What Should I Set My Subsonic Filter To?

Norvan Martin
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Firstly, to understand how or what to set your subsonic filter to, we have to explain what a subsonic filter is.

A subsonic filter is an audio filter intended to eliminate or attenuate sounds below a particular cutoff frequency. It is also referred to as a low-cut filter or high pass filter. This means they attenuate or “cut” out low frequencies while allowing “high” frequencies to pass through. It is frequently used in audio systems, especially in home theaters, sound reinforcement systems, and recording studios.

A subsonic filter’s job is to filter out extremely low-frequency noise that cannot be heard by humans but can drain amplifier power, degrade speaker performance, and even potentially induce distortion.

These filters attenuate frequencies known as subsonic or infrasonic frequencies, which are ordinarily below 20 Hz.

Below are some provided steps or guidelines on how you can successfully set your subsonic filter:

Step 1: Think About the Content

The settings for your subsonic filter depend on the audio content. Decide what kind of audio content you’ll be using. Different types of content can contain variable levels of low frequencies.

For instance, movie sound effects often have less subsonic effects than music recordings. You can get an idea of the right cutoff frequency by having a good understanding of the content.

Step 2: Check The Specifications

You should check the specifications of your subwoofers and enclosure as they may indicate the recommended subsonic filter frequency range as set by the manufacturer. Normally, the recommended range is a low-pass frequency range (e.g., 20 Hz to 35 Hz).

Step 3: Start with a Safe Setting

Setting the subsonic filter’s initial setting to be around 30 Hz is a typical beginning cutoff frequency because it strikes a good balance between eliminating unneeded low-frequency information and maintaining the natural sound.

To think about this another way, a common starting point is to set the subsonic filter frequency half octave below the enclosure tuning. You can also set it to about 80% of the enclosure’s tuning frequency (e.g., if the enclosure tuning is 35 Hz, set the subsonic filter to 28 Hz which is 35 * 0.8)

Step 4: Audio Evaluation

Play a variety of audio files via your system and pay close attention while you listen to each one. Keep an eye out for any perceptible changes in the sound as well as the low-frequency response.

Determine whether the subsonic filter is successful in minimizing low-frequency rumble, enhancing speaker performance, or resolving the problems you previously noted.

Once you have done that, find specific audio material that contains low-frequency content e.g. movie scenes with deep bass, funk, metal, etc.

Now pay close attention to any signs of distortion or excessive movement of the speaker cone. This might mean low-frequency sounds are playing that are too low for the subsonic filter to manage.

If this happens, turn up the subsonic filter’s frequency a little at a time; which should get rid of those undesirable frequencies. But be careful not to crank it up too much or you might miss out on some good, deep bass sounds.

If your equipment allows slope adjustment, consider trying various settings for this function. It will help you find just the right balance between blocking out the super low sounds and keeping the sound smooth as it moves from one frequency to another.

Step 5: Adjust the cutoff frequency 

You may need to change the cutoff frequency if you discover that low-frequency content is still having an impact on the system.

Reduce the cutoff frequency incrementally (e.g., 5 Hz at a time), listening for audible changes or improvements as you do so. Don’t set the cutoff frequency too low because this could start to influence the ideal bass frequencies or the natural sound.

Step 6: Test Different Audio Content

To make sure your subsonic filter works with different audio content, test it with a range of songs, movies, or other media that you frequently listen to. This will enable you to verify that the filter settings are effective in a variety of situations.

Subsonic filter design


Why Would I Want a Subsonic Filter?

Most people who are a fan of bass find it difficult to exclude subsonic frequencies from their music. Because that is where the window-rattling pleasure lies. But this may mean that they must constantly repair their subwoofers.

Subsonic filter

Although subsonic notes have fantastic sound quality, when they become excessive, they might harm your device.

Your subwoofer may be overtaxed by too many loud bass thuds and degrade much more quickly than it otherwise would.

Is a Subsonic Filter Necessary?

It can be advantageous to utilize a subsonic filter if the audio contains material that produces a distorted sound. Before using such a choice, it is advised to take the following into account:

  • Type of subwoofer: A subsonic filter can guard against harm from low-frequency sound waves to your subwoofer and speakers. If your speakers or subwoofers aren’t made to withstand harmful frequencies, you should employ such a feature to stop them from blowing up.
  • You can notice a rattling sound when listening to music with a lot of low audio frequencies or sound effects. As a result, this function will assist you in avoiding these types of noise.
  • Room acoustics: If you use a strong subwoofer in a small vehicle or room, the bass will be reflected by the acoustics, and you will hear a rattling sound as a result. As a result, you also need to apply a subsonic filter in that scenario.

Should I use a Subsonic Filter on a Sealed Box?

On a sealed box speaker system, a subsonic filter is typically not required or advised. Without the need for extra filtering, sealed box designs naturally offer low-frequency roll-off characteristics that effectively suppress very low frequencies.

The air confined inside the enclosure gives sealed box speaker systems acoustic compliance. Low frequencies below the system’s resonant frequency gradually roll off as a result of this compliance’s high-pass filtering effect.

As a result, the speaker cannot reproduce extremely low frequencies, such as subsonic or infrasonic content, due to the sealed box design.

Applying a subsonic filter to a sealed-box speaker system can not provide many advantages and even have an unfavorable impact.

Is the High Pass Filter the Same as the Subsonic Filter?

Yes, in essence, a subsonic filter is a high-pass filter. Both phrases are frequently used synonymously to refer to a filter that attenuates or eliminates frequencies below a particular cutoff point while permitting frequencies beyond that point to pass through.

In audio engineering and signal processing, the term “high-pass filter” is more frequently used to refer to filters that eliminate low-frequency components so that higher frequencies can pass. It is a general phrase that covers a range of filter designs and uses.

However, the phrase “subsonic filter” refers exclusively to a high-pass filter that is used to filter out subsonic frequencies, which are extremely low-frequency noises that fall below the human hearing threshold (usually below 20 Hz).

Subsonic filters are made to reduce or eliminate certain infrasonic frequencies to avoid problems like mechanical stress, speaker distortion, and power loss.

Subsonic filters can therefore be viewed as a particular kind of high-pass filter that specifically targets subsonic or infrasonic frequencies, notwithstanding a little difference in their utilization.


Subsonic filters are audio filters intended to eliminate or attenuate sounds below a particular cutoff frequency. They are often used in audio systems, especially in home theaters, sound reinforcement systems, and recording studios. To set a subsonic filter, it is important to think about the content and start with a safe setting.

Set the subsonic filter’s initial setting to 30 Hz, evaluate the sound, adjust the cutoff frequency if necessary, and test different audio content to ensure the filter settings are effective in a variety of situations. A subsonic filter is necessary if the audio contains material that produces a distorted sound.

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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