Crunchy Sound, Right Out Of The Box (Guitar World 1992)

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Ronnie Montrose and Allan Holdsworth on recording with an isolation box.



CAPTURING THE BEEFY, beautiful sound of an electric guitar has long meant sticking a microphone in front of an amp. Unfortunately, mikes can pick up all sorts of other sounds - many of them undesirable. Multitrack recording practically demands that each track receives only one kind of sound, so instead of dealing with microphones, which can pick up unwanted sounds, it's often easier to just run a line from the amp's preamp to the mixer. This gives you complete isolation. It's also useful when running your amp flatout disturbs everyone around you. The drawback is that much of an amp's sound comes from its power amp and speakers, so using a direct output can make your tone thin and unsatisfying.

There is a way to get most of the benefits of going direct and miking an amp at the same time. Build a box, place a speaker and a microphone in it, seal it up, then plug your amp's output into the speaker and the microphone into your mixing console. Although it takes a bit of experimentation and carpentry, since no such boxes are commercially available, it's a tried-and-true approach. One of the pioneers in guitar amplifier isolation boxes is Ronnie Montrose, who began experimenting with one in 1980, when he was working with keyboardist Mitchell Froom. Later, Allan Holdsworth got hooked, and is still using them. To gain insight into this approach, I spoke with Ronnie, whose band, Gamma, recently released The Best Of Gamma (Crescendo), and with Allan, whose Wardencliff Tower [sic] is slated for release in October on Restless.

"We wanted to have all of our instruments-keyboards, drum machine and guitar-go through the P.A.," Montrose says. “I wanted to treat the guitar like any other direct-input instrument, and get away from that open-air, resonant-feedback microphone."

Almost instantly, he discovered an inherent problem with the box: "It was really easy to forget that you can only pump so much level into a 12-inch speaker before you blow it. When the engineers wanted more volume, they would turn up the amp, instead of the fader on the board. Another problem was that, like any enclosure, it has its own resonant frequency. Harbinger Sound (of Menlo Park, California] built three commercially available boxes, which had a box sealed inside of another box, with about three inches of foam between them. The internal box was 1-1/2' by 1-1/2' by 3', and the baffle board [the board on which the speaker is mounted] was angled so that one end was about 8 inches from the enclosure's end, and the other was about 12 inches from the end. The inside was lined with foam, to break up resonances a little bit."

Ronnie's box had a Sennheiser 409 dynamic microphone, which has a large diaphragm and can handle a lot of level: "I had good luck with that and a Celestion speaker."

Montrose wasn't particular about the amplifiers he used: "I don't think it makes much difference when you're below 50 watts, because the preamp creates most of the tone. I used different preamps and whatever power amp I had. I just made sure that I drove the speaker to the level I wanted. I put an LED level meter on the speaker, so I could get it to sing without damaging it."

Ronnie doesn't use the "iso" box anymore, but you can hear it in the last solo of "Odd Man Out," on Territories (Passport). He overdrove the speaker, and used the box's resonance as an effect.

Allan Holdsworth, who began using an isolation cabinet sometime after Montrose, coupled it with a technology with which he had been working since the 1970's: a circuit he designed that enables him to capture the tone of a loud amp without blasting himself out of the room. (A refined version, the Juice Extractor, is made by Rocktron).

“I often used to record guitar in my garage, because I didn't have a room for it," says Allan. “So I designed a cabinet with a speaker and a microphone on a stand. The speaker was positioned in the middle of the box so that the air space in front of it was equal to the air space behind it. The box was pretty big-it looked like a coffin for a 10-foot-tall guy. The baffles slid out, so I could put in a different speaker in a matter of seconds, without moving the mic.”

Before building his "coffin," Holdsworth tried going direct from his amp into the board (which is how he records rhythm guitar tracks), but he found the tone less than satisfying. "So now I run out of my amp into the Juice Extractor, then to a clean power amp, and then into a speaker.”

“For lead, I record a completely naked guitar sound. It's mono, and if I want to add anything, I do it later. When it's naked, you can tell more easily if the basic sound is right. You can use reverb and everything else to cover up the gremlins, but you really want it to be as gremlin-free at the start as possible."

The speakers Allan drops into the box are Celestions of various wattages. “Each has a different sort of eq," he explains. “I use a single 35-watt 12-inch, which is lively-sounding, and is good if you're not pushing the box too loud, but I don't use them live, for fear they'll wilt. I also like the K85's, although they sound best in a 4x12. You always have to consider the box as well as the speaker."

Holdsworth's "coffins," which can be heard on every one of his albums since Sand, have been built in various sizes—from 2' by 1' by l' up to 10' by 3' by 4'. "The baffle slides right down in the middle," Allan says, "as if you were sawing a dummy in half. I can put a 10-inch, a 12-inch, or even a 15inch speaker inside. The bigger coffins always sound better because their fundamental resonance frequency is lower."

Allan offers one final bit of advice to experimenters: "Above a certain volume, iso boxes don't sound very good, because you start to hear the box. Keep the volume down inside the box. "Use a large-diaphragm mic as close as possible to the speaker. A lot of engineers like to move a mic away from the speaker to capture reflections, but you can record with no ambience and add room sound or reverb later. Even if it means recording onto tape with no ambience, you can play it back through flat-response monitors into a room and put mikes around and re-record, picking up the room's ambience."

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