do you need a subwoofer?
Whether you’re listening to music during a dinner party or watching the latest comic book blockbuster, having a good subwoofer is the key element to getting the most out of your sound system. Not only does it provide more, richer, and deeper bass than floor standing speakers alone can provide, it also provides a wider more detailed sound stage.
A good active subwoofer also has its own powered amplifier which shoulders some of the burden placed on your surround sound receiver or separates amplifier. And because the low frequency bass duty is removed from the speakers workload they too can breathe a bit easier.
are all subwoofers created equal?
Unfortunately the kind of subwoofers found in most Home Theaters In A Box and included with most soundbars have poor quality drivers, are woefully underpowered, and unable to produce the kind of deep rich base that you want. Thankfully a quality active subwoofer can be had for 300 to 500 dollars from any number of great manufacturers including SVS, HSU, and Polk Audio. While that isn’t cheap by any standard, it is an investment that will last you for many years. I paid 600 dollars for my SVS PC-2000 and it has been going strong for over a decade.
why does placement matter?
The biggest influence on the way your system sounds is the room itself. The sound waves from a subwoofer are more or less omnidirectional so they bounce all over the room, reflecting off the walls, ceiling, hardwood floors, and any other hard surfaces. This causes them to bounce into each other creating standing waves.
Standing waves are when a frequency reflected off the wall hits a frequency coming from the subwoofer creating a peak or a null. A peak causes the sound to be boomy or too loud and a null causes the sound to be empty otherwise known as a dead spot. If you’re sitting in one of these spots it simply won’t sound good.
so where do you put it?
As we stated at the beginning, where you place the subwoofer requires compromise. If you have a dedicated theater room, you have probably already placed your subwoofer optimally, so we’re going to focus on the living room home theater. Take a look around your living room and, given the size of your subwoofer, determine all the options you have for placement and make a note of them.
If you have no restrictions on where to place it then you, my friend, like the mythical unicorn, are extremely rare and lucky! Go ahead and skip to the next section.
If you have an entire wall available to you, preferably the front wall, then you should consider placing the subwoofer 25% of the width of the room away from the side wall. As acoustical engineer Art Noxon says in his article Home Theater Acoustics Vol. 3:
“A listening room can be approximated as if composed of three intersecting pipes. These pipes would lay along the three room axis — front to back, side to side, and floor to ceiling. This means that the subwoofer location for best, non-resonant playback will be about one-quarter of the ceiling height off the floor, one-quarter the width of the room off the side walls, and one-quarter the room length off the front or back wall. When discussing speaker location, it is only the dimensions to the center of the driver cone that count. The location of the edge of the box really doesn’t matter.
No computer program is needed to properly position the subwoofer in a room; a tape measure is your only investment. Note also that the currently popular “rule of thirds” placement formula is not consistent with the understanding of an aresonant speaker placement. This overpublicized “rule of thirds” would only be applicable if the subwoofer roll off was set so that the speaker did not play the third harmonic.”
If on the other hand the only option you have for placement is in a corner of the room, then that’s where you’ll have to place it. Placing it in the corner is not necessarily a good or bad thing. Try to place it 6 to 12 inches away from the walls if you can, and if the sub has a port hole pointed at the wall, use the manufacturer included foam plug to seal it. If they didn’t give you a plug, you can buy some thick foam at a craft store and make one yourself.
There are however some placement options that are not ideal. Placing the subwoofer underneath a table is generally not a good idea. And placing the sub inside of a cabinet is probably the worst thing you can do. If one of these is the only option you have, then do some Googling and you can find some ways to mitigate the problems that come with these options.
Once you know where in your living room each placement contender is, you’re ready for the Subwoofer Crawl.
what is the “subwoofer crawl”?
Where you place the subwoofer and where you sit are interchangeable. That means the bass will sound the same if you sit where the subwoofer is and put the subwoofer on the couch where you normally sit. This provides the perfect way to find your ideal sub placement. The process is simple:
- Place the subwoofer either on the couch or chair where you sit when you watch a movie or in that spot after moving the couch or chair off to the side.
