How To Turn On High Pass Filter (HPF) On Car Amp

How To Turn On High Pass Filter (HPF)

How To Turn On High Pass Filter (HPF) On Car Amp


If you’ve amplified the front and back speech speakers, you’ll need to turn on the high pass filter, which is also known as HPF. This is because the frequency response of the amplified sound will be higher. This is because you’ll need to configure this feature to ensure that no bass is sent to them in order to fine-tune the car amp to provide the best sound possible.

As a result, your car’s speakers will not distort as soon, and the purity of its sound will be improved. Only a treble-connected vehicle amplifier should be used in conjunction with the high pass filter. If the subwoofer is already connected to the amplifier, there’s no need in configuring it because it won’t be playing low-end bass; instead, it’ll be playing voice.

1) On the amplifier, locate the high-pass filter (HPF) switch and turn it on.

2) Take a flat-head screwdriver and hold it in your hand.

3) Increase the HPF’s frequency to 80 hertz. This means that everything over 80 Hz will be played, while anything below that will be considered bass and filtered off for the car sub to handle.

How to Use a Car Stereo Receiver’s High-Pass and Low-Pass Frequency Filters

Many car audio stereo receivers include an integrated and user-adjustable crossover mechanism that distributes specific sound frequency ranges to specific speakers connected directly to the head unit or via low-level outputs for external audio amplifiers. “High-pass” filters limit bass frequencies from mid- to high-range speakers in a “two-way” crossover system, whereas “low-pass” filters only allow low-frequency bass signals to reach larger subwoofers. To maintain speaker longevity and maximum sound quality, the high-pass and low-pass filter settings should be adjusted properly.


Step 1

Have a look at the user manual that was included, if there was one, with your speakers and subwoofers. Note the “frequency response” range of the spectrum. The frequency response range of automobile audio speakers and subwoofers is measured in hertz (Hz) and kilobits per second (kHz). This step does not need to be completed if the car does not already have aftermarket speakers installed.

Step 2

It is important to take note of the frequency slope diagram that is included in the speaker documentation. Take note of the precise frequency at which the graph reveals a dramatic drop in the low-frequency range for high-range or coaxial speakers. Take note of the flattening out that occurs in the curve at high frequencies for subwoofers.

Step 3

Find the correct high-pass and low-pass frequency cutoff values for the speaker system. Think about the cutoff frequency points for the high-pass filter (HPF) and the low-pass filter (LPF) so that you can achieve a “flat” transition between the high- and low-range speakers that are connected to the system. This will result in consistent sound reproduction across all frequencies and speakers.

Step 4

Check the manual that came with your stereo receiver to see if it has any frequency crossover spaces available. Determine the crossover points that are closest and most suited to the speakers. The mounting position of the speakers, the resonant frequencies of the vehicle, and the type of enclosure used for the subwoofer system will all have a significant impact on the final adjustments. Although using the documentation that came with the speakers and receiver to determine the appropriate crossover cutoff points will get you in the ballpark, keep in mind that the mounting position of the speakers will have a significant impact on the final adjustments.

Step 5

After turning on the stereo in the vehicle, use the crossover menu to pick the high-pass filter for the “front” speaker. Select the frequency cutoff setting that works best for you. Make adjustments to the high-pass filter setting for the “back” speaker using the same method. Adjust the low-pass filter on the subwoofer to the appropriate setting. The frequency at which the crossover points for the LPF and HPF settings are set should preferably be the same in order to guarantee a seamless transition between the various speaker components.

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Step 6

Either turn off the subwoofer system or lower the “Gain” setting on the amplifier so that it produces the least amount of volume. Perform music that contains a wide range of sounds, both high and low in frequency. Just before the sound starts to distort, turn the volume up all the way to its maximum setting.

Step 7

While you are seated in the driver’s seat, make any necessary adjustments to the fader and the balance settings. The crossover on the subwoofer should be switched to the “pass-through” or “off” position. Because you will be controlling the low pass filter settings from the stereo receiver, you won’t need to make use of the amplifier’s built-in crossover mechanism.

Step 8

To prevent the sound from becoming distorted, turn the “Gain” control on the amplifier up to its maximum volume. Adjust the volume on the receiver to a point where it is easy to listen to.

