How To Tune A Subwoofer Box
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Subwoofer bass tuning is very important in any good audio system. It takes time and effort to get the type of sound you want from your subs. However, the rewards of a well-tuned subwoofer system are very satisfying. Motivated by that reason, in this article, we shall learn how to tune a subwoofer and a subwoofer box to get the best bass experience.

There are two ways to tune a ported subwoofer box –  mechanically and by using a  mathematical equation.

How To Tune A Subwoofer Box

Before tuning a subwoofer box, you need to assemble the following:

  • Speaker cables
  • Ammeter or high-end multimeter
  • A functional generator
  • Screwdrivers, wire strippers, among other tools

Step 1: Decoupling The Sub

Decoupling involves breaking the direct contact between the sub and the ground to avoid rattling noises that would otherwise disturb the tuning process. Lay down an isolation pad between the sub and the floor or place some decoupling feet below the subwoofer. 

The decoupling feet and pads are spongy and have many air spaces that help absorb vibrations and prevent them from traveling down the floor. This helps enhance the low-frequency response of your subwoofer. In addition, it will help streamline the sub tuning to match your preferences. 

Step 2: Determine The Resonant Frequency

Plug the positive cable of your ammeter into the current socket and set it up to measure current. Take precautions to ensure you are safe from high voltage. 

Connect the ammeter in series between the subwoofer and the amplifier and connect the amp’s inputs to the signal generator. 

Vary the frequency of the signal while watching the ammeter movement. It should read the highest current at the resonant frequency of the box. This is because when the subwoofer reaches its resonant frequency, the impedance significantly drops. 

Step 3: Adjust The Resonant Frequency 

If the resonant frequency you have identified is not your preference, you will need to adjust your box design. It is much easier to do this by decreasing or increasing the length of the port. You will be able to do this with the help of the following equation: 

Fb = the desired tuning frequency of the enclosure in Hertz

Lv = the length of the port in inches 

R = the inside radius of the vent tube

Vb = the internal volume of enclosure in cubic inches

LV = [(1.463 x 10^7 x R^2)/(Fb^2 x Vb)] – 1.463 x R

You can convert the cubic feet to inches by multiplying by 1728. 

Once the port length is changed, recheck the resonant frequency to confirm that the subwoofer box is well-tuned. However, as much as this can be easy to do by yourself, you should consult an industry professional to get proper guidance on the best and safest way to do this.

Best Tuning Frequency For A Subwoofer Box

Tuning of a ported subwoofer box depends on a combination of factors. These include net volume of the box, port area, and port length. The tuning changes the peak frequency and can also change how the box sounds.

Best Tuning Frequency For A Subwoofer Box

For best SPL tuning, you will need to tune your sub fairly high. High SPL tuning is usually 45 Hz or higher. Although the sound quality will not be as good, it will be louder than what you get at a lower tuning.

A good mix between SPL and SQ (sound quality) is better achieved within frequencies lower than 40. At 35 Hz, the box delivers a fair amount of SPL and good sound quality.

How To Tune A Sealed Subwoofer Box To 30Hz

Set the multimeter’s measurement to current and attach it in series in the middle of the subwoofer and amplifier. Use the frequency generator to drive the subwoofer and allow the impedance in the subwoofer box to get low.

The meter reads higher when the subwoofer box is at its resonance frequency. If the resonance frequency measured is higher, tune the box to your desired frequency. You will be able to learn this through trial and error.

Loudest Subwoofer Box Design

If you want to experience the best bass tones, you will need to choose a large subwoofer and fix it in a sealed box. Generally, JBL CS1204B is the best, sealed sub box. With an excellent bass output, it is ideal for both cars and home stereo systems.

How To Find Out What A Subwoofer Box Is Tuned To

You can only be able to find out the tuning point of a subwoofer box by playing a series of test tones around where you suspect it is tuned. You should be able to find the point where the sub moves the least. That frequency is the tuning frequency of the box.

How To Calculate Hz For A Sub Box

The tuning frequency of a subwoofer box is a combination of the volume of the box, air compliance and speaker resonance frequency. Use the formula below to calculate the tuning frequency of your box.

Fb = (A / V)0.31 x Fs


Fb = Hz for the box

A = air compliance

V = box volume

Fs = speaker resonance frequency

Types Of Subwoofer Boxes

There are different types of sub boxes with specific designs. These are:

· Sealed Subwoofer

These boxes are built tightly and are best used to deliver precise and defined bass. They demand more power to run.

· Ported Subwoofer

This type of box utilizes a port to augment law bass response. They are suitable for music such as metal, rock, or any hard-driving music. they are more efficient in delivering deeper bass than sealed ones.

· Free-Air Subwoofer Box

This type of box does not use a particular enclosure. Here, subwoofers are installed on a board that is usually placed in the backseat of a car. The sound quality is however compromised.

Why Tune A Subwoofer Box?

When it comes to tuning a subwoofer system, everyone has their preferences. Tuning your subwoofer box helps you achieve the maximum potential of your sound system.

While professional-grade equipment has a much smaller frequency range (20-80 Hz), a typical car sub can recreate sound frequencies between 20 Hz to 200 Hz.

However, it is recommended that you set up a low pass filter on your amplifier to cut frequencies above 100 Hertz and send them to the mid-range driver through a crossover network.

Also, some of the subwoofers available in the market will recreate bass much lower than 20 Hz. Because this is much lower than the audible range, such subwoofers may not give you a good listening experience. 

The ideal frequency to tune your subwoofer box is 35Hz, as frequencies below this value do not experience lower frequency extension. Besides, lower frequencies require more power to reproduce. In addition, the frequencies around 35 HZ easily pass through walls making a significant impact in the surrounding rooms. 

Before you tune that subwoofer, however, you need to consider some factors to give quality and sweet sound. We have discussed some of these factors below. 

· Location

Before tuning to your desired frequency level, experts’ advice is that you mind the location of your subwoofer box. This will be the determinant of your audio quality. 

· Crossover Frequency

The crossover frequency is the frequency from which a subwoofer starts to play bass notes, and thus your crossover frequency should be put where your speakers begin to roll. You can check this on your subwoofer for specifications. It is made available in modern subwoofers. 

· Size Of The Room Or Car

To achieve an acoustic and quality sound, give much consideration to the size of the area where you want to install your subwoofer, especially if it is a sealed subwoofer.

· The Position Where You Listen From

Do you realize that there are some parts of your room or car that even the low frequencies could sound nearly loud while you can hardly hear them in some parts? Therefore, always be keen when placing your subwoofer box before tuning.