PART 3 - REACTIVE LOADS AND IMPULSE RESPONSES
Do you need a $1500 tube amp head with a $10 impulse-response loaded into a $600 reactive load box to record directly without waking the family? Maybe, but maybe not.
WHAT IS A NON-REACTIVE LOAD?
To understand the importance of the reactive load we need to look at a non-reactive load. A non-reactive load is basically a high-power resister with a fixed value that matches the output impedance of your amp. An example of this is the original Mesa Cabclone. Featuring an internal resistor load that can also be defeated, the CABCLONE can be used to capture a direct signal either with or without a live speaker connected to the amplifier. You use the original CabClone instead of putting a microphone in front of a speaker. The CABCLONE is designed for amps rated at 150-Watts or less.
The original CabClone can be used as a load with no speaker connected. When used like this the sound is not as good as it is when there is a speaker connected. The transformer output on a tube amp craves the reactions of the speaker cone, as the cone moves in and out responding to different frequencies a varying impedance is presented to the amplifier output, that varying impedance is the reactivity of the speaker load. With no speaker connected there is no reactivity so the sound is less dynamic, duller, less lively, more compressed sounding.
You can connect a Cabclone to a speaker to get the rich tone of a reactive load but this setup still leaves you with a lot of guitar amp volume to get rid of. If you unplug the speaker and record without it then you get a much less dynamic performance.
WHAT IS A REACTIVE LOAD?
|OX AMP TOP BOX, REACTIVE LOAD BY UNIVERSAL AUDIO|
A reactive load attempts to fool your tube amp into thinking it is connected to a speaker which is also a type of reactive load. Most speakers have a nominal advertised impedance of say 8 or 16 ohms. The actual impedance presented to the amplifier output transformer is an impedance curve that swings all over the place depending on the frequency your guitar is putting out while you’re playing.
A reactive load box can be substituted instead of a speaker, the box will present a swinging impedance (like a speaker) and power-disapation devices (load resisters) to suck up the speaker power and turn it into heat instead of sound. With a properly designed reactive load your amplifier does not know or care that it is not connected to a real speaker. Depending on which box you choose will greatly affect your tone.
WHAT IS AN IMPULSE RESPONSE?
Have you ever heard the acoustic sound of a massive Catholic church? I worked in many of them over my career and I can tell you it is not uncommon for the structure to have a 3 to 6 second reverb decay time. It’s fun being in that space alone and clapping your hands to create your own real-time impulse response, live, which you can experience with your ears and brain in real time.
In our guitar application an impulse response is a recording of the reverberation that is caused by an acoustic space when an ideal impulse is played in that space. Creating impulse response profiles have been associated with starter pistols and balloons-popping, sometimes referred to as transient methods, the response is contained at the beginning of the recording in an impulse.
What does that mean?
In our contemporary digital era an impulse means using a small slice of an acoustic recording to influence what you’re hearing in real time. Is this small slice of an ambient, acoustic footprint necessary for you to have a good electric guitar tone? If it is, what is the shortest path to get there?
IMPULSE RESPONSE PLATFORMS UNDER TEST
For my own education about modern “impulse response technology” I obtained several guitar processors which utilize some form of it.
Three have reactive loads:
Four of the gadgets process signals at guitar-level and have 1/4” input and output jacks:
Two Notes CAB M+ (also XLR output with ground lift switch)
Joyo Cab Box (also XLR output with ground lift switch)
The Two Notes CAB M+ has input attenuators to allow it to be inserted inline between a guitar amp and speaker.
EPILOGUE - PART 3 DIRECT RECORDING
It has been a ton of fun trying out and digging into all these different boxes. They are all capable of making good tone and great sounds.
My personal favorites will remain a secret for now as I continue to explore what these boxes are capable of.
Enjoy the journey, Good Music to You!
©Sept 2021 by Mark King
It's not ok to copy or quote without written permission. Thanks