Calibrating Your Subwoofer: It's All About That Bass
As George Lucas has famously said, "Sound is half the experience in seeing a film." Of course, sound is the entire experience when listening to music. Either way, half of the sound experience is found in the lowest two octaves of the complete audible range. If your sound system can't reproduce those octaves well, you're really missing out.
To bring out the bottom end in movie soundtracks and music, you need one or more subwoofers. Without that critical component in your system, massive explosions and roaring rockets are merely ho-hum, and bumping bass lines don't make you want to shake your booty. A subwoofer can help you become much more immersed in the experience and take you away from the cares of daily life.
However, simply buying a subwoofer, taking it out of the box, plugging it in, and turning it on might not do the trick. If the sub is not set up properly, you could be wasting the money you just invested. It might overpower the rest of the speakers, or it might wimp out just when it's needed the most.
When you have one of the best home subwoofers, it's fairly easy to tweak your subwoofer so it integrates perfectly with the rest of your audio system. Just follow these simple steps to bass nirvana.
Subwoofers for Home Cinema
Let's start with a surround-sound system for a home theater that includes an AV receiver or preamp/processor with a dedicated subwoofer output, which connects to the sub's input. Also, let's assume the sub is self-powered—that is, it has a built-in power amplifier.
Step 1 - Does the sub have an analog or digital volume control?
If it's analog: it probably has a rotary knob; set the knob to its 12 or 1 o'clock position, about midway in its range.
If it's digital: the control might be in an app from the manufacturer; start at a setting of -15 (assuming the max value is 0).
These settings will give the AVR or preamp/processor enough leeway to set the final sub-level correctly during its auto-setup routine.
Step 2 - Set the LPF controls
Most subwoofers also have phase and low-pass filter (or LPF) controls.
Set phase to 0.
Set LPF to its highest frequency or off. If the LPF control is a rotary knob, turn it to its fully clockwise position, which might be marked "LFE." If the LPF control is digital, disable it entirely.
Step 3 - Run the auto-setup routine in the AVR or preamp/processor with the calibration microphone at the listening position.
This will play test signals from each speaker and the subwoofer.
Step 4 - Confirm the subwoofer level
After the routine is complete, take a look at the subwoofer level within the AVR or preamp/processor. In Onkyo, Marantz, and Denon AVRs, this value ranges from -12 to +12; in Yamaha and Pioneer AVRs, it's between -10 and +10.
Step 5 - Did the AVR automatically set the subwoofer level at its lowest value?
If so, turn down the sub's onboard level control somewhat and run the auto-setup routine again. Repeat until the automated sub level in the AVR or preamp/processor is not the lowest possible value.
This ensures that the sub volume is correct as far as the auto-setup routine is concerned.
Step 6 - Confirm the bass-management settings
Take a look at the bass-management settings in the AVR or preamp/processor—specifically, whether or not the auto-setup routine identified any of the main speakers as "large."
Make sure all main speakers are set to "small" so the low frequencies in all main channels are redirected to the subwoofer, which is much better at reproducing those low frequencies than just about any main speaker.
Step 7 - Set the crossover for each speaker
Once all the main speakers are set to "small," set the crossover for each one, which determines the point at which low frequencies start being redirected to the sub.
This depends on the make and model of each speaker. Set the crossover 10-15 Hz above the speaker's measured or specified bass extension. For example, if the speaker's bass extension is 40 Hz (-3 dB), the crossover for that speaker should be set to 50-55 Hz.
Step 8 - Push play - How does it sound?
Play some of your favorite content, and don't forget about those clips with lots of low bass to really put it to the test.
How does it sound to you? Is the bass well integrated with the rest of the sonic spectrum? Does its impact seem lacking?
If you want a bit more, try increasing the level by 2-4 dB. But be careful; if you goose it more than that, the bass will likely overpower the rest of the sound.
Step 9 - Need more bass? Increase the subwoofer level.
If you want to increase the subwoofer level, a common question we receive is: should you do it in the AVR or on the sub itself?
If the sub has an analog rotary volume control, adjust the level in the AVR, which offers more precise and repeatable settings.
If the sub provides a digital level control, it doesn't matter where you make the adjustment.
Subwoofers for Stereo Audio
A subwoofer (or two) is often a big improvement when added to the two main speakers in a 2-channel audio system. In this case, there is no bass management, no time alignment, and no automatic level matching. The main speakers receive a full-range signal from the electronics, and the preamp does not typically provide a separate subwoofer output. If you're looking to buy a sub but own an older stereo receiver and/or amplifier that has no dedicated subwoofer output, some SVS subwoofers have speaker inputs - such as the SVS SB-1000 and PB-1000.
Step 1 - Connect the preamp or stereo amplifier to the sub
If the preamp or stereo amplifier has dual outputs: connect one set to the power amp and the other set to the sub(s).
If the preamp or stereo amplifier has one pair of outputs: use "Y" splitters to send the signal to the power amp and sub(s) from the same outputs.
Step 2 - Look up the bass extension of your main speakers
(That is, the -3 dB point at the low end). Ideally, you can find this in the measurements from a review by a reputable publication; otherwise, find it in the manufacturer's specs.
Step 3 - Set the sub's internal low-pass filter cutoff frequency
Set the sub's internal low-pass filter cutoff frequency to the same value as the main speaker's bass extension. For example, if the speaker's bass extension is 40 Hz (-3 dB), set the sub's LPF to 40 Hz.
Step 4 - Adjust the slope of the LPF (if available)
Some subs—such as those from SVS—also offer a control that adjusts the slope of the LPF above the cutoff point, which greatly helps to integrate the sub(s) with the main speakers.
If the speakers are ported: their cutoff slope is 24 dB/octave.
If the speakers are sealed: their cutoff slope is 12 dB/octave.
Set the sub's cutoff slope to match the speakers'.
Step 5 - Push play - How does it sound?
Play some favorite music and adjust the sub's level control by ear until it sounds just right—blending, not overbearing.
You can also play around with the sub's LPF-cutoff setting, maybe nudging it up a bit to overlap with the main speakers. But watch out; if you have too much overlap, you'll get boomy, one-note bass and possibly some phase problems.
Step 6 - Need more bass?
If your main speakers do not have low bass extension—say, somewhere in the range from 50 to 80 Hz—it's a good idea to have two subs, which give you stereo bass.
If your speakers reach down as low as 30 Hz or so, a single sub is fine, since frequencies that low are not directional.
Don't Go Overboard
Loads of bass can be lots of fun and very impressive. But too much of a good thing gets tiresome after a while, and it's not usually how the artist intended their content to sound. Creators work very hard to balance the bass with the rest of the sonic spectrum, and your audio system should reproduce it as accurately as possible.
If you follow the steps presented here, you can achieve that goal and get the most out of any recorded audio. You'll forget about the speakers and subwoofers and simply get lost in the experience. After all, isn't that what's it's all about?
To see all the subwoofers that World Wide Stereo carries, click here.
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