Today's Top Stories:
 Sweetwater Price Drop: Roland RS-70 Keyboard!
Sweetwater Price Drop: Roland RS-70 Keyboard!
We've lowered the price on the RS-70 keyboard from Roland. This keyboard makes music creation simple with Direct Access buttons for selecting Patches PLUS a brand-new Loop Sequencer that takes the mystery out of multitracking! Chocked full of sounds, the RS-70 is now available for under $1000 for the first time! Check it out today.
| Recent inSync News: |
|
| · |
Wednesday, May 19, 2004 |
| · |
Tuesday, May 18, 2004 |
| · |
Monday, May 17, 2004 |
| · |
Friday, May 14, 2004 |
| · |
Thursday, May 13, 2004 |
| · |
View Entire inSync Archive |
|
|
 |
Sign up to receive the weekly inSync summary by email each weekend!
|
|
 |
| Sympathetic Vibration |
A vibration produced in one material by the vibrations of the same frequency, or a harmonic multiple of that frequency, from a sound wave in contact with the object, by means of the air or an intervening material.
A common example of sympathetic vibration is to sound a tuning fork and bring it close to, but not touching, another fork of the same frequency. The second fork will then begin to vibrate sympathetically. If the forks are mounted on resonating boxes, the effect will be stronger and thus heard better. The same effect can be observed by shouting or singing near a set of undamped (sustain pedal down) piano strings.
In physics, vibration is commonly referred to as an oscillation - a movement, first in one direction and then back again in the opposite direction. You can observe this, for example, by striking the prongs of a tuning fork, or by plucking the string of a musical instrument. Sound is produced by the vibrations of a body that are transmitted through material media (air, for example) in waves of varying pressure. When a sound wave of one frequency strikes a surface (a wall, for example) that will vibrate naturally at the same frequency, that vibration is called sympathetic vibration. Any reinforcement (increase) of sound resulting from the sympathetic vibration is called resonance.
Most construction materials have low resonant frequencies, so low frequency sounds can easily cause sympathetic vibrations in such structures. This is commonly experienced when bass notes of music penetrate walls and ceilings. At the other end of the frequency spectrum is the classically trained singer who is able to smash a wine glass, by finding its resonant frequency and attacking that pitch at full volume. |
 View the Complete Glossary |
| Sympathetic Vibrations in Live Sound Applications. |
Q: "I play solo acoustic guitar/vocal gigs in small clubs. Although I'm not a very loud act, at some clubs I shake the mirrors behind the bar, or the ceiling tiles! What's happening and how can I stop this?"
A: What's happening is the output of your sound system is triggering resonant frequencies through sympathetic vibrations from different elements of the environment around you: the mirrors and parts of the ceiling assembly (we'll bet the room in question has a suspended ceiling - more on this in a moment). It doesn't require a lot of volume to generate sympathetic vibrations. Instead, they are caused by sound waves that match the resonant frequency of the vibrating element - the glass, the ceiling, whatever.
Major touring groups (and smart regional rock bands) check every arena or room for resonant frequencies by using a Real Time Analyzer, or by running a test tone through the system, sweeping from 20Hz to 20kHz at different volume levels. They can locate and mark problem frequencies and adjust them by cutting corresponding levels via EQ (although technically only a band-aid it does help significantly).
If your sound system doesn't already have one, you need a good equalizer. A 31-band equalizer (because of its 1/3-octave precision in frequency adjustments) will give you the most control over offending resonances. The combined output of your voice and guitar are generating thousands of frequencies, and some of them are triggering the vibrations in the room. Once you locate the resonant frequency of the bar mirrors (which you can do fairly simply through experimentation) lower that frequency by a few dB to reduce the problem. You may have to lower the level of that frequency a lot, but be aware that too much adjustment can adversely effect your sound in other parts of the room that may not be experiencing the problem. If the problem persists after lowering the problem frequency you may want to investigate adding some damping to the resonating items.
A word about suspended ceilings: if you've ever looked above the tiles, you know that these systems are made up of hundreds of wires, tied to up to thousands of feet of metal framework. It's the equivalent of a very poorly made musical instrument, and is likely to resonate at multiple frequencies, from low to high, though the tiles themselves mitigate this to a degree. After you've made some preliminary EQ adjustments, there's not much you can do about this; you could spend days tracking down individual resonances. A less painful step would be to simply reduce your stage volume. |
| View all 1,700+ Tech Tips |
|
