Hi-Fi Fundamentals: What is a woofer?

What is a woofer 

Since the development of the first multi-driver speakers, frequencies have been split between a high-frequency drive unit (the tweeter) and midrange/low frequencies (the woofer) in simple two-way designs.  

In more complex designs, a midrange driver can be added to the mix, leaving the woofer to focus on reproducing the bass frequencies at around the 40–500 Hz range. But even in this configuration, the woofer needs to span quite a wide frequency range in order to ‘reach up’ and integrate with the midrange driver.

And of course in two-way speakers, the woofer will need an even wider upper-frequency extension in order to ‘meet’ the tweeter, while still extending down to the lower frequency limits of the speaker. This is where a subwoofer comes into play... 

Positioning the woofer

In a typical loudspeaker design, the woofer is positioned at the lower section of the front baffle. This placement is not arbitrary; it’s a deliberate choice that supports both acoustic performance and cabinet architecture.

• Bass Distribution: Low-frequency sound waves are naturally less directional than high-frequency ones. That’s why the woofer is typically placed lower on the speaker cabinet, while the tweeter is placed at the top, as close to ear height as possible for the best possible precision, detail and spatial cohesion.

• Cabinet Synergy: The bottom of the cabinet often provides the most space and stability for housing the larger woofer. Designers can take advantage of the extra internal volume to make the woofer interact more effectively with the cabinet’s tuning for optimised airflow, resonance control and pressure management.

What is a subwoofer 

A subwoofer doesn’t take away any of the function of the woofer in your speakers, but it specialises in low bass, from around 100–120 Hz and down. Adding a subwoofer to your setup takes some pressure off your main speakers when it comes to delivering really deep bass – the kind you can feel as well as hear. Also, it often means you can run your setup at a lower volume level without losing any of the sense of weight and susbtance.

Subwoofers have a number of advantages over the woofer(s) built into your main speakers: 

•  Most subwoofers offer a line level input, allowing connection to any amplifier or preamp with a dedicated subwoofer output – whether stereo or a summed mono signal – or via a pair of preout sockets. Some subwoofers offer the option of a ‘high-level’ (or speaker-level) input, allowing them to be connected in parallel with the main speakers in your system.

• Dedicated subwoofer bass drivers are typically larger than those found in even the biggest stereo speakers. This makes them ideal for moving the large amounts of air needed to produce the long wavelengths of very low frequencies.

• Most modern subwoofers are of an active design, meaning they have their own high-power amplification and a low-pass filter on the input. This ensures only the bass frequencies they are designed to handle are sent through the amplification to the driver(s). The filter can be adjusted to tailor the upper-frequency roll-off of the subwoofer to match the lower limit of the main speakers’ frequency response.

The main differences between woofers and subwoofers 

Frequency range and sound output 

As already noted, the functions of woofers and subwoofers are rather different: they both produce bass – and in some of the largest speakers, conventional passive woofers can reach down to the kind of low frequencies managed by some dedicated subwoofers. 

However subwoofers, as the name suggests, are designed to take over where most woofers run out of low-frequency energy at the lowest part of the audible frequency range – this is sometimes referred to as “the final octave”. But they’re not just for fans of church organs or those cannon effects in the 1812 Overture: this extended bass can have a profound effect on the enjoyment of a wide range of music, not just bass-heavy material. 

Design and construction 

While woofers used in main stereo speakers are designed with an eye to integration with the other drivers, the task of a subwoofer is somewhat simpler. It’s all about shifting a lot of air, required for those really low frequencies, swiftly and accurately. 

So whereas even a large floorstanding speaker my feature multiple woofers of 8” or so diameter, subwoofers take it one step further with 12”, 16”, 32” and even larger drivers, especially models designed to carry the low frequency effects (LFE) channel in large home cinema systems. You can even find a 100” subwoofer on the market, if you have the space! 

The requirements of a driver cone for these applications are the same as those elsewhere in a speaker system: stiffness and speed with as little distortion as possible. But with powerful amplification built into an active subwoofer, and an electronically-controlled limited frequency range, absolute lightness isn’t as much of a priority as it is in passive speaker drivers. For that reason, subwoofers can use everything from paper/pulp cones to more exotic materials such as aluminium and even ultra-stiff lightweight weaves such as Kevlar. 

To move sufficient amounts of air, long-throw suspension systems are common in subwooofers. and it’s not unusual for some designs to have multiple drivers or passive bass radiators designed to amplify the effect of the driver. After all, these very low frequencies are much less directional than those in the midband and treble, so a subwoofer is more about energising the air in the listening room, leaving the main speakers to provide all the spatial fine detail. 

Do you need a subwoofer? And are two better than one? 

In smaller listening rooms, you might feel a pair of compact speakers deliver all the bass you need. Meanwhile in larger spaces, big multidriver speakers, perhaps with multiple dedicated bass units driven by powerful amplification, will be more than capable of delivering a substantial, credible sound. And of course you’ll be saving the money involved in buying a dedicated subwoofer. 

However, in many cases you may find you have to run the system at fairly high levels to achieve a satisfying sense of scale and weight, whether you’re listening to rock music or a full symphony orchestra. While speaker designers aim to deliver consistent tonality across a range of volume levels, as a certain Starfleet engineer once said, “Ye cannae change the laws of physics.” Scotty wasn’t talking about speakers, but the point holds: to get convincing bass, you need to move a lot of air. That’s why in HiFi, louder almost always means bigger. 

Paradoxically, the effect of adding a subwoofer to a Hi-Fi system means you can run it at a lower level without losing that bass weight: adding a dedicated bass system, controlled by its onboard electronics, isn’t all about adding more weight and loudness, but rather refining the low-frequency performance of your set-up. 

Furthermore, in some rooms you may find two compact subwoofers will produce a better, more controllable low-end than one much larger model – and will also have the advantage of being easier to hide away for a clean look. After all, that low bass isn’t directional.

Comparing woofers and subwoofers

Here's a short summary of what we've covered...

Typical Frequency Response 

• Woofer: ~40–500 Hz (upper frequency can extend higher with mid/bass drivers in a 2-way design) 

• Subwoofer: 20–100 Hz 

Typical Size 

• Woofer: 4” / 10 cm to 8” / 20 cm 

• Subwoofer: Up to 20” / 50 cm

Design 

• Woofer: Part of a multi-driver configuration in the main speaker 

• Subwoofer: Standalone design, usually driven actively