How to choose a speaker. High-frequency tweeter speakers: even the highest notes can be heard. In what range does the tweeter work?
Speaker power
Maximum noise power of the speaker, maximum long-term power of the speaker, maximum short-term power of the speaker.
Noise power limit (PHC)- power that the dynamic head can withstand for a long time without thermal and mechanical damage. The duration of continuous testing is indicated by the manufacturer in hours and on what signal.
Continuous Power Limit (RMS)- the power that the dynamic head can withstand without thermal and mechanical damage for 1 minute at an interval of 2 minutes for 10 consecutive cycles.
Maximum short-term power (PMPO)- the power that the dynamic head can withstand without thermal and mechanical damage for 1 second with an interval of 60 seconds for 60 cycles in a row.
By the word power in colloquial speech, many mean “power”, “strength”. Therefore, it is only natural that consumers associate power with volume: “The more power, the better and louder the speakers will sound.” However, this popular belief is completely wrong! It is not always the case that a speaker with a power of 100 W will play louder or better than one that has a power rating of “only” 50 W. The power value rather speaks not about volume, but about the mechanical reliability of the acoustics. The same 50 or 100 W is not at all the volume of sound produced by the speaker. Even the best dynamic drivers themselves have low efficiency and convert only 2-3% of the power of the electrical signal supplied to them into sound vibrations, and for most speakers even less (although the sound produced is quite enough to create soundtrack).
The value indicated by the manufacturer in the passport of the speaker or the system as a whole only indicates that when a signal of the specified power is supplied, the dynamic head or speaker system will not fail (due to critical heating and interturn short circuit of the wire, “biting” of the coil frame, rupture of the diffuser , damage to flexible suspensions of the system, etc.).Thus, the power of an acoustic system is a technical parameter, the value of which is not directly related to the loudness of the acoustics, although it is somewhat related to it. The rated power values of the dynamic heads, amplifier path, and speaker system may be different. They are indicated rather for orientation and optimal pairing between components. For example, an amplifier of significantly lower or significantly higher power can damage the speaker in the maximum positions of the volume control on both amplifiers: on the first - due to the high level of distortion, on the second - due to abnormal operation of the speaker.
Power can be measured in different ways and under different test conditions. There are generally accepted standards for these measurements. Let's take a closer look at some of them, most often used in the characteristics of products from Western companies:
RMS(Root Mean Squared - root mean square value). Power is measured by applying a 1000 Hz sine wave until a certain level of harmonic distortion is reached. Usually in the product passport it is written like this: 15 W (RMS). This value indicates that the speaker system, when supplied with a 15 W signal, can operate for a long time without mechanical damage to the dynamic heads. For inexpensive speakers, power values in watts (RMS) that are higher than for Hi-Fi speakers are obtained due to measurements at very high harmonic distortion, often up to 10%. With such distortions, it is almost impossible to listen to the soundtrack due to strong wheezing and overtones in the dynamic head.
PMPO(Peak Music Power Output - peak music power). In this case, power is measured by applying a short-term sine wave of less than 1 second duration and a frequency below 250 Hz (typically 100 Hz). In this case, the level of nonlinear distortions is not taken into account. For example, the speaker power is 500 W (PMPO). This fact suggests that the speaker system, after playing a short-term low-frequency signal, had no mechanical damage to the dynamic heads. Watt power units (PMPO) are popularly called “Chinese watts” due to the fact that power values using this measurement technique reach thousands of watts! Imagine - small speakers with a diameter of 10 cm playing from a cheap balalaika (radio tape recorder), having an electrical power of 15 VA and developing a peak musical power of 1500 W (PMPO).
P.H.C. Maximum (maximum) noise (nameplate) power (English power handling capacity), characterizing the resistance of the acoustic system to thermal and mechanical damage during long-term (for 100 hours) operation with a noise signal of the “pink noise” type, the spectrum of which approaches the spectrum of real musical signals;
Along with Western ones, there are also Soviet standards for various types of power. They are regulated by GOST 16122-87 and GOST 23262-88, which are still in force today. These standards define concepts such as rated, maximum noise, maximum sinusoidal, maximum long-term, maximum short-term power. Some of them are indicated in the passport for Soviet (and post-Soviet) equipment. Naturally, these standards are not used in world practice, so we will not dwell on them.
