There are several ways to connect subwoofers to home music and cinema systems. The information you need is a bit different for Home Theater (multi-channel) systems than for two-channel, or stereo, systems. Here we discuss many aspects of subwoofer connection that we at Velodyne have encountered:
1. Defining some key terms
2. Crossover networks and how they work
3. Home theater receivers: multichannel amplifier hook-up
4. Stereo receivers: two-channel amplifier hook-up.
5. Subwoofer placement
Defining some key terms:
What is a subwoofer? Subwoofers are dedicated low-frequency speaker cabinets that fill in the deep, rich bass that is missing from most main speakers. Subwoofers are specialized, and don't reproduce midrange or high frequencies. See our article on "What Is a Subwoofer, and Why Do I Need One" for more information.
What does LFE mean? LFE refers to the Low-Frequency Effects channel that is a part of the specification for five channel and seven channel home theater receivers and processors. The LFE signal is a filtered connection, encompassing the LFE channel signal along with the bass content of any channel that is designated as "Small" in the receiver or preamp/processor.
What is a speaker-level connection? Older stereo receivers (and some current stereo receivers) do not have RCA-connector based line level or LFE connectors. Those receivers can still be used with a subwoofer via speaker cables. The speaker level connection is a full-range, amplified signal connection, so the subwoofer's crossover network will remove the high frequency content and reproduce the low-frequencies only.
What is a subwoofer input? This refers to the RCA signal connection on the back of the subwoofer. It accepts the signal from your receiver or preamp/processor, which in multi-channel receivers has usually already been filtered, or processed, by the receiver's crossover network.
Crossover networks and how they work:
Crossover networks in subwoofers: A loudspeaker's crossover network is a set of components designed to act as a "traffic cop", directing the full-range audio signal to where it can provide the best sound. The tiny tweeters in a speaker would be quickly destroyed if asked to handle the long wavelengths involved in reproducing deep bass frequencies. Large woofers don't really move fast enough to reproduce clearly the high frequency notes that tweeters handle. Crossover networks divide the frequency range between speakers (bass to the woofers, most of the music to the midrange driver in a three-way speaker, and high frequencies to the tweeter). Most crossover networks are analog devices, using a combination of inductors, capacitors, and resistors to filter the signal. Digital crossover networks are becoming more common in our products. They handle the signal-processing functions even more precisely, via computer-chip technology that is programmed by our engineers.
Velodyne subwoofers include a crossover network. The low-pass crossover is set at a specific level, often 80 Hz, allowing the sub to reproduce frequencies below this level, while filtering out higher frequencies. Most subwoofer crossovers are user-adjustable (i.e., from 40 Hz to 120 Hz), so that you can determine the sub's upper frequency limit.
Crossover adjustment involves attaining a seamless blend between the main speakers and subwoofer, so bass sounds cannot easily be localized. If you listen to the music and can clearly hear bass notes coming directly from the subwoofer's location, something is wrong! Some main speakers are very bass-capable (i.e., large, costly floor-standing speakers). Others are less bass-capable (i.e., compact satellite speakers, and most in-wall or in-ceiling speakers). Try a crossover point below 80 Hz for large speakers (perhaps 60 Hz) or above 80 Hz for compact or inexpensive speakers (perhaps 100 Hz). This may give a better blend with your main speakers than the 80 Hz starting point. A little experimentation with some bass-heavy music can go a long way toward adjusting this setting so that you are very happy with your subwoofer purchase.
Crossover networks inside a multi-channel receiver: Modern home theater receivers and preamp-processors have crossover networks built into them. Stereo receivers generally do not. When using a home theater receiver, many people prefer to use its crossover, especially if it is of the "continuously variable" type. In such cases, we suggest deactivating the subwoofer's crossover network. Using both crossovers poses no risk of damage, but if the crossover networks compete with each other, distortion can result. Many Velodyne subs have a crossover-bypass switch, usually labeled on the amplifier as "Direct", "Subwoofer Direct" or "Subwoofer By-Pass". This switch de-activates the internal crossover for use with an already filtered signal from a home theater receiver.
