• Isolating high frequencies
  • Cymbals and high frequency splash
  • The shield and internal acoustic absorption

It would be great if we could claim that we ‘invented’ the CrashGuard. Truth is; devices like the CrashGuard have been custom built by recording engineers for years. Some have tried cardboard and duct tape, others have attempted to cut & glue plastic bottles.

Although these home-made jobbies work to a certain degree, they are usually fragile, hard to position and probably do not afford as much isolation as one would like.

The point here is that necessity is usually the driver for innovation. The CrashGuard is a device whose time has come to break out of obscurity… and this page explains how it works.

Isolating high frequencies
It is well known that wherever air is free to wonder, sound tends to follow. Sound travels through air like waves on water by compressing air molecules. High frequencies and low frequencies both sound different and behave differently. The table below shows some examples.

Given the fact that bass goes everywhere and high frequencies are more directional, highs are easier to predict. And since high frequencies contain less energy than lows, they require less effort to control. This is, in fact, why the CrashGuard is designed to control spill from the cymbals. Highs are easy to mange compared to bass. And controlling low frequencies from the toms is practically impossible.

Reality check: Unless you completely isolate the snare or tom microphone with an air tight heavy mass, sound will get in. And last time we checked, drums are never isolated from the cymbals. Point being, the CrashGuard will not stop the sound of a cymbal from getting into the drum mic, it will attenuate it.

 

  High Frequencies Low Frequencies
Wavelength waveform1High frequencies have shorter wavelengths. waveform2Low frequencies have longer wavelengths.
Directivity waveform5High frequencies are uni-directional. They can be aimed using a horn. waveform6Low frequencies are omni-directional. Bass goes everywhere.
Energy waveform4High frequencies (when at the same amplitude as low frequencies) have less energy per cycle. waveform3Low frequencies (when at the same amplitude as high frequencies) have more energy per cycle.