Drawing conclusions: The most important in practice is the power value specified in Watts (RMS) at harmonic distortion distortion (THD) values of 1% or less. However, comparison of products even by this indicator is very approximate and may have nothing to do with reality, because sound volume is characterized by sound pressure level. Therefore, the information content of the “speaker system power” indicator is zero.
SENSITIVITY
Sensitivity (SPL)- one of the parameters indicated by the manufacturer in the characteristics of speaker systems. The value characterizes the intensity of the sound pressure developed by the speaker at a distance of 1 meter when a signal is supplied with a frequency of 1000 Hz and a power of 1 W. Sensitivity is measured in decibels (dB) relative to the hearing threshold (zero sound pressure level is 2*10^-5 Pa). Sometimes the designation “Sound Pressure Level” (SPL) is used. In this case, for brevity, in the column with units of measurement, dB/W*m or dB/W^1/2*m (or 2.83V) is indicated.
It is important to understand that sensitivity is not a linear proportionality coefficient between sound pressure level, signal power and distance to the source. Many companies indicate the sensitivity characteristics of dynamic drivers measured under non-standard conditions.Sensitivity - a characteristic that is more important when designing your own acoustic systems. If you do not fully understand what this parameter means, then when choosing acoustics you can not pay special attention to the sensitivity (fortunately, it is not often indicated) if you have an external power amplifier.
An amplifier and a loudspeaker are links in the same chain; one simply cannot work without the other. In the last issue we examined in some detail the question: “What power should the amplifier have?” and now let’s try to answer the second: “What power should the speaker be?” Partially the answer to this question was given in the previous material, since, as mentioned above, it is impossible to consider one without the other, but a number of details remained untouched and, as we promised, this time we will analyze them in more detail.
TYPES OF POWER
Many manufacturers of automobile speakers use non-standard methods for measuring power, which, by the way, are not always more attractive than those generally accepted for household equipment - it’s just more convenient for them. However, most use standardized parameters, among which we are usually interested in three: rated (RMS), maximum and peak power. The main one of these parameters is the rated power, and this is what we will mean in the future when we simply say “power”. The numerical ratio is as follows: the maximum is usually 2 times higher than the rated power, and the peak is 3-4 times higher. This rule cannot be called strict: there are some models whose maximum power is only slightly higher than the rated one.
Be that as it may, since the rated power is the smallest of the above, a number of manufacturers use a little trick: on the packaging and the first page of the instructions, unreasonably large power figures are given in large numbers without indicating its type, and the truth can only be established by finding the technical parameters in the document , or by looking at the back of the speaker, or by looking for some inconspicuous inscription on the packaging. Don't fall for this trick.
So, the rated power is precisely the one within which you can listen to music on these speakers for a long time without fear of nonlinear distortion and, even more so, of speaker failure.
WHAT IS MORE IMPORTANT – POWER OR SENSITIVITY?
In the last article we noted that doubling the power raises the sound pressure level by 3 dB. That is, a speaker with low power but high sensitivity is capable of developing the same sound pressure (the same sound volume) as a more powerful but less sensitive head. Therefore, if you have to choose between two speakers of equal sound quality, one of which is more sensitive, but less powerful than the second, then it is better to choose the first. Why overpay for the power of the amplifier, if even with a low-power one you will get the same volume?
By the way, due to certain circumstances (for example, the characteristics of transistor amplifiers), truly highly sensitive speakers for the automotive sector are practically not produced. But within each class, significant discrepancies in sensitivity can be found, and this is the source of all sorts of speculation: our tests extremely rarely confirm the correspondence between the declared values and the real ones, so we advise you to pay attention to our “special prizes”, and not to the given figures.
Sometimes you come across speakers with low sensitivity, but really high rated power, which at low power play not only quietly, but also with worse quality, but if you “twist the knob” well, the sound becomes optimal. This option can be recommended for those who listen only to loud music most of the time and are ready to purchase an amplifier with a power of at least a hundred watts per channel.
