It’s one of the hallmarks of a fantastic home theater; great bass. Everyone wants the kind of bass you can feel, that slams you back against the seat when it has to, and makes your pant legs flap. What too many people get is either weak, anemic bass or boomy bass that sounds like mud. In many cases you’ll have pretty good bass at one seat and little or no bass at other seats. Sometimes you try to crank up the subwoofer level to compensate for these deficiencies. Usually that makes the bass even more bloated and boomy. Sometimes it makes your subwoofer run out of gas and it’s amp clips, the cone starts bottoming, or both.
What can you do? How can you get that great bass you’re looking for, not just at one seat, but everywhere in your home theater? How can you get bass that sounds great for slam-bam action movies and also for music? Is that $800.00 subwoofer you got a total loss?
The good news is that you can get great bass in your home theater, and probably at every seat too! It usually comes down to two things; subwoofer selection and placement. Your sub needs to be appropriately sized for its intended duty. If your home theater is larger, say 27′ x 17′ x 10′, especially if it is a multi use room that is open to the rest of the house on one or more sides, you’ll need a larger sub than if your room is small. It comes down to basic physics. To make bass you need to move the air in the room. To make a lot of bass you need to move a lot of air. If your room is larger, your sub must move more air to get the same effect as it would in a smaller room.
In the old days, when comparing subs from good manufacturers, you could just look at the size of the subwoofer cone and the power of its amp. This would give you a general idea of the output. Most subwoofers used similar designs, either a bass reflex (ported) or acoustic suspension (sealed) box. Most quality subwoofer drivers had somewhat similar excursion specifications. Now, with the advent of high power digital amplification and super long throw drivers, things are a bit more difficult.
There are 10″ subs on the market now that move as much air as some of the old 15″ units. This is because the cone has a very large peak to peak excursion specification. It is important that the driver is designed correctly so that it stays in it’s linear range when moving this far. This is probably nothing you need be concerned about if you are buying a sub from a quality manufacturer. That is what their design engineers are for.
The main advantage to this is that, using the high power digital amplifiers, a long throw driver can get very good performance in an undersized box. A small box has many more placement options and does not intrude so much on the room’s aesthetics. Two of the notable companies producing these types of very small subwoofers are Sunfire and Velodyne. Most manufacturers will have recommendations about which of their subs to use in a given room size.
Now for the biggest key to getting great bass in your home theater; use multiple subwoofers. According to some of the latest research, the way multiple subwoofers interact with the room is the single biggest factor in being able to get great bass in every seat of your home theater. One of the biggest problems in small room acoustics is caused by standing waves. These are created when the wavelengths (or ½ or ¼ wavelengths) of certain frequencies coincide with one or more room dimensions.
For example, a 49Hz tone has a wavelength of almost exactly 23 feet. Standing waves cause certain frequencies to be reinforced and cancelled at different locations throughout the room. These problem frequencies are known as room modes. The effect of standing waves is to have areas of the room where bass is very boomy and others where there is no bass at all. An equalizer will do nothing to fix these problems and can even make them worse!
You should use either two or four subs. There is not too much benefit from using more than four. When using two subs, they should be placed on the floor, in the front corners of the room. For even better bass and smoother frequency response throughout your home theater, use four subwoofers. These should be located on the floor, at the midpoints of each wall.
You will still have some peaks but they can be taken care of with a good parametric equalizer. You can use a graphic equalizer but the equalizer should have better than 1/3 octave resolution. This will help to ensure you are able to target the precise peak frequencies. If you can, however, use a parametric.
Using the correct subwoofers for your room and using multiple subwoofers with a good equalizer will help you get that spectacular bass your home theater has been missing.