What Should I Set My Low Pass Filter To?

Getting that sweet bass sound really isn’t so hard if you know the basics. The right low pass frequency can make a big difference!

In this article, I’ll share what you need to know along with some other helpful info, too!

What should I set my subwoofer low pass filter to?

subwoofer frequency range limit examples image

A subwoofer has a specific range of sound it’s best suited for – pretty much only low-end bass in most cases (this is true for both a home or car audio system). That’s because the cone size is large enough to produce bass audio waves well unlike smaller speakers.

Likewise, a subwoofer (in most cases) is poor at producing high frequency audio in music like vocals or treble due to its limited frequency response. We want to prevent that from happening so choosing the correct cutoff frequency is important.

subwoofer audio frequency range diagram

Home stereo low pass filter crossover frequency settings

Table #1: Recommended home subwoofer low pass frequencies

Woofer type Cutoff frequency
Powered or non-powered (amp) subwoofer 70 to 80Hz
Midbass woofers in a 3-way system 250Hz
Woofers in a 2-way speaker 1.5 to 3.5Khz, depending on the design

A good rule of thumb for a home stereo subwoofer low pass filter (LPF) setting is 70 to 80Hz. Once you’ve set it, adjust slowly and listen for what sounds the best to you.

Ideally you’ll have only pure, clean bass from the subwoofer and hear music or movie sound without any gaps in the audio signal (no areas where bass seems lacking). In some cases, you may need to increase the gain on a powered subwoofer if the level seems too low.

A home receiver’s low frequency effect (LFE channel) output may have some different modes that depend on the mode. Some have a fixed cutoff frequency (especially for surround sound mode) or may offer an adjustable lowpass filter for stereo music playback.

Should I use a high pass filter for my main speakers?

It’s not always necessary but sometimes can help prevent having too much bass. Not all main speakers for a home receiver or home theater receiver can produce bass well. For those that can, it’s possible you’ll end up with “boomy” bass when both your subwoofer and the main speakers are producing it.

In that case, if your amp or receiver has a high pass filter (HPF) option, 60 to 80Hz is often a good choice. It’s always worth trying out to see how it sounds to you as there are so many thin

gs that affect the sound, including the room, carpet vs hardwood floors, and much more.

Car stereo low pass filter crossover frequency settings

Table #2: Recommended car subwoofer low pass frequencies

Woofer type Cutoff frequency
Powered or amp-driven subwoofers 70 to 80Hz
Midbass woofers in a 3-way system 250Hz
Woofers/midbass in a 2-way speaker 1.5 to 3.5Khz, depending on the design and speakers

The same rules also hold true more or less for a car audio system as well. 70 to 80Hz is usually a great choice. As small speakers (especially those installed in a car or truck dashboard or doors) are usually pretty bad for low frequency sound, a high pass crossover can help reduce distortion and provide better sound.

For example, in addition to the low-pass filter for your subs, using a high-pass filter set to about 56-60Hz for the front speakers will prevent them from distorting heavily especially at higher power levels. This also means you can drive them harder for more volume.

Understanding crossover slope options

What crossover slope do you need image of man thinking

A crossover slope is the steepness of a crossover’s filtering ability. In other words, it’s how effective it is at reducing sound frequencies beyond the crossover frequency point.

Slopes, just like the crossover frequency, are categorized in terms of decibels (dB) per octave. A negative sign (-) is used to represent an attenuation, or reduction, of the input signal.

In the audio world, we commonly measure a range of sound frequencies between two points using an octave. An octave is a doubling or halving of a frequency number. (100Hz, 200Hz, 400Hz, etc.)

When we refer to a crossover having a cutoff of -6dB per octave, we mean it will continue to reduce the output by an additional 6dB for every doubling of the previous frequency.

Example: -6dB @ 1KHz, -12dB @ 2KHz, -18dB @ 4KHz, -24dB @ 8KHz, -32dB @ 16KHz, up to 20KHz.

What crossover slope should I use for a subwoofer enclosure?

While you might think “the higher, the better” would be right, things get more complicated once you get past 2nd or 3rd order designs.

