factor of the speaker is high and equal, for example, to 2 or 3, then the vibrations in it will continue even after the force that caused them has disappeared. This, of course, will lead to a decrease in sound quality. Annoying noise effects will begin to appear in the speaker.
When the quality factor is low (less than 1), the vibrations in the device decay very quickly. That is, the membrane in dynamics aftersharp impact almost immediately comes to a stable state. As a result, the device produces a cleaner and more pleasant sound. Accordingly, experts rarely think about how to increase the quality factor of the speaker. Basically, when designing acoustic systems, masters try to make this figure lower.
Exact definition
The quality factor of the speaker - what it is, we found out in general terms. More precisely, this characteristic is a parameter indicating how many times the energy reserves in the considered oscillatory system exceed its losses when the phase changes by 1 radian. This is how the quality factor can be defined in terms of physics.
Where energy reserves are concentrated in dynamics
When a strong sinusoidal signal is applied to the head, the energy reserves will be concentrated primarily in the stretched springs, with damped oscillations tending to return the DIV to the central position. DIV in modern speakers can have different weights. Accordingly, the springs in the design of the sound emitter are used with unequal stiffness. That is, the heavier the speaker, the more energy reserves it has.
Speaker power loss
Devices of this type are designed primarily to emit sound that is perceived by the human ear. The transmission of such vibrations to the environment is the energy loss of the speaker. However, the efficiency of modern speakers is usually very low. Therefore, sound transmission accounts for only a small part of the consumption of the device.energy. Typically, less than 1% of all losses occur this way.
The cost of sound vibrations in dynamics is the most important indicator. After all, it is for the transmission of sound that such devices are designed and manufactured. But still, much more losses in such equipment are purely mechanical. A lot of energy in such devices is spent on friction:
- in suspensions;
- in the magnetic gap;
- about air, etc.
The biggest power consumption of speakers is in their motor. Modern devices of this type work on the principle of small generators that create quite a lot of resistance.
Stock to loss ratio
Thus, a speaker with sufficiently strong springs and heavy displacement will accumulate a lot of energy. Accordingly, its amount in the device will significantly exceed the losses. Such a speaker can be considered high quality. The oscillations in it will decay slowly. In a lightweight device with not particularly powerful springs, less energy is accumulated. Accordingly, the indicator of the ratio between the available and consumed energy in it will be small. Such a speaker is considered low-quality and, accordingly, of better quality.
Electrical and mechanical performance
The quality factor of the speakers can be calculated in several ways. In some cases, when determining this parameter, only sound losses are taken into account, as well as friction losses. Usingsuch a calculation method gives an indicator of mechanical quality factor.
Sometimes only the flow rates for the resistance of the speaker motor are taken into account in the calculations. This quality factor is called electrical. This indicator in the dynamics usually has small values. In any case, the mechanical quality factor in sound emitters always exceeds the electrical one. Usually such an indicator in the dynamics has a value greater than one.
Notation
When designing acoustic systems and performing various kinds of calculations, the following designations are used:
- Qts - full quality factor.
-
Qms - mechanical quality factor of the speaker.
- Qes - electric.
In any case, the quality factor of the speakers in the formulas is always denoted as Q.
What the indicator may depend on
Modern speakers are considered to be of the best quality if they have an overall quality factor (electrical and mechanical loss) of about 0.7 or less. However, this value should characterize the speaker, taking into account, among other things, its acoustic design. It should be borne in mind that the latter always raises the net quality factor of the device.
For example, quite often the acoustic design of a speaker is a closed box. In this case, the elasticity of the air in the closed space is added to the elasticity of the spring. That is, there will be more energy reserves in dynamics designed in this way. The quality factor will increase andwhen using a phase inverter, horn, etc.
Thus, acoustic design should always be taken into account when choosing a speaker. The pure quality factor of the purchased device should in any case be equal to or lower than 0.7. This will allow you to create a speaker system with high-quality sound.
It is believed, for example, that the quality factor of a speaker for a closed box should be approximately 0.5-0.6. this requires even lower numbers as it can drive the speakers very hard.
What affects the quality factor of the speaker
Influences Q in acoustic systems primarily on the frequency response and on the impulse response of the speakers. That is, this indicator largely determines the characteristics of the sound of the speakers. With a quality factor of 0.5, for example, the best impulse response can be achieved. With an indicator of 0.707, an even frequency response is obtained. Also at:
- Q factor 0, 5-0, 6 speakers produce audiophile bass;
- indicators 0, 85-0, 9 bass becomes elastic and embossed;
- of a quality factor of 1, 0, a “hump” with an amplitude of 1.5 dB appears in the cut, perceived by the human ear as a biting sound.
As the Q increases further, the “hump” in the sound grows and characteristic buzzing noises begin to emanate from the speakers.
Theory and practice
What does the quality factor of the speaker affect, thusunderstandably. As we found out, when using acoustic design, this indicator should be quite low. This is how it works in theory. However, in practice, low-quality speakers are, unfortunately, quite rare. Even, for example, when using a phase inverter, which, as we found out, requires an indicator of 0.5-0.6, heads with an indicator above one are often used.
