I didn't vote either up or down. I can’t for reasons of lack of faith in the device. Against because
feelings of camaraderie. You can brand me with disgrace for the second.
I can say right away that I have not used or even assembled a resonant frequency generator (RFG). I don’t know how it works in practice. The reason is that at that time I already had a generator and a millivoltmeter, and after reading Golunchikov’s article I didn’t understand how the FI could be configured correctly using the GRF. And now I don’t understand. Familiar, but practically did not work.
Let's think about it and carefully read what is written in the articles:
V. Burundukov writes that using this device you can quickly measure the resonant frequency of an acoustic unit. Okay, but how? We started the generator, it generated, so what? How can you determine this frequency? Aurally? Exactly how many hertz are there?
Can anyone answer?
He further writes that resonant frequencies are determined using appropriate measuring instruments. We've arrived. The resonant frequencies are already known. Most likely dynamics without a box. And we are most likely talking about comparing this and that. That is, the meaning of using the device is not completely clear.
As for setting up the FI, everything is clear; all the articles clearly state: lasing occurs at the resonance frequency of the loudspeaker in the corresponding volume. That is, it's not
The resonant frequency of the speaker in open space is the resonance of the system. We put the din in a large volume - resonance one, take a smaller volume, resonance another.
Right or wrong?
The times were long ago, few people knew about Thiel and Small, at least the mathematical calculation of FI was inaccessible. There were different methods, it doesn’t matter.
Speaker Golunchikova it is possible and can be adjusted acceptably, after all, the volume of the box is not small, and even filled to capacity with a sound absorber. that is, the resonance of the dyne in the box should increase slightly. Apparently the same applies to other large speakers.
Let's move on. We are asked to tune the FI to the resonant frequency of the speaker in the box.
Let be. Let Fs (resonance in free space), equal to about 30 Hz, become equal in the box to, well, 40 Hz. We denote the resonance in the box as Fc. In principle, it’s normal; by tuning the FI to this frequency, nothing nasty will happen. It will work, no question. Not entirely accurate, but if you also take into account the room and location of the speaker, everything is fine. The not-smooth theoretical frequency response is not scary; anyway, indoors it resembles mountains at low frequencies.
Now let's take another example and try to configure Saltykov's AS in the same way.
Volume about 9l. Din 6GD-6 or 10GD-34. The resonance (Fs) of these dins is about 80 Hz. Rare examples below. But rare. So, in a 9 liter box the resonance will go above 80 Hz.
I hope no one will argue with this? It is to this frequency that the FI is tuned when using this device. And it is necessary, as you remember, it is necessary (in my opinion) about 50-55Hz.
How do you like it?
Tell me what I'm doing wrong?
Now about the modern one. According to authoritative sources (Vinogradova and Aldoshina are quite authoritative, if not legendary), there is a total quality factor equal to 0.383
, in which the FI is tuned to the resonant frequency of the dyne in open space (not in a box). In this case, the volume of the box is taken to be 1.41 times less than the equivalent volume of the dyne.
That is, the flexibility of the air in the box is less than the corresponding dynamic parameter.
It is probably possible to calculate cases when the FI needs to be tuned to the resonance of the dyne in the box, I think these cases are combinations of unit parameters.
If the quality factor is greater than 0.383, then FI is always adjusted lower than Fs. Without fail.
By and large, FI will always work, the only exception being when it is set so low that FI becomes a closed box with a hole. But this is an unlikely case.
If the entire chain (amplifier, cable to the speakers, and speakers) is built normally, there may even be a hump
It won't hurt the frequency response. Maybe even the increased quality factor of the dyne is not a hindrance. If the other components (PA and cable) can cope with this, there is nothing wrong with the frequency response curve.
If, of course, the ear likes it. All the same, everywhere the final tuning of FI is done by ear.
Something like that. In my opinion, it turns out that the device is useless. Neither quickly measure nor adjust.
The calculation of the bass reflex enclosure (box) can be divided into 3 parts, but before that you need to find the Thiel-Smol parameters for the subwoofer speaker, otherwise nothing will come of it. To calculate the FI of a box, three parameters Fs, Vas and Qts are sufficient
- Fs – resonant frequency of the speaker, indicated in Hz (hertz).
- Vas is the equivalent volume, indicated in liters.
- Qts – total quality factor of the speaker.
