Isolation cabinet (guitar)

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A guitar speaker isolation cabinet enables turning up the volume of a vacuum tube guitar amplifier to produce power-tube distortion and then driving a guitar speaker and microphone to produce a signal that captures the resulting complex dynamics, at a largely reduced listening volume.

Contents

[edit] Sizes and types

A guitar speaker isolation cabinet has a built-in mounting baffle for a guitar speaker and a permanently mounted microphone clip. A guitar speaker isolation box is large enough to contain a standard guitar speaker cabinet such as a 1x12" or 2x12" cabinet and a couple of compact microphone stands. The next step up in size is an isolation booth, and finally, the live room of a recording studio.

A compact isolation cabinet contains a small guitar speaker such as 6 1/2" diameter and sometimes an attached power attenuator to prevent blowing the speaker. Equivalent but less-effective methods are to bury a guitar speaker and microphone in a closet; place gobo partitions around a speaker cabinet to somewhat deflect the sound; or form a tent with multiple layers of heavy blankets over a guitar speaker cabinet and microphone.

The frequency response of an isolation cabinet depends on the number of microphones, the type of microphones, microphone positioning, cabinet dimensions, speaker size, speaker model, and the amount of sound-absorption material inside the speaker cabinet. To adequately control the resulting response, a dedicated equalizer can be used in the mixer channel's Insert jack, such as a 10-band graphic equalizer.

[edit] Degree of sound isolation

A single-layer isolation cabinet or isolation box reduces the sound but does not make the speaker silent; significant bass leaks out. A double-layer box with dead space between the layers still leaks audible bass, if typical plywood thickness is used. Getting closer to silencing would require two very massive layers of plywood, MDF board, or soundproofing board such as Homasote or Wonderboard. An additional layer may be needed, such as for a 100-watt guitar amp with multiple efficient guitar speakers inside the box.

[edit] Combined approaches

To reduce the volume leakage or to prevent blowing the speaker or microphone, a power attenuator is sometimes used, between the tube power amp and the guitar speaker in the isolation box.

To reduce volume on stage while staying near to a traditional guitar amp setup, a guitar amp can drive two parallel loads: a power attenuator driving a conventional guitar speaker cabinet (with no microphone), and a speaker isolation cabinet providing the signal for the mixer board and sound reinforcement system.

[edit] Overstressing components

Blowing a speaker is a significant possibility when using an isolation cabinet. A blown speaker usually has a broken wire in the coil and would need to be reconed. A blown speaker appears as an open or infinite resistance to the tube power amplifier and can "fry" expensive components in the amp, such as the output transformer or power tubes, which would then need to be replaced.

"Cranking an amp" means turning up a guitar power amplifier well into the region at which power-tube distortion is produced, generating as much as twice the amplifier's rated non-distorting wattage. Pushing a guitar amp to such an extent can destroy components of an amplifier whether using an isolation cabinet, dummy load, power attenuator, or conventional guitar speaker cabinet.

[edit] See also

[edit] External links

  • Amptone - list of isolation cabinet products, and do-it-yourself isolation cabinet projects
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