Almost every professional PA system that's been set up for live music will include one or two subwoofers. The deep thump of an electronic beat or the flowing, sultry notes played by a bassist just wouldn't have half the body-shaking impact they do without the help of subwoofers. If you're looking for a subwoofer complete with an integrated amplifier, audio inputs and its own power port, then you'll need an active sub.
Active Subwoofers
In the first place, a subwoofer is a category of speaker fitted with a single woofer and no tweeter, so it's only designed to produce low bass frequencies. Subwoofers usually have a larger cabinet than standard full-range speakers, and it's the woofer that takes up the most internal space. Because a woofer needs to displace a lot of air to efficiently produce those ultra-low pitched notes, it requires more energy than a full-range speaker set to the same volume level.
8 inch to 18 inch Woofers: Go Big or Go Small?
What's the difference between an 8 inch subwoofer with a 100 Watt peak power and an 18 inch subwoofer with a 100 Watt peak power? Obviously, the 18 inch sub is a lot bigger than the 8 inch, so it's actually able to produce low frequencies with greater efficiency, which is why the 18 inch sub will always sound heavier, while the 8 inch sub will sound more punchy. Unsurprisingly, larger subwoofers are capable of producing higher volume levels as well, because they create more vibrational energy in the space they're set up in. This is why you'll usually see a 12 inch to 18 inch sub set up on larger stages, while smaller venues will opt for a smaller sub to match.
What Speakers Can You Combine with an Active Subwoofer?
When browsing through subwoofers, you'll probably come across terms like '2.1' or '5.1'. These numbers refer to common speaker configurations that are even used at home, so a 2.1 system is two full-range speakers and a subwoofer and a 5.1 system is a set of five full-range speakers and a subwoofer. When it comes to professional sound systems, you'll often see two or four speakers combined with one or two subwoofers, and the subwoofers will be at least a little bit bigger than the speakers. For example, you would team up two 12 inch full-range speakers with a 15 inch sub, or four 8 inch full-range speakers with two 12 inch subs. The configuration is different depending on the size of the space and what the system is being set up for. If you need some advice, then feel free to reach out to our Helpdesk and they can put you in contact with one of our PA specialists.
Connecting Speakers Up to an Active Subwoofer
You can often combine active as well as passive speakers with an active subwoofer, but if you're hooking up passive speakers, there are some things you need to be aware of. Active speakers have their own power input and set of audio inputs, so you'll have no problem plugging them directly into an active sub.
Passive speakers
, on the other hand, don't have a built-in power input or audio inputs, so need to be fed power and an audio signal by the
amplifier
they're plugged into. Some active subwoofers have a bi-amped design, meaning that they have two amplifiers built-in: one to run the sub, and one to run passive speakers. You could also connect the outputs of an active speakers up to an external amplifier which can then be used to feed your passive speakers with power and an audio signal. You can also do it the other way around, by connecting a passive subwoofer up to active speakers. In that case, you need to make sure that the speakers feature a low-pass filter, which can split lower frequencies of the audio signal and send them to the connected sub.
Connecting Active Subwoofers Up to Mixers & Amplifiers
Any active subwoofer will need to be fed an audio signal at line level, so they usually come fitted with balanced XLR and/or TRS jack input. To support optimal performance, you'll need to connect it up to the balanced outputs of your mixer or other audio equipment. Most PA mixing desks will have balanced outputs for a sub, but sometimes, you might be working with gear that doesn't have any balanced outputs, but does have something like an unbalanced RCA output. Using the right adapter cable, you can still connect your subwoofer but because the signal is unbalanced, be aware that it'll be less stable over longer distances.
Can You Get Wireless Bluetooth Subwoofers?
Some active subwoofers feature an integrated Bluetooth receiver, so they can actually be set up as the core of your sound system so you can stream music directly from a phone, tablet or laptop to the sub. Then you can plug a set of full-range speakers into the sub to chain the audio signal and set up your system without needing a mixer to play back music.
Frequently Asked Questions About Active Subwoofers
What's the best active subwoofer?
The best active subwoofer for your sound system will produce around the same level of power and sound pressure level (SPL) as the full-range speakers you want to combine them with. Preferably, you'd use speakers from the same series as the subwoofer and make sure that the speakers are calibrated to one another. To gain the best audio performance, it's better to choose a subwoofer with balanced connection ports, an adjustable high-pass filter and a phase switch.
What's the difference between active and passive subwoofers?
An active subwoofer comes fitted with its own power socket, audio ports, a built-in amplifier and controls for adjusting the tone. Some active subs will also features filters, a crossover, phase switch, a digital sound processor (DSP) and more. Passive subwoofers basically have none of these features.
How do you set up an active subwoofer?
An active subwoofer will usually come fitted with balanced XLR and/or TRS jack ports, two inputs, two high-pass outputs, and sometimes two link outputs. A line level stereo signal is connected to the two inputs while two full-range speakers can be linked via the two high-pass outputs. If it has link outputs, these can be used to chain a second subwoofer, two more full-range speakers or an external amplifier.
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