Measuring speaker parameters at home and one way to configure bass reflexes. Basic parameters of woofers Thiel-Small method of measuring parameters

(To help beginner bass players )

Chapter A - Measurements

I’ll immediately make a reservation that the most convenient way to measure the parameters of woofers is described in the method. I suggest that program owners use this method (I haven’t tested it myself, but I think there are no glitches there). For those who do not have this program or do not have enough measuring equipment, I will describe the method I learned from “RADIO” magazines of past years. I used this method, and with a certain degree of accuracy and perseverance, you can use it to get fairly accurate (certainly more accurate than in a reference book or user manual) parameters.

So, let's begin:

1) Let's assemble a diagram.

I think it’s clear where the speaker under test is in the diagram. The remaining elements of the diagram require detailed explanation.

Generator - either an audio frequency generator capable of producing a voltage of 10-20 V, or a generator-amplifier combination that satisfies the same requirement.

1000 Ohm – a 1000 Ohm resistor that stabilizes the current through the speaker. The resistor value can be taken less, but this will reduce the accuracy of the Qts calculation. (True, when using a resistor of only 200 Ohms, the measurement error is unlikely to exceed 10%, but, as they say, save...).

a, b, c – points for connecting a voltmeter.

The voltmeter itself is not indicated in the figure, but it should be: - firstly, alternating current; - secondly, be able to measure voltages of the order of 100 mV. If the voltmeter does not have such a measurement limit, it can be connected through an amplifier. And since modern amplifiers are usually “stereo” or more, there are no special problems with this.

The diagram is assembled.

2) Place the speaker away from the walls, ceiling and floor (hanging it is often recommended).

3) Connect the voltmeter to the points A And With, and set the voltage to 10-20 V at a frequency of 500-1000 Hz.

4) Connect the voltmeter to the points V And With, and by changing the frequency of the generator we find the frequency at which the voltmeter readings are maximum, see the figure below in the text. This is Fs. We record the Fs and Us readings of the voltmeter.

5) By changing the frequency upward relative to Fs, we find frequencies at which the voltmeter readings are constant and significantly less than Us (with a further increase in frequency, the voltage will begin to increase again, in proportion to the increase in speaker impedance). Let's write down this value, Um.

A graph of the impedance of a speaker in free space and in a closed box looks something like this.

6) We find it from the graph (if we built it) or measure the cutoff frequencies F1 and F2 at the level U12=(Us*Um)^0.5;

7) Calculate the acoustic quality factor Qa=(Us/Um)^0.5*Fs/(F2-F1), and

8) Electrical quality factor Qe=Qa*Um/(Us-Um);

9) And, finally, the total quality factor Qts=Qa*Qe/(Qa+Qe).

To find out Vas, we need a box (a good sealed box, by no means cardboard, but with thick walls) with a round hole that matches the diameter of the speaker cone. It is better to choose the volume of the box, V, closer to the one in which we are then going to listen to this speaker.

10) Install the speaker in the box and seal all the cracks;

11) We carry out all measurements and calculations according to points 1)-6) and obtain the values of Fs" (actually this is Fc) and Qts" (Qtc);

12) Calculate Vas=((Fs"/Fs)^2-1)*V;

13) We calculate Qtc=Qts*(1+Vas/V)^0.5, if the measured Qts"=Qtc is well or almost equal, then everything is done correctly, and you can proceed to designing the acoustic system.

Chapter B – FI Setup

The proposed setup method is also copied from the Literature, but is simple enough to become the property of the curious masses. The only caveat (I came up with it myself) is that this technique allows you to easily tune FIs made on the basis of speakers with a quality factor of Qts = 0.3...0.5. For other FIs, you will have to additionally use your natural ingenuity. So.

The methodology is based on the relationship that exists between the parameters of the FI and the closed box (closed box). If in a FI with a smooth frequency response (according to spl) the tunnel hole is closed, then the total quality factor of the system, Qtc, will be equal to 0.6, and the resonant frequency, Fc, will be related to the FI tuning frequency by the dependence: Fb=0.61…0.65*Fc. If we allow an error in determining the FI tuning frequency of 5%, then the Fb/Fc ratio for real structures can be taken equal to 0.63.

Setting:

14) We close the tunnel hole hermetically and assemble a circuit for measuring Fc (see chapter A).

15) We select the amount of sound-absorbing material and achieve the minimum Fc value;

16) We fix the material inside the box and measure Fc;

17) Calculate Fb=0.63*Fc;

18) Calculate the length of the tunnel: Lv=31*10^3*S/(Fb^2*V)-1.7*(S/PI)^0.5, where S is the area of the FI port opening in sq. cm., V – volume of the box in liters;

19) We make a tunnel, insert it inside the box (inside, if in the finished design it is supposed to be inside) and measure Fb."

It should look something like:

20) We substitute the resulting value Fb" into formula 18) and calculate the adjusted value V";

21) Substitute V" into formula 18) and calculate Lv" for the calculated value of Fb (who forgot, this happened in step 17);

22) We shorten (it is impossible to lengthen it, so it is better to take measures in advance) the tunnel and measure again;

23) Using the method for determining Qtc (Chapter A), we determine the quality factor of the system and, if it is less than 1, we calm down. If it is larger, then something was probably done wrong somewhere, but it’s too late to redo it. Let's listen, if he really mumbles (which is not at all necessary), we will take action.

Possible measures:

24) Dampen the FI tunnel with a partially acoustically transparent material. In other words, close the tunnel with padding polyester, cotton wool, carpet, etc.;

25) Dampen the speaker itself by gluing the materials listed above to the windows of the diffuser holder (but not all at once).

These measures will reduce the overall quality factor of the system, Qtc.

Literature:
Saltykov O., Calculation of loudspeaker characteristics, Radio 1981
Zhbanov V., Setting up the bass reflex, Radio 8/1986
Aldoshina I. Where the basses live, AM 2/1999
Frunze, On improving the sound quality of speakers, Radio 9/1992

) dynamics. The methods described below are sufficient for the novice car audio technician and allow you to measure T/S parameters with a minimum of equipment.

To measure these parameters using the method described below, you will need to have the following items:

One (1) amplifier
One (1) tone generator (generator of specific audio frequencies, can be software, for example AudioTester or Tone Generator from NCH Software)
One (1) digital multimeter
One (1) 5 watt resistor (approximately 4 or 8 ohms)
Two (2) pairs of wires with crocodile ends

Preferably, the multimeter should be able to measure frequency, as well as voltage, resistance and current. The amplifier must be able to reproduce from 20 Hz to 200 Hz without any change in output power and it must be insensitive to loads above 4 ohms. The frequency tone generator must also be able to produce a signal whose voltage does not change as the frequency is adjusted.

