This article will tell you how to make a high-pass filter with your own hands. But before we get into this, we need to understand something. What are the high and low pass filters themselves.
Definition
Filters can be divided into upper (high) and lower (low) frequencies. Why do people often say "high" and not "high" frequencies? This happens due to the fact that high frequencies in sound engineering start from two kilohertz. But two kilohertz in radio engineering is the frequency of sound, and therefore it is called “low”.
There is also such a thing as the average frequency. It refers to sound engineering. So what is a mid-pass filter? This is a combination of several of the above devices. It can also be a bandpass filter.
A high-pass filter is an electronic or some other device that passes the upper frequencies of the signal, and which, at the input, suppresses the signal frequency in accordance with a previously set cutoff. The degree of suppression will also depend on the particular type of filter.
Low-frequency is different in that it can pass the incoming signal,which will be below the set cutoff, while at the same time suppressing the high frequencies.
Scope of application
The high pass filter can be used to isolate high frequency signals. It is also often used in the processing of audio signals, for example, in separate filters, which are also called crossover filters. They are also used for image processing so that frequency domain conversion can be performed.
This is what a simple high-pass filter consists of:
- Resistor.
- Capacitor.
The work of resistance on capacitance (R x C) is the time constant (duration of the process) for this filter, which will be inversely proportional to the cutoff frequency in hertz (a unit of measurement of oscillation processes).
Calculating the high pass filter
So how can we calculate? To complete all the steps at home, you need to make one of the simplest automatic calculation tables in Microsoft Excel, but for this you need to be able to use the formulas in this program.
You can use this formula:
Where f is the cutoff frequency; R is the resistance of the resistor, Ohm; C is the capacitance of the capacitor, F (farads).
Types
The presented devices come in five types, and now we will consider them one by one.
- U-shaped - they look like the letter P;
- T-shaped - resemble the letter T;
- L-shaped - resemble the letter G;
- single element (capacitor serves as a filter for highfrequencies);
- multi-link - these are the same L-shaped filters, only in this case they are connected in series.
U-shaped
You can say that these filters are the same as the L-shaped ones, but they are joined in addition by one more part at the beginning. Everything that will be written for T-shaped will be true for U-shaped. The only difference is that they will increase the shunting effect on the radio circuit in front.
To calculate a U-shaped filter, you will need to use the voltage divider formula and add an additional shunt resistor to the first element.
Here are examples of the transition of the L-shaped RC filter to the U-shaped RC filter also high frequencies:
In the image, you can see that another 2R resistor is added to the original circuit, parallel to the first one.
Here is an example of conversion to RL:
Here, instead of a resistor, an inductor will appear. A second (2L) is also added, located parallel to the first.
And the third example - conversions to LC:
T-shaped
T-shaped filter is the same L-shaped filter, only with the addition of one more element.
They will be calculated in the same way as the voltage divider, which will consist of two parts with a non-linear frequency response. Next, to the obtained value, you must add the number of reactance of the third element.
You can also use another calculation method,however, it is less accurate in practice. Its essence lies in the fact that after the obtained value of the first calculated part of the L-shaped filter, the variable grows or falls in doubling and is distributed over two elements.
If it is a capacitor, then the value of the capacitance of the coils doubles, if it is a resistor or a choke, then the value of the resistance of the coils, on the contrary, drops twice.
Conversion examples are shown below.
Transition from L-shaped RC filter to T-shaped:
The image shows that a second capacitor (2C) must be added for the transition.
Transition RL:
In this case, everything is by analogy. For a successful transition, you must add a second resistor connected in series.
Transition LC:
L-shaped
An L-shaped filter is a voltage divider that consists of two components with a non-linear frequency response (frequency response). For this filter, it is allowed to use the circuit and all voltage divider formulas.
It can be represented like this:
If we replace R1 with a capacitor, we get a high-pass filter. You can see a photo of the modified scheme below:
Formulas for calculation:
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U in=U out(R1+R2)/R2; U out \u003d U inR2 / (R1 + R2); R total=R1+R2 R1=U inR2/U out - R2; R2=U outR total/U in |
Nowlet's take a look at how to calculate.
High pass filter for tweeters
The structure of such a filter is quite simple. It will consist of only two parts - a capacitor and a resistor.
The role of the filter, which will filter out the mid-frequency and low-frequency components in the audio signal, will directly play the role of the capacitor itself. And pardon the tautology, resistance will act as resistance, that is, reduce the volume level.
Important: high frequencies are not cut off by the equalizer from the main device - this will lead to bad sound. It is better to reduce their number with resistance.
Optimal resistance will be considered 4.0 and 5.5 Ohm.
Crafting Consumables
To create a high pass filter for the tweeter you will need the following materials:
- one resistance 5.5 ohm;
- one resistance 4.0 ohm;
- two capacitors MBM 1.0uF;
- duct tape or heat shrink tubing.
Active High Pass Filter
Active filters have a huge advantage over their passive counterparts, especially at frequencies below 10 kHz. The fact is that passive ones contain coils of increased inductance and capacitors, which have a large capacitance. Because of this, they turn out to be bulky and expensive, and therefore their performance is far from ideal in the end.
Great inductance is achieved due toan increased number of turns of the coil and the use of a ferromagnetic core. This releases its properties of pure inductance, because the long wire of the coil with a large number of turns has a significant resistance, and the ferromagnetic core is affected by temperature, which greatly affects its magnetic properties. Due to the fact that it is necessary to use a large capacitance, it is necessary to use capacitors that do not have the best stability. These include electrolytic capacitors. Filters, called active, are largely devoid of the above disadvantages.
Differentiator and integrator circuits are built using operational amplifiers, they are the simplest active filters. When circuit elements are selected according to clear instructions, observing the dependence on the frequency of the differentiator, they become high-frequency filters, and on the frequency of integrators, on the contrary, they become low-frequency filters. A photo explaining all of the above is given below:
High pass filter on amplifier
Let's consider setting up an amplifier in a car.
Before you set up the amplifier in the car, you need to reset all the settings of the main device to zero. The crossover frequency must be set in the range of 50-70 Hz. The front channel filter on the amplifier in the car is set to high frequencies. The cutoff frequency in this case is set in the range of 70-90 Hz.
If the design will provide for channel-by-channel amplification of the front speakers, then you need to conduct a separatetweeter settings. To do this, the filter must be set in the appropriate position and the cutoff frequency should be selected in the region of 2500 Hz.
Among other things, you need to adjust the sensitivity of the amplifier. To do this, it must initially be reset to zero, the main thing is to transfer the device to the maximum volume mode, and then begin to increase the sensitivity. At the moment when sound distortion appears, you need to stop turning the knob, and you should also slightly reduce the sensitivity itself.
There is still a simple way to check the sound quality: if, after turning on, clicks are heard in the subwoofer, and crackling in the speaker, this means that there is interference with the signal.
Bass should not be tied to a subwoofer. To do this, turn the phase control on the subwoofer 180 degrees. If this regulator is not present, then you need to swap the positive and negative connection wires.
Set up the sound processor. To do this, you need to adjust the time delays for each of the channels. You need to set a time delay on the left channel so that the sound coming from the left speakers reaches the driver at the same time as the right one. It should feel like the sound is coming from the center of the cabin.
In addition to all of the above, the sound processor can remove the bass binding to the rear of the cabin. In order to do this, you need to set the same delays in the right and left channels of the front acoustics. This will eliminate bass localization around the subwoofer.
Now you know not onlyhow to calculate and assemble a frequency filter with your own hands, but also how to set up its operation as accurately as possible.