Significantly increases the sound volume and reduces the speaker resistance to 3, and even to 2 ohms - recently more and more such models are appearing. The only circumstance. What must be taken into account is that the amplifier must cope well with such a load. We categorically do not recommend connecting 2-3 ohm speakers directly to the built-in amplifier of a car radio or CD receiver - even if this works, it will be a severe test for the head unit and, most likely, it will eventually fail.
RATIO OF SPEAKER POWER AND AMPLIFIER POWER
In principle, there is nothing wrong if the RMS of the amplifier is less than that of the speakers, but in this case you need to handle the sensitivity control even more carefully. The paradox is that a less powerful amplifier, when it starts to overload, is more likely to burn out your speakers than a more powerful amplifier! It's all about a phenomenon called “clipping” - i.e. operation in limiting mode, when the amplifier produces a highly distorted signal with a large content of higher harmonics. It is for this reason that tweeters most often burn out in speakers. By the way, in head units there are no sensitivity regulators in principle, so you just need to once by ear determine the beginning of the appearance of distortion when the volume increases, and then never turn the regulator knob further than this level.
POWER AND FREQUENCY RANGE SPEAKERS
Another reason for the failure of speakers, especially those reproducing the low/mid ranges, is ignoring the frequency range they actually reproduce. Many manufacturers indicate an extended frequency range of their speakers to attract buyers. For example, for a coaxial speaker with a standard size of 10 cm and a power of 30 W, the frequency range is 50 - 20,000 Hz. It is not the upper value that is confusing, but the lower one. If you put a 50 Hz signal at the stated power level into this speaker, not only will you not hear 50 Hz, but you could easily destroy the speaker. This often happens when, being carried away by various schemes for raising the bass, they forget that the speaker is simply not capable of reproducing the lower register. The result is a torn cone of the woofer/midrange speaker. To prevent this from happening, the range of frequencies reproduced by the speaker should be limited using at least a second-order high-pass filter. The set filter cutoff frequency depends on the speaker size. So, practice shows that for 10 cm heads it should be about 100 Hz, for 13 cm heads - 80 Hz, and for 16 cm heads - 60 Hz. Anything below should be reproduced by the subwoofer. Moreover, by limiting the lower frequency range of the signals reproduced by the LF/MF speakers, you will immediately feel better output in the rest of the range, their more lively and loud operation. Speakers that can perform well without a low-bandwidth filter do exist, but they are in the minority.
The general rule is this: the narrower the frequency range sent to the speaker or a separate head, the more power it can withstand. For example, for many individual high-frequency speakers, several power values are given at once, depending on the high-pass filter cutoff frequency: if the speaker operates starting from 2000 Hz, this is one power, if from 5000, the power value is much higher. The same applies to midrange speakers, bass/midrange heads and subwoofers - the only difference is that they can vary two limits of the reproduced frequency range at once: upper and lower.
Typical relationships between the power of HF, MF, LF/MF and subwoofer heads are the same as for amplifiers; they were discussed in the last issue.
SUBWOOFERS AND THEIR PARAMETERS
Separately, we should consider a special class of speakers - subwoofers. This type of loudspeaker has recently become part of car audio systems, but due to the fact that it allows you to reproduce deeper bass, it has become very popular among car enthusiasts. However, a car subwoofer is very different from a home subwoofer. So, if for home equipment the power of a subwoofer of 300 W is considered “above the roof”, then for a car it is an average, normal parameter. Why such power? Let us remember that a subwoofer in a car must “shout out” road noise, but at home there is no such need. In addition, the design of car woofers has its own characteristics. To obtain deep bass in small volumes, manufacturers make a number of sacrifices, the main one of which is a reduction in sensitivity. To get sufficient volume with low sensitivity, you have to supply high sound power. Creating a powerful car amplifier is also not an easy task, so recently the design of a subwoofer with two separate voice coil windings has become popular, and some manufacturers go even further, installing as many as 4 voice coil windings. Such a solution gives greater flexibility when selecting the optimal resistance for a specific amplifier - to put it simply, it allows you to “squeeze” the maximum watts out of it. The required resistance is obtained through the appropriate connection of the windings (series, parallel, parallel-series). True, power, resistance and the number of windings do not affect the musicality of the subwoofer. Even a low-power, but properly built subwoofer can surpass its monstrous SPL counterpart in sound quality. Although to create the required sound pressure you will need at least two low-power subwoofers. Depending on the task at hand or the genre orientation of the speakers, the rated power of the subwoofer is chosen to be 2-4 times higher than the power of the full-range speakers. The greater its power, the better, because you can always make it play quieter, but louder – not. But at the same time, it is necessary to take into account the real capabilities of the on-board network of your car (and wallet, of course).
