DIY high-pass filter

This article will talk about how to make a high-pass filter with your own hands. But before we begin to figure this out, 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” rather than “high” frequencies? This is due to the fact that with two kilohertz high begin in sound engineering. But two kilohertz in radio engineering is the frequency of sound, and therefore it is called “low”.

There is also such a thing as average frequency. It relates to sound engineering. So what is a medium-pass filter? This is a combination of several of the above devices. It can also be a band-pass filter.

A high-pass filter is an electronic or some other device that passes the high frequencies of the signal, and which at the input suppresses the frequency of the signal in accordance with a previously defined cutoff. The degree of depression will also depend on the particular type of filter.

Low-frequency differs in that it can pass an input signal that will be lower than a given cutoff, while suppressing high frequencies.

Application area

A 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 conversion in the frequency domain can be carried out.

This is what a simple high-pass filter consists of:

• Resistor.
• Capacitor.

The work of the resistance on the capacitance (R x C) is the time constant (the duration of the process) for a given filter, which will be inversely proportional to the cutoff frequency in hertz (a unit of measurement of oscillation processes).

High Pass Filter Calculation

So how can we make a calculation? To perform all the actions at home, you need to make one of the simplest tables of automatic calculation 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 resistor resistance, 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;
• singleton (capacitor serves as a filter for high frequencies);
• multilink ones are the same L-shaped filters, only in this case they are connected in series.

U-shaped

We can say that these filters are the same as the L-shaped ones, but in addition one more part is attached to them at the beginning. Everything that will be written for the T-shaped will be true for the U-shaped. The only differences are that they will increase the shunt effect on the radio chain in front.

In order to calculate the U-shaped filter, you will need to use the voltage divider formula and add additional shunt resistance of the first element.

Here are examples of the transition of an L-shaped RC filter to a U-shaped RC of also high frequencies:

In the image, you can see that another resistor 2R is added to the original circuit, parallel to the first.

Here is an example conversion to RL:

Here, instead of a resistor, an inductor coils. A second (2L) parallel to the first is also added.

And the third example is conversions to LC:

T-shaped

A T-shaped filter is the same L-shaped, 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, the number of reactance of the third element must be added to the obtained value.

You can also use another calculation method, but in practice it is less accurate. 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 twins and is distributed into two elements.

If it is a capacitor, then the value of the capacitance of the coils doubles, if it is a resistor or inductor, then the resistance value of the coils, on the contrary, drops twice.

Conversion examples are given below.

Transition of the L-shaped RC filter to the T-shaped:

The image shows that for the transition it is necessary to add a second capacitor (2C).

RL transition:

In this case, all by analogy. For a successful transition, you must add a second resistor connected in series.

LC Transition:

L-shaped

A L-shaped filter is a voltage divider that consists of two components with a nonlinear frequency response (amplitude-frequency characteristic). For this filter, it is allowed to use the circuit and all the formulas of the voltage divider.

It can be represented as follows:

If we replace the resistance R1 with a capacitor, then we get a high-pass filter. You can watch the photo of the changed scheme below:

Formulas for calculation:

Now let's take a look at how to calculate.

Tweeter High Pass Filter

The structure of such a filter is quite simple. It will consist of only two parts - a capacitor and a resistance.

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 I'm sorry for the tautology, the resistance will play the role of resistance, that is, reduce the volume level.

Important: high frequencies with the equalizer from the main device will not be cut off - this will lead to poor sound. It is better to reduce their number with the help of resistance.

The optimal resistance will be considered 4.0 and 5.5 ohms.

Spent materials to create

To create a high-pass filter for tweeters, you will need the following materials:

• one 5.5 ohm impedance;
• one 4.0 ohm impedance;
• two MBM capacitors 1.0 uF;
• electrical tape or heat shrink tube.

Active high pass filter

Active filters have a huge advantage over their passive "relatives", especially at frequencies whose value is less than 10 kHz. The fact is that passive ones contain high-inductance coils and capacitors, which have a large capacity. Because of this, they turn out to be cumbersome and expensive, and therefore their characteristics as a result are far from ideal.

Great inductance is achieved due to the increased number of coil turns and the use of a ferromagnetic core. This exempts its properties of pure inductance, because the long wire of the coil with a large number of turns has significant resistance, and the ferromagnetic core is affected by temperature, which significantly affects its magnetic properties. Due to the fact that it is necessary to use a large capacity, it is necessary to use capacitors that have not 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 elements of the circuit 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, low-frequency ones. Photos explaining all of the above are shown below:

Amplifier high pass filter

Consider tuning an amplifier in a car.

Before you configure the amplifier in the car, you need to reset all the settings of the main device to zeros. The crossover cutoff 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 separately configure the tweeters. To do this, the filter must be installed in the appropriate position and the cutoff frequency selected in the region of 2500 Hz.

Among other things, you need to adjust the sensitivity of the amplifier. To do this, it must first be reset to zero, the main thing is to transfer the device to maximum volume mode, and then begin to increase the sensitivity. At the moment when the sound distortion appears, you need to stop the rotation of the control, and it is also worth a little decrease the sensitivity itself.

There is still a simple way to check the sound quality: if you hear clicks after turning on the subwoofer, and crackling in the dynamics, this means that there is interference to 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 wires of the connection.

Customize your sound processor. For this, it is necessary to adjust the time delays for each channel. It is necessary to set the 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 give the impression that the sound is coming from the center of the cabin.

In addition to all of the above, the sound processor can remove the binding of bass to the rear of the cabin. In order to do this, you need to set the same delays in the right and left channel of the front speakers. As a result, bass localization in the subwoofer area will be eliminated.

Now you know not only how to calculate and assemble a frequency filter with your own hands, but also how to configure its operation as accurately as possible.