Thiel-Small method for measuring parameters

Measure the resistance (Re) of the speaker directly.
Measure the resistance (Rs) across the resistor.
Connect a tone generator to the amplifier's input terminals.
Connect a multimeter to the amplifier's speaker output terminals.
Set the tone generator to approximately 100 Hz.
Set the amplifier output to Vs, where Vs~0.5 to 1.0 Volts. You may need to experiment with different voltages, depending on the accuracy of your measuring device.
Calculate Is, where Is = Vs/(Re+Rs)
Connect the following circuit (using alligator clips when necessary):
- Attach one leg of the resistor to the positive terminal on the amplifier
- Attach the second leg of the resistor to the positive terminal on the speaker
- Connect the negative terminal of the speaker to the negative terminal on the amplifier
- Connect the multimeter terminals to each side of the resistor
Adjust the frequency until the voltage across the resistor reaches the minimum level.
We fix the frequency value, Fs
We fix the voltage on the resistor, Vm
Let's calculate the current, Im = Vm/Rs, flowing through the circuit
We calculate the impedance of the speaker at the resonant frequency, РRm = (Vs-Vm)/Im
We get -3dB current, Ir = (Im*Is)^0.5
Let's calculate r0=Is/Im
Let's calculate -3dB voltage, Vr = Ir*Rs
We obtain the frequencies Fl and Fh, for which the voltage through the resistor is equal to Vr
Make sure (Fl*Fh)^0.5 = Fs
If everything agrees, then Qes, Qms and Qts can be calculated as follows:
- Qms = Fs*(r0^0.5)/(Fh-Fl)
- Qes = (Qms/(r0-1))*(Re/(Rs+Re))
- Qts = Qms*Qes/(Qms+Qes)

You can use the following table to perform the calculations automatically:

Vas measurement (equivalent speaker volume)

To measure Vas, you need to use a good, sturdy enclosure of known volume that matches the nominal size of the speaker. Install the speaker with the cone facing outwards and ensure easy access to the contacts. Calculate the volume of the case taking into account the losses from the speaker installed inside. Measure the resonant frequency in this position.

Vas = Vb((Fb/Fs)^2 - 1)

VB is the volume of the speaker cone plus the volume of the box
Fb - resonant frequency of the speaker in the box

I want to collect subwoofer, but not simple, but well calculated. Everyone is already proficient in these calculations: both installers and amateurs, and there also seem to be enough programs, for example JBL SpeakerShop. Only one “but” - no parameters Tilya-Smolla you won't get far.

Unfortunately, inexpensive and especially interesting speakers often end up in hands without any numbers at all. It also happens that the characteristics seem to be there, but different, depending on the year of manufacture. This occurs even among well-known manufacturers.
In general, the ability to measure these quantities will not be superfluous. Traditional measurement methods are described in many sources and are no secret. Moreover, in the program mentioned above JBL SpeakerShop There is a convenient “wizard” that eliminates the need to manually calculate intermediate and final values of voltages, frequencies and quality factors: you need to assemble the circuit shown there and act in accordance with the instructions of the program.

I myself have repeatedly used this technique, everything is great, only for measurements you need:
a) generator,
b) frequency meter,
c) AC voltmeter,
d) low frequency amplifier.

I think that somewhere around point c) from this list, the research fervor of many has already faded a little. But that is not all. The measurement process itself, the constant “catching” of the required frequency and voltage values can tire even a phlegmatic person: at best, one speaker takes half an hour. It's a shame to waste time on such a routine, so when I came across the program SpeakerWorkShop, joy knew no bounds.

Great, all you need is a computer with a sound card and basic cables. The first few days I honestly tried to do everything as the instructions said. Here I was disappointed. That is, the program itself is good, but its help is something. I probably read it twenty times, tried this and that, but nothing worked. What to do - free software is akin to cheese of the same price.

For several months I continued to measure “three figures” in the usual ways, until a new link appeared on the website where the program itself is located. Thanks to the champion RASKA among amateurs Kostya Nikiforov for what he said about her. The description below is my own, simplified version of the console and brief instructions for working with the program.

It happens in life - just as a nickname sticks to a person, it haunts him until the end of his days. This also happened with the device that I will describe below - “ box", and that's all. No matter how I tried to come up with a more scientific name, nothing came of it. The diagram is shown in Fig. 1

Some comments about the elements used.
X1 - connector connected to the power amplifier output (Spkr Out) of the sound card, usually a mini-jack. The signal from the right and left channels from the amplifier is the same, so you can use any pin of the connector. When using an external amplifier, you CANNOT connect this connector to the sound card output at the same time!

X2, X3 will be needed if you use an external power amplifier. This is a more preferable option, although a little more cumbersome. “Speaker” terminals, preferably screw terminals, are suitable. In addition, if an external amplifier is used, an additional mini-jack to two tulip cable will be required.

X4, X5 - terminals similar to X2, X3. They will be joined by the subject of the study. It is very useful to duplicate these terminals with a pair of alligator clips.

X6 is a “mini-jack” that will be connected to the Line-In input of the sound card. I don’t show the wiring of the right and left channels - for now, connect as it turns out, we’ll clarify later. The wire to the connector must be shielded.

R1, R2 - resistors used as reference when calibrating the program. The ratings do not play a special role and can be from 7.5 to 12 Ohms, for example the MLT-2 type.
R3 is a resistor with the value of which the program “compares” the unknown impedance. Therefore, the value of this resistor must be commensurate with the one being tested. If you are mainly going to measure car speakers, the value of R3 can be taken to be about 4 ohms. The power can be selected the same as for R1.

R4, R5, R6, R7 - any power. The resistances may differ slightly from those indicated, it is only important that R4/R6 = R5/R7 = 10...15. This is a divider that attenuates the signal at the sound card input.

SA1 is used to select between two reference resistances. It is only used for calibration. You can use a toggle switch, I installed P2K, connecting several sections in parallel.

SA2 is perhaps the most responsible. It is important that it provides reliable and stable contact; the accuracy of the results largely depends on this.

So, " box» collected. Now you will need an ohmmeter, with the highest possible accuracy, preferably a measuring bridge. It is necessary to set the switches to all positions according to the table and measure the indicated resistances.

	position switch	position switch	resistance	resistance
	SA1	SA2	X4-X5	X2-X4
CAL1	Upper	Lower	10	4
CAL2	Lower	Lower	5	4
LOOP	Any	Upper	Infinity	0
IMP	Any	Average	Infinity	4

I draw your attention to the fact that during work you will need exactly measured resistance values. It is best to write them, as well as the purpose of all switches and inputs and outputs, directly on the case - I don’t recommend relying on memory.

