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Big Guitars in Small Spaces

January 1, 2006
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Guitarists with home studios constantly face the problem of recording the sound of their amplifiers while maintaining the peace. Keeping the neighbors from calling the police while capturing the bone-crushing volume required for many guitar amplifiers to sound their best can be a daunting task.

In this article, I'll discuss several effective ways to record guitar amps within the confines of a one-room apartment or a home studio. Your preferences, work habits, budget, and the size of your room will determine which method works best for you. And remember, you're not limited to one option — you may find different methods work better for different amps or setups.

A Room Inside a Room

Nothing allows more options for mic and speaker cabinet placement than building a completely soundproof project studio. In other words, no sound from the outside comes into your project studio, and no sound from the inside escapes.

Although soundproofing can be part of the process of acoustically treating your space, sound isolation and acoustic treatment are not the same. Acoustic treatment refers to the process of tuning the acoustics of a room to eliminate standing waves, dead spots, and so on. That doesn't necessarily produce the isolation you need to record excruciatingly loud guitar amps. (See “Special Treatment” in the May 2005 issue of EM for a detailed discussion of acoustic treatment.)

To completely isolate a guitar amp from the rest of the outside world, you need a floating room. A floating room is a room within a room — the outer room has acoustically absorptive material on the walls, floor, and ceiling and encloses the smaller, inner room. While ideal, that is expensive and is not always compatible with your living situation.

Amp in the Booth

Fortunately for the home recordist, several manufacturers make portable isolation and vocal booths. (The sidebar “Manufacturers and Developers” lists contact information for all companies discussed in this article.) Isolation and vocal booths typically measure 4 feet by 4 feet with a 7-foot ceiling. They are constructed with sound-absorption materials on all sides and corners (including the booth's top and bottom), cable passage tubes, and ventilation systems. They are not 100 percent soundproof, but they generally do a good job, and are large enough to allow considerable flexibility in the number and placement of microphones.

FIG. 1: The VocalBooth Amplifier -Enclosure is an example of an isolation booth -especially designed for guitar amplifiers and speaker cabinets.

Sound Pressure Level (SPL) reduction will vary with frequency and the type of sound absorption material used. As a general guide, at the lowest frequencies a guitar can reproduce (around 125 Hz), you can expect an SPL reduction of 26 to 30 dB. SPL reduction increases with frequency, and at the highest frequency ranges that a guitar can reproduce (around 5 kHz), you can expect an SPL reduction of 40 to 45 dB.

Although isolation booths are more affordable than a completely soundproofed room or garage, they are still very costly. Prices range from $1,800 to more than $10,000 for the largest and most noise-suppressing models. For guitarists who can settle for a smaller isolation box to hold just their amplifiers, there are less expensive options.

For example, Vocal Booth makes four sizes of amplifier enclosure, from 30 to 48-inches square, with prices ranging from $695 to $895 (see Fig. 1). These boxes still have ventilation and cable tubes, but are only large enough for guitar speaker cabinets or combo amplifiers. For those adept at home construction projects, there are plans online at www.amptone.com for building your own guitar speaker isolation booth.

Speaker in a Box

If you don't need to mic a specific speaker cabinet or amp-speaker combo, and all you need is to record the amplifier through a genuine guitar speaker, you have a few additional options. A number of manufacturers package a single 10- or 12-inch guitar speaker in a sound-absorbent box with a microphone gooseneck inside and an XLR connector for a mic cable outside.

FIG. 2: The Demeter Silent Speaker Chamber is an example of a soundproof box with a built-in guitar speaker and microphone gooseneck.

Randall Amplification and Demeter Amplification both have such products (see Fig. 2). Randall has two models in its Isolation series: the Isolation 10 for $399 has a 10-inch Eminence speaker, and the Isolation 12 for $499 has a 12-inch Celestion speaker. Demeter's Silent Speaker Chamber comes in three configurations: a box with no speaker for $550, a box with a 12-inch Eminence speaker for $650, and a box with a 12-inch Celestion speaker for $750. Demeter also offers the option of two microphone goosenecks, and the company will be introducing newer cabinets with extra porting and soundproofing in the near future.

You can expect an SPL reduction with those speaker boxes comparable to that achieved with vocal booths and amplifier enclosures. Demeter Amplification, for example, reports an average SPL reduction of 36 dB for the Silent Speaker Cabinet. But, if you use a speaker-in-a-box solution, be sure that you don't turn your amp up so loud that you blow the speaker inside! Depending on the wattage of your amp and the wattage of the speaker, you may need to use an attenuator between the amp and the speaker.

The Hard Way

Hardware devices emulating guitar speaker cabinets have been around since the arena-rock heyday of the '80s, when guitarists with monster racks used direct boxes to send the signal from their amplifier to various processors and PA systems. Some of those devices are very simple. The only control on the Hughes & Kettner Redbox Pro or the Behringer GI100 is a button to activate the simulation (see Fig. 3). Other simulators such as the Voodoo Labs Cab-Tone offer a variety of speaker simulations. Still more expensive speaker simulators, such as the Sequis Motherload or the Palmer PGA04, offer complete EQ to adjust the sound of the cabinet.

