A subsonic filter is a type of high-pass filter or bass filter that is designed to prevent the subwoofer or bass driver from reproducing audio frequencies that are below its safe operating range. This is achieved by allowing frequencies above the set cutoff frequency to pass through while attenuating (making quieter) or blocking frequencies below that cutoff frequency.
Subsonic frequencies are audio frequencies that are considered to have a frequency lower than the lower limit of human hearing, and they are often referred to as infrasonic frequencies. Generally, the subsonic filter plays an important role in maintaining audio system performance, and protecting the subwoofer and other components from damage, while enhancing overall sound quality.
This blog post will highlight the importance of the subsonic filter and provide a detailed guide on how to set the subsonic filter on your subwoofer.
Importance of Subsonic Filter
Protecting the subwoofer
Subwoofers are designed to reproduce low-frequency audio content, usually below 100 Hz or even lower. However, some subwoofers may not be capable of handling extremely low frequencies, such as those below 20 Hz, without risking damage to the speaker cone due to over-excursion.
This is where a subsonic filter comes in to help prevent the subwoofer from reproducing frequencies that are outside its safe operating range, thus protecting it from potential damage caused by excessive cone movement or overloading.
Preventing amplifier overload
Generally, subsonic frequencies require a significant amount of power to reproduce. If the amplifier driving the subwoofer is not designed to handle these frequencies, it may become overloaded and distort or clip. This can result in poor audio quality or irreversible damage to the amplifier.
A subsonic filter can help reduce the load on the amplifier by blocking or attenuating subsonic frequencies that the subwoofer cannot effectively reproduce, which in turn helps to prevent amplifier overload and distortion.
Enhancing audio clarity
Subsonic content, such as very low-frequency rumble or infrasonic vibrations, may not be audible to human ears, but can still impact audio quality. These frequencies can cause unwanted resonances, rattling, or buzzing noises in the subwoofer or other parts of the audio system, leading to reduced audio clarity. Luckily, the subsonic filter can help minimize these unwanted effects, by allowing the subwoofer to reproduce only the intended low-frequency content, resulting in clearer and more accurate audio.
Reducing power consumption
Amplifiers driving subwoofers consume more power when reproducing subsonic frequencies, which may not be necessary or desired for some audio systems or listening environments. By using a subsonic filter to block or attenuate subsonic content, the power consumption of the amplifier can be reduced, resulting in more efficient operation and energy saving.
Improving system integration
Subsonic filters can also be useful in optimizing the integration of a subwoofer into an audio system. By setting the cutoff frequency of the subsonic filter to match the capabilities of the subwoofer and the characteristics of the audio content being played, it can help ensure that the subwoofer is operating in its intended frequency range while complementing the performance of other speakers in the audio system and providing a more balanced and cohesive audio experience.
What Does Subsonic Mean on an Amp?
In the context of an amplifier, a subsonic filter on an amplifier is used to prevent these low-frequency signals from being amplified and reproduced by speakers, including subwoofers, as they may cause issues such as over-excursion of speaker cones damage to speakers, amplifier overload, and unwanted resonances or vibrations.
Subsonic filters are commonly used in amplifiers to ensure that only audible frequencies are amplified, thereby optimizing their performance. The subsonic filter on an amplifier can typically be adjusted or set to a specific cutoff frequency, which determines the point at which the filter begins to attenuate or block the low-frequency signals.
The cutoff frequency is typically set slightly below the resonant frequency of the speakers being used, to prevent speaker cone over-excursion and potential damage while still allowing for accurate amplification of audible low-frequency content.
How to Set Subsonic Filter
Setting a subsonic filter in an audio system typically involves adjusting the cutoff/crossover frequency of the filter to a level that meets the specific requirements of the audio system and the type of audio content being reproduced. Here’s how you can set a subsonic filter on a subwoofer;
Identify the crossover frequency
The crossover frequency is the frequency below which the subsonic filter will start attenuating or removing signals. Generally, the optimal crossover frequency will depend on your specific audio system and the type of audio content you are playing.
As we have mentioned, the common starting point is around 20 Hz, which is the lower limit of human hearing. However, you may need to adjust it higher or lower based on your speakers, amplifiers, and audio content.
Locate the subsonic filter control
Check the specifications or user manual of your subwoofer or audio source to determine if it has a subsonic filter and where it is located in the settings. The subsonic filter is often labeled as ‘subsonic’ ‘low cut’ or something similar. This feature is often located in the settings or control panel of your subwoofer.
Adjust the cutoff frequency
Once you have identified the subsonic filter control, adjust it to the desired cutoff frequency. This is usually expressed in Hertz (Hz) and determines the frequency below which the subwoofer will not reproduce sound.
Adjusting the frequency is achieved by turning a knob, selecting a switch, or inputting a value in a digital interface. As a general guideline, you can set the subsonic filter frequency to be slightly lower than the lowest frequency that your subwoofer is designed to reproduce.
For example, if your subwoofer is rated to reproduce frequencies down to 20Hz, you may set the subsonic filter frequency to around 15Hz. As such, it’s important to consult your subwoofer’s specifications and recommendations to determine the optimal setting.
Fine-tune and test
After setting the cutoff frequency, listen to the audio content being played and make adjustments as necessary. Play audio through your subwoofer and listen for any improvements in sound quality or reduction in distortion. If needed, you can fine-tune the subsonic filter frequency by repeating the steps above and making minor adjustments until you achieve the desired performance.
Play some audio content that includes deep bass frequencies, and listen to the performance of your subwoofer. If you notice any distortion or muddiness in the bass, you may need to further fine-tune the subsonic filter frequency. You can try adjusting it up or down slightly to find the optimal setting that provides clean and clear bass without overloading the subwoofer with frequencies it can’t handle.
Repeat for multiple subwoofers
If you have multiple subwoofers in your audio setup, you’ll need to repeat the above steps for each subwoofer individually, as they may have different recommended subsonic filter frequencies.
Parting Shot!
The primary purpose of a subsonic filter is to protect the subwoofer from trying to reproduce frequencies that are below its capabilities, which can result in distortion or damage to the subwoofer. The setting for a subsonic filter should be chosen carefully to strike a balance between removing unwanted low-frequency content and preserving the overall audio quality. By experimenting with different settings and listening for any audible changes in audio quality can also help in finding the optimal subsonic filter setting for your system.