Any sound emitting device has its own resonant frequency. And it is through it that the membranes, after sharp signals, come to an equilibrium state. In many cases, with a high quality factor, the speaker will not even prolong or finish playing any notes. When the external influence stops, it will simply begin to buzz unpleasantly. This is how cheap computer speakers behave at a certain frequency, for example.
Low quality factor of the speakers - this is most often very good for the speaker system. However, in our time, unfortunately, even relatively expensive sound transmitting devices can be quite high-quality. For example, in equipment sold in a store at a price of about 5-6 thousand rubles, sound emitters are often completely unsuitable for this indicator. They usually have it too high.
With all this, expensive speakers with a high quality factor often produce a fairly high-quality sound. The point here lies primarily in the fact that such devices usually also have a rather low resonant frequency. Under this condition, noise is not perceived particularly well.acoustically trained human ear, not as annoying "interference", but simply as a very powerful sound. Such “dirt” becomes especially imperceptible when listening to simple music, for example, modern pop music. That is, the hum in this case passes through the “correct” frequency.
What else depends on
Design thus has a great influence on the quality factor of the speaker. Also, this indicator for such equipment depends on:
- The power of his motor. The higher this characteristic, the lower the quality factor of the head.
- Masses of movement. With an increase in this indicator, the efforts of the motor in the sound transmitting device become less noticeable. Friction losses increase as a result. As a result of all this, the quality factor of the device increases.
- Wire diameter. In the event that the wires in the speaker give a large resistance, the electrical quality factor of the device will increase. Indeed, in this case, the load on the speaker, which is a kind of generator, drops.
How to measure the quality factor: formulas
In the home, this speaker setting is often calculated using a simple AC millivoltmeter. Also, for this procedure, a board and a 1000 Ohm resistor are prepared to stabilize the current through the speaker. In addition, when using this technique, you will need a software generator from a computer and a power amplifier (to supply a signal to the speaker). The procedure for measuring the quality factor using such equipment is carried out as follows:
- the speaker is suspended in a free state, for example, on some rope;
- gathering the scheme.
Before assembling the circuit, a graph is built, where the voltage in millivolts (100, 200, 300) is plotted along the y-axis. At the same time, the frequency is indicated on x (10, 20, 30 … 140, etc.). Next, they assemble a circuit where the signal from the amplifier is fed to the resistor, and then goes to the speaker.
Next step:
- include a millivoltmeter in the circuit at points a and c and set the voltage to 10-20 V at a frequency of 500-1000 hertz;
- connect a voltmeter to points in and c, by adjusting the generator, find the frequency where the volts values \u200b\u200bare maximum (Fs);
- change the frequency up in relation to Fs and find points where the voltmeter readings are much less than Fs and constant (Um).
Measuring the voltage at a certain frequency of the speaker, build the corresponding graph. The next step is to find the average value between the minimum voltage and the maximum. In this case, the formula U1/2=√UmaxUmin is used. The resulting value in the form of a horizontal line is transferred to the graph and the points of intersection with the lines of the ratio F1 and F2 (with the corresponding frequency indicators) are found.
Next, find the acoustic quality factor by the formula Qa=√Umax/UminFs/F2-F1, where Fs is the frequency value at the maximum millivoltmeter readings. Then you can find the electrical quality factor:
Qes=QaUmin/(Umax-Umin).
After that, the total quality factor of the speaker is calculated:
Qts=QaQes/(Qa+Qes).
The next step is to build a graph for the second speaker and make the same calculations.
What other parameters can be measured
What is it - the quality factor of the speakers, we found out. This indicator is usually determined when choosing the most suitable design, designing acoustic systems. However, in order for the speakers to subsequently transmit the highest quality sound, calculations in this case must be made according to some other indicators.
When choosing an acoustic design, the so-called Thiel-Small parameters are always taken into account. One of these characteristics is precisely the quality factor, denoted, as we found out, Qts. Also, when choosing acoustic design, such indicators of the vehicle as:
- resonant frequency Fs;
- Vas speaker suspension springiness.
In addition to the three main characteristics, when calculating the design of acoustic systems, specialists can use such parameters as:
- diffuser area and diameter;
- inductance;
- sensitivity;
- impedance;
- peak power;
- mass of the mobile system;
- motor power;
- mechanical resistance;
- relative hardness, etc.
It is believed that most of thethese characteristics can be easily measured at home with not particularly sophisticated measuring instruments.
Resonance frequency
The speaker, as we found out, is an oscillatory system. Being left to itself, its diffuser oscillates with a certain frequency when exposed to it. That is, it behaves in much the same way as a string after a pluck or, for example, a bell after a strike.
It is believed that the resonant frequency can be:
- for subwoofer heads not installed in the cabinet - 20-50 Hz;
- Mitbass speakers - 50-120Hz;
- tweeters - 1000-2000 Hz;
- diffuser midrange - 100-200 Hz;
- dome - 400-800 Hz.