FIG. 3: You can use a hardware direct box with a speaker simulator circuit, such as the Behringer GI100 (shown below), to eliminate the need for miking a speaker.

To record through a hardware speaker simulator, first connect a cable from your amplifier to the simulator. If your amplifier has a line output (sometimes called a slave output), you can connect the cabinet simulator to this output with an instrument cable. If your amplifier doesn't have a line out, you will need to connect a cabinet simulator to the speaker output of your amp using a speaker cable. If your amplifier has a line out, you may still want to connect the speaker simulator to the speaker output, especially if the line output comes before the power amp stage, which can have an important effect on the tone. After you connect the amplifier to the speaker simulator, connect the simulator directly to your mixer or DAW interface using the appropriate cable.

Keep in mind that the output transformer of your amplifier expects the reactive load of a speaker cabinet. If you connect a speaker simulator to your amplifier, you will still have to connect the amplifier to either a real speaker cabinet or a speaker load to avoid the risk of blowing the output transformer of your amp. The Palmer PGA04 and Sequis Motherload incorporate a speaker load. With cabinet simulators that don't, such as the Behringer GI100 or the Hughes & Kettner Redbox Pro, you can use an attenuator such as the THD Electronics Hot Plate or Gibson Power Stealth to deliver the proper speaker load to your amplifier.

Take a Load Off

If you are using a speaker load instead of a speaker, you will need to monitor your guitar sound through your mixer or DAW. That allows you to turn your guitar amplifier up for maximum power-amp saturation while monitoring your guitar through your mixer or DAW at normal listening levels. If you don't need maximum power-amp saturation, you can plug your amplifier into a speaker simulator for direct recording and into a speaker cabinet for low-volume monitoring. Then, you can record your guitar amplifier direct at lower volumes while avoiding the problem of microphone bleed from ambient noise due to the low-volume level.

Randall Amplification's MTS and XL speaker cabinets with mic eliminator circuits work well when you can turn down the amp. Randall specifically matched its Celestion Vintage 30 loaded 4 × 12 cabinets to recordings made with a Shure SM57 as well as various condenser microphones. The circuit has voicing options for each microphone's response. The speaker cabinet does not include any attenuation, so the volume of the direct signal is controlled by the amplifier volume.

How close to the real thing do hardware speaker simulators get? As Web Clip 1 shows, although the amp-speaker-microphone sound doesn't exactly match the sound of the same amp through the GI100, they both sound like an amplifier through a speaker.

JLH Products' AxeTrak is the most hybrid solution. This small box combines the speaker-in-a-box concept with a hardware speaker simulator. It consists of a small, soundproofed box with the driver of a 6-inch speaker and the mic element of a microphone. As with the speaker isolation boxes, if your amp puts out more watts than the speaker driver can handle, you'll need an attenuator between your amp and the AxeTrak.

A Soft Option

Hardware devices are not the only option for emulating guitar speaker cabinets; there are software speaker simulations as well. Many guitar amp simulator plug-ins — Native Instruments Guitar Rig (see Fig. 4 and Web Clip 2), MDA Combo, and Logic Pro 7 Guitar Amp Pro, to name a few — allow independent access to the plug-in's speaker cabinet simulations.

FIG. 4: Native Instruments Guitar Rig gives a large variety of speaker-cabinet models, microphone types and placements, and other options for dialing in your virtual cabinet.

Software speaker simulations are designed to replicate hardware simulator circuits, measuring the responses of the interaction of speaker cabinets with microphones. Most software speaker simulators use some form of convolution to place the audio signal in a digital environment that re-creates the speaker-microphone interplay.

One advantage software plug-ins have is that you can switch between simulations to choose the best match for a specific amplifier, instead of being committed to a single hardware cabinet simulation. Also, plug-ins typically give you many more simulations to choose from than hardware devices, and they often allow you to configure not only the variety of speaker cabinet, but other options such as microphone type, placement, and distance; the physical dimensions of the cabinet; and so on.

Plugging In

You will need to plug a line-level signal from your guitar amp into your mixer or DAW to run your guitar amplifier's output through a software speaker simulator. If your amplifier has a line out, you can use that. Most attenuators also have line outputs. Even if your amplifier has a line output, if it is not after the amplifier's power stage, you may prefer to use an attenuator. As with hardware cabinet simulators, if your amplifier is not plugged into a real speaker cabinet for monitoring purposes, be sure to use a speaker load such as an attenuator, or you'll risk damaging your amp's output transformer.

Once you have the amplifier signal routed through a line output into your computer, you will need to turn on software monitoring in your host application in order to hear your guitar amplifier through your speaker simulator as you play live. Unfortunately, whenever you use software monitoring, you have to deal with software-monitoring latency.