Home theater receiver connections:
LFE Input: Home theater (multi-channel) receivers have an LFE (Low Frequency Effects) channel as a part of the 5.1 or 7.1 specification. The most common way to connect a subwoofer to an HT receiver is to use a single audio cable with RCA connections on both ends. Hook the cable from the LFE Out connection on the receiver (often labeled "SW" for subwoofer; "Sub Out"; or "LFE") to the LFE input on the subwoofer. The receiver sends an unamplified, bass-managed signal to the subwoofer. Set the sub for "Subwoofer Direct" (as above).
Velodyne Digital Drive subs also have a balanced XLR input for LFE. Over long signal runs, XLR connections are less prone to noise than standard RCA cables.
Line-level Input: Some older receivers don't have a bass-managed LFE output. In that case, line-level outputs can be used. This sends the sub an unamplified, low level signal down the same type of audio cable used for LFE output. You will need a stereo pair of such cables. This signal is not filtered, so you will use the sub's crossover network to manage the signal. Do not use Subwoofer Direct.
Stereo system (aka two-channel) connection:
Line level: Many modern stereo receivers have a sub-out connection, an unfiltered, single RCA line level connection dedicated for the subwoofer. If there is no sub-out, standard line level connections work fine. If the receiver has no sub-out or line level connection, but has jacks marked "Pre-out", those work too.
Connect an RCA cable from the sub-out (or a pair of RCA cables from the line-out or pre-out) connection on the receiver to the LFE or line-in connection on the subwoofer. The subwoofer's crossover network will manage the signal, so do not use Subwoofer Direct.
Speaker level: If the receiver has no sub out, line out or pre-out connections, you can connect the subwoofer using speaker level inputs. This sends a full-range, amplified signal to the subwoofer. The subwoofer's crossover will manage the signal, so do not use Subwoofer Direct.
We suggest using speaker cable of 16-gauge or lower. Connect the speaker cables to the receiver's left and right speaker outputs, and run those cables to the subwoofer's speaker level input connections. Make sure to that you are consistent with positive and negative connections. In other words, make sure that the wire connected to the positive (+) terminal on the receiver is also connected to the (+) terminal on the sub. The wire connected to the negative (-) terminal on the amp must also be connected to the (-) terminal on the sub.
Then connect your main left and right speakers to the sub. Simply run another set of speaker wires from the subwoofer's speaker level outputs to the left and right speakers. You now have a stereo system with a wonderful addition: a subwoofer dedicated to handling the lowest frequencies, which removes quite a bit of the load that the speakers, and receiver, would otherwise have to handle.
The quality of bass that we hear depends on how the subwoofer is placed in a room. The room itself has a far greater effect on the bass than most people realize, and is one of many factors that determine the sound quality of bass:
- Of what quality is the subwoofer?
- Is the subwoofer integrated optimally with your system?
- Where in the room is the subwoofer located?
- Where is your listening position, relative to the sub's location?
- Are multiple subwoofers being used?
- What is the room configuration: large, small, rectangular, square?
- How resonant, or absorbent, are the room's surfaces?
Change any one of these elements, and the quality and quantity of the bass will change. It is common that listeners who are seated in different spots of the room will report vastly different levels of happiness with the bass. One may hear the bass as sounding ideal, while another believes "It sounds too bass-heavy", or "Is the subwoofer even turned on? I barely hear any bass."
The key idea with subwoofer placement is to experiment! If you can, play some music that is rich in bass, and try a variety of locations in your room. If you cannot move the position of the subwoofer, you may instead be able to re-position your favorite chair or listening position. Often times they recommend and showcase the benefits of using multiple subwoofers to help enhance and even out tone, however the size of the room and factors above will help you to make the correct decision.