Subwoofer – Connections & Setup
Standard loudspeakers such as compact boxes or satellite speakers typically reproduce high and mid-range frequencies particularly well. For low frequencies, it can be advisable to use a subwoofer to make the lower frequency spectrum audible and perceptible. These are specialized speaker cabinets designed and optimized for low-frequency sound waves. In this case, we are referring to active subwoofers, meaning those that have their own built-in amplifier.
Connections
How to connect the subwoofer depends on whether a stereo amplifier or an AV receiver is being used. For a stereo amplifier with existing pre-outs, an RCA cable can be used. If there are no pre-outs on the amplifier, a standard speaker cable can be used. Modern AV receivers have at least one pre-amplifier output (Pre-Out), usually also a dedicated subwoofer stereo/mono output, so that a mono RCA cable can be used here if necessary.
Rear of the Dali Sub P-10 DSS; Connection Terminal
Setup (Crossover Frequencies & Phase Shift)
Before diving into the setup settings, let’s first explain the core purpose of a subwoofer in more detail. As noted earlier, a subwoofer is responsible for reproducing low-frequency sounds. It ideally activates at the frequency range where bookshelf or floor-standing speakers can no longer perform, as they cannot reproduce those frequencies. The setup process also differs between stereo amplifiers and AV receivers. It is critical to tune the subwoofer to your speakers to create as consistent a sound profile as possible.
Phase Shift, Crossover Frequency, Volume
Crossover Frequency
This is the previously mentioned range where satellite speakers cease operating and the subwoofer takes over its duties. Depending on which speakers you are using and whether you have a stereo amplifier or AV receiver, the subwoofer must be adjusted accordingly. On the rear of the subwoofer, you will find adjustment options (e.g., a potentiometer in the form of a dial or electronic controls) with a scale ranging from, for example, 0–200 Hz. If you are using smaller speakers, the crossover frequency on the subwoofer should be set higher. For small speakers, this is typically around 120–150 Hz. With small speakers, however, it is important to position the subwoofer between the front speakers. Since sound signals in this frequency range can be localized audibly, placing the subwoofer next to or behind the listening position would be a poor choice. With larger speakers, however, 40–80 Hz is sufficient. This “rule” only applies when using a stereo amplifier, however.
The exact crossover frequency in Hertz you need for your subwoofer settings can be found in greater detail in your speaker’s instruction manual. The lower threshold of the speakers’ frequency range is also the value you should set on the subwoofer. With all due attention to detail, however, the settings on an AV receiver take priority over the speaker guidelines. If the subwoofer is connected to the pre-amplifier output, the frequency range on the subwoofer should be set to the maximum level of, for example, 240 Hz, to avoid frequency response corrections getting out of hand. Using the AV receiver’s bass management functionality, the crossover frequency can be controlled by the receiver, for example via an auto-calibration process.
Phase Shift
Phase shift determines whether the subwoofer’s driver first moves forward or backward (or up or down) in response to signal pulses. It is optimal for the front speakers and subwoofer to vibrate in phase. If the subwoofer is positioned frontally between or next to the front speakers at the same distance from the listening position as the speakers themselves, a phase setting of 0° can be used on the subwoofer. If the subwoofer is located to the side of the listening position or elsewhere in the room, it may be necessary to reverse the phase, which corresponds to 180°. Some models also offer infinitely variable adjustment. Your ears and personal perception will serve as the measuring tools here. If the subwoofer has an infinitely variable phase control, ask a second person to slowly adjust the phase knob while you are seated in your listening position. A test CD with a variety of low bass tones is ideal for adjusting the phase. If the phase is misaligned, the bass in the crossover frequency range will be quieter or imprecise, or its acoustic imaging in the listening room will appear unusual. With correctly set volume and phase, all bass tones will be reproduced at roughly the same volume. Experiment and leave the phase knob in the position that gives you the most enjoyable listening experience.
AV receivers, however, can automatically perform and adjust the phase setting using their built-in calibration system. When using an AV receiver with automatic calibration, it is advisable to set the phase on the subwoofer to 0°.
Volume Adjustment
The easiest way to correctly set the volume of an active subwoofer is via the menu of the connected AV receiver. Use its test tone generator to tune the subwoofer to match the rest of your speakers. At the listening position, the subwoofer’s volume should not be too quiet or too loud relative to the other speakers. Anyone who lives by the motto “You can never get enough bass” will soon get their comeuppance during intense thunderstorm effects, which will quickly push the entire system to its performance limits. Even if this does not occur, the quality of the entire acoustic setup will suffer. Instead of experiencing effects with a differentiated, realistic soundstage, you will only hear an overly intrusive, overly massive bass that acoustically covers up the rest of the sound foundation.
To adjust the volume, first turn up the level knob on the active subwoofer, then finish calibrating using the test tone generator of the AV amplifier. For THX subwoofers, the level knob on the active subwoofer is usually set to the maximum value. Audiophiles who prioritize absolute acoustic homogeneity and level consistency should calibrate the system, including the active subwoofer, using a sound pressure level meter (SPL meter). Many current AV receivers also include automated calibration systems that operate with varying degrees of accuracy.
We would be happy to provide you with comprehensive advice on the subject of subwoofers.
Update 05.12.2017:
In this video, created as part of our home theater grand opening, Raphael Vogt explains the basics of the subwoofer topic:
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