You can measure the resonant frequency of a speaker, for example, by driving a sound generator signal through it (by connecting a resistor in series with it) or by any other similar methods. This indicator is determined by the peak impedance of the device.
Vas score
This parameter for speakers can be measured by two methods:
- additional mass;
- additional volume.
In the first case, measurements are made using some kind of weights (10 grams per inch of diffuser diameter). It can be, for example, weights from pharmacy scales or old coins, the denomination of which corresponds to their weight. The diffuser is loaded with such objects and its frequency is measured. Furthermake the necessary calculations using the formulas.
When using the method of additional volume, the sound emitter is hermetically fixed in a special measuring box with a magnet outside. Next, the resonant frequency is measured and the electrical and mechanical quality factors of the speaker, as well as the total, are calculated. Then, taking into account the data obtained, the formula determines Vas.
It is believed that the smaller Vas, ceteris paribus, the more compact design can be used for the speaker. Usually small values of this parameter at the same resonant frequency are the result of a combination of a heavy moving system and a rigid suspension.
Methods for measuring additional parameters
As already mentioned, in addition to the three main characteristics of the vehicle, other indicators can be used in the design of acoustic systems. For example, the head winding resistance to direct current Re is measured at a frequency close to 0 Hz or simply using an ohmmeter.
The diffuser area Sd or, as it is also called the effective radiating surface, coincides with the constructive one at low frequencies. This parameter is found using the simple formula Sd=nR2. In this case, half the distance from the middle of the rubber suspension along the width from one side to the middle of the opposite is taken as the radius. This is primarily due to the fact that half the width of the suspension is also a radiating surface.
What you need to know
Measuring the parameters of the vehicle, including the quality factor, correctly when designing acoustic systems is very important. To avoidlarge errors, the speaker must be “stretched” before taking measurements. The fact is that for devices of this type that are new or have not been used for some time, the parameters of the vehicle may differ significantly from the indicators used before the start of equipment calculations.
You can “knead” the speakers before measurements, for example, with sinusoidal signals, just music, white and pink noise, test disks. At the same time, the procedure for such preparation of the device should, according to experts, for at least a day.
Types of acoustic design
The most popular types of speaker boxes at the moment are closed boxes and bass reflexes. The first type of design is considered the simplest. Structurally, a closed box is a box of 6 walls. The advantages of such a design are primarily compactness, ease of assembly, good impulsive characteristics, fast and clear bass. The disadvantage of closed boxes is considered to be a low level of efficiency. This design is not suitable for creating high sound pressure. Closed boxes are usually used for listening to jazz, rock, club music.
Phase inverters are a rather complex type of design. They are usually made from plastic. At the same time, phase inverters have a high efficiency and also allow the speaker to cool quickly. Also, this design can be easily reconfigured if necessary.
Sometimes an openacoustic design. In this case, the rear wall of the sound-emitting surface of the diffuser is not separated from the front. Most often, an open box is a box that does not have a back wall (or has many holes in it).
Horn design for heads is most often used in combination with other types. However, in some cases, such designs can be 100% original. Such systems are used, for example, for low-Q speakers. Acoustic design of this type has a lot of advantages. Its main advantage is the high volume. At the same time, the disadvantages of such a design include the impossibility of obtaining a uniform frequency response, low sound volume, etc.
Speaker quality and design
It is believed that heads with Fs / Qts>50 should be used in closed cases, Fs / Qts>85 - with phase inverters, Fs / Qts>105 - with bandpass resonators, Fs / Qts>30 - with screens and open boxes.
You can choose acoustic design for speakers, as already mentioned, and simply by their quality factor. For example, heads with Qts> 1, 2 are most often used for open boxes. The optimal quality factor for them is 2, 4. Speakers with Qts<0, 8-1, 0 are designed for closed boxes. In this case, the optimal indicator, as we found out earlier, is 0.5-0.6.
The quality factor of the speakers for a phase inverter should be: Qts<0, 6. The optimum in this case will be 0.4. Devices with Qts<0.4 are suitable formouthpieces.
How to change the quality factor, reduce or increase
Sometimes, in order for sound transmission equipment to work better, this parameter needs to be increased or decreased. Quite often, masters, for example, are interested in how to reduce the quality factor of a speaker. This task can actually be very difficult. In order to reduce the quality factor of the speaker, it is usually necessary to radically alter its motor. And this, of course, is a rather complicated procedure and in most cases not very justified.
Some experts note the fact that you can reduce the quality factor of the speakers by gluing a magnet. However, in this case, its indicator will change by no more than 5-10%. In addition, this method is only suitable when the speaker's own magnet is very weak.
Also, the answer to the question of how to lower the quality factor of the speaker, there may be other technologies. For example, this can be done by:
- using resonators;
- diffuser impregnation;
- cutting sectors, for example, according to the Ephrussi method.
The answer to the question of how to increase the quality factor of the speaker is quite simple. To do this, as we have already found out above, usually you just need to increase the mass of the movement of the device.
