How To Set The Low Pass Filter On An Amplifier

Norvan Martin
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Electronic circuits called audio filters are used to amplify components of a certain frequency range. This enhances the tone of the output audio and assists in removing unwanted noise from the audio source. To get high-quality sound reproduction for subwoofers or other low-frequency speakers, it is important to set a LOW PASS FILTER on an amplifier.

LPF (Low Pass Filters) are devices within amplifiers that only allow low-frequency signals to pass through them, however, they block all high-frequency signals. As such, low pass filters are used specifically to emphasize the bass frequencies. This is why they use what is called a cut-off frequency or crossover frequency which is the highest frequency that the amplifier will allow. LPFs also remove or reduce unwanted high-frequency noise or distortion from an audio signal by preventing them from reaching the speakers.

Before we continue, if you are setting the low pass filter specifically for a subwoofer, check out our article on what your subwoofer low pass filter should be set to.

Below we will show you how to successfully set an amplifier’s low pass filter:

Step One: Find the LPF (low pass filter)

Depending on the brand or model, the location of the low-pass filter varies between amplifiers. In certain instances, you’ll need to consult the user manual to locate it.

low pass filter on an amp

In most cases, however, the low pass filter will be a knob on the back of the amplifier.

Step Two: Determine the frequency range

Before adjusting the low pass filter in an amplifier, it is important to be aware of the precise frequency range. Please consult the image below to get a better idea of what the low pass frequency range should be for an amplifier:

how to set low pass filter on an amp

Generally speaking, the low pass filter’s crossover frequency should be set to about 80Hz or so. Of course, you can play around with the filter setting to get the best crossover filter setting.

This will enable you to properly select the low pass filter frequency and create a great sound.

Step Three: Set the low pass filter

After successfully identifying the low pass filter’s center, you may set the low pass filter to the required or desired frequency range. You can reach this setting via a remote control or the amplifier control. Depending on the amplifier product or type,

Generally speaking, the Low-Pass Filter should be set at a value that is about equivalent to (or below) 73% of the lowest frequency response of your primary speaker. The frequency response of your speaker, for instance, drops to 45Hz. You should adjust the low pass filter on the subwoofer to 31Hz since 70% of 45Hz is equivalent to 31.

Step Four: Test Run

Once the low pass filter’s frequency has been set as desired, you should test the amplifier to see how well the sound comes out. You can also readjust the amplifier’s frequency range correctly while testing it to create a fantastic sound.

It is crucial to remember that depending on the particular amplifier and speaker configuration, the low-pass filter setting procedure may change. If you are unclear on how to set the low pass filter on your amplifier, it is advised that you consult the owner’s handbook or get expert advice.

To get high-quality sound reproduction for speakers, establishing a low pass filter on an amplifier is a necessary step. Regardless of the music or audio source, by knowing the function of a low pass filter and following the above instructions, you can be sure that your audio system is creating accurate and clear sound.


Low Pass Filter Subwoofer Setting

Setting the low pass filter on a subwoofer is an important part of integrating it with your main speakers for a seamless audio experience. Here are easy steps on how to do it:

  1. Understand the Low Pass Filter: Low pass filters block high sounds and let through just the low sounds (bass) that your subwoofer will play.

  2. Determine the Crossover Frequency: Learn the lowest sound your main speakers can handle by checking their manual or the manufacturer’s website. Set your subwoofer’s low pass filter to match this sound level. Usually, you’ll set it between 80-120 Hz.

  3. Adjust the Low Pass Filter on the Subwoofer: Find the LPF knob or setting on your subwoofer, which might be marked as “LPF” or “Crossover”. Set it to the sound level you decided on before.

  4. Fine-Tuning: Try out some music or a movie and listen. If the bass from your main speakers is too strong or fuzzy, turn down the crossover frequency on your subwoofer. If the bass seems weak or disconnected from higher notes, raise the crossover frequency a little.

  5. Balancing the Volume: Make sure your subwoofer isn’t louder than your main speakers. They should work well together without one drowning out the other.

  6. Experiment and Adjust: Because the way a room is shaped affects sound, test different settings. Move around to different spots in the room and adjust the low pass filter till the sound from your speakers and subwoofer blends smoothly.

Always aim for a smooth blend of sounds from your speakers and subwoofer, giving you a better listening experience.

Find the spot where the deep tones (bass) mix perfectly with the middle and high tones. There should be no clear dips or extra sounds. You may need to tweak it a little here and there until it’s exactly right.

How Does A Low Pass Filter Improve Sound Quality?

Remember, a low pass filter’s purpose is to prevent higher-frequency sounds and let only low-frequency sounds get through to the speakers and subwoofer. By doing so, distortion is less likely to occur and the speaker will only reproduce sounds that fall inside its specified frequency range. It is essential to make sure that the speakers are delivering precise and clear sound by setting the low pass filter to the right frequency range.

The crossover point, or the frequency at which the low pass filter starts to decrease higher frequency sounds, should be taken into account while setting the low pass filter. The crossover point needs to be set at a frequency that is just more or less higher than the speaker’s lowest frequency response.

his helps to improve sound quality and guard against speaker damage by ensuring that the speaker is only reproducing sounds that fall within the desired range of frequencies.

It’s also crucial to keep in mind that different low-pass filter settings may be necessary to produce the best sound quality for various music genres and audio sources. Hip-hop for instance may need a low-frequency range, whereas classical music might need a little high-frequency range.

Advantages Of Low Pass Filter 

Using a low pass filter has many advantages in an amplifier, some of the benefits are listed below

  • One of the most important aspects of using a low pass filter in an amplifier is to prevent distortion in the speaker. This allows only low-frequency sound to pass through the speaker, which makes the speaker produce excellent  and distortion-free sounds
  • Filtering out all the unwanted high-frequency sounds with the use of a low pass filter improves the quality of the sound produced by the speaker, it makes the sounds more clearer and unique.
  • Another advantage of a low pass filter in an amplifier is that it helps protect the speakers from damage. A low pass filter ensures that the speaker produces sounds within the desired frequency, which helps to prevent damage to the speaker over time.

Ways To Use Low Pass Filter When Mixing

Whenever you are mixing sounds low pass filter plays some important role that helps to produce sounds of great quality, some of these roles are listed below:

  • Create Depth: In real life, it might be difficult to hear the person next to you while you’re walking in a noisy place. Similar to how low pass filters function in amplifiers, they are used to add depth to sounds and make them crystal clear by filtering out the top end and lowering the instrument level. 
  • Frequency masking: Low pass filters are used to separate one instrument from another and reduce frequency masking when combining sounds when there are two or more instruments that sound similar. This allows listeners to distinguish the sounds of each instrument.
  • Muffled effect: Low pass filters are occasionally used to provide a muffled quality to sounds, giving the impression that they are underwater. This can help to enhance the originality of the sound mix.

Conclusion

Audio filters are used to amplify components of a certain frequency range, enhancing the tone of the output audio and removing unwanted noise from the audio source. The use of a low pass filter on an amplifier is essential to ensure accurate and clear sound reproduction.

It is important to set the filter to the right frequency range, taking into account the crossover point. If you wish to read more, check out our article on how to set both the high and low pass filter on an amplifier. If you are setting the low pass filter specifically for a subwoofer, check out our article on what your subwoofer low pass filter should be set to.

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Norvan Martin is the founder of BoomSpeaker.com. He is a professional Electronics Engineer and is passionate about home theater systems and AV electronics. BoomSpeaker was created as an online hub to share his knowledge and experiences as it relates to home theaters and home audio electronics. My email: [email protected]  Connect on Pinterest and Linkedin