Your subwoofer is a critical element in your home theater system. The low frequency from the subwoofer is what puts the boom in an explosion, the rumble in a spaceship and the thud in a gunshot. However, even the biggest and baddest subs may not meet your expectations if they aren’t placed and set up properly.

“It’s a classic story amongst Home Theater Professionals – the client spends all this money getting a giant subwoofer to complement the rest of their system. But, when they sit down to watch a movie, the person next to them complains about too much bass, while others feel the bass is too weak.

– John Dahl, Director of Education at THX Ltd.

It could simply be a difference in personal preference, but more than likely it’s the room itself that is the root of the problem.

Room Modes

In layman’s terms, a Room Mode is how a room’s dimensions change the bass coming from a subwoofer. The frequency at which a room resonates directly correlates to its dimensions, acting much like a giant pipe organ. The result can be a change in both bass volume and tone as you shift your listening position from seat to seat.

How do you Test for Room Modes?

To identify Room Modes, begin by placing the subwoofer in the corner of the room and play either music or a movie with lot of bass. As you move from seat to seat, listen for volume and tone changes. A rectangular room made of heavy rigid construction like concrete or cinder block materials will exhibit fairly obvious effects – you may even see a pattern, where the volume dips and peaks throughout the room. If lighter weight, more flexible construction materials such as dry wall are used, or the room is large and open, the effects will be less obvious.

If you’re looking to identify and correct bass mode problems, THX recommends you consult a THX Certified Professional.

Recommendations for Reducing Room Modes

  • Set up your home theater system in a more bass friendly room or build a better room. (Don’t panic, any room can be made to sound good)
  • Place the subwoofer(s) at a spot in the room where they reduce the amount of peaks and dips in bass response (Good subwoofer placement can be very complex)
  • Move the seats so they are not in a peak or dip (often a foot or so will do the job)
  • If your budget/space allows, use more than one subwoofer to balance the bass from seat to seat
  • Use acoustic treatments specially designed to control bass (These are highly specialized items which may require research)
  • Equalize by pulling down the bass mode peaks only

Note that equalization is the last item on the list. Equalization works best if all the other solutions are applied first.