Any speaker, in fact, is an oscillatory system. Based on this, almost all calculations of the parameters of such sound emitters are performed. One of the most important characteristics of modern speakers is the quality factor. This parameter indicates primarily the quality of devices of this variety.
What a characteristic
So, the quality factor of the speaker - what is this indicator? Focusing on this characteristic, we can first determine how the oscillatory movements of sound emitters damp. 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, 2 or 3, then the fluctuations in it will continue even after the force that caused them disappears. This, of course, will lead to a decrease in sound quality. In the dynamics, noise-annoying noise effects will begin to appear.
With a low Q factor (less than 1), the oscillations in the device damp out very quickly. That is, the membrane in dynamics after a sharp impact almost immediately comes to a stable state. As a result, the device produces a cleaner and more pleasant sound for hearing. Accordingly, experts rarely think about how to increase the quality factor of a speaker. Basically, when designing speaker systems, masters try to make this figure lower.
Precise definition
The quality factor of the speaker - what is it, we have generally found out. More precisely, this characteristic is a parameter that indicates how many times the energy reserves in the considered oscillatory system exceed its losses when the phase changes by 1 radian. In this way, the quality factor can be determined from the point of view of physics.
Where the energy reserves are concentrated in dynamics
When a strong sinusoidal signal is supplied to the head, the energy reserves will be concentrated primarily in extended springs, which, with damped vibrations, tend to return the DIV to its center position. The DIV of modern speakers may have different weights. Accordingly, springs in the design of the sound emitter are used uneven stiffness. That is, the heavier the speaker, the more energy reserves it has.
Speaker energy loss
Devices of this type are primarily intended for the emission of sound perceived by the human ear. The transfer of such fluctuations into 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 device’s energy consumption. Typically, less than 1% of all losses occur in this way.
The flow of sound vibrations in dynamics is the most important indicator. After all, it is precisely 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 energy consumption in the speakers occurs in their motor. Modern devices of this type work on the principle of small generators, which create quite a lot of resistance.
Stock to loss ratio
Thus, a speaker having sufficiently powerful springs and heavy movement will accumulate a lot of energy. Accordingly, its quantity in the device will significantly exceed losses. Such a speaker can be considered high-quality. Fluctuations in it will fade out slowly. In a lightweight device with not very powerful springs, less energy is accumulated. Accordingly, the ratio of the available and spent energy in it will be small. Such a speaker is considered low-quality and, accordingly, better.
Electrical and mechanical indicators
The Q factor of the speakers can be calculated in several ways. In some cases, when determining this parameter, only losses due to sound, as well as friction, are taken into account. Using this calculation method, an indicator of mechanical quality is obtained.
Sometimes, when calculating, only flow rates for the speaker motor resistance are taken into account. This quality factor is called electric. This indicator in the dynamics usually has small values. In any case, the mechanical figure of merit in sound emitters always exceeds the electric one. Typically, such an indicator in the dynamics has a value greater than unity.
Designations
When designing acoustic systems and performing various kinds of calculations, the following notation is used:
In any case, the quality factor of the speakers in the formulas is always denoted as Q.
What the indicator may depend on
It is believed that the best quality is distinguished by modern speakers that have a common figure of merit (electrical and mechanical losses) equal to about 0.7 or lower. However, such a 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 the speaker is a closed box. In this case, the elasticity of the air in the enclosed space is added to the spring elasticity. That is, there will be more energy reserves in the dynamics designed in this way. The figure of merit will also increase when using a bass reflex, horn, etc.
Thus, the acoustic design when choosing a speaker should always be considered. The net quality factor of the purchased device should in any case be equal to or lower than 0.7. This will 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. When used as a bass reflex design, the optimal net quality factor of the device will be 0.3-0.5. At the same time, the horn requires even lower indicators, since it is able to load the speakers very much.
What affects the quality factor of the speaker
Q affects acoustic systems primarily on frequency response and impulse response of speakers. That is, this indicator largely determines the sound characteristics of the speakers. With a quality factor of 0.5, for example, the best impulse response can be achieved. When the indicator is 0.707, a smooth frequency response is obtained. Also with:
quality factors of 0.5-0.6 speakers produce audiophile bass;
indicators of 0.85-0.9 bass becomes elastic and embossed;
quality factor 1.0 in the slice appears "hump" with an amplitude of 1.5 dB, perceived by the human ear as a whip sound.
With a further increase in the Q indicator, the “hump" in the sound grows and characteristic humming noises start to come from the speakers.
Theory and practice
What affects the quality factor of the speaker, therefore, is understandable. As we found out, when using acoustic design, this figure should be quite low. This is precisely the case in theory. However, in practice, low-quality speakers are, unfortunately, quite rare. Even, for example, when using a phase inverter, which requires, as we have found, an index of 0.5-0.6, heads with an index higher than one are often used.
Any sound-emitting device has its own resonant frequency. And it is through it that membranes after sharp signals come into equilibrium. In many cases, with high Q, the speaker will not even extend or finish any notes. When the external influence ceases, it simply starts to buzz unpleasantly. That is how they behave at a certain frequency, for example, cheap computer speakers.
Low quality factor of the speakers - this is most often very good for the speaker system. However, unfortunately, even relatively expensive sound-transmitting devices can be quite high-quality nowadays. For example, in equipment sold at a store at a price of about 5-6 thousand rubles, sound emitters are often completely unsuitable for design in this respect. They are usually very overpriced.
At the same time, expensive speakers with high quality factor often produce quite high-quality sound. The point here is primarily that such devices usually also have a fairly low resonant frequency. Under this condition, the noise is not perceived by the human ear, which is not particularly well-trained in terms of acoustics, not as annoying “interference”, but simply as a very powerful sound. Such “dirt” becomes especially inconspicuous when listening to simple music, for example, modern pop music. That is, the hum in this case passes by 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.