Step 9

Put in a frequency test CD that has a test track labelled “sine sweep,” and start the player. A continuous sound will be produced during the listening test, and it will “sweep” between low and high frequencies.

Step 10

It is important to make a note of any variations in the sound levels that occur when switching between the speakers and the subwoofer system. Make adjustments to the “dB/Oct” slope levels for each of the filter settings. Perform the test once again and adjust the crossover parameters accordingly if necessary after each iteration.

While doing so, listen to a range of music and, if you so like, make some minor adjustments to the bass, treble, and other sound field options.

When should I use a high pass filter?

How To Turn On High Pass Filter (HPF) - when to use a high pass filter section image

It is dependent on the type of speaker system that you have as to whether or not high pass filters will be of significant assistance to you or more of a “nice to have” option. In general, you should employ a high pass filter when the following conditions are met:

  • You’re utilising tweeters without a crossover, or the crossover that comes with them isn’t good enough (see the crossover slope section below for more info). 
  • In a car audio system, when you want increased volume and clarity from small speakers while avoiding distortion and “bottoming out” from powerful bass they can’t handle. 
  • For a home audio system with a subwoofer that you want to avoid having too much bass. When employing a powered subwoofer with your main speakers, this is useful to avoid having too much bass. 
  • Bi-amping means bypassing a passive crossover (speaker crossover) and driving each speaker straight from the amplifier channels. 
  • Keeping bass out of small or rear surround home audio speakers that can’t handle deep bass.

When it comes to tweeters, it’s especially important to avoid using low bass frequencies to drive them. Many varieties of midrange speakers fall into the same category. They are unable to cope with the frequency range of particular musical elements, such as bass notes. When driven strongly enough, it creates deformation and can possibly permanently harm them. Bass frequencies necessitate a huge speaker cone, which is impossible to achieve with the tiny cone or dome they have.

What should I set my high pass filter to?

determining speaker crossover frequency section image

It can be perplexing at first, but with a little practise with speakers, it gets a lot easier, thank goodness! I’ll simplify the HPF frequency you should use for each instance in the sections below, as well as provide some remarks to assist illustrate why it matters.

1. Speaker manufacturer recommendations

tweeter speaker recommended frequency use example Manufacturers frequently give specs that inform you what frequency to use as a cutoff. Sometimes the recommended cutoff is plainly mentioned, while other times you’ll have to rely on frequency response data from a speaker. The tweeter, for example, has a useable frequency range of 3.5kiloHertz (kHz) and above, as shown in the image above. If neither is available, the tables below can be used. The good news is that most speakers have information on their frequency response range that you may use to select the high-pass filter.

2. Home audio high pass crossover frequency table

Speaker type/systemCrossover frequency
Main/tower type front speakers (small)60 to 80 Hz high-pass. Works best with a subwoofer to complement them.
Main/tower type front speakers (large)60-80Hz high-pass.
Center or surround sound (small)100-120Hz high pass. These types of speakers are very poor for bass and can distort easily.
Center or surround sound (medium/large)60-80Hz high pass. Most center speakers are not designed for bass production.
On-wall or mini satellite speakers100-120Hz high pass. This helps avoid bad distortion since they can’t handle deep bass.
2-way speaker systems3kHz to 3.5KHz. Very common crossover frequency
3-way speaker systems3.5kHz high pass (tweeter) & 250-500Hz high pass (midrange)
Subwoofer subsonic filter20-30Hz high pass. Useful for vintage audio like vinyl records to block rumble & power-wasting signals.
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Home stereo satellite or rear speaker use


Home stereo rear or satellite speakers (such as surround sound speakers) are typically weak and unable to handle deep bass due to small speaker drivers and a poor enclosure. One of the reasons they sound bad in noisy surroundings, like as movies with surround sound or loud music, is because of this. This is especially true for home theatre systems with single-cone back speakers.

It’s worth noting that the house and car amplifiers you buy might only have fixed settings (non-adjustable). They’re usually similar to what’s stated above, and they’re set up to meet the most prevalent speaker needs.