The principle of operation of the system is very simple. The noise signal generated by the program is fed through an amplifier to the object under study through resistor R3 of known resistance. The program compares the voltage on one channel (upper terminal R3) with the voltage on the other (lower terminal R3 and upper terminal of the measured object). The ingenious simplicity of the idea is that to calculate the unknown impedance, not the absolute values of the voltages are used, but their ratio. Thanks to preliminary calibration using known resistances (R2 and R2-R1), quite acceptable measurement accuracy is achieved.

Now you can attach the “box” to the sound card. For the first time, you should not use an external amplifier: to understand the principle of operation, it is not particularly needed. And when the principle becomes clear, its connection will no longer raise questions.

Setting up the program
Perhaps the description of the settings will seem too detailed to some, but, as practice shows, it is convenient when the entire process is described in order, and not according to the principle “you already know this, everything is obvious here, in general, you’re smart - you’ll figure it out yourself.”

After launching the program for the first time, you need to check whether your sound card supports “full duplex mode,” that is, whether it allows you to simultaneously play and record sound. To check, you need to select the menu item Options-Wizard-Check sound card. The program will perform further actions on its own. If the result is negative, you will have to look for another board or update the driver.

If everything is ok, open Volume Control. With Options-Properties selected, set Mute to all controls except Volume Control and Wave. It is necessary to disable all “extra” options, such as Enhanced Stereo and tone control. Set the volume control to the middle position. Finally, move the Volume Control window as shown in Figure 2.

rice. 2

rice. 3

Now open another copy of Volume Control. Select Options-Properties, set the recording mode (Recording). The window name changes to Recording Control. Similarly to the above, set Mute to all controls except Recording and Line-In. Set the level control to the maximum position. Then the level may need to be changed, but more on that later. Move the Recording window as shown.

One of the most critical stages of setup is to select the correct input and output signal levels. To do this, create a new signal by selecting Resource-New-Signal. Give it some name, like sign1. By default, the sinusoidal signal type (Sine) will be selected, which suits us quite well. The name of the new signal should appear in the project window (the one on the left).

In order to do something with a signal or speaker, it must be opened. Do you think double-clicking is enough for this? Here lies one of the features of the program interface: to open a resource, you must first click on the resource name with the left mouse button, then either select Open from the menu that appears when you right-click, or press F2 on the keyboard. Right-click again and go to Properties. There you need to select the Sine tab and enter a frequency value of 500 Hz. Signal phase - 0. OK.

Set the box switches to the LOOP position (according to the table). After making sure that the signal is open, enter the Sound-Record menu - the Record Data dialog will appear. Enter there the values shown in Fig. 3. Click OK; If a speaker is connected to the Test terminals, a short “spike” will be heard.

Let's look at the project tree. There will be several new objects with names starting with sign1. Open the resource named sing1.in.l. On the chart that appears on the right, right-click and select Chart properties. Select the X Axis tab and set the Scale section to a maximum value of 10. Then select the Y Axis and set the Minimum and Maximum values to 32 K and 32 K respectively. Click OK. The graph should look like 4.5 sine cycles. Do the same with the sing1.in.r resource.

Now we need to find out the output signal level at which the limitation occurs. To do this, gradually increase the level with the volume control, repeating the recording procedure each time (menu item Sound-Record Again) and analyzing the graphs sign1.in.r and sign1.in.l. Once visible amplitude limitation appears (usually at ~20 K levels), the signal level should be reduced slightly. At this point, the process of setting the level can be considered complete.

In the original method, the author now suggests checking the correspondence of the left and right channels. I did this, but later it turned out that they had to be swapped. So it’s better to go straight to calibrating the program using known resistances - there we’ll check “right-left” at the same time.

First, make sure that nothing is connected to the test terminals (X4, X5). Then open the Option-Preferences menu and select the Measurements tab there. Set the Sample Rate to the far right position, and the Sample Size to 8192. The Volume should be set to 100. In the future, for real measurements, for greater accuracy, you need to set a larger Sample Size. However, this increases the file size. Accuracy can be increased by decreasing the Sample Rate - this will reduce the upper limit measurement frequency, but for subwoofers this is completely unimportant.

Now we need to check the channel imbalance. To do this, select Option - Calibrate-Channel Difference and click the Test button. The program will prompt you for further actions. The test results will be located in the Measurement.Calib section of the System folder (in the project window). I don’t know what exact values should be obtained; in practice, the imbalance is on the order of tenths (in dimensionless units), and the signal level at the output of each channel is in the region of 20,000 of these same units. I think this ratio can be considered acceptable.

Next comes the most interesting part. We will measure known resistances. Go to Options-Preferences and select the Impedance tab. In the Reference resistor field, enter the measured resistance value between terminals X2 and X4. In the adjacent field (Series resistor) you can enter a value, for example 0.2, and the program will then itself substitute there what it deems necessary. Now click the Test button. Set the box switches to CAL1 mode and enter the value of the reference resistance R2 measured at the terminals. (Have you already forgotten it? But I advised you to write it down.) Press the Next button and repeat the same thing, but in CAL2 mode. By the way, I advise you to constantly monitor the indicator, which is located near the level regulator, when calibrating and measuring. When “red bars” appear there, I slightly reduce the volume level. After this, you need to repeat the calibration. At first, the learning process takes a long time, but after a couple of sessions of working with the program, all settings will need to be mostly controlled. It only takes a few minutes.

So, the program showed what, in its opinion, are the values of the Reference and Series resistors. If the differences from the values we entered are small (for example, 4.2 ohms instead of 3.9) - everything is fine. To be sure, you can go through the process one more time and start taking real measurements. If the program produces obvious nonsense (for example, negative values), it means that you need to swap the right and left channels in connector X6 and repeat the settings again. After this, as a rule, everything becomes normal, although some colleagues showed a persistent reluctance to configure the program. Whether the sound card is somehow different, or something else, I don’t know. Let us know about any difficulties you encounter and the ways you find to overcome them, and we’ll put them in the form of an FAQ (I have a feeling we’ll have to).

Looks like we're in the mood. You can start reaping the fruits of your labor. We take some capacitor or inductor, click the toggle switch to the IMP position, select the sign1 signal created earlier, the Measure-Passive Component menu item... Is there a result? It should be. I don’t know who it is, but I experience some kind of primitive joy when I see that the program itself recognized what kind of component I connected and gave its value “in simple written form.”

The measurement accuracy of passive components is conservatively estimated at 10-15%. For the manufacture of crossovers, this, in my opinion, is quite enough.