In addition, the type of acoustic design of the subwoofer is of great importance. In particular, the additional power reserve for the worst option in terms of output is especially welcome - an endless acoustic screen; the speaker plays into a large volume, for example, into the trunk. Models in a closed case have higher sensitivity, but also low, and the best in terms of output are models with a bass reflex, especially in a bandpass type case.
WHAT HAPPENS WHEN THE NUMBER OF HEADS INCREASES
You often find installations with dual or triple bass/midrange heads, and there are a great many options with two subwoofers. What does this do and why is it needed? By doubling the heads, you increase the sound pressure level by at least 3 dB, this is equivalent to doubling the power, provided that the electrical power supplied to them from the amplifier also doubles. If two heads receive the same power from the amplifier as one, then the sound pressure level will change little. In this case, we do not gain anything in terms of power, but the increased radiation area from the diffusers will give deeper bass. However, this effect depends on the distance at which the heads are separated, and will appear at frequencies for which this distance is commensurate with the wavelength or exceeds it. Those interested in details are referred to the book “Broadcasting and Electroacoustics” edited by Yu.A. Kovalgin, published by the publishing house “Radio and Communications” in 1999. There, on page 224, the problem of the efficiency of speakers, which include several heads of the same type, is discussed. In acoustics, such speakers are usually called speakers. They are used to increase directivity and increase the efficiency of speaker systems.
It is precisely because of the improvement in bass response that dual heads are used only for bass/midrange or subwoofer heads. There are also options for dual tweeters, but they are rare and have other tasks, for example, reducing the directivity of speakers at high frequencies. In many cases, using two LF heads can solve complex problems - in particular, two 12-inch heads are easier to accommodate than one 15-inch. However, it is worth considering that the cost of two heads will be clearly higher than one of the same series, but of a larger standard size.
TYPES OF POWER OF SPEAKER SYSTEMS
Nominal– root mean square value of electrical power limited by a given level of nonlinear distortion.
Maximum sine– the power of a continuous sinusoidal signal in a given frequency range, at which the speaker can operate for a long time without mechanical and thermal damage.
Maximum noise– electrical power of a special noise signal in a given frequency range, which the loudspeaker can withstand for a long time without thermal and mechanical damage.
Peak– the maximum short-term power that the speakers can withstand without damaging them when a special noise signal is applied to them for a short period of time (usually 1 s). The tests are repeated 60 times with an interval of 1 minute.
Maximum long-term – electrical power of a special noise signal in a given frequency range that the loudspeaker can withstand without irreversible mechanical damage for 1 minute. The tests are repeated 10 times with an interval of 2 minutes.
Material provided by Car&Music magazine, No. 12/2003. Rubric "Useful tips", text: Edouard Seguin
Professional tweeters Designed for installation in multi-way installation and concert acoustics. Professional high-frequency speakers must have increased sound output, providing the speakers in which they are installed with the ability to fully cover large rooms, as well as high reliability. Professional acoustics are traditionally used with increased power input for a long time. This mode of operation is especially dangerous for high-frequency speakers, which, due to the relatively small dimensions of the magnetic systems, are prone to overheating and failure. In addition, amplifiers operating at near maximum output power generate a large amount of distortion, also in the high-frequency region.