3. Car audio high pass crossover frequency table

Speaker type/systemCrossover frequency
Front or rear full-range coaxials or component speakers56, 60, to 80 Hz high pass. Blocks low end bass that causes distortion.
Tweeters3-3.5kHz high pass
Midrange or woofer speakers250-500Hz high pass
2-way speaker systems3kHz to 3.5KHz to tweeters. Same for midrange/woofers
3-way speaker systems3.5kHz (mid/treble) & 500Hz (mid/woofer)
Subwoofer subsonic filter20-30Hz high pass. Helpful when you’re dealing with audio power-wasting bass frequencies due to certain audio tracks or equipment.

During bass-heavy music and especially under high power, car audio systems are prone to poor sound, distortion, and “bottoming out.” When a speaker voice coil assembly is stretched to its limits and beyond when trying to produce bass notes, it bottoms out and touches the speaker magnet.

How they help you get better sound

This is a rather typical issue. When coaxial speakers are positioned in a dashboard or door without a decent enclosure, for example, the open-air state implies the speaker cone faces less opposition (no backpressure). This permits the cone to move too freely, resulting in noise, distortion, and in some situations, even damage. This is especially true if you use the bass boost tool, as you may notice distortion right away. High pass filters can completely eliminate this! It also has another advantage: you may push your speakers to their maximum output while maintaining excellent sound quality and volume. When done correctly, this allows you to get the most out of even low-cost speakers.

What crossover slope should I use?

diagram of what is a crossover slope

What is a crossover slope?

The slope of a crossover’s filtering ability is its steepness. In other words, it measures how well it blocks sound past the crossover’s cutoff point. Slopes are measured in decibels per octave, which is represented as “dB/octave.” A negative symbol (-) is used to indicate that the signal has been attenuated or reduced beyond the cutoff point.

We use an octave to measure the range of sound frequencies between two places in audio. A frequency number is doubled or halved every octave. (For example, 100Hz, 200Hz, 400Hz, etc.) When we say a crossover has a -6dB per octave cutoff, we indicate that it will reduce the output by another 6dB for every doubling of the prior frequency. -6dB at 1KHz, -12dB at 2KHz, -18dB at 4KHz, -24dB at 8KHz, -32dB at 16KHz, up to 20KHz are some examples.


What slope filter setting should I use?

In general, a -12dB slope is the ideal option for most speaker systems. I propose at least a 12dB slope, or better yet, an 18dB slope if you have the option, to prevent bass to small speakers or tweeters. The following slopes are the most frequently used:

  • -6dB – common for inline high pass filters on low-cost tweeters, but not very effective in blocking undesirable sounds.
  • -12dB – This is the best option and one of the most prevalent.
  • -18dB – Good for blocking.

Electronic crossovers are usually -12dB (particularly in vehicle amplifiers). When they do, it’s worth experimenting with them to see how they sound with your audio system.

Can I use a high pass filter with speakers that already have crossovers?


using high pass filter with a speaker crossover diagram

Summary – How To Turn On High Pass Filter (HPF)

In most circumstances, you certainly can! In reality, while it is not always necessary, it can be beneficial in some situations. The built-in crossover on a stereo, amplifier, or receiver will work in addition to the speaker crossover already in place. In many circumstances, a steeper slope (better blocking) will result than either one alone. When an amp’s 12dB HPF crossover at 3.5KHz is combined with a tweeter with a 6dB @ 3.5KHz crossover capacitor in situ, the result is an 18dB slope – a steeper and more effective cutoff than you’d get otherwise. However, there are a few key aspects to clarify:

  • If the HPF cutoff frequency is near to the speaker crossover frequency, their slopes will almost always add up.
  • It won’t be as useful if the amp’s HPF cutoff is significantly lower than the speaker’s crossover (or could even be useless). The crossover on the speaker will take precedence.
  • If the HPF is substantially higher than the speaker crossover, the speaker crossover will be essentially ignored because it will not be used. In that situation, the amp’s HPF will take precedence.

If you’re working on an audiophile-level project, you can remove the speaker crossover entirely. This is because phase shift is introduced by crossover components (capacitors and inductors), whereas an electronic crossover does not.

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