These parameters can be found in the instructions for the subwoofer speaker or on the manufacturer’s website.
1. Calculation of the net volume and tuning frequency of the bass reflex port.
Net volume (Vb) is the internal volume of the box, excluding the volume of the bass reflex port and the volume displaced by the speaker.
Port settings (Fb)– this is the configuration of the port (length, width, height) relative to the net volume of the housing, tuned to a certain frequency to amplify it, which leads to the formation of the desired frequency response.
We can make this calculation in the JBL SpeakerShop or BassBox 6 pro programs. I recommend using the first one, it is simpler and much clearer. In the program we enter the parameters Fs, Vas and Qts, then by changing the values of Vb (volume) and Fb (port setting) we achieve the desired frequency response graph. For a universal box, the graph should not be very humpbacked with a peak in the region of 35Hz - 40Hz. If you encounter any difficulties with the program, you can view the instructions for it.
In the program we found out what net volume of the box and port settings we need, in in this example Vb- 45l. Fb- 36Hz.
2. Calculation of the bass reflex port.
We will perform the calculations of the bass reflex port in the BassPort program.
Enter in the program:
- Required frequency of setting the FI port (Fb)
- Previously obtained net volume of the box (Vb)
- Effective area of the subwoofer speaker cone (measured as the length at the center of the speaker from one center of the suspension to the opposite center of the suspension)
- Maximum diffuser stroke in one direction (indicated in the instructions or on the manufacturer’s website as Xmax, can be indicated in one direction or in both directions at once)
- Enter port dimensions W And h
- Click the recalculate button.
In this example, a slot port is calculated, 35 cm high and 4 cm wide, the length of which is 61 cm and has a volume 8.5l. (rounded)
When selecting port sizes, it is impossible for the port length L to exceed 1000 mm, and maximum speed the air coming out was red.
3. We calculate the total volume of the FI body and make a drawing.
We have the following data that needs to be added up to get the total volume of the box (dirty volume) - clean volume 45 liters, port volume 8.5 liters, and we also add here the volume that will displace the speaker itself, this is within 2-4 liters . Let’s take 3L in this case, but since this is a slot port and one of the walls will also displace some volume, it also needs to be taken into account, but here it will be 4L.
To calculate the displacement of the wall, multiply the length of the inner wall of the port by its height and thickness, then divide by 1000.
We count: 45+8.5+3+4= 60.5l.
In total, we need a box with a total volume 60.5l.
Let's move on to the drawing of the box.
We have a volume of 60.5 liters. We measure the trunk, see what dimensions suit us, for example: height - 39cm, length - 50cm, we just need to find out the width. We subtract the thickness of the walls from the height and length, in this case it is 2 cm and we get: height - 35 cm, length 46 cm.
Now we calculate the width of the box: 60,5 1000 ÷ 35 ÷ 46 = 37.57 cm(round up to 38cm) – width of the body, excluding walls, with walls it will be 42cm.
This is how the calculation of a bass reflex enclosure looks like for a specific subwoofer speaker that will play as we need.
The design of enclosures with a bass reflex requires the presence of one or more designed holes. The holes should tune the body to the Fb frequency. This program includes calculation of hole dimensions, which makes this task easier.
There are two types of openings commonly used: ports and ducts. A port is a hole cut into the wall of the case (usually the front wall). The hole can be round, square or rectangular. The duct is usually a pipe that is attached to the wall of the housing (usually the front wall). The duct is usually installed flush with the outer surface of the housing.
Both ports and air ducts must be large enough to avoid the introduction of unwanted sounds, such as whistling, created by turbulence of air moving in and out of the case through the port. The size that has the greatest influence on the occurrence of such interference is the cross-sectional area. Hole nonlinearity reducing output power at high power levels, is also determined by the cross-section being too small. One way to increase the cross-sectional area is to use multiple ports and ducts. The practicality of this method depends on the design you use. The larger the cross-sectional area, the longer the ports or ducts must be. This length often limits the size of the port or duct that can be used in a particular enclosure. This can be one of many challenges when choosing a bass reflex cabinet design, with the cabinet volume Vb and tuning frequency Fb needed to determine the proper bore sizes for a given cabinet.
