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Guitar Amplifier Isolation Cabinet – For a Higher Quality Recording!

Can’t wait to record that groovy, bluesy guitar riff you just wrote? Well, before you do that, take note that one of the most common problems troubling many home recordists, is getting a clean and decent quality guitar recording. This is due to the fact that most home studios, do not have the proper acoustic treatment, similar to professional studios. Hence, today we will talk about the remedy to that problem – the guitar amplifier isolation cabinet!

In this article, you would be surprise to know how much the amplifier isolation cabinet can be a benefit. You will be able to learn more about topics pertaining to its functionality, the different aspects of its construction and also how it exactly impacts the quality of recording. This will be a rather brief article, but hopefully even beginners will be able to have a good understanding of it. So, are you ready to rock that riff!? Then lets begin!

Introduction – What does it do?

A guitar speaker isolation cabinet acts as a sound-proof enclosure that allows the amplifier to be used at a loud enough volume (suitable for recording), without affecting the external environment. It surrounds the speaker (which is usually miked up with a microphone) and prevents unwanted sound from leaking into the surrounding environment.

Isolation Booth

Photo by Brad Hoffman / CC BY 3.0

Recording an amplifier at high volumes, ultimately poses a risk to hearing and is also disruptive to neighbours. Other instruments in a mix might also be masked as a result. The signature sound of tube guitar amplifiers (commonly heard on most professional productions) is achieved by having the amplifier set at a loud volume, while using one or more microphones for higher quality recording.

Another benefit to recording at high volumes, is that it adds distortion to the amplified guitar tone. This is due to the pre-amplifier (having enough gain) to drive the power amplifier into distortion, thus “breaking up” the loudspeaker and producing distortion as a result. Higher sound pressures will also be produced by the speaker cone, delivering a wider dynamic range and detail to the microphone.

Now, let us look at the various aspects of the amplifier enclosure that we will touch on:

  • Various types and sizes
  • Degree of sound isolation
  • Alternative methods
  • Over-stressing risks

Various types and sizes

In general, most guitar speaker isolation cabinets have a built-in mounting baffle (for the guitar speaker) and a microphone clip that is left permanently mounted. A more compact, or smaller isolation cabinet is often able to house a small guitar speaker (such as 6½” diameter) and sometimes comes with a power attenuator attached to it, in order to prevent blowing the speaker.

Guitar Amp Box

Photo by guitarDouchebaggery / CC BY 3.0

On the other hand, an amplifier isolation box would be large enough for guitar speaker cabinets with sizes such as 1×12″ or 2×12″, together with a couple of compact microphone stands. A cheaper but less effective alternative to this approach, is to place a guitar speaker (with microphone) in a closet, place gobo partitions around the speaker cabinet (to deflect sound), or construct a tent (out of multiple heavy blankets) and put it over the speaker and microphone.

Take it to another level, and you will get an isolation booth. It is fundamentally a small sized room, but has enough space to house a single performer (or recording artist) along with a set-up of musical gear and equipment (also known as “rig”), allowing the instrument to interact with the amplifier while being isolated in order to prevent the rest of the band from being affected by the extreme volume.

Frequency response

An isolation system’s frequency response is determined by a number of factors such as the number of microphones, the type of microphones used, positioning of the microphones, cabinet dimensions, speaker size, speaker design or model, and the amount (and effectiveness) of sound-absorption material inside the cabinet.

In order to have control and manipulate the resulting response, an “equalizer” is often used to increase or reduce specific frequency ranges. The small space that exists within an isolation cabinet will not produce any room reverb (at least not audible to the human ear). Hence, for most professional recordings in general, the very “dry” recording has to be enhanced with an electronic reverb “plug-in”.

Degree of sound isolation

Most cost-effective isolation cabinets or isolation boxes, are constructed with a single-layer. This reduces the sound leakage but is unable to completely make the speaker silent (considerable bass frequencies leaking out). Even a double-layered box with a dead space (vacuum) between the layers, will still leak audible bass frequencies, if the typical thickness of plywood is applied.

Medium Density Fibreboard

Loudspeaker enclosure constructed with MDF / Photo by Daniel Christensen / CC BY 3.0

In order to vastly increase the sound dampening quality of the isolation boxes, certain components have to be added or modified. This includes two very thick layers of plywood, MDF (Medium Density Fibreboard), or the use of soundproofing boards such as “Homasote” or “Wonderboard”. Another layer might need to be added, in order to have better isolation for a higher powered guitar amp (100-watts and above) with multiple guitar speakers inside the box.

