Why bass traps?

All rooms have walls, ceiling and a floor.  Sound reflects off these surfaces in complex ways and forms standing (stationary) waves or ‘room modes’.  This gives rise to audible nulls and peaks in the room.  Such nulls and peaks cause vast level (volume) changes in different parts of the room.  Bass traps absorb the energy that cause room modes and turn it into heat; don’t worry, we are talking about miniscule amounts!

Room modes cause extremely complex 3 dimensional standing (stationary) wave patterns in a room.  Even though low frequency wavelengths are very long -  many metres - the distances between the nulls and peaks within the room’s standing waves may not be that great.  This is easily demonstrated by playing back a single low frequency tone at one of your room’s modal frequencies and walking around the room listening to the varying levels.  To discover the frequencies of your room’s modes click here to download a copy of my Room Modes Calculator  

The free audio editor Cool Edit 96 can generate the necessary tones:  http://www.threechords.com/hammerhead/cool_edit_96.shtml

At a few points in the room you will encounter a null where almost complete cancellation occurs.  Move your head just an inch or two and the level (volume) of the tone changes dramatically.  The same is true of the peaks too but the affect is much more startling with nulls because - if you have never heard it before - you probably wouldn’t believe how a sound can almost completely disappear simply by moving your head by such a small amount. 

Some people protest that such a demonstration of modal effects is irrelevant because no one routinely listens to single tones.  But that would be to miss the point.  Music is a series or combination of tones.  If the tempo of a piano song is slowed right down, individual tones are clearly heard.  The piano notes that correspond to the room’s modal frequencies - even when the song is played at the correct tempo - still excite these same standing waves that they do when the notes are played in isolation.  The result is the same, nulls and peaks; in other words, an irregular response throughout the room. 

You may say that you sit in a fixed position so it doesn’t matter if the response at other points in the room isn’t flat.  Again, that would be to miss the point that modal problems and the standing waves they cause, interact in extremely complex ways that are further complicated when confronted with the evolving mixture of different tones that music is composed of.  (pun intended)

So, if you want to hear music without the room affecting what you hear, the answer is bass traps, and lots of them.  See the bass traps page for further information.

© Tim Rainey 2008

Shameless Plug:

Nishikigoi Varieties is a 90 minute visual bonanza of beautiful koi carp…read more

 Feedback, questions and comments welcome

Last updated:  2 January 2010

Privacy Policy

Powered by admin©