Enhancing the audio experience: The role of a subwoofer in a home cinema

What is a subwoofer?

A subwoofer is a specialised loudspeaker designed to produce low-frequency sounds and effects, typically in the range of 20 Hz to 200 Hz. Low frequencies are referred to as bass and below those low frequencies we have the sub-bass, which is the subwoofer’s area of expertise. Sub-bass or Low Frequency Effects (LFE) are crucial for reproducing the natural depth of sound, especially for sound effects and musical scores in films. The subwoofer is engineered to handle these deep, rumbling sounds that normal speakers often can’t reproduce effectively or even at all.  

Why do you need a subwoofer in your home cinema system? 

Enhanced movie effects 

In movies, especially action-packed blockbusters, explosions, rumbling engines, and thunderous sound effects are common. Without a subwoofer, these low-end sounds often fall flat or are absent, reducing the overall intensity of the experience. A subwoofer is responsible for delivering these powerful sounds that make you feel the impact and immerse you into the scene. Imagine watching a car chase without the thunderous roars of engines or a battle scene with no booming explosions – it's the subwoofer that brings these elements to life. The typical movie or TV series audio mix will have a separate audio channel dedicated to the subwoofer, called the LFE channel (Low Frequency Effects).  Without a dedicated subwoofer to handle this LFE channel, the low frequencies will be missing important sound information.  

Improved audio balance 

A good home cinema system needs a balance between the high, mid, and low frequencies to sound natural and immersive. Without a subwoofer, the system may lack the necessary depth, especially in the low-end frequencies. The subwoofer complements the main speakers (usually the front and surround speakers) by filling in this gap. It ensures that your home theatre sound system can reproduce the full spectrum of sound, from the softest whispers to the deepest bass notes, creating a more well-rounded and complete audio experience. 

Physical impact 

Subwoofers are not just about sound – they provide a physical experience. The deep bass they produce can create vibrations that you feel throughout your body. This adds a layer of realism to the movie-watching experience, making it feel like you’re part of the action. It’s the difference between hearing an explosion and feeling it. 

Greater sound precision 

Subwoofers are specifically designed to handle low-frequency sounds that regular speakers may distort or struggle to reproduce. By offloading the deep bass from the other speakers, the subwoofer allows the rest of the system to focus on the upper bass, mid and high frequencies, resulting in clearer, more accurate sound across the entire audio spectrum. This improves dialogue clarity, musical detail and overall sound fidelity. 

Musical impact 

Subwoofers aren’t just about movies. They also play an important role in the reproduction of music, especially in genres like rock, electronic, hip-hop or any style with heavy or deep bass elements. In a home cinema setup, they enhance music sequences in films, but they are equally important for creating a powerful listening experience for music tracks. Whether it’s deep drum beat or the low rumble of a synth bassline, a subwoofer brings these musical elements to the forefront. 

How does a subwoofer work? 

Subwoofers typically use a larger driver than regular speakers, which allows them to move more air and generate the low-frequency sounds that smaller drivers can’t. These drivers are powered by amplifiers specifically designed to drive the subwoofer’s output. Depending on your setup, subwoofers come in two types: 

Active subwoofers: These subwoofers have their own built-in amplifier, making them easier to connect to your system. They are the most common type in home cinemas.  

Passive subwoofers: These require an external amplifier to power them and are often used in more advanced or custom home theatre setups. 

Best practices for subwoofer placement 

The placement of your subwoofer can significantly affect its performance. Unlike full-range speakers, subwoofers are considered omnidirectional at low frequencies (typically below 80–100 Hz), meaning their sound is harder to localise. As a result, subwoofers offer more flexibility in placement compared to main speakers. However, finding the right spot in the room is important to get perfect timing and coherence with your main speakers, and to prevent unwanted peaks or dips in the in-room bass response. 

Common subwoofer placement tips include: 

Corner placement: Placing a subwoofer in a corner can amplify the bass due to the reflective surfaces of the nearby walls. Corner placement can often have a good timing but an uneven frequency response. Therefore, corner placement may need a bit of equalization or room correction to work at its best.  

Wall placement: Placing the subwoofer against a wall can help get a full and deep bass reproduction with good timing. The distance to the wall and main speakers can influence the performance so a bit of experimentation with placement is recommended.   

“The Subwoofer Crawl”: As the name suggests, this technique to find the optimum placement of the subwoofer in a room involves crawling! Here’s how to you do it: Place the subwoofer in your main listening position and then crawl around the perimeter of the room while listening for the best bass response. When you have found the perfect spot, place your subwoofer as close to this spot as possible. 

Calibration and timing for optimal subwoofer performance 

When you have found your optimum placement of the subwoofer, it’s time to calibrate it. Since we’re using the subwoofer in a home cinema system, we will calibrate it by using the A/V receiver or home theatre processor.  

Setting distance and phase 

Start by setting the volume of the subwoofer to a level where you can clearly hear it in the mix. For the perfect timing and phase, go to the setup page where you set the distance to all your speakers. Measure the distance from the listening position to the subwoofer cabinet, using a tape measure or a laser measurement gauge.  When you’ve set your measured distance, it’s time to calibrate the subwoofer using your ears.  

Preferably, you should choose music with a continuous and tight bass in the mix. A music track or a concert will work perfectly. Adjust the subwoofer distance in 5-10 cm / 0.16-0.32 feet increments back and forth, while listening for timing. You want the subwoofer to follow the main speakers as precisely as possible, without rushing or dragging relative to the bass rhythm. When you have found the perfect spot, leave the setting there.  

How to set the perfect crossover frequency 

The crossover frequency defines the frequency at which the subwoofer and main speakers hand over the reproduction of sound to each other. If your main speakers are set to “large” in your A/V receiver, they’ll play the full frequency range, and the subwoofer will only play the LFE channel. 

If you set a crossover frequency on your main speakers or set them to “small”, the main speakers will be rolled off with a high pass filter, allowing only higher frequencies to pass through, while the subwoofer will handle all frequencies from the crossover point downward. A good starting point is usually 80 Hz, but fine-tuning the crossover frequency using your ears can greatly improve system integration and overall coherence. Begin at 80 Hz, experiment with 70, 60, 90 and 100 Hz. Trust your ears – choose what sounds best. The goal is seamless integration, making the subwoofer feel like a natural extension of your main speakers, not just added bass. 

Once you've set the correct distance and crossover frequency, adjust the subwoofer volume. You want the subwoofer to be there, but not to be heard all the time. Typically, you want to adjust it a few dBs down from where you had it during calibration.  

Room calibration software for home cinemas 

Many modern home theatre systems also include automatic room calibration systems, which adjust the main system and the subwoofer’s output to account for room acoustics, ensuring optimal bass performance. Many room correction systems also provide automatic distance measurement. As helpful as they are, we still recommend that you validate the settings with your ears and do small adjustments if needed. Some examples of room calibration systems are RoomPerfect™ by Steinway Lyngdorf, Dirac Live and Audyssey.