Alternative methodsPower Attenuator

Preventing the speaker or microphone from blowing and reducing volume leakage is often done by placing a power attenuator between the guitar power amp and the guitar speaker within the isolation box. This functions to reduce the power that is being channelled to the speaker and thus the volume. But this has some effect (in terms of sound colouration) on the speaker and microphone response.

To minimize the volume on stage while still keeping to a conventional guitar amp set-up, a guitar amp can drive two parallel loads – a power attenuator which then drives a typical guitar speaker cabinet (not miked up), and a speaker (inside an isolation cabinet) providing the signal which is sent to the mixing console and ultimately, to the sound reinforcement system.

A “Direct Injection” signal (produced by a “DI” box) can also be used with a guitar amplifier enclosure. A DI signal comes directly from the guitar amplifier or from a guitar amp power attenuator, and sent to one channel on the mixing console. Another signal (coming from the miked up guitar speaker) in the isolation cabinet is then sent into another channel on the mixing console.

Direct Injection

Photo by Kajttek / CC BY-SA 4.0

The sound engineer (whether live or in the studio) will then have the freedom of selectively blending the DI signal with the miked guitar speaker signal in order to achieve a richer sound. The DI in this case, provides the “dry signal” which is a more immediate, present, bright sound, and the microphone (recording the guitar speaker) provides a coloured, punchy, and darker sound.

Over-stressing risks

The chances of damaging (blowing) a speaker, is very high when using an isolation cabinet. In a blown speaker, you would normally find a broken wire in the coil and it would need to be re-coned. A blown speaker presents itself as an infinite resistance to the power amplifier and has the potential to “fry” crucial components in the amp, such as the output transformer or power tubes.

Broken Vacuum Tube

Broken Tube / Photo by FU FONG SIN, SANYFU / CC BY-SA 3.0

“Cranking an amp” is a slang term for turning up a guitar power amplifier to the extent where distortion will be produced, generating up to twice the amplifier’s rated non-distorting wattage. If you constantly push a guitar amp to such a level, it will damage internal components, even when used with an isolation cabinet, dummy load, power attenuator, or conventional guitar speaker cabinet. Just take note that tubes wear out quicker when they are consistently pushed into saturation.

Okay folks, that should give you enough information on amplifier enclosures, in order to help you decide whether you need to use one. But seriously though, if you are not planning to speed up the “hearing-loss process” for the old couple next door, then you need one!

Thanks for reading and do share, leave a comment below or ask questions if you like!

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Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

8 Comments

  1. Hello, This post is very interesting, The information you provide is very creative, I am into music myself, I create music with FL Studio.

    The images you have used are relevant, I took a look at your other posts too, Really good.

    I look forward to your upcoming content

    Wish you all the best

    Matteo

    • Howdy Matteo!

      It is great to have people such as yourself, who produces music, commenting on my site. I am happy that you have found my website to be very informative and enjoyable to some extent!

      Don’t worry, there will be more articles coming soon, so stay tuned!

  2. Hi Farhan, this is a great website! I had no idea about all of the intricacies of recording. My boyfriend is a bass player and the information was very helpful. I like the posts about audio basics, especially the one about soundproofing. I see that you have some advertisements in the sidebars. I would probably add different advertisements in the sidebars or more related to your topic. You can change the sidebars by getting a plugin to do this. Beautiful site and great job!

    • Hi Rene!

      Thank you for your kind compliments. I am glad that you have found my website to be of some value to you. Yes. my website is pretty young, and there is still quite a few things I still need to work on in terms of how it looks, and how to better promote my other articles.

      I appreciate your advice, and do come back for more!

  3. Hey there man, it’s Alexey. Thank you so much for such a great information. I liked it, and it was extremely thorough – I understood some things that I did not even knew about. I play the guitar and love rock music for almost 8 years as a hobby, but never thought about my amplifier in such a way. Well, now I know what to do with it, in case it blows.

    • Hello Alexey!

      Its great news for me, to know that you have enjoyed the article and have benefited from it. Wow, almost 8 years of playing rock guitar huh? That’s quite a commitment to music!

      Do come back for more articles, or if you have any other questions!

      Thanks =)

    • Hey there Jerry!

      Thanks for the compliments! Do drop by again for more updates!

      Cheers =)

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