Our top picks for subwoofers

What is a subwoofer?

A subwoofer is a speaker that delivers low frequencies, i.e., 20-200 Hz, broadening the soundstage of a mix and allowing you to feel the music and that low-end thump. Although subwoofers can be added to home audio setups to improve your listening experience, in this article, we’ll focus specifically on the benefits of a subwoofer for PA systems.

Subwoofers ensure that the deep resonances of your mix – the bass guitar or kick drum, for example – are heard and felt to their full potential. This means that when you’re performing on stage, your crowd can hear the mix exactly as you intended, with all frequencies in their own space.

It’s not just its output that’s so beneficial, a subwoofer has a positive impact on the rest of the PA system. To put it simply, it takes some of the strain away from the other PA speakers, allowing them to focus on the mid and high frequencies while the subwoofer does the heavy lifting in the lower register.

How do subwoofers work?

In order for a subwoofer to effectively handle the frequencies that standard speakers struggle to reproduce, it needs to be designed slightly differently. It works by using a large woofer driver housed in a specialised enclosure with either a closed, vented, or band-pass design.

Drivers

A subwoofer uses a large driver (woofer) that typically measures from eight to 16 inches in diameter – the larger the driver, the more air it moves, and the greater the bass output.

To move this air, the driver takes electrical signals and turns them into sound waves through a moving coil mechanism. This coil interacts with a fixed magnet, causing the diaphragm to move back and forth, pushing air and generating bass​.

Enclosure design

You’ll tend to find subwoofer cabinets made from medium-density materials like plywood. These are cleverly designed and constructed to reduce vibrations and prevent unwanted resonance, so only clean and accurate bass reproduction is heard.

Closed enclosures are sealed, providing tight and controlled bass with minimal distortion. They require more amplifier power since there is no port to enhance efficiency, but they deliver a natural and accurate low-end response.

Vented enclosures are also known as bass reflex designs. These include a port that extends low-frequency output and improves efficiency, producing louder bass with less power. However, they can introduce resonance and a “boomy” sound if not designed properly.

Band-pass enclosures are basically a hybrid between the two, using two chambers – one sealed and one vented – to boost efficiency within a specific frequency range. They deliver high output with minimal distortion but have a more complex design and limited frequency response​.

Active vs. passive subwoofers

When shopping for a subwoofer, you’ll also come across active and passive designs.

Active subwoofers come with built-in amplifiers, making them easier to integrate with your existing system, while passive subwoofers require an external amplifier​. Active subs are more common than their passive counterparts – this is because subwoofers need more power than standard speakers.

If you were to go with a passive sub, you’d need to make sure to choose an amplifier that can offer enough power.

Crossover filter

A crossover filter is used to ensure that the subwoofer operates only within its intended frequency range. A low-pass filter removes high frequencies, allowing exclusively bass to be played through the sub, and a high-pass filter can be applied to the main speakers to prevent them from handling low-end frequencies.

You’ll need to set your crossover filter properly to ensure a balanced and powerful low-end without overpowering the rest of the mix.

Choosing the right subwoofer

To get the best subwoofer for your setup, look at what PA speakers you already have and the kind of environments you’ll be using the system in.

First, do you want an active or passive sub? If this is your first venture into the world of PA, we recommend active – this takes away the stress of buying a separate amplifier.

Next, what’s your venue? For standard use, we recommend 15 – 18-inch subs, but go smaller or larger depending on the size and capacity of your environment.

You’ll also want to think about wattage and SPL. The bigger the space, the more power you’ll need. But be mindful that higher wattage doesn’t necessarily mean more volume; instead, you’ll want to look at sensitivity – this gives you a more accurate idea of how far the sub can throw those low frequencies.

Sensitivity is worked out by calculating the SPL (sound pressure level, measured in decibels) that a speaker can produce from a 1-watt signal with a 1-metre distance. The subs recommended above all have at least 118 dB SPL – enough for strong bass in mid-sized to large venues.

Of course, frequency response is a significant factor. Consider the type of music you’ll be playing through these speakers and how low you need those frequency reproductions to be. In the same vein, you should look at the crossover frequency.

Look at your other PA speakers and set the crossover frequency to suit. A good place to start is 80 Hz, but you should adjust this to avoid any overlap with the lowest frequencies that your main speakers can handle.

Additionally, look at the connectivity options. Subwoofers offer 6.35mm Jack and XLR options, while passive subs tend to use speakON – and some even come with wireless/Bluetooth connectivity. Choose the one that’s best suited to your setup.

Finally, once you know all the technical details you need, think realistically about the size of the sub and how you’ll transport it around. If you want a portable unit that you can take from gig to gig – go for one that’s easy to carry and perhaps has a built-in handle for transportation.

How to add a sub to your PA system

If you’ve opted for an active subwoofer, connecting it to the rest of your PA is fairly easy as it has a built-in amplifier. Simply connect a line-level signal from your mixer to the subwoofer using XLR or RCA cables, then link the sub to your main PA speakers if required. Adjust the sub’s crossover settings to ensure only low frequencies are sent to it​.

A passive subwoofer requires an external amplifier. Connect your mixer’s output to a crossover unit to split the frequency range. Send the low-frequency output to the amplifier powering the subwoofer, and the mid/high frequencies to the amp for the main speakers. Some setups use a speaker management system for better control over crossover points.

You’ll then want to ensure your sub is placed strategically for optimal sound. A centre front stage position ensures even bass coverage and reduces phase cancellation. If space is limited, an off-centre placement can work but may lead to uneven bass distribution.

For mobile setups, pole-mounted tops are popular. The subwoofers sit on the floor, with the main PA speakers mounted above them on poles, keeping the sound aligned and improving efficiency​.

If you’re setting up in a large venue, you might find it most effective to position multiple subwoofers around the venue, such as stage corners or along the edge of the room. This would provide balanced bass coverage and prevent dead spots.

Once you’ve settled on your setup, make sure to conduct a sound check and alter the sub placement accordingly.

FAQs

Do you need a subwoofer with a speaker?

You don’t always need a subwoofer with a speaker, but if your system is struggling to reproduce the low frequencies of your music, integrate a subwoofer to really get that bass across.

Does a subwoofer improve sound?

A subwoofer gives you a heavier bass response and widens the soundstage, therefore improving the overall sound. Adding a sub is a great way to make sure the bass can be felt and heard.

What are the disadvantages of a subwoofer?

The main disadvantage of a subwoofer is that it can be quite cumbersome to set up. Subwoofers tend to be heavy and bulky and you’ll need to take time to understand which sub will work with the rest of your system.

Final thoughts

If you’re getting into live sound, either as a performer or engineer, you’re probably already well-versed in PA systems. But if you’ve been wondering what exactly a subwoofer is and how it works, we hope this guide has provided everything you need to know.

If you have any questions about a sub you already have, contact us, and if you’re trying to find the right sub for your setup, our list of the best subwoofer brands is a great place to start. For a broader insight into PAs, check out our favourite PA speakers.