Excessive duct length can create organ pipe resonance at very high power outputs. Do not use ducts that are too long. One way to reduce the required duct length is to increase the volume of the housing (or the volume of the corresponding chamber). Remember that the resonant frequency of the housing (or chamber) is a derivative of its volume and the dimensions of the duct. If the resonant frequency of the housing is maintained constant, then the smaller the volume of the housing, the longer the air duct should be, and vice versa.
The duct calculation is optimized for ducts in the form of pipes. The algorithm for completing the calculation assumes that the air duct will be fixed flush at one end, and the other end will be far enough from the internal walls to avoid obstructing air circulation. The general rule is to keep the end of the duct at least one diameter away from any side wall or other internal structures. The following table contains some reference values for single duct enclosures.
The minimum duct diameter/area in the table is for loudspeakers that travel a distance close to Xmax. When calculating the duct dimensions, the minimum recommended size is obtained to operate without distortion at maximum movement. Note: The minimum recommended duct diameter for a high frequency port in a cabinet design designed to reproduce a particular frequency band may be larger than indicated in the table because air movement through the port has greater velocity at higher frequencies.
To calculate duct dimensions, select Vent from the Box menu or press Ctrl + V. The Vent Dimensions window will open.
Keep in mind that it has sections for all three bass reflex cabinet designs. If any construct is not used, this section does not appear. Also pay attention to the text instructions. It can be read using the scroll bar.
The Vent Dimensions window is designed to calculate one of two vent sizes, Dv or Lv. First enter the number of ports, select whether Dv will be the diameter or area of the hole, then enter Dv or Lv and the unknown parameter will be automatically calculated. Each of the options is described below.
Vent Parameters
Number: The number of ports you want to use. All ports must be the same size.
Diameter/Area: The size of the first opening, Dv, can be entered as either the diameter (for a circular port or duct) or the cross-section of the opening. By entering this value as an area, you will be able to calculate square and rectangular ports.
Minimum Size: Pressing this button will cause the program to recommend the minimum diameter or area of the duct that will allow you to avoid noise in the hole at maximum speaker deflection. The program also calculates the approximate length of the duct. These recommendations may seem overwhelming because they are based on the maximum deflection of the speaker. If you do not send such a signal to the loudspeaker high level, you can use the more moderate recommendations shown in the table on the previous page.
Dv: Dv can be either the diameter of the hole (if it is circular) or the cross section, depending on which of the Diameter or Area buttons is pressed. Once the Dv value is entered and you move the cursor, the Lv value will be automatically calculated. The Dv value can be entered in inches (square inches if the Area button is pressed) or centimeters (or square centimeters if the Area button is pressed). To change the units of measurement for Dv, double-click the units label.
Important: The hole calculation algorithm is optimized for calculating air ducts with a circular cross-section. It also works well when calculating air ducts with a square cross-section. With a different cross-sectional shape, for example, a rectangle, when the height and width of the hole are not the same, the calculation will not be entirely accurate. It is not recommended to calculate narrow gaps.
If the Dv value is entered as a cross-sectional area, the value will appear in the corresponding column of the housing spreadsheet with the indication "a" indicating the difference between area and diameter. If the enclosure has multiple ducts or ports, the Dv value will be preceded by the number of ports and an x. For example, two 4-inch diameter ducts are designated 2 x 4.00. Two ports with a cross section of 16 inches are designated 2 x 16.00a.
Lv: Duct length. After entering the Lv value and moving the cursor to another position, the Dv value will be calculated automatically. The Lv value can be entered in inches or centimeters. To change Lv units, double-click the units label.
Build a full-fledged sound system any car owner can do it inside a car. Many people install front speakers. This is where it begins high quality sound. They provide natural sound even at low frequencies. When this becomes not enough, they think about using a subwoofer. It emphasizes the depth of bass and increases sound pressure. With the help of a properly selected and installed subwoofer, you can completely change the sound.
Description of the bass reflex
Subwoofers come in a variety of types and quality. But to achieve the highest quality acoustics, it is recommended to design their enclosures. The most popular design method is a closed box and bass reflex. Sometimes sound fans prefer bandpass, passive radiators or acoustic loads. What is a bass reflex and how is it installed? Let’s look at it in detail.
A closed box (box) is the speaker housing. Its volume is comparable to the volume of the column.
