How to Connect a Subwoofer

We could all use some tips on connecting a new subwoofer to an amplifier or AV receiver, no matter what brand of subwoofer we choose.

Most AV receivers have two types of outputs: Subwoofer and LFE Output. On the surface, both connections may look as though they have the same function. But they are actually quite different. 

Subwoofer Output

This is a line-level output that can typically be connected to your subwoofer via an RCA-type connector. The output can be full-band, in which case the crossover in your subwoofer would filter out the high frequencies. Or, your receiver may have a built-in low-pass filter you can set before sending the signal to the subwoofer. If your receiver allows you to adjust the crossover frequency, set it there and position the subwoofer crossover as high as it will go (this will allow the crossover control from the receiver to play without interference from the subwoofer).

In a Dolby or DTS mix, the subwoofer output contains bass information from up to six channels, all of which are directed to the subwoofer. The combination of bass information in the subwoofer output is determined by the bass management settings selected on the receiver.  Specifically, the subwoofer output may include the bass information from the front channels when those speakers can’t reproduce the bass frequencies.

Connectors

Subwoofer outputs can use up to two connectors. If your receiver has one connector and your subwoofer has two, use the left connector. It's also good practice to use an RCA Y-adapter to connect to the left and right channels – some subwoofers will only play at half the volume or may enter standby mode more frequently if you use only one side of the input. KEF’s SmartConnect subwoofers (Kube, KF92, KC62) feature circuitry that compensates for this, so whether you use one connector or two, your output will remain uncompromised. 

LFE Output

The LFE channel carries additional bass information for movie and soundtrack playback, which supplements the bass information going to the main channels. The LFE channel is mixed during soundtrack production to produce 10 dB higher bass SPL than any one of the three front channels. Even if all three front channels are active, the LFE channel alone produces enough bass to balance the subwoofer, along with the front channels. This lessens the bass load on the main channels, which helps overall response and articulation and clarity in the front channels. When the fronts are required to produce full bass, the LFE channel may increase the bass output by up to 6 dB.

The LFE channel is typically one connector, so follow the connection instructions as above.

Speaker Level Input

If your AV receiver does not have a dedicated subwoofer output,  be sure to choose a subwoofer that has speaker-level inputs (like any one of these KEF subwoofers).

Speaker-level input subwoofer connections can be set-up in two ways:
  1. Connect the subwoofer via the ‘B’ or second speaker output. This is for subwoofers that do not have a secondary output to your speakers. Be sure your receiver can run both ‘A’ and ‘B’ speakers simultaneously.

  2. For subwoofers equipped with a speaker-level input and a speaker-level output, simply connect the receiver speaker outputs to the speaker-level input on the subwoofer, and then the speaker-level output of the subwoofer to your speakers. Make sure that the receiver’s crossover is set to 20Hz or ‘off’ as the crossover in the subwoofer will act as the system crossover for the sub and speakers in this configuration.

No Subwoofer Output?

If your gear is slightly older than 10 years, it's likely that you won't have a Tape Monitor output. However, you may well have a subwoofer output. If your receiver doesn’t have an output for your subwoofer, and your subwoofer doesn’t have speaker level inputs, you can use the Tape Monitor or Pre-Amp output from your receiver as a line-level input to your subwoofer. 

Phase Switches

Some subwoofers have a phase switch. These are generally set to ‘0’, but depending on a few variables, may need to be set to ‘180,’ or somewhere in-between. There's an easy way to figure this one out: play your favourite song on each setting. Listen carefully, and you'll hear a definite increase in bass frequencies in one setting over the other. When you hear that increase, you'll know you've found the right setting. 

Kube 12b

Subwoofer

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Kube 10b

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Kube 8b

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KF 92

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KC 62

Subwoofer

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Kube 12b

Subwoofer

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Kube 10b

Subwoofer

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Kube 8b

Subwoofer

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KF 92

Subwoofer

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KC 62

Subwoofer

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