Bass Traps …
So, how does bass behave in a room ?.
Well, despite hideous misunderstandings of this acoustic design area,
it’s really simple.
Imagine your bath at home, with a decent amount of water in it.
Flap your hand around in the water right at one end, to make a “wave”.
Watch with stunned amazement, as the “wave” reaches the far end of the bath, crashes with the end of the bath, then starts heading back towards you. Given a large enough wave to start with, the wave will get back to your end of the bath, crash with that end, and start off in the direction of the far end again. Exactly what happens in a room to sound waves.
In a room, this happens kind of automatically at certain frequencies. It’s all to do with the size of the room. Without getting into boring maths, if your room is 17 feet long the first and lowest note of one of these “automatic” waves (that us acoustician’s call “standing waves”) is about 33 Hz.
That’s a pretty womb trembling low frequency, and just one of many low frequencies at which, the room will resonate with the slightest sniff of audio input from your speakers.
The sound wave, just like in the bath, bangs up and down the rooms length and will do so for some time unless it’s actively stopped.
Typically, with say pop music, you could still be hearing a standing wave frequency excited by a bass drum, some 2 or 3 bass drum beats later !.
Oddly, taming these blighters, and restoring your sloppy, ill defined wadgy mess of a bass response back to something tight and dynamic that actually starts and stops at the correct time, is just as simple as the problem wave itself.
Rather elegantly ironic too – the problem is born of resonance, so we’ll kill it with resonance.
If you take any “vessel” or “cavity” it will, just like a room, resonate. They becomes a bass traps !.
Take a pipe or tube, with one end open and the other closed and it will resonate at a frequency dependent on it’s size. If you imagine blowing across the top of a milk bottle, you’ll get a note. Well, the flute players among us will, the rest of us might struggle a bit !. The note however is the resonant frequency of said bottle. Now put some water in the bottle, and you have effectively changed it’s dimensions (size!). Blow across the top now, and you’ll have a different note. A different resonant frequency.