Now let's move on to the speakers. Everything is just as easy and simple here. Create a new speaker (Resource-NewDriver), give it a name, open it (remember, F2 key). Now we study the Measure menu. Basically, the program (its hint) advises getting the impedances of the speaker in the free state (Fre - Air), then in a closed box, entering the value of the box volume in the Properties of this speaker, and then calculating the Thiele - Small parameters (to do this, having opened the speaker, you need to enter in the Driver Estimate Parameters menu). Here, however, I encountered another pitfall, since the program refuses to calculate the equivalent volume value (the default value remains, 1000 l). It doesn’t matter, from two impedance graphs we take the values of the resonant frequencies Fs and Fc and calculate Vas manually using the well-known formula: V as =V b ((F c /F s) 2 -1). Someone is probably already grumbling, they say, here’s another thing, you have to calculate something yourself - I advise you to remember how many calculations are made with a completely “manual” method of determining parameters. In fact, I hope that this and other annoying errors will be eliminated in future versions of the program.

I hope that the simple and inexpensive tool I described will make the work of a creative installer easier. Of course, it will not compete with Brühl&Kjær, but the investments required are quite small.

Repeat - you won't regret it.
O. Leonov

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Hi all! Today I will try to talk about the main parameters of car subwoofers. What might they be needed for? And they are needed in order to correctly assemble the box for your speaker. If you do not calculate the future box, the subwoofer will hum and there will be no loud and deep bass. In general, a subwoofer is an independent acoustic system that plays low frequencies from 20 Hz to 80 Hz. It's safe to say that without a subwoofer you will never get high-quality bass in a car. The speakers, of course, try to replace the woofer, but it turns out weakly, to put it mildly. A subwoofer can help unload the speakers by taking over the low-frequency range, while the front and rear speakers will only have to play the middle and high frequencies. Thanks to this, you can get rid of distortions in the sound and get a more harmonious sound of music.

Now let's discuss the main parameters of the woofer. Understanding them will be very useful when building a subwoofer box. The minimum data set looks like this: FS (speaker resonant frequency), VAS (equivalent volume) and QTS (total quality factor). If the value of at least one parameter is unknown, it is better to abandon this speaker, because... It will not be possible to calculate the volume of the box.

Resonance Frequency (Fs)

Resonant frequency is the resonance frequency of the woofer head without design, i.e. without a shelf, a box... It is measured as follows: the speaker is suspended in the air, as far as possible from surrounding objects. So its resonance will depend only on itself, i.e. on the mass of its moving system and the rigidity of the suspension. There is an opinion that a low resonant frequency allows you to make an excellent subwoofer. This is not entirely true; for certain designs, too low a resonance frequency will only be a hindrance. For reference: low resonance frequency is 20-25 Hz. It's rare to find a speaker whose resonant frequency is below 20 Hz. Well, above 40 Hz, it will be too high for a subwoofer.

Total quality factor (Qts)

In this case, it does not mean the quality of the product, but the ratio of viscous and elastic forces existing in the moving system of the LF head near the resonance frequency. The moving system of the speaker is very similar to the suspension of a car, which contains a shock absorber and a spring. The spring creates elastic forces, that is, it collects and releases energy during movement. In turn, the shock absorber is a source of viscous resistance; it does not accumulate anything, but only absorbs and dissipates in the form of heat. A similar process occurs when the diffuser and everything attached to it vibrates. The higher the quality factor, the more elastic forces predominate. It's like a car without shock absorbers. You hit a small bump and the wheels jump on one spring. If we talk about dynamics, this means an overshoot from the frequency response at the resonance frequency, the greater the greater the total quality factor of the system. The highest quality factor is measured in thousands, and only for the bell. It sounds exclusively at the resonant frequency. A common way to check a car's suspension is by rocking it from side to side, which is a homemade way to measure the quality factor of the suspension. The shock absorber destroys the energy that appeared when the spring was compressed, i.e. Not all of it will come back. The amount of wasted energy is the quality factor of the system. It seems that everything is clear with the spring - its role is played by the diffuser suspension. But where is the shock absorber? And there are two of them, and they work in parallel. Total quality factor consists of two: electrical and mechanical.

The mechanical quality factor is usually determined by the choice of suspension material, mainly the centering washer. As a rule, losses here are minimal, and the total quality factor consists of only 10-15% mechanical.

The majority is electrical quality. The stiffest shock absorber available in a speaker propulsion system is a tandem magnet and voice coil. Being essentially an electric motor, it operates as a generator near the resonance frequency, when the speed and amplitude of movement of the voice coil is maximum. Moving in a magnetic field, the coil generates current, and the load of the generator is the output resistance of the amplifier, i.e. zero. The result is the same electric brake as on electric trains. There, in approximately the same way, traction motors are forced to work as generators, and brake resistor batteries on the roof act as a load. The amount of current generated will depend on the magnetic field. The stronger the magnetic field, the greater the current will be. As a result, it turns out that the more powerful the speaker magnet, the lower its quality factor. But, because When calculating this value, you need to take into account both the length of the winding wire and the width of the gap in the magnetic system; it will not be correct to draw a final conclusion based on the size of the magnet.

For reference: a low speaker Q will be less than 0.3, and a high Q will be more than 0.5.

Equivalent volume (Vas)

Most modern speakers are based on the principle of “acoustic suspension”. The point is that you need to select a volume of air at which its elasticity will correspond to the elasticity of the loudspeaker suspension. That is, another spring is added to the speaker suspension. If the new spring is equal in elasticity to the old one, this volume will be equivalent. Its value is determined by the diameter of the speaker and the stiffness of the suspension.

The softer the suspension, the larger the air cushion will be, the presence of which will begin to vibrate the head. The same thing happens when changing the diameter of the diffuser. A larger diffuser, with the same displacement, will compress the air in the box more strongly, and thereby experience greater output. This is exactly what you should pay attention to when choosing a speaker, because the volume of the box depends on this. The larger the diffuser, the higher the output of the subwoofer will be, but the size of the box will also be impressive. The equivalent volume is strongly related to the resonant frequency, without knowing which you can make a mistake. The resonant frequency is determined by the mass of the moving system and the rigidity of the suspension, and the equivalent volume is determined by the same rigidity of the suspension and the diameter of the diffuser. It may turn out like this: there are two woofers of the same size and with the same resonance frequency, but for one of them the resonance frequency depends on a heavy diffuser and a hard suspension, and for the second - on a light diffuser and a soft suspension. The equivalent volume, in this case, can differ very significantly, and when installed in the same box, the results will be very different.

I hope I helped a little to understand the basic parameters of woofers.