HF speakers for professional acoustics, as a rule, have larger dimensions than, and to increase sound output they are equipped. The magnetic gaps of their voice coils are often filled with coolant, and the housings have special elements that allow them to effectively dissipate heat. Otherwise, the choice of a tweeter for professional acoustics should be treated the same as for ordinary ones, based on the required frequency range of reproduced frequencies, resistance and sensitivity. Of course, it is necessary to turn on a professional high-frequency speaker through an appropriate isolation filter, which may also contain elements to protect it.
First, let's dot the i's and understand the terminology.
Electrodynamic loudspeaker, dynamic loudspeaker, speaker, direct radiation dynamic head are various names for the same device that serves to convert electrical vibrations of sound frequency into air vibrations, which are perceived by us as sound.
You have seen sound speakers or, in other words, direct radiation dynamic heads more than once. They are actively used in consumer electronics. It is the loudspeaker that converts the electrical signal at the output of the audio amplifier into audible sound.
It is worth noting that the efficiency (efficiency) of the audio speaker is very low and amounts to about 2 – 3%. This, of course, is a huge minus, but so far nothing better has been invented. Although it is worth noting that in addition to the electrodynamic loudspeaker, there are other devices for converting electrical vibrations of sound frequency into acoustic vibrations. These are, for example, loudspeakers of the electrostatic, piezoelectric, electromagnetic type, but loudspeakers of the electrodynamic type are widely used and used in electronics.
How does the speaker work?
To understand how an electrodynamic loudspeaker works, let's look at the figure.
The speaker consists of a magnetic system - it is located on the back side. It includes a ring magnet. It is made of special magnetic alloys or magnetic ceramics. Magnetic ceramics are specially pressed and “sintered” powders that contain ferromagnetic substances – ferrites. The magnetic system also includes steel flanges and a steel cylinder called core. The flanges, core and ring magnet form the magnetic circuit.
There is a gap between the core and the steel flange in which a magnetic field is formed. The coil is placed in the gap, which is very small. The coil is a rigid cylindrical frame on which a thin copper wire is wound. This coil is also called voice coil. The voice coil frame is connected to diffuser- it then “pushes” the air, creating compression and rarefaction of the surrounding air - acoustic waves.
The diffuser can be made from different materials, but more often it is made from compressed or cast paper pulp. Technologies do not stand still and in use you can find diffusers made of plastic, paper with a metallized coating and other materials.
To prevent the voice coil from touching the walls of the core and the flange of the permanent magnet, it is installed exactly in the middle of the magnetic gap using centering washer. The centering washer is corrugated. It is thanks to this that the voice coil can move freely in the gap without touching the walls of the core.
The diffuser is mounted on a metal body – basket. The edges of the diffuser are corrugated, which allows it to oscillate freely. The corrugated edges of the diffuser form the so-called top suspension, A lower suspension- This is a centering washer.
Thin wires from the voice coil are led out to the outside of the diffuser and secured with rivets. And on the inside of the diffuser, a stranded copper wire is attached to the rivets. Next, these multi-core conductors are soldered to the petals, which are mounted on a plate isolated from the metal body. Due to the contact petals, to which the multi-core leads of the voice coil are soldered, the speaker is connected to the circuit.
How does the speaker work?
If you pass an alternating electric current through the voice coil of a speaker, the magnetic field of the coil will interact with the constant magnetic field of the magnetic system of the speaker. This will cause the voice coil to either be pulled into the gap in one direction of current in the coil, or pushed out of it in the other. The mechanical vibrations of the voice coil are transmitted to the diffuser, which begins to oscillate in time with the frequency of the alternating current, creating acoustic waves.
Speaker designation on the diagram.
The graphical symbol for the speaker is as follows.
Letters are written next to the designation B or B.A. , and then the serial number of the speaker in the circuit diagram (1, 2, 3, etc.). The conventional image of the speaker in the diagram very accurately conveys the real design of the electrodynamic loudspeaker.
Basic parameters of the audio speaker.
The main parameters of the audio speaker that you should pay attention to:
But in addition to active resistance, the voice coil also has reactance. Reactance is formed because the voice coil is, in fact, an ordinary inductor and its inductance resists alternating current. Reactance depends on the frequency of the alternating current.