- If you have a THX calibration disc or a Disney WOW disc turn on the 200Hz to 20Hz frequency sweep test otherwise put on some music that has steady deep instrumental base line. Whichever you choose, put it on a loop.
- Crawl on your hands and knees, your head level at knee height, at each possible placement position and listen to the quality of the bass. Keep an ear out for the spot where it has the best balance of being loud, tight, and defined.
- After evaluating all the possible positions, put the subwoofer in the spot that sounded best and listen again to the pink noise or music track from your sitting position. It will sound the same as when you were in that spot.
how do you get the most out of your subwoofer?
Now that you have the perfect position for your subwoofer you can start dialing it in for optimized sound. The first thing you’ll want to do is set the subwoofers crossover. With the majority of speakers you can use the THX recommended 80Hz however with some speakers you may have to set the crossover as high as 120Hz, depending on the capability of the speaker. Check your speaker manual and find their frequency response limits. If the speaker doesn’t play down to 80Hz, lets say it bottoms out at 90Hz, then you will want to set your crossover for 100Hz to give the speaker some breathing room.
To set the crossover on your subwoofer, there should be a dial on the amp that allows you to choose the frequency. If you like you can dial it all the way up and let your receiver or processor control the crossover. Next you will need to go into your receiver/processor settings and set the crossover there as well. Consult your manual for where to find this setting.
Next you will want to set the volume setting on the subwoofer. It’s a good idea to set the knob at half or 3/4 of the way up and then use the subwoofer volume setting in your receiver or surround processors settings menu to decrease the volume as needed.
Finally we come to the Phase control knob. The phase control knob adjusts the soundwaves in a way similar to physically moving the subwoofer along a wall and this changes where the peaks and nulls form in the room. So if you are limited in placement options or have only one place the sub can go, adjusting the phase can help improve the quality of the bass in your primary sitting position. Just as when you were doing the crawl, you’ll want to listen to the frequency sweep or music track while a friend slowly turns the knob.
what about using digital room correction?
Many modern receivers and surround processors come with some form of room correction such as Audyssey or ARC that can be used to automatically configure your speaker and subwoofer settings in an attempt to correct the limitations of your listening environment. While a lot of people sing their praises there are just as many who argue against their use. What seems to be a common sentiment in regards to the less expensive forms of DRC is that sometimes it sounds better with it and sometimes it doesn’t.
Where proponents say it shines is with the equalization of your subwoofers low frequencies which can provide real benefits for those of us with challenging listening rooms. On my own system I’ve found that movies definitely sound better with Audyssey room correction than without it. But your mileage may vary. For more information on the different flavors of DRC and their strengths and weaknesses, check out this article on Home Theater Review.
what about physical room correction?
The topic of acoustical treatments is enough for a dedicated article and then some. Using sound absorbing and diffusing panels along with bass traps can and does help correct many of the problems you might face in your home theater. However the panels are not likely to be attractive enough to garner your spouses approval in a living room theater and they can be exceedingly expensive.
If you have a dedicated home theater space, or you’re single and don’t mind that recording studio look in your living room, you can find all kinds of do it yourself options for building relatively inexpensive acoustical treatments. Google the term and DIY and you’ll find a lot of different resources to help you out.
if one subwoofer is good, how about two?
If you can afford the expense and you have the room then you definitely want two subwoofers. And if you have a dedicated theater room you will likely want four subwoofers. Multiple subwoofers smooth out the bass response across all of the listening positions and help to reduce the peaks and nulls we discussed earlier. In addition to those benefits multiple subs output more bass as well. And taken all together, dual subwoofers simply sound amazing!
While you face many challenges when it comes to finding the perfect placement of your subwoofer most of them can easily be overcome with a bit of time and effort. But you’ll find that the end result is most definitely worth it. And the next time you host a movie night with your family and friends you may just convert a few new acolytes into the church of the holy subwoofer.