Taken from the website of the magazine "Avtozvuk"
Context
In the previous part of our conversation, it became clear what is good and what is bad about different types of acoustic design. It would seem that now “the goals are clear, let’s get to work, comrades..” But that was not the case. Firstly, the acoustic design, in which the speaker itself is not installed - just a box assembled with varying degrees of care. And often it is impossible to assemble it until it is determined which speaker will be installed in it. Secondly, and this is the main fun in the design and manufacture of car subwoofers - the characteristics of a subwoofer are worth little outside the context of the characteristics, at least the most basic ones, of the car where it will work. There is also a third thing. A mobile speaker system that is equally suited to any music is an ideal rarely achieved. A competent installer can usually be recognized by the fact that, when “taking readings” from a client ordering an audio installation, he asks to bring samples of what the client will listen to on the system he ordered after its completion.
As you can see, there are a lot of factors influencing the decision and there is no way to reduce everything to simple and unambiguous recipes, which turns the creation of mobile audio installations into an activity very much akin to art. But it is still possible to outline some general guidelines.
Tsifir
I hasten to warn the timid, lazy and humanitarian educated - there will be practically no formulas. As long as possible, we will try to do without even a calculator - a forgotten method of mental calculation.
Subwoofers are the only part of car acoustics where measuring harmony with algebra is not a hopeless task. To put it bluntly, it’s simply unthinkable to design a subwoofer without calculations. The initial data for this calculation are the speaker parameters. Which? Yes, not the ones they hypnotize you with in the store, rest assured! To calculate, even the most approximate, characteristics of a low-frequency loudspeaker, you need to know its electromechanical parameters, of which there are a ton. This includes the resonant frequency, the mass of the moving system, the induction in the gap of the magnetic system, and at least two dozen other indicators, some understandable and some not so clear. Upset? Not surprising. Two Australians, Richard Small and Neville Thiel, were similarly upset about twenty years ago. They proposed, instead of the Tsifiri mountains, to use a universal and fairly compact set of characteristics, which, quite deservedly, immortalized their names. Now, when you see a table in the speaker description entitled Thiel/Small parameters (or simply T/S) - you know what we're talking about. And if you don’t find such a table, move on to the next option - this one is hopeless.
The minimum set of characteristics that you will need to find out is:
Natural resonant frequency of the speaker Fs
Full Qts quality factor
Equivalent volume Vas.
In principle, there are other characteristics that would be useful to know, but this, in general, is enough. (the diameter of the speaker is not included here, since it is already visible without documentation.) If at least one parameter from the “extraordinary three” is missing, the matter is at seams. Well, now what does all this mean?
Natural frequency- this is the resonance frequency of the speaker without any acoustic design. This is how it is measured - the speaker is suspended in the air at the greatest possible distance from surrounding objects, so that now its resonance will depend only on its own characteristics - the mass of the moving system and the stiffness of the suspension. There is an opinion that the lower the resonant frequency, the better the subwoofer will be. This is only partly true; for some designs, an excessively low resonance frequency is a hindrance. For reference: low is 20 - 25 Hz. Below 20 Hz is rare. Above 40 Hz is considered high for a subwoofer.
Complete quality. The quality factor in this case is not the quality of the product, but the ratio of elastic and viscous forces existing in the moving speaker system near the resonance frequency. The moving speaker system is much like a car suspension, where there is a spring and a shock absorber. A spring creates elastic forces, that is, it accumulates and releases energy during oscillations, and a shock absorber is a source of viscous resistance; it does not accumulate anything, but absorbs and dissipates in the form of heat. The same thing happens when the diffuser and everything attached to it vibrates. A high quality factor means that elastic forces predominate. It's like a car without shock absorbers. It is enough to run over a pebble and the wheel will start jumping, unrestrained by anything. Jump at the very resonant frequency that is inherent in this oscillatory system.
In relation to a loudspeaker, this means an overshoot of the frequency response at the resonance frequency, the greater the higher the total quality factor of the system. The highest quality factor, measured in thousands, is for a bell, which, as a result, does not want to sound at any frequency other than the resonant one, fortunately, no one demands this from it.
A popular method for diagnosing a car's suspension by swaying is nothing more than measuring the quality factor of the suspension using a homemade method. If you now put the suspension in order, that is, attach a shock absorber parallel to the spring, the energy accumulated during compression of the spring will not all come back, but will be partially destroyed by the shock absorber. This is a decrease in the quality factor of the system. Now let's go back to the dynamics. Is it okay that we go back and forth? This, they say, is useful... Everything seems to be clear with the spring on the speaker. This is a diffuser suspension. What about the shock absorber? There are two shock absorbers, working in parallel. The total quality factor of a speaker consists of two things: mechanical and electrical. The mechanical quality factor is determined mainly by the choice of suspension material, mainly by the centering washer, and not by the external corrugation, as is sometimes believed. There are usually no large losses here and the contribution of the mechanical quality factor to the total does not exceed 10 - 15%. The main contribution comes from the electrical quality factor. The stiffest shock absorber operating in the oscillating system of a speaker is an ensemble of a voice coil and a magnet. Being an electric motor by its nature, it, as befits a motor, can work as a generator and this is exactly what it does near the resonance frequency, when the speed and amplitude of movement of the voice coil are maximum. Moving in a magnetic field, the coil generates current, and the load for such a generator is the output impedance of the amplifier, that is, practically zero. It turns out to be the same electric brake that all electric trains are equipped with. There, too, when braking, the traction motors are forced to work as generators, and their load is a battery of braking resistors on the roof.
The amount of current generated will naturally be greater, the stronger the magnetic field in which the voice coil moves. It turns out that the more powerful the speaker magnet, the lower, other things being equal, its quality factor. But, of course, since both the length of the winding wire and the width of the gap in the magnetic system are involved in the formation of this value, it would be premature to draw a final conclusion based only on the size of the magnet. And the preliminary one - why not?...
Basic concepts - the total quality factor of the speaker is considered low if it is less than 0.3 - 0.35; high - more than 0.5 - 0.6.
Equivalent volume. Most modern loudspeaker drivers are based on the "acoustic suspension" principle.
We sometimes call them “compression”, which is incorrect. Compression heads are a completely different story, associated with the use of horns as an acoustic design.
The concept of an acoustic suspension is to install a speaker in a volume of air whose elasticity is comparable to the elasticity of the speaker suspension. In this case, it turns out that another spring was installed in parallel to the spring already existing in the suspension. The equivalent volume will be the one at which the newly appeared spring is equal in elasticity to the already existing one. The amount of equivalent volume is determined by the stiffness of the suspension and the diameter of the speaker. The softer the suspension, the larger the air cushion will be, the presence of which will begin to disturb the speaker. The same thing happens with a change in the diameter of the diffuser. A large diffuser at the same displacement will compress the air inside the box more strongly, thereby experiencing a greater response force of elasticity of the air volume.
It is this circumstance that often determines the choice of speaker size, based on the available volume to accommodate its acoustic design. Large diffusers create the prerequisites for high output from the subwoofer, but also require large volumes. The argument from the repertoire of the room at the end of the school corridor “I have more” must be used carefully here.
The equivalent volume has interesting relationships with the resonant frequency, without awareness of which it is easy to miss. The resonant frequency is determined by the rigidity of the suspension and the mass of the moving system, and the equivalent volume is determined by the diameter of the diffuser and the same rigidity.
