Hardware Steven Kippel on 21 Feb 2009
How to set up your subwoofer
One of the trickiest parts of setting up a home theater system is calibrating the subwoofer. This article will help you set up a basic single-subwoofer system. This does not help with most home-theater-in-a-box systems, though some do have subwoofer settings.
Before we begin, you should have a few items. Check your surround receiver to see if it outputs tones to each channel independently. Most receivers do, and it is in the “speaker level” section – often as “manual setup.” A better option is to pickup a setup disc like the Digital Video Essentials (available on Blu-ray). These discs have proper tones for different speaker setups. But if you don’t want to spend the money, you can use your receiver’s tones. (Hint: most THX optimized DVDs and Blu-rays have a THX setup in the menu with useful tones. Look for Terminator 2, or The Incredibles)
Another item you might consider getting is a sound pressure level meter (SPL meter). You can pick this up at Radio Shack. It is not essential, but it will give you the peace of mind that you have set up your system as close as possible.
Finally, you might need to get a longer RCA audio cable. This is so you can move your subwoofer further away from your receiver if need be.
This is the first step in subwoofer setup, but also one of the most contentious topics amongst enthusiasts. Some suggest placing the sub in a corner to use the room’s natural acoustics to create louder bass. But the point is not to create loud bass, but defined, smooth bass. Along the wall is the best for smooth bass. But it can’t just be thrown against any wall, you need to find the right wall. How is this done?
Place your subwoofer on a study stand or table at about head level where you intend to sit while watching movies/playing music. Connect it to your receiver and play a CD with music you’re familiar with with a strong bass line (hopefully an ascending/descending line). Next, crawl around the walls with your head at subwoofer level listening to the bass until you find the a spot where the bass sounds clearest, and most articulate. You may have to make concessions to keep the sub out of a walkway or for aesthetic purposes, but you can determine spots that would be acceptable before you do this and then find the best spot within those limits.
Subwoofer crossover settings
Most subwoofers have a knob on the rear (sometimes the front) for crossover control. The crossover is the level where the main speakers meets the sub. The vast majority of receivers have a digital crossover to send low frequencies to the LFE (low frequency effects) channel. You will want to use the receiver’s cross over because it will mix the frequencies below a set point from all channels to the subwoofer channel. In this case, the crossover on the sub should be set to the highest possible point.
Dolby Laboratories suggests the crossover should be set at 100Hz. This is where most receivers default. THX suggests 80Hz so more low freqncey information is driven by your surrounding speakers. What to chose?
I have large floor standing speakers than can go down to 40Hz no problem. In my case I set the crossover at 80Hz. If you have smaller satellite speakers you should probably use 100Hz. You might try both settings and see what sounds best in your situation. (Hint: the THX optimizer has a subwoofer crossover test that drops from a high frequency to a low frequency. You can use this to check for the best crossover point for your system. There level should not drop off in the middle of the test but should remain at a constant level throughout.)
Setting the phase on your subwoofer
Most subwoofers have phase control, which is most commonly a knob which can turn from 0-180 degrees. Other subwoofers just have a switch for 0 and 180.
Proper phase alignment is crucial to bass management. If the sub is out of phase with the other speakers the sound will not reach you at the same time and the sound stage will be nondescript.
Some receivers have phase control built in, these receivers come with a microphone and an automatic setup. If your receiver does not have phase control, or you just want to make sure your system is set up correctly, you will want to test your system.
First you want to check your crossover setting and use your setup disc (in this case you’ll need it) to play a tone at the crossover frequency. Take the speaker wire to the main speakers and reverse the wiring (at the speaker side only) so the red side is connected to black and the black to red. Play the tone from the setup disc and have a friend adjust the phase knob until you head the least amount of bass. Next, you will switch the wiring to the speakers back to correct phase (red on red, etc) and your sub will now be in phase with the speakers.
Setting the sub level on your subwoofer
The easiest way to do this is use a setup disc with a sub level test and an SPL meter. The tone will switch between one of your front speakers and your sub and you will match the levels between the two. If you do not have a setup disc, you will use the receiver’s tones and adjust levels by ear so the front left/right speakers are matched to the subwoofer level. This second way is less precise and you will have to adjust the subwoofer level to taste with a source you are familiar with. (Hint: use the subwoofer crossover test on the THX optimizer. The level should not rise or fall after the crossover point is reached.)
When you do get your sub dialed in, you will either be very glad or realize you need to upgrade. Either way, at least you know you’re getting the best you can get out of what you have.