Mass shifts. With an increase in this indicator, the motor forces in the sound transmitting device become less noticeable. The friction losses increase. 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 lot of resistance, the electric 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
At home, this speaker parameter is often calculated using a simple AC millivoltmeter. Also, for this procedure, a board and a 1000 Ohm resistor are prepared, stabilizing the current through the speaker. In addition, when using this technique, you will need a software generator from the computer and a power amplifier (for supplying a signal to the speaker). The procedure for measuring the quality factor is carried out using such equipment as follows:
Before assembling the circuit, a graph is constructed where the voltage in millivolts (100, 200, 300) is plotted along the y axis. In this case, the frequency is indicated on x (10, 20, 30 ... 140, etc.). Next, they assemble a circuit where the signal from the amplifier is supplied to the resistor, and then goes to the speaker.
In the 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 the voltmeter to points b and c, by adjusting the generator, find the frequency where the volts are maximum (Fs);
change the frequency upward with respect to Fs and find the points at which the voltmeter readings are much less than Fs and constant (Um).
Measuring the voltage at a certain frequency of the speaker, build an appropriate graph. In the next step, find the average value between the minimum voltage and the maximum. In this case, the formula U1 / 2 = √Umax * Umin is used. The obtained value in the form of a horizontal line is transferred to the graph and the intersection points with the relationship lines F1 and F2 are found (with the corresponding frequency indicators).
Next, find the acoustic quality factor by the formula Qa = √ Umax / Umin * Fs / F2-F1, where Fs is the frequency value at the maximum millivoltmeter readings. Then you can find the electric quality factor:
After that, calculate the total quality factor of the speaker:
At the next stage, a graph is built for the second speaker and the same calculations are performed.
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 speaker systems. However, in order for the speakers to subsequently transmit the most high-quality sound, calculations in this case should also be made for 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, by Qts. Also, when choosing an acoustic design, such vehicle indicators as:
In addition to the three main characteristics, when calculating the design of acoustic systems, specialists can use such parameters as:
It is believed that most of these characteristics can be easily determined at home using not very sophisticated measuring instruments.
Resonant frequency
The speaker, as we found out, is an oscillatory system. Being left to its own devices, its diffuser oscillates at a certain frequency when exposed. That is, it behaves in much the same way as a string after a pinch, or, for example, a bell after an impact.
It is believed that the resonant frequency may be:
for subwoofer heads not installed in the enclosure - 20-50 Hz;
Mitbass speakers - 50-120 Hz;
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 (turning on a resistor in series with it) or by any other similar methods. This indicator is determined by the peak impedance of the device.
Vas indicator
This parameter for speakers can be measured using two methods:
additional mass;
additional volume.
In the first case, measurements are made using any weights (10 grams for every inch of the diameter of the diffuser). This can be, for example, weights from pharmacy scales or old coins, the denomination of which corresponds to their weight. Such objects load the diffuser and measure its frequency. Next, make the necessary calculations according to the formulas.
When using the method of additional volume, the sound emitter is hermetically fixed in a special measuring box with the magnet facing out. Next, measure the resonant frequency and calculate the electrical and mechanical quality factor of the speaker, as well as the full one. Then, taking into account the data obtained, Vas is determined by the formula.
It is believed that the smaller Vas, all other things being equal, the more compact the 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 mobile 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 resistance of the head winding to direct current Re is measured at a frequency close to 0 Hz or simply using an ohmmeter.
The area of the diffuser Sd or, as it is also called the effective radiating surface, at low frequencies coincides with the constructive one. Find this parameter using the simple formula Sd = nR 2 . Moreover, the radius is half the distance from the middle of the rubber suspension in width from one side to the middle of the opposite. This is due primarily to the fact that half the width of the suspension is also a radiating surface.
What you need to know
It is very important to measure the parameters of the vehicle, including the quality factor, correctly when designing acoustic systems. To avoid large errors, the speaker must be “kneaded” before taking measurements. The fact is that for new or not used for some time devices of this type, the parameters of the vehicle can differ significantly from the indicators used before the equipment was calculated.
You can “knead” speakers before measurements, for example, with sinusoidal signals, just music, white and pink noise, test disks. In this case, the procedure for such preparation of the device should last, according to experts, for at least a day.
Types of acoustic design
The most popular types of boxes for speakers at the moment are closed boxes and bass reflexes. The first type of design is considered the simplest. Structurally closed box is a box of 6 walls. The advantages of this design are primarily attributed to compactness, ease of assembly, good impulsive characteristics, fast and clear bass. The disadvantage of closed boxes is considered a low level of efficiency. . , , .
. . . .
. . , ( ).
. 100%. , , - . . . , .
, Fs/Qts>50 , Fs/Qts>85 — , Fs/Qts>105 — , Fs/Qts>30 — .
, , . , Qts> 1,2 . 2,4. Qts<0,8-1,0 . , , 0,5-0,6.
: Qts<0,6. 0,4. Qts<0.4 .
,
Sometimes, in order for sound-transmitting equipment to work better, this parameter must 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, usually you need to radically redo its engine. 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%. Moreover, this method is suitable only when the own magnet in the dynamics is used very weak.
Other technologies may also be answers to the question of how to lower the quality factor of a speaker. For example, this can be done by:
the use of resonators;
impregnation of diffusers;
cutting sectors, for example, by the method of Efrussi.
The answer to the question of how to increase the quality factor of the speaker, there is quite simple. To do this, as we already explained above, usually you just need to increase the mass of the device.