As a result, such a situation is possible. Let's assume there are two speakers of the same size and with the same resonance frequency. But only one of them achieved this frequency value due to a heavy diffuser and a rigid suspension, while the other, on the contrary, had a light diffuser with a soft suspension. The equivalent volume of such a pair, despite all the external similarity, can differ very significantly, and when installed in the same box, the results will be dramatically different.
So, having established what the vital parameters mean, let’s finally begin to choose a betrothed. The model will be like this - we believe that you have decided, based on, say, the materials of the previous article in this series, the type of acoustic design and now you need to choose a speaker for it from hundreds of alternatives. Having mastered this process, the reverse process, that is, choosing the appropriate design for the selected speaker, will be easy for you. I mean, almost without difficulty.
Closed box
As was said in the above article, a closed box is the simplest acoustic design, but far from primitive; on the contrary, it has, especially in a car, a number of important advantages over others. Its popularity in mobile applications is not fading at all, so we’ll start with it.
What happens to the speaker's performance when installed in a closed box? It depends on one single quantity - the volume of the box. If the volume is so large that the speaker practically does not notice it, we come to the infinite screen option. In practice, this situation is achieved when the volume of the box (or other closed volume located behind the diffuser, or more simply put, what is there to hide - the trunk of a car) exceeds the equivalent volume of the speaker by three times or more. If this relationship is satisfied, the resonant frequency and overall quality factor of the system will remain almost the same as they were for the speaker. This means that they must be chosen accordingly. It is known that the acoustic system will have the smoothest frequency response with a total quality factor of 0.7. At lower values, the impulse characteristics improve, but the frequency decay begins quite high in frequency. At large values, the frequency response becomes higher near resonance, and the transient characteristics deteriorate somewhat. If you are focused on classical music, jazz or acoustic genres, the optimal choice would be a slightly overdamped system with a quality factor of 0.5 - 0.7. For more energetic genres, emphasizing the lows, which is achieved with a quality factor of 0.8 - 0.9, will not hurt. And finally, rap fans will have a blast if the system has a quality factor equal to one or even higher. The value of 1.2 should, perhaps, be recognized as the limit for any genre that claims to be musical.
We must also keep in mind that when installing a subwoofer in the car interior, low frequencies rise, starting from a certain frequency, determined by the size of the cabin. Typical values for the beginning of the rise in frequency response are 40 Hz for a large car, such as a jeep or minivan; 50 - 60 for medium, like an eight or a loin; 70 - 75 for a small one, from Tavria.
Now it’s clear - to install in infinite screen mode (or Freeair, if you don’t mind that the latter name is patented by Stillwater Designs) you need a speaker with a total quality factor of at least 0.5, or even higher, and a resonant frequency no lower than 40 hertz - 60, depending on what you bet. Such parameters usually mean a rather rigid suspension, which is the only thing that saves the speaker from overload in the absence of “acoustic support” from the closed volume. Here's an example - Infinity produces in the Reference and Kappa series versions of the same heads with the indices br (bass reflex) and ib (infinite baffle). The Thiel-Small parameters, for example, for the ten-inch Reference differ as follows:
Parameter T/S 1000w.br 1000w.ib
Fs 26 Hz 40 Hz
Vas 83 l 50 l
It can be seen that the ib version, in terms of its resonant frequency and quality factor, is ready to work “as is,” and judging by both the resonance frequency and the equivalent volume, this modification is much tougher than the other one, optimized for operation in a bass reflex, and, therefore, is more likely to survive in difficult conditions Freeair.
But what happens if, without paying attention to the small letters, you drive into these conditions a speaker with the br index that looks like two peas in a pod? But here's what: due to the low quality factor, the frequency response will begin to fall off at frequencies of about 70 - 80 Hz, and the unrestrained “soft” head will feel very uncomfortable at the lower edge of the range, and overloading it there is as easy as shelling pears.
So, we agreed:
For use in the “infinite screen” mode, you must select a speaker with a high total quality factor (not less than 0.5) and a resonant frequency (not less than 45 Hz), specifying these requirements depending on the type of predominant musical material and the size of the interior.
Now about the “non-infinite” volume. If you place a speaker in a volume comparable to its equivalent volume, the system will acquire characteristics that are significantly different from those with which the speaker came into this system. First of all, when installed in a closed volume, the resonant frequency will increase. The rigidity has increased, but the mass has remained the same. The quality factor will also increase. Judge for yourself - by adding the rigidity of a small, that is, unyielding air volume to help stiffen the suspension, we thereby, as it were, installed a second spring, and left the old shock absorber.
As the volume decreases, the quality factor of the system and its resonant frequency increase equally. This means that if we saw a speaker with a quality factor of, say, 0.25, and we want to have a system with a quality factor of, say, 0.75, then the resonant frequency will also triple. What is it like on the speaker? 35 Hz? This means that in the correct volume, in terms of the shape of the frequency response, it will be 105 Hz, and this, you know, is no longer a subwoofer. So it doesn't fit. You see, you didn’t even need a calculator. Let's look at the other one. Resonant frequency 25 Hz, quality factor 0.4. The result is a system with a quality factor of 0.75 and a resonance frequency somewhere around 47 Hz. Quite worthy. Let’s try right there, without leaving the counter, to estimate how big the box will be needed. It is written that Vas = 160 l (or 6 cu.ft, which is more likely).
(I wish I could write the formula here - it’s simple, but I can’t - I promised). Therefore, for calculations at the counter, I’ll give you a cheat sheet: copy and put in your wallet if buying a bass speaker is part of your shopping plans:
The resonant frequency and quality factor will increase in If the volume of the box is from Vas
1.4 times 1
1.7 times 1/2
2 times 1/3
3 times 1/8
For us it’s about double, so it turns out to be a box with a volume of 50 - 60 liters. It will be a bit much... Let’s go with the next one. And so on.
It turns out that in order for a conceivable acoustic design to emerge, the speaker parameters not only must be in a certain range of values, but also be linked with each other.
Experienced people have combined this relationship into the Fs/Qts indicator.
If the Fs/Qts value is 50 or less, the speaker is born for a closed box. The required volume of the box will be smaller, the lower Fs or the smaller Vas.
By external data, “natural recluses” can be recognized by heavy diffusers and soft suspensions (which gives a low resonant frequency), not very large magnets (so that the quality factor is not too low), long voice coils (since the cone stroke of a speaker operating in a closed box , can reach quite large values).
Bass reflex
Another type of popular acoustic design is a bass reflex, which, with all the ardent desire, cannot be counted at the counter, even approximately. But you can estimate the suitability of the speaker for it. And we will generally talk about calculation separately.
The resonant frequency of a system of this type is determined not only by the resonant frequency of the speaker, but also by the bass reflex setting. The same applies to the quality factor of the system, which can change significantly with changes in the length of the tunnel, even with a constant volume of the housing. Since the bass reflex can be, unlike a closed box, tuned to a frequency close to or even lower than that of the speaker, the self-resonant frequency of the head is “allowed” to be higher than in the previous case. This means, with a successful choice, a lighter diffuser and, as a result, improved impulse characteristics, which the bass reflex needs, since its “innate” transient characteristics are not the best, worse than that of a closed box, at least. But it is advisable to have the quality factor as low as possible, no more than 0.35. Reducing this to the same Fs/Qts indicator, the formula for choosing a speaker for a bass reflex looks simple:
Speakers with an Fs/Qts value of 90 or more are suitable for use in a bass reflex.
External signs of phase-inverted rock: light diffusers and powerful magnets.
Bandpasses (very briefly)
Bandpass loudspeakers, for all their loud advantages (this is in the sense of greatest efficiency in comparison with other types), are the most difficult to calculate and manufacture, and matching their characteristics with the internal acoustics of a car with insufficient experience can turn into absolute hell, so with this type When it comes to acoustic design, it’s better to walk the rocks and use the recommendations of the speaker manufacturers, although this ties your hands. However, if your hands are still in a free state and itching to try: for single bandpasses, almost the same speakers are suitable as for bass reflexes, and for double or quasi-bandpasses, they are the same or, more preferably, heads with an Fs/Qts index of 100 and higher.
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19.01.2006 15:47 # 0+