Generally speaking, a -12dB crossover slope is often the best choice and works well for most speaker systems. A subwoofer usually sounds very good with a 12dB or 18dB slope.

One reason is that it has a relatively affordable and uncomplicated design but still gives a good cutoff ability. This works great both for single speakers and 2-way speakers.

The most commonly used slopes are:

  • -6dB
  • -12dB
  • -18dB

You’ll find that -12dB per octave crossover slopes are the most common for consumer electronics you buy.

Do I need a subsonic filter?

diagram of how a subsonic filter works

What does a subsonic filter do?

A subsonic filter is a high pass filter with a very low crossover frequency – often around 30 or 20Hz for example. The idea is to prevent bass waves that we can’t hear from being sent to a subwoofer box to prevent wasting power for no reason.

The frequency range for human hearing varies from person to person, but most people can hear somewhere down to around 30Hz or a bit below. 20Hz sound waves can be felt but not heard, so it’s pretty pointless to draw a lot of amplifier power for something you can’t even hear.

Not only this but most audio is mixed with the most enjoyable bass being around 40 to 50Hz or so for “thump” in music and rumbling or action sound in movies meaning 20 to 30Hz isn’t needed.

Do I need to use one?

Generally speaking no you don’t and in fact, in most cases, you won’t hear a difference. However, it certainly won’t hurt anything, and for some audio such as vintage record players where low-frequency rumble is present, it can be useful.

What is a bass boost control? Do I need to use it?

what is a bass boost control diagram

A bass boost control is an optional feature in some home stereos, car stereos, and amplifiers to increase the signal output at a certain point in the subwoofer output signal. It’s very common on today’s car amplifier products but is also sometimes a feature in home receivers.

It’s usually one of a few types:

  • An on/off switch with a fixed boost level
  • A selectable switch (ex.: 0dB, 6dB, 9dB boost)
  • A rotary dial with an adjustable output level, usually up to 12dB

It doesn’t boost all bass frequencies. Instead, it’s centered at a point called the center frequency. This is usually a fixed point at about 45 or 50Hz, right where the most “boomy” or “thumping” bass can be heard in music.

example of a bass boost control on a car amplifier

Are they helpful?

It’s more of a fun thing to have especially if you’d like some extra punch in your favorite music or if you feel your system is lacking in bass performance. Generally speaking, it’s not necessary with a well-performing subwoofer, but it can be nice to have. It’s worth giving it a try to see what you think.

Car amplifiers sometimes include a plug-in remote bass knob that lets you adjust it from the driver’s seat – very handy for when the music you love starts playing!

Why do some amplifiers have bass boost control and some do not?

Including a boost feature is entirely up to the manufacturer and marketing – some customer types would never use it (example: audiophiles for home stereo sound) while others like car audio customers may love having the option.

Marty

About the author

Marty is an experienced electrical, electronics, and embedded firmware design engineer passionate about audio and DIY. He worked professionally as an MECP-certified mobile installer for years before moving into the engineering field. Read more »

Your comments are welcome.
  1. I must say that this is a very interesting and knowledgeable post you’ve made. I’m not a beginner nor am I an expert when it comes to this stuff but this read has really drawn me in and taught me what I was after. I just want to say thanks for your time on this. It’s been a big help!

    Reply
  2. I need your expertize please.
    In my front doors i have a set of components: woofer (50 – 5000 hz), crossover, tweeter (3200 – 30000 hz)
    plus another woofer (39 – 5000 hz). In my amp i have all 4 channels on FULL, which i love the bass coming out of the speakers; but have been advised against it.

    How do i adjust my amp ( has this options: HTF between 25 – 300 hz, LTF between 50 – 500 hz or full) so that i can appreciatte the bass while being safe. Thank you.

    Reply
    • Hello Nuno. Can you please clarify a little bit what speakers you have?

      Do you have 1) a pair of 2-way speakers in the front doors and 2) a separate subwoofer? Are the door speakers connected to 2-way speaker crossovers also?

      If you have component speakers in the front doors and a separate subwoofer it is often best to use these settings:
      • 60-70Hz high pass to the front (door) speakers.
      • Low pass (bass to subwoofer): around 70 to 80Hz.

