Low pass filters can best be described as noise filters for circuits. This doesn’t mean actual noise coming from a circuit, but rather a high-frequency signal passing through the circuit. When the signal enters the low pass filter, the noise is eliminated and the frequency is reduced.
So, in a nutshell, a low pass filter will turn a high-frequency signal into a low-frequency signal. You can literally hear the results of this when you listen to the sounds coming out of the speakers. For example, when you have a high-frequency signal passing through a circuit, and it is so powerful that it causes a hissing sound to be heard from the speaker, then you would want a low pass filter to eliminate the hissing sound. That is the gist of what a low pass filter can do for you.
Electric circuits are made with a cutoff frequency. When the frequency of an energy signal exceeds the cutoff frequency, the flow of energy is reduced by the low pass filter. Electrical engineers refer to this as attenuating the signal. If the frequency of an energy signal is lower than the cutoff frequency, then the energy is allowed to pass through the filter unchanged. The filter design is what really determines the frequency response.
Do not confuse low pass filter with high pass filter because they are the opposite. A high pass filter passes energy signals with a higher frequency than the cutoff frequency. But if the energy signals have a lower frequency than the cutoff frequency, the filter boosts the frequency to the cutoff frequency level. Sometimes a high pass filter will work together with a low pass filter to produce a bandpass filter. This is a filter that only passes frequency signals if they’re within a particular range.
There are many different kinds of low pass filters. For instance, sound recording equipment uses a hiss filter to reduce the noise coming from a sound signal. A lot of lower quality sound recording equipment will generate a hissing sound because the output voltage manipulation is flawed. But if there is a hiss filter present in the speaker or amplifier, then it might do a good job of reducing the hissing.
Anti-aliasing filters are another type of low pass filter. They work to condition sound signals before an analog to digital conversion takes place. In more modern times, you see the rise of digital filters being used in a variety of ways. They help smooth out signals, data sets, and blurred images.
Low pass filter applications are used in sound speaker systems, amplifiers, and equalizers. Their function is to reduce the high-frequency noises, such as the hissing, from coming out of the larger speakers. However, we don’t see low pass filters as often as we used to. With the rise of digital audio technology, there are other mechanisms used to make this function easier.
Analog devices are the most common to have low pass filters in them. Any unwanted signals of higher frequency sounds will be reduced or rejected by the filters. Most analog devices are preconfigured for passing signals through low-pass filters, which are integrated into them.
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When you purchase a speaker, amplifier, or equalizer, it should tell you the cutoff frequency amount in the instruction manual. Some manufacturers may even put this information on the outer packaging of the devices, but not all of them will. You’ll need to look for the information in the manual specifically. That way, you’ll have a better understanding of which electronic devices should be connected to them in order to have the best audio output possible.