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Parameters Thiele & Small
This is a group of parameters introduced by A.N. Thiele and later R.H. Small, with the help of which it is possible to fully describe the electrical and mechanical characteristics of mid- and low-frequency loudspeaker heads operating in the compression region, i.e. when longitudinal vibrations do not occur in the diffuser and it can be likened to a piston.
Fs (Hz) - natural resonance frequency of the loudspeaker head in open space. At this point its impedance is maximum.
Fc (Hz) - resonance frequency of the acoustic system for a closed enclosure.
Fb (Hz) - bass reflex resonance frequency.
F3 (Hz) - cutoff frequency at which the head output decreases by 3 dB.
Vas (cubic m) - equivalent volume. This is a closed volume of air excited by the head, which has a flexibility equal to the flexibility Cms of the movable system of the head.
D (m) is the effective diameter of the diffuser.
Sd (sq.m) - effective diffuser area (approximately 50-60% of the design area).
Xmax (m) - maximum diffuser displacement.
Vd (cubic m) - excited volume (product of Sd by Xmax).
Re (Ohm) - resistance of the head winding to direct current.
Rg (Ohm) - output impedance of the amplifier, taking into account the influence of connecting wires and filters.
Qms (dimensionless quantity) - mechanical quality factor of the loudspeaker head at the resonant frequency (Fs), takes into account mechanical losses.
Qes (dimensionless quantity) - the electrical quality factor of the loudspeaker head at the resonant frequency (Fs), takes into account electrical losses.
Qts (dimensionless quantity) - the total quality factor of the loudspeaker head at the resonant frequency (Fs), takes into account all losses.
Qmc (dimensionless quantity) - the mechanical quality factor of the acoustic system at the resonant frequency (Fs), takes into account mechanical losses.
Qec (dimensionless quantity) - the electrical quality factor of the acoustic system at the resonant frequency (Fs), takes into account electrical losses.
Qtc (dimensionless quantity) - the total quality factor of the acoustic system at the resonant frequency (Fs), takes into account all losses.
Ql (dimensionless quantity) is the quality factor of the acoustic system at frequency (Fb), taking into account leakage losses.
Qa (dimensionless quantity) is the quality factor of the acoustic system at frequency (Fb), taking into account absorption losses.
Qp (dimensionless quantity) is the quality factor of the acoustic system at frequency (Fb), taking into account other losses.
N0 (dimensionless quantity, sometimes %) - relative efficiency (efficiency) of the system.
Cms (m/N) - flexibility of the moving system of the loudspeaker head (displacement under the influence of mechanical load).
Mms (kg) - effective mass of the moving system (includes the mass of the diffuser and the air oscillating with it).
Rms (kg/s) - active mechanical resistance of the head.
B (T) - induction in the gap.
L (m) - length of the voice coil conductor.
Bl (m/N) - magnetic induction coefficient.
Pa - acoustic power.
Pe - electrical power.
C=342 m/s - speed of sound in air under normal conditions.
P=1.18 kg/m^3 - air density under normal conditions.
Le is the inductance of the coil.
BL is the magnetic flux density value multiplied by the length of the coil.
Spl – sound pressure level in dB.