Software-monitoring latency is the delay between the time the guitarist plays a note on the guitar and when it comes out of the computer monitors. Software-monitoring latency occurs because the audio signal needs to enter your computer and be processed before you hear it. By contrast, when a guitarist strums a note, it is transferred almost instantaneously through the amplifier to the speaker.

Software-monitoring latency cannot be completely avoided; however, if your computer is fast enough and your audio interface has low-latency drivers, you may be able to reduce the audio buffer size to 128 samples or lower. That results in a latency of less than 10 ms, which is almost undetectable. If you get clicks and pops or CPU overload errors, however, you'll have to increase the buffer size until you can monitor without problems.

If you don't mind hearing a different sound in the room, set your amplifier to a comfortable volume and connect it to a real guitar speaker. That way you won't have to deal with software-monitoring latency, nor will you have to use a speaker load to keep your amplifier's output transformers happy. The downside is that you won't hear the same sound that you are recording.

Do the Convolution

You can make your own convolution model of your speaker. The first step is to record an impulse response of the space — in this case, a guitar speaker cabinet. The software then uses its convolution engine to convolve — literally, to roll together — your impulse response with the audio signal being processed.

Many convolution reverbs allow you to make your own impulse responses. Audio Ease's AltiVerb, Waves' IR series, and Apple's Space Designer plug-in for Logic Pro are examples. You can use any of those applications to make an impulse response of your specific speaker cabinet.

The process of creating an impulse response varies from program to program, but the basic idea is that you send an amplified sine-wave sweep through your speaker, then record the result. (Because the line-level output of your audio interface will not produce a sufficiently loud sign sweep, you will need to amplify its output with a power amp.) The convolution software then deconvolves the recording to produce the impulse-response curve used by the reverb. Web Clip 3 is an example of Apple's Space Designer being used to simulate my speaker cabinet.

The Same Only Different

The accuracy of your homegrown impulse response will depend on a number of factors. Those include how clean the power amplifier sending the sine-wave sweep is, how well you record the response, and the quality of your convolution plug-in's impulse response generating algorithm.

FIG. 5: Wave''s Q-Clone is a new type of convolution processor that uses two real-time plug-ins, Q-Capture and Q-Player, to create impulse responses from hardware on the fly.

For example, if you are trying to get an accurate simulation of a Mesa Boogie 4 × 12 cabinet, sending a sine-wave sweep through the power section of a Mesa Boogie Dual Rectifier and recording it with a Sennheiser ribbon mic will create an accurate impulse response of the Dual Rectifier 4 × 12 cabinet and Sennheiser mic chain. But if you then use that impulse response on a Marshall DSL head, it will not sound very much like a Marshall DSL through a Mesa Boogie 4 × 12 cabinet. Moreover, impulse-response generation can be a time-consuming, offline process.

Waves' innovative new convolution based application, Q-Clone, tries to take some of the tedium and guesswork out of impulse-response creation by using two plug-ins: the Q-Clone plug-in and the Q-Clone Capture plug-in (see Fig. 5). Q-Clone Capture creates the sine-wave sweep and captures the result, creating an impulse response on the fly. With that system, a guitarist can be playing through the amplifier live while the recordist tests microphones and mic placement to get the best impulse response. As Web Clip 4 shows, Q-Clone's results are on a par with other convolution processors.

Who's Better, Who's Best

Is it better to create your own speaker simulation for a convolution reverb or to use an amplifier simulator? Making your own impulse response is a compelling way to capture the sound of a specific speaker-cabinet and power-amp combo. But if you don't have the right microphone or if you want to use simulations of a number of different amps, you're probably better off with a professionally designed guitar-amp simulator.

Having a project studio in a small noise-sensitive space doesn't prevent you from recording that Marshall stack or Fender Twin combo. Soundproof booths, enclosures, or speakers; hardware cabinet simulators; software speaker emulators; and convolution processors can all be used to record even the loudest amplifiers without getting arrested.


Orren Merton, author of Logic Pro 7 Power (Muska & Lipman, 2004) and Logic 7 Ignite (Muska & Lipman, 2005), believes that too loud is never loud enough. The author wishes to thank Derrick Davis, Jan Duwe, Adam Fifield, and Doug Reynolds for their contributions to this article.

MANUFACTURERS AND DEVELOPERS

Here is the contact information for the hardware manufacturers and software developers listed in the main text.

Apple Computer
www.apple.com

Audio Ease
www.audioease.com

Behringer USA, Inc.
www.behringer.com

Demeter Amplification
www.demeteramps.com

Hughes & Kettner, Inc.
www.hughes-and-kettner.com

JAMS Audio (Palmer)
www.palmergear.com

JLH Products
www.axetrak.com

MDA
www.mda-vst.com

Native Instruments USA
www.native-instruments.com

Randall Amplifiers
www.randallamplifiers.com

Sequis
www.motherloadusa.com

THD Electronics, Ltd.
www.thdelectronics.com

VocalBooth
www.vocalbooth.com

Waves, Inc.
www.waves.com

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