The active and reactance of the voice coil forms the total impedance of the voice coil. It is denoted by the letter Z(so-called impedance). It turns out that the active resistance of the coil does not change, but the reactance changes depending on the frequency of the current. To bring order, the reactance of the speaker voice coil is measured at a fixed frequency of 1000 Hz and the active resistance of the coil is added to this value.
The result is a parameter called the nominal (or total) electrical resistance of the voice coil. For most dynamic heads this value is 2, 4, 6, 8 ohms. Speakers with an impedance of 16 ohms are also available. As a rule, this value is indicated on the housing of imported speakers, for example, like this - 8Ω or 8 Ohm.
It is worth noting the fact that the total resistance of the coil is somewhere between 10 and 20% greater than the active one. Therefore, it can be determined quite simply. You just need to measure the active resistance of the voice coil with an ohmmeter and increase the resulting value by 10 - 20%. In most cases, only purely active resistance can be taken into account.
The nominal electrical resistance of the voice coil is one of the important parameters, since it must be taken into account when matching the amplifier and load (speaker).
Frequency range is the range of sound frequencies that a speaker can reproduce. Measured in Hertz (Hz). Let us recall that the human ear perceives frequencies in the range of 20 Hz – 20 kHz. And, this is just a very good ear :).
No speaker can accurately reproduce the entire audible frequency range. The quality of sound reproduction will still differ from what is required.
Therefore, the audible range of sound frequencies was conditionally divided into 3 parts: low-frequency ( LF), mid-frequency ( midrange) and high frequency ( HF). So, for example, woofers best reproduce low frequencies - bass, and high-frequency ones - “squeak” and “ringing” - that’s why they are called tweeters. There are also full-range speakers. They reproduce almost the entire audio range, but their playback quality is average. We win in one thing - we cover the entire frequency range, we lose in another - in quality. Therefore, wideband speakers are built into radios, televisions and other devices, where sometimes high-quality sound is not required, but only clear voice and speech transmission is needed.
For high-quality sound reproduction, the bass, midrange and tweeter speakers are combined in a single housing and equipped with frequency filters. These are speaker systems. Since each speaker reproduces only its part of the sound range, the total work of all speakers significantly increases the sound quality.
Typically, woofers are designed to reproduce frequencies from 25 Hz to 5000 Hz. Woofers usually have a large diameter cone and a massive magnetic system.
The midrange speakers are designed to reproduce a frequency range from 200 Hz to 7000 Hz. Their dimensions are slightly smaller than woofers (depending on power).
The tweeters perfectly reproduce frequencies from 2000 Hz to 20,000 Hz and higher, up to 25 kHz. The diffuser diameter of such speakers is usually small, although the magnetic system can be quite large.
Rated power (W) - this is the electrical power of audio frequency current that can be supplied to the speaker without the threat of damage or damage. Measured in watts ( W) and milliwatts ( mW). Recall that 1 W = 1000 mW. You can read more about the abbreviated notation of numerical values.
The amount of power that a particular speaker is designed to handle may be indicated on its housing. For example, like this - 1W(1 W).
This means that such a speaker can be easily used in conjunction with an amplifier whose output power does not exceed 0.5 - 1 W. Of course, it is better to choose a speaker with some power reserve. The photo also shows that the nominal electrical resistance is indicated - 4Ω(4 ohms).
If you apply more power to the speaker than what it is designed for, it will work with overload, begin to “wheeze,” distort the sound, and soon fail.
Let us remember that the efficiency of the speaker is about 2 – 3%. This means that if an electrical power of 10 W is supplied to the speaker, then it will convert only 0.2 - 0.3 W into sound waves. Quite a bit, right? But the human ear is very sophisticated, and is capable of hearing sound if the emitter reproduces an acoustic power of about 1 - 3 mW at a distance of several meters from it. In this case, an electrical power of 50 - 100 mW must be supplied to the emitter - in this case, the speaker. Therefore, not everything is so bad and for comfortable sounding of a small room it is quite enough to supply 1 - 3 W of electrical power to the speaker.
These are just three basic parameters of the speaker. In addition to them, there are also such as sensitivity level, resonance frequency, amplitude-frequency response (AFC), quality factor, etc.