      You will want to adjust the crossover frequencies on the amp **slightly** to see what sounds best to you (mostly for the subwoofer), but 90% of the time, the ranges I gave should work well. Using a high-pass on the front speakers will prevent distortion from low bass. Also, you can give them more power from the amp for more volume & enjoyment because they will not be forced to produce low bass they cannot handle well.

      Best regards! :)

      Reply
      • I have this speakers:

        https://musway.de/english/ml6.2e.html
        (component speakers)

        plus this:
        https://musway.de/english/mg6.2w.html
        (all in my front doors)

        My question is if i choose htf 60 hertz on all channels, will i be safe?

        The component speakers have a crossover woofer and tweeter
        But my concerne is the other speaker… In htf ill prevent distortion from low bass, but how about the top hertz. Wont 20000hertz destroy it since it only reachs 5000 hz?

        Should i install a processor?

        Thank you for your help?

        Reply
        • Helllo, Nuno.

          – You can use a high pass filter for the front (component) speakers and rear speakers.
          – For speakers that don’t have a full-range output, going above 5,000Hz for example won’t hurt them – just that they usually don’t sound good.

          The MG6.2Ws are woofers so you can use them on dedicated amp channels with a low-pass filter if you like. 60Hz would work but you can try out a bit higher (like 70-80Hz) to see what sounds best. They can be used to compliment the bass lacking from the component speakers.

          You probably won’t need a signal processor unless you want to be able to tune it with an EQ, use time alignment, and so forth.

          Best regards!

          Reply
      • So, this is my full system: ( Soon i’ll add a subwoofer)

        6 channel amp

        Front doors: 1 set component speakers (6 1/2 speaker, croossover, tweeter)
        plus a set 6 1/2 speaker ( no crossover, no tweeter)

        rear deck 6 1/2 speaker ( no crossover, no tweeter)

        My question is: Am i safe in HTF for the speakers that dont have crossovers or tweeters? Since they have a range of 60 hz to 5000 hz? Wont 20000 Hz cause damage? Should i use a processor?
        Thank you.

        Reply
  3. Recommended Settings Help!

    Hi All,

    I own a Mercedes GLA 2019 plate and recently upgraded my speakers and added a subwoofer.

    Front and Rear Speakers and Tweeters: https://www.focal-america.com/product/ps-165-v1/

    Sub Woofer: https://www.focal.com/products/isub-active

    I need some experts on what the actual settings i should set my box in the picture above!

    PLEASE HELP 😭

    P.S. i like my music to sound clear and the bass not to overpower the vocals and instruments. I don’t want the car to vibrate or my music to sound boomy or boxy.

    My current settings:

    Car Head Unit (3 way) EQ:
    Treble: 3
    Mid: 2
    Bass:0

    Fader:+3
    Balance:0

    ISub Active:

    Gain: 1/4 mark
    Subsonic: 25hz
    Bass Boost: 0
    Low Pass Filter: 80hz

    Remote bass control: 3/4 of the way.

    Please advise!

    Reply
    • Hello Anson. Sorry about the delay in replying.

      – You really don’t need the subsonic filter in most cases, although it shouldn’t hurt anything (most music doesn’t contain any bass that low…it’s below what we can hear anyway).
      – If you adjust it with music you’re very familiar with, that’s often one of the best ways to dial in the sound you think is good.

      Mainly, with the EQ to to “flat” (all zeroes), you will want to play music at moderate listening level and increase the gain until the bass level sounds about right. Then adjust the gain until the *general* bass sound matches what the rest of the musical content as you’d expect.

      If it still sounds “thin”, you can then try either the bass EQ feature or try the bass boost on the subwoofer. As a rule you don’t want to use both because it makes adjustment very difficult.

      For a remote bass control, it depends on if it has a center position or not as to what to do. If it does, you set it to the center then make adjustements first. If it only has an increasing range, you can set the bass very high and then turn it down until it’s at a level you’re happy with.

      Generally, you wan to start at “flat” and adjust one thing at a time to avoid having to many tuning variables to affect the sound.

      Best regards!

      Reply
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