Room EQ
Small rooms, square ones especially, make certain bass notes boom. This page plays a sweep, listens with your microphone, finds the frequencies your room piles up, and cuts them back so the bass evens out.
1 Measure the room
Put your laptop or mic where your head usually is and set the volume to a normal listening level. You will hear a rising tone for about five seconds. Keep the room quiet while it plays.
Measurement microphone calibration
Laptop mics are tuned for voice and may roll off in the deep bass. A measurement mic such as a UMIK-1 comes with a calibration file. Load it here and it is subtracted from every measurement.
2 What the room is doing
- Your room
- Boomy: above the target
- Target
- After correction
- Background noise
What gets cut
Point at a chart to read the values.
| Frequency | Cut | Width (Q) |
|---|
3 Listen before and after
Switch between Before and After while it plays. Removed plays only what the correction takes out; if it is silent, nothing was cut that your speakers can play. The bass scale makes the change easiest to hear: listen for notes that jump out louder than their neighbors. With voices, a boomy room makes deep voices sound muddy and chesty.
The voices are LibriVox recordings, which are in the public domain: John W. Michaels reading T. S. Eliot, Tomas Peter reading George C. Michael, Helen Z. Ferrara reading Rupert Brooke, and a LibriVox volunteer reading Ella Wheeler Wilcox.
4 Use it everywhere
A web page can only change its own audio. To correct everything your computer plays, type these filters into a system-wide equalizer such as eqMac on a Mac or Equalizer APO on Windows. The format is the one REW exports.
Measure first.
How it works
Sound bounces between parallel walls. At frequencies where a whole number of half wavelengths fits the room, the reflections stack up into a standing wave and that note gets much louder. In a 4.2 m room the first one is at 41 Hz. A square room has the same distance both ways, so its peaks land on the same notes twice and get even worse.
The sweep is a tone that glides from 15 Hz to 2 kHz. Dividing what the mic heard by what was played gives the room's impulse response, and from that the level at every frequency. The page then places narrow cut filters on the biggest peaks above the target, the same peaking filters a parametric EQ uses.
It only cuts. Some spots in a room have dips where reflections cancel, and boosting a dip mostly wastes amplifier power without filling it in. Where the response falls away on its own, because the speaker or the mic runs out of bass, the target follows that trend instead of the flat line, so notes that stick out above their neighbors are still evened out while the natural roll-off is left alone.
Before the sweep starts, the page listens to the room's background noise. Wherever the sweep did not come through at least 10 dB above that noise, usually the deepest bass on small speakers, the mic was hearing the room's hum rather than the speakers, so nothing is cut there.
The correction is tuned to where the mic was. Measuring a few spots around where you sit averages them and gives a correction that holds up as you move.