A bass reflex for a subwoofer is a design that is a special housing hole. Also, it can be a pipe built inside it that connects the internal volume and the external space. It is otherwise called a bass reflex port. This system differs from a closed box in that it does not dampen vibrations emanating from the back of the diffuser. On the contrary, in this way it complements the radiation. This gives a significant increase in sound.
The bass reflex has another type - passive radiator. The port here is a special system or a simple speaker that is not connected to an amplifier.
Box calculation
The acoustic system, as well as subwoofers, can be easily calculated using online programs. You can simply download them from the Internet. Automatic calculation is carried out by substituting data on sound elements. Here you need to find out information about technical specifications necessary for calculation.
All information can be obtained from the built-in database program. If the characteristics are already known, they are entered manually. Online program It is also convenient because it makes it possible to select speakers that will provide the best output.
The most simple forms The acoustics are a closed box and a bass reflex. It is not necessary for them to know the exact data. Calculation using formulas is enough.
How to calculate a closed box
You will need to find out three main indicators of the dynamics. The result will be the selection of the internal volume of the column. Pay attention to the ratio of the resonant frequency in the passport to the quality factor. If the indicator is less than 100, it is not recommended to install this speaker in a closed box. Since the air is compressed in a locked body, the stiffness of the suspension increases.
Special formulas have been derived that relate the resonant frequency, quality factor and volume: Fc, Qtc, Vb, respectively, with the same parameters in the passport. The formulas can be carefully examined in the photo.
Using formulas, the required volume of the case is selected. It is important to ensure that the resonant frequency of the speakers is not higher than 50 Hz. And the quality factor was approaching 0.7.
How is the bass reflex calculated?
The phase inverter is calculated by selecting speakers whose quality factor is from 0.3 to 0.5, and the resonant frequency ratio is 50 (not less).
In this case, it is necessary to calculate the following parameters:
- Subwoofer volume.
- Cross-sectional area.
- Pipe length and diameter.
- Bass reflex port.
Information about the box is selected using the same formulas as when calculating a closed box. Only here the quality factor of the column differs: from 0.6 to 0.65. The port data is determined using the frequency value at which the bass reflex is tuned. She is chosen along with resonant frequency dynamics. But it could be less. The calculation is carried out using the formulas that are also in the photo.
The calculated length is sometimes longer than the recommended maximum value. But there are ways that help reduce this length. The output of the round bass reflex is placed on the panel plane. This allows for a length gain of approximately 0.85. And the bass reflex pipe has flanges at the end, which can enhance the effect to a greater extent.
Approximately 15% of the length can be saved by placing the bass reflex close to one side of the speaker. If you use the port as a truncated cone (round or rectangular), this will make it possible to reduce the length by 35%.
The above methods are quite simple and do not require complex measuring instruments and mathematical calculations. It is important to consider a few more points:
- the resonance frequency should be slightly lower than the resonance frequency of the speakers located in the box;
- The bass reflex expands the reproduced frequencies towards low frequencies. you need to be able to choose the right one;
- when choosing too low frequencies the output of the speakers will decrease.
In order to configure the bass reflex online, in one of the programs, you will need very accurate data on all parameters. But the program can still produce a large error. Therefore, most users try to adjust the acoustics themselves.
BassPort program, created specifically for calculating parameters bass reflex. Capable of performing calculation Various types of ports: hourglass, funnel, round, round with flanges, slotted, etc. The BassPort program is also equipped with a calculator that allows you to make pre-setting port already in the actual subwoofer box.
The program is an invaluable tool when calculating and creating a bass reflex housing. Knowing the required volume for a specific speaker, and entering the necessary indicators, BassPort will calculate: what length the bass reflex port should have, indicate the air speed in the subwoofer, as well as the volume of air that it displaces.
Description of BassPort
The program is equipped with a simple and clear interface, all required fields for data entry are clearly indicated. Let's look at the interface of this program.
The first thing that catches your eye is the speed of sound value, which by default is 344 meters per second. This field is editable. The next step in calculating FI is to record incoming data in the following windows:
- The bass reflex tuning frequency is indicated in Hz;
- Volume of the subwoofer box, in liters;
- Speaker diffuser diameter (measured at the center of the diffuser corrugation);
- Number of woofers;
- Diffuser stroke (indicator in the speaker passport);
- Number of ports in the case;
- Port cross-section (circle or rectangle).
After entering all the necessary data, click recalculate. Then he presses the next button below, and we get a drawing of the future subwoofer.
