One of the most important settings for a subwoofer is the cutoff frequency for the low-pass filter. As such, people commonly ask, “What frequency should I set my subwoofer low-pass filter to?” In this article, we will discuss subwoofer low-pass filters and the frequency to which you should set them.
In general, it is often safe to set your subwoofer’s low-pass filter to 80 Hz or to a value approximately equal to (or below) 70% of your main speaker’s lowest frequency response. For example, if your speaker’s frequency response goes down to 115Hz, your subwoofer’s low-pass filter should be set to 80.4Hz (70%).
When considering a subwoofer’s low-pass filter setting, you should also ensure that the subwoofer’s low-pass filter is set below the cutoff filter of the AV receiver.
We will discuss this further below.
What Is The Low-Pass Filter Setting On Your Subwoofer?
A subwoofer low-pass filter prevents a subwoofer from playing frequencies above it. For instance, a low-pass filter of 80 Hz will only allow frequencies below 80 Hz to pass through to the subwoofer. This means frequencies above the cutoff frequency Fc (in this case 80Hz) are prevented from reaching the subwoofer driver.
Setting Your Subwoofer Low-Pass Filter Based On The Main Speaker’s Frequency Response
As a general guideline:
- The Low-Pass Filter of a subwoofer should be set at a value approximately equal to (or below) 70% of your main speaker’s lowest frequency response.
- Example: If your speaker’s frequency response goes down to 57 Hz, then 70% of 57 Hz is 39.9 Hz. In this scenario, you might set the subwoofer’s low-pass filter to 40 Hz.
- If unsure of your main speaker’s low-frequency response, start with a 35Hz setting and refer to the manual. If that doesn’t provide clarity, experiment to discover the optimal sound.
On a subwoofer, the low-pass filter setting allows you to tweak the low-pass frequency for both left and right (RCA or speaker level) inputs. This setting doesn’t apply to the LFE (RCA or XLR) inputs. For the LFE inputs, bass management is handled by the audio/video processor.
Through bass management, a subwoofer can relieve your main loudspeakers and amplifier from generating the deepest frequencies. Without this, those frequencies would require significant amplifier power and would limit your dynamics.
Setting Your Subwoofer Low-Pass Filter Based On The Main Speaker’s Size
Here’s a general approach:
- The suggested setting for a subwoofer low-pass filter frequency of 80 Hz assumes the speakers have a diameter of at least 5.25 inches.
- For speakers smaller in size, the frequency for the High-Pass Filter should exceed 80 Hz. The best starting point is 300 Hz. Gradually reduce this value while evaluating the sound quality. Once you identify the sweet spot, maintain that setting.
Layman’s Guide (If you are having a hard time figuring out the above)
Look at the size of your speaker’s woofer:
- For smaller woofers (6 inches or less), set your subwoofer to cover from 20 Hz up to 80 or 100 Hz. If it sounds too boomy, reduce it to below 100 or 80 Hz.
- For bigger woofers (especially 10 inches or 12 inches and above), set your subwoofer to 80 Hz or lower. For example, with a 12-inch woofer that can produce around 40 Hz, set the subwoofer between 60 to 90 Hz.
Remember, these are general guidelines. Some high-quality speakers can handle lower frequencies. Experiment with the settings to find what sounds best. Adjust the subwoofer’s volume to match your system so it complements, not overwhelms, your speakers.
What Frequency Should I Set My Subwoofer Low-Pass Filter To?
Most subwoofers are optimized for handling 50 Hz and below. However, you are generally safe if you set your subwoofer cutoff filter to 80 Hz or so. Many are set to 80 Hz by default. In general, the choice of cutoff frequency is often selectable.
The reason your subwoofer has a low-pass filter is that higher frequencies (above the cutoff frequency) getting to the subwoofer will not be reproduced. Otherwise, this would result in distortion and an undesirable sonic effect.
What About The Low-Pass Filter In My Receiver?
If your subwoofer is connected to a receiver, there’s a high chance your receiver has a built-in low-pass filter as well.
Function of the Low-Pass Filter:
- The subwoofer’s low-pass filter offers additional control, allowing for even finer frequency filtering.
- You should be careful when configuring the AV receiver. Improper frequency settings—either setting the subwoofer low-pass too low or excessively high—can lead to potential issues.
Subwoofer LFE vs Stereo 2.0
In general, a subwoofer will handle either stereo (2 channels: left and right) or multi-channel (LFE In) audio. 
The best subwoofers must offer the ability to connect both Left In/Right In and LFE In. This ensures that you achieve an optimum setup for 2-channel listening while still allowing for multi-channel (movie) mode listening.
LFE is particularly great for watching most movies. In this case, the bass from the surrounds can be fed to the subwoofer using the low-pass crossover settings from the processor’s bass management system.
Low Pass Filter Setting Modes
There are various modes to which you can set your subwoofer low-pass filter:
- Bypass: With this setting, the low-pass filter will pass signals with a frequency lower than a selected cutoff frequency and attenuate signals with frequencies higher than the cutoff frequency. Select this option if you plan to use your receiver/processor’s bass management to set a low-pass filter. Learn more about low-pass bypass filters here.
- Third Order: A third-order filter has a slope of 18dB per octave, which is a slower roll-off than a fourth-order and requires a third-order crossover. Learn more about third-order low-frequency filters here. In case you are using the subwoofer L/R inputs, this option will adjust the roll-off characteristics of your subwoofer’s upper frequencies as they approach the low-pass filter frequency setting.
- Fourth Order: A fourth-order filter has a slope of 24dB per octave, which is a faster roll-off than a third order. In case you are using the subwoofer L/R inputs, this option adjusts the roll-off characteristics of your subwoofer’s upper frequencies as they approach the low-pass filter frequency setting.
Check here to learn more about 4th order low-pass filters.
How To Turn A Subwoofer Low Pass Filter On Or Off
You can turn the low-pass filter for the subwoofer output on or off quite easily. In fact, you can even set the function for each input to which an audio input jack is assigned independently.
You should turn the function on if you connect a subwoofer without the crossover frequency function.
Here is the process:
- Select [Setup] – [Audio Settings] from the home menu.
- Select [Subwoofer Low Pass Filter].
- Select the setting you want.
On: Always activates the low-pass filter with a cutoff frequency of 120 Hz.
Off: Does not activate the low-pass filter.