Ken J
Room Resonance Control: Why you monitors appear to sound like crap.
by , 02-01-2012 at 04:36 PM (1077 Views)
I have heard so many stories on why monitors / speakers sound like crap in a home studio. For the purpose of this article I will refer to all speakers no matter what they are call as monitors because in the home or professional studio we monitor the sound tracked or mixed. Monitor accuracy is subjective and we tend to look at the specs with a grain of salt. For the end user the accuracy of a monitor is not in its specifications but in real time usage in the studio. So many people state that they have tried many monitors from the budget basement to top of the line and have had problems with all of them. Maybe it's not the monitors. Just maybe it the room and how that room sounds in relationship to the monitors. No monitor will be accurate unless the listening environment is corrected.
Bass Traps
Sound is conveyed through waves in the air. Waves that exist between a pair of surfaces can create standing wave resonances whenever the distance between the surfaces is any even multiple of one-half of the wavelength. At resonant frequencies (tones), the sound is louder and decays much more slowly than at non-resonant frequencies, causing uneven tonal quality and interference with clarity. Resonant frequencies occur mainly in the bass range, due to the relationship between the wavelengths of low-frequency sounds and the typical sizes of listening rooms.
This wave is in a standing wave resonance since it's wavelength equals the distance between the pair of surfaces.
Every room has its associated resonant frequencies. Rooms built using preferred dimensions ratios have potentially more even distributions of these resonant frequencies. Room built with angles walls or ceilings have more complicated resonant modes than typical rectangular rooms and the resonances can be potentially less severe. But, no matter what the size or shape of the room, resonant frequencies can be controlled through the use of bass traps.
Bass frequencies occupy all the notes on the left half of the keyboard (Everything below middle C). Since this is such a large portion of the musical spectrum, and because every room has potential resonant frequency problems in this bass range, it is imperative that the low frequencies be the first issue to address in improving any room's acoustics. Of course, each specific room's geometry, setup, and application dictate how to best optimize the bass performance.
Comb Filtering
Sound and music propagate through waves and, therefore, must abide by the laws of wave physics. This means that when 2 waves "collide", they do not bounce off one another as is the case with physical objects. Instead, at that location in space and moment in time, they either add their combined amplitudes to some degree or cancel their combined amplitudes to some degree.
Waves exactly in phase add to make a wave with twice the amplitude.
Waves exactly out of phase add to make a wave of zero amplitude.
Waves out of phase to a small degree add to make a wave with
slightly higher amplitude than either wave individually.
The wavelength of the 2 sound waves and the difference in the distances they have traveled determine whether they add to or subtract from the combined resulting amplitude. This means that there are a series of adds and cancels at various frequencies of sound for any given room setup.
There are many potential reflection points that can cause a sound launched from a source to return to that source and interfere with itself. There are also many potential ways for sounds to travel from one source to another and cause interference. Likewise, there are many ways for sounds launched from single or multiple sources to arrive at a central listening position at different times and interfere with one another there. All of these interfering waves cause the resulting amplitude of the sound to either increase or decrease to some degree depending upon the frequency (tone) of the wave. The resulting adjustment to the amplitudes at each frequency is called a comb filter.
Comb filtering effects are reduced by placing acoustically absorptive materials at the reflection points responsible for the interfering waves. The materials must be of a size and type to properly address the frequencies of each specific problem. Rearranging the speaker setup will simply shift the locations of reflections and alter the problem frequencies, but does not remove the problem.
Although locating the precise positions of problem reflections can be a complex task, there are a few locations where controlling the reflected wave is sure to make an improvement to the sound.
Primary sidewall reflection points
Perpendicular reflection points
Convectuoso and JoshERTW like this.
Email Blog Entry
Go to Profile
Mark as Read