Re: Thiel-Small parameters and acoustic design of the speaker.

Cool program BassBox 6.0 PRO for calculating the acoustic design of a 12MB speaker, serial number inside in *.txt file:
The program has a huge database of din parameters from a large number of manufacturers, and can calculate the volume taking into account the wall thickness. In general, very comfortable.

Small-Thiele parameters

Small-Thiele parameters
Until 1970, there were no convenient, accessible, industry-standard methods for obtaining comparative data on loudspeaker performance. Individual tests performed by laboratories were too expensive and time-consuming. At the same time, methods for obtaining comparative data on loudspeakers were needed both by buyers to select the desired model, and by equipment manufacturers to more accurately describe their products and reasoned comparison of various devices.
Loudspeaker DesignIn the early seventies, a paper was presented at the AES conference, authored by Neville Thiele and Richard Small. Thiele was Chief Engineering and Development Engineer at the Australian Broadcasting Commission. At that time, he was in charge of the Federal Engineering Laboratory and was analyzing the operation of equipment and systems for transmitting audio and video signals. Small was a postgraduate student at the School of Engineering at the University of Sydney.
Thiele and Small's goal was to show how the parameters they derived could help match a cabinet to a specific speaker. However, the result is that these measurements provide much more information: they can draw much deeper conclusions about how a loudspeaker performs than based on the usual data on size, maximum output power or sensitivity.
List of parameters called “Small-Thiele parameters”: Fs, Re, Le, Qms, Qes, Qts, Vas, Cms, Vd, BL, Mms, Rms, EBP, Xmax/Xmech, Sd, Zmax, operating frequency range (Usable Freq. Range), rated power (Power Handling), sensitivity (Sensitivity).
Fs
Re
This parameter describes the DC resistance of the speaker as measured using an ohmmeter. It is often called DCR. The value of this resistance is almost always less than the rated resistance of the speaker, which worries many buyers because they are afraid that the amplifier will be overloaded. However, because loudspeaker inductance increases with frequency, it is unlikely that the constant impedance will affect the load.
Le
This parameter corresponds to the inductance of the voice coil, measured in mH (millihenry). According to the established standard, inductance measurements are performed at a frequency of 1 kHz. As the frequency increases, the impedance will increase above the Re value, since the voice coil acts as an inductor. As a result, the impedance of the loudspeaker is not constant. It can be represented as a curve that changes with the frequency of the input signal. The maximum value of impedance (Zmax) occurs at the resonant frequency (Fs).
Q parameters
Vas/Cms
The Vas parameter tells you what the volume of air should be, which, when compressed to a volume of one cubic meter, would have the same resistance as the suspension system (equivalent volume). The flexibility factor of the suspension system for a given loudspeaker is denoted as Cms. Vas is one of the most difficult parameters to measure as air pressure changes according to humidity and temperature and thus requires a very high-tech laboratory to measure. Cms is measured in meters per newton (m/N) and represents the force with which the mechanical suspension system resists the movement of the diffuser. In other words, Cms corresponds to a measurement of the stiffness of the loudspeaker's mechanical suspension. The relationship between Cms and Q parameters can be compared to the choice made by car manufacturers between increased comfort and improved driving performance. If we think of the peaks and troughs of an audio signal as the bumps in a road, then the loudspeaker suspension system is similar to the springs of a car - ideally it should withstand very fast driving on a road littered with large boulders.
Vd
This parameter indicates the maximum volume of air that can be pushed out by the diffuser (Peak Diaphragm Displacement Volume). It is calculated by multiplying Xmax (the maximum length of the part of the voice coil that extends beyond the magnetic gap) by Sd (the working surface area of the diffuser). Vd is measured in cubic centimeters. Subwoofers usually have the highest Vd values.
B.L.
Expressed in tesla per meter, this parameter characterizes the driving force of the loudspeaker. In other words, BL indicates how much mass a loudspeaker can “lift.” This parameter is measured as follows: a certain force is applied to the cone, directed inside the loudspeaker, and the current required to counteract the applied force is measured - the mass in grams is divided by the current in amperes. A high BL value indicates a very strong speaker.
mms
This parameter is a combination of the weight of the cone assembly and the mass of air flow moved by the speaker cone during operation. The weight of the diffuser assembly is equal to the sum of the weight of the diffuser itself, the centering washer and the voice coil. When calculating the mass of the air flow displaced by the diffuser, the air volume corresponding to the Vd parameter is used.
Rms
This parameter describes the mechanical resistance losses of the loudspeaker suspension system. It is a measurement of the absorptive qualities of a loudspeaker surround and is measured in N i s/m.
EBP
This parameter is equal to Fs divided by Qes. It is used in many formulas related to the design of loudspeaker cabinets, and in particular to determine which cabinet is better to choose for a given loudspeaker - a closed-back or a phase-reflex design. When the EBP value approaches 100, it means that the speaker is best suited for use in a bass reflex enclosure. If the EBP is close to 50, it is better to install this speaker in a closed enclosure. However, this rule is only a starting point when creating an acoustic system and allows exceptions.
Xmax/Xmech
The parameter defines the maximum linear deviation. The loudspeaker output becomes non-linear when the voice coil begins to move out of the magnetic gap. Although the suspension system can create non-linearity in the output signal, distortion begins to increase significantly at the moment when the number of turns of the voice coil in the magnetic gap begins to decrease. To determine Xmax, you need to calculate the length of the part of the voice coil that extends beyond the upper cut of the magnet and divide it in half. This parameter is used to determine the maximum sound pressure level (SPL) that a loudspeaker can provide while maintaining signal linearity, i.e. the normalized THD value.
When determining Xmech, the voice coil stroke length is measured until one of the following situations occurs: either the centering washer is destroyed, or the voice coil rests against the safety back cover, or the voice coil moves out of the magnetic gap, or other physical limitations of the cone begin to play a role. The smallest of the obtained coil stroke lengths is divided in half and the resulting value is taken as the maximum mechanical displacement of the diffuser.
Sd
This parameter corresponds to the area of the working surface of the diffuser. Measured in cm2.
Zmax
This parameter corresponds to the impedance of the loudspeaker at the resonant frequency.
Usable frequency range
Manufacturers use different methods to measure the operating frequency range. Many methods are considered acceptable, but they lead to different results. As the frequency increases, the off-axis radiation from a loudspeaker decreases in proportion to the diameter. At a certain point it becomes sharply directed. The table shows the dependence of the frequency at which this effect occurs on the size of the loudspeaker.
File:///C:/Documents%20and%20Settings/artemk01klg/Desktop/1.jpg
Rated power (Power handling)
This is a very important parameter when choosing a speaker. It is necessary to know for sure that the emitter will withstand the power of the signal supplied to it. Therefore, you need to choose a loudspeaker that can withstand the power supplied to it with a reserve. The determining criterion for how much power a loudspeaker will have is its ability to dissipate heat. The main design features that influence effective heat dissipation are voice coil size, magnet size, design ventilation, and the high-tech, advanced materials used in the voice coil design. The larger voice coil and magnet provide more efficient heat dissipation, and ventilation keeps the design cool.
When calculating the power of a loudspeaker, in addition to its ability to withstand heat, the mechanical properties of the loudspeaker are also important. After all, the device can withstand the heating that occurs when a power of 1 kW is supplied, but even before reaching this value it will fail due to structural damage: the voice coil will rest against the back wall or the voice coil will come out of the magnetic gap, the diffuser will be deformed, etc. d. Most often, such breakdowns occur when playing too powerful a low-frequency signal at high volume. To avoid breakdowns, you need to know the real range of reproduced frequencies, the Xmech parameter, as well as the rated power.
Sensitivity
This parameter is one of the most important in the entire loudspeaker specification. It allows you to understand how efficiently and at what volume the device will reproduce sound when a signal of one or another power is supplied. Unfortunately, loudspeaker manufacturers use different methods to calculate this parameter - there is no single established one. When determining sensitivity, the sound pressure level is measured at a distance of one meter when a power of 1 W is applied to the loudspeaker. The problem is that sometimes the 1m distance is calculated from the dust cap, and sometimes from the speaker hanger. Because of this, determining the sensitivity of speakers can be quite difficult.
Taken from