Low Pass Filter Vs High Pass Filter for a Subwoofer

Norvan Martin
As an Amazon Associate, we earn from qualifying purchases made on our website.

One of the most important ways to get rich, powerful bass is to adjust the audio filters. When used well, they may add space and clarity to your mix. 

So what is a filter? A filter is a method for applying a predetermined EQ (equalization) shape to your sound. This type of filtering device is often used in music studios to make dynamic music sounds. A subwoofer filter is important because it helps the subwoofer to produce a clean and clear sound.

This is done by either reducing (blocking) or boosting (passing) a certain frequency region so that you can shape individual sounds to your liking. A low pass filter is used to pass through low frequencies and block high frequencies while a high pass filter is used to block low frequencies and pass high frequencies. As such, the name of the filter depends on how you boost or decrease particular frequencies. 

Low Pass Filter vs High Pass Filter Comparison Table

CriteriaLow-Pass FilterHigh-Pass Filter
Frequency RangeAllows Low FrequenciesAllows High Frequencies
Crossover SlopeVariable SlopeVariable Slope
Crossover Point ControlAdjustableAdjustable
Integration with Main SpeakersSeamless IntegrationSeamless Integration
Filter TypeVarious Types (e.g., Butterworth)Various Types (e.g., Linkwitz-Riley)
Phase AlignmentMay Include Phase AlignmentMay Include Phase Alignment
Signal DelayMinimal DelayMinimal Delay
Filter Quality and DistortionHigh QualityHigh Quality
Ease of AdjustmentUser-Friendly ControlsUser-Friendly Controls
low pass filter
Low pass filter
high pass filter
High pass filter

For your subwoofer, your low pass filter should be set to a value that is about equivalent to (or below) 70% of the lowest frequency response of your main speaker. In practise, this is often about 50Hz – 80Hz. On the other hand, your high pass filter should not be set for your subwoofer because it will cut out the bass.

Read on if you want more details.

The Fundamentals Of A Filter

Cutoff Frequency

This determines the frequency range around which the filter will be applied and is sometimes referred to as the crossover frequency.

A low pass filter allows frequencies below the cutoff frequency and a high pass filter allows frequencies above the cutoff frequency.

Resonance

The Q or Bandwidth parameter, also known as resonance, determines the importance of the frequencies close to the cutoff point. Filters with high “Q” will amplify the signal at the cut-off frequency and thereby narrow the filter’s effective bandwidth.

Setting the Q point too high can create unpleasant frequency resonances, so pay extra attention to this setting. 

Slope

The Slope controls how steep the current audio filter type is. A steep slope will suddenly increase or decrease frequencies, but a gentle slope will be more gradual. The typical slope for a subwoofer is a 12 db or 24 db slope.

Low Pass Filter vs. High Pass Filter

An audio filter is built on a predetermined EQ shape that will add or subtract frequencies.

The filter’s name is subsequently given by the selected shape. Let’s look at the most popular ones and see how you might use them in your music.

Low-Pass Filter

As its name suggests, a low-pass filter will allow frequencies below the cutoff threshold to pass. A low-pass filter also called a high-cut filter, eliminates frequencies that are higher than a specific cutoff.

low pass filter

For components that are too high in your mix, it is advisable to apply a low-pass filter.

What Setting On My Subwoofer’s Low Pass Filter Should I Use? 

Your subwoofers receive low frequencies through low-pass filters. Typically, you should set your low pass filter to 80 Hz (12 dB or 24 dB Slope).

To be more precise, you should set the Low-Pass Filter to a value that is about equivalent to (or below) 70% of the lowest frequency response of your main speaker. If your speaker’s frequency response drops to 60Hz, as an illustration.

You should set the low pass filter on the subwoofer to 42Hz since 70% of 60Hz is equal to 42.

High-Pass Filter

A high-pass (or low-cut) filter, on the other hand, will eliminate frequencies that fall below a specified threshold. As such, your high pass filter should not be set for your subwoofer because it will cut out the bass.

high pass filter graph

Frequency filters known as high-pass filters allow high frequencies from input sources to pass while blocking low frequencies. Numerous audio applications and gadgets require these bandpass filters. They purge signals of undesired noise and isolate particular frequencies for amplification, filtering, or other operations.

Because they remove the lows while keeping the highs, they are also low-cut filters. In other words, high-pass filters let in higher frequencies while blocking out lower ones. Moreover, they are found in all modern audio systems.

A high-pass filter helps;

  • To prevent low-frequency bass from being heard by the main speakers so that subwoofers can control it for better sound quality.
  •  Prevents bass-related distortion or damage to tweeters
  • Use small speakers and tweeters to produce audio that is more powerful and clear

When to Use a High Pass Filter

You should use a high pass filter;

  • For a home audio system that uses a subwoofer and you want to avoid having too much bass. This is useful to avoid having too much bass when using a powered subwoofer in addition to your primary speakers.
  • Preventing bass from reaching surround speakers at the back or small rooms of a home that are incapable of producing deep bass.
  • Removing a passive crossover (speaker crossover) to drive the speakers directly from amplifier channels.

How to Set High-Pass and Low-Pass Frequency Filters

The precise procedures you must take to make the low-pass and high-pass filter settings are listed below:

  1. To determine the appropriate frequency response (measured in Hz and kHz), consult the owner’s manuals for your subwoofers.
  2. Focus on the reduction in the high-frequency slope.
  3. Pick the most appropriate frequency cutoff option.
  4. Adjust the LPF to have the same frequency as the HPF.
  5. Adjust the amp Gain to the lowest setting. Play music that features both low and high-frequency ranges, and then adjust the volume to the highest and most precise position.

The primary distinction between high-pass and low-pass filters is that the former passes signal with frequencies higher than the cut-off frequency, whereas the latter does so with frequencies lower than the cut-off frequency.

Other types of audio filters are;

3. Band-Pass Filter

A low-pass and a high-pass audio filter are simply combined to form a band-pass audio filter.

4.  Shelf Filter

A shelf filter can be a preferable choice if high-cutting or low-cutting is too extreme. The frequencies are effectively placed on a flat “shelf” and then are either amplified or muted after that.

How Do I Align The Receiver Volume With My Subwoofer Level?

You should turn up your receiver’s volume to match your sub-level to the receiver volume. Make sure there are no distortions. Continue and gradually increase the sub amp’s gain until you begin to hear a balanced sound.

If it doesn’t help, try adjusting the level slider slightly up and down to check if the subs are merging their sounds.

Conclusion

You now possess the necessary knowledge and suggestions needed to configure the high-pass and low-pass frequency filters for subwoofers. Depending on your need, you can align your receiver volume with the subwoofer level, shape your sound  and enjoy your music just as you want it. If you want more general information on how to set a high pass and low pass filter on a car stereo, check out this article.

Share This Article
Follow:
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