Amp into load — Post-Prog-Metal

Amp into load (6)

24. THE ELECTRICAL HALF OF LOUD

Cranked amp → Attenuator — The Echoplex-front rig, Plexi at full volume, no pedals

• Mechanisms: Attenuator limits, Reactive vs resistive load, Thermal power compression, Mechanical non-linearity, Power supply sag, Power scaling
• The move: A full-output amplifier into a load that dissipates most of its power as heat.
• The friction: It preserves the output stage's behaviour and none of the speaker's. A cabinet at volume contributes excursion-dependent cone breakup and thermal power compression — a voice coil going from 20 °C to 200 °C loses 4.7 dB of sensitivity — and an attenuator cannot reproduce any of that, because the cone is no longer moving that much air.
• The recipe: Use a reactive attenuator, not a resistive one: a flat resistive load makes the tone more compressed and dark as attenuation rises, and records far too bright and buzzy. Expect to add treble back as you attenuate further. And accept the limit — heavy attenuation of a Plexi will never sound like a loud Plexi, because half the mechanism has been removed.

Overdriven valve amplifier tone at moderate volume, with all the electrical compression of a cranked amp and none of the cabinet's own breakup, four minutes, 96 BPM, thick and slightly flat. The power stage is genuinely at full output — the tubes are working, the supply is sagging on hard attacks and swelling back behind them, and the transformer is contributing its own soft saturation on low notes. But the speaker is barely moving, so the ragged excursion-dependent cone cry and the thermal compression that a loud cabinet would add are simply absent: the tone is smooth, even and controlled where a loud amp would be unruly. It sounds like a photograph of loudness rather than loudness. The top end needs help and is bright as a result. Playing is blues-rock lead and rhythm, dynamic and dependent on pick attack, with the guitar's volume control used constantly. Drums and bass are recorded at natural volume in the same room, so the guitar's restraint is obvious against them. It ends on a sustained chord that decays without ever blooming into feedback, because there is not enough acoustic energy in the room to start one.

25. THE FROZEN CABINET

Cranked amp → Reactive load and IR — The silent rig, The djent direct rig, The profiler and modeller rig

• Mechanisms: Impulse response, Reactive vs resistive load, Mic placement, Impedance curve, Attenuator limits
• The move: A full amplifier into a speaker-like electrical load, with the cabinet replaced by a linear filter.
• The friction: An impulse response is a linear time-invariant capture. It holds frequency response, phase, inter-speaker cancellation and the entire mic and converter chain — and it categorically cannot hold distortion, dynamic compression or cone breakup. So the amp responds correctly and the cabinet does not respond at all.
• The recipe: The load must be reactive so the output stage sees a speaker-like impedance curve; a resistive one changes what the amp does. Then pick the IR by the mic position you would actually have used — moving an SM57 from dust cap to cone edge is worth 8 dB at 1.6 kHz, which is a bigger move than most EQ. Blend two IRs rather than EQ-ing one.

Silent-recorded valve amplifier tone, perfectly repeatable and completely consistent from take to take, five minutes, 124 BPM, precise and modern. The amplifier is real and running at full output into a reactive load that presents a speaker-like impedance curve, so the output stage behaves exactly as it would into a cabinet — sagging, compressing and saturating naturally. The cabinet itself is a fixed linear capture: it applies the frequency and phase response of a specific speaker, cabinet, microphone and preamp, and it never changes. That means hard playing gets louder and more distorted at the amplifier but never adds the ragged cone breakup a real speaker would contribute, so the top end stays smooth and identical at every dynamic level. The tone is tight, focused and slightly two-dimensional, sitting perfectly in a dense mix. Two guitars are tracked left and right with different cabinet captures — one brighter and centred on the dust cap, one darker and further out toward the cone edge — and the difference between them creates the width. Bass and drums are programmed and tight. It ends on a stereo chord with the two captures decaying at slightly different rates.

26. DOUBLE OR HALF

Amp head → Mismatched impedance — The doom and sludge rig, Plexi at full volume, no pedals

• Mechanisms: Impedance mismatch, Impedance curve, Amp output impedance, Output transformer, Negative feedback
• The move: A valve output stage driving a load that is not what its transformer tap says.
• The friction: The load is a curve, not a number: a measured 8 Ω driver reads exactly 8 Ω at three frequencies, peaks near 70 Ω just above 100 Hz and climbs to around 50 Ω by 20 kHz. Against that, a nominal mismatch is a smaller change than it sounds — until it is not, and then it is a repair rather than a tone.
• The recipe: The convention that keeps appearing: mismatches within double or half the rated impedance are generally considered safe. Beyond that, too high a load stresses the transformer and tubes with excess voltage and too low pulls excess current. Solid-state amps are the opposite — too low a load is the dangerous direction and there is no transformer to protect.

Loud valve guitar tone with a slightly loose, unusual feel, four and a half minutes, 84 BPM, woolly and characterful. The output stage is driving a load that does not quite match its rating, so the damping factor is off and the amplifier's grip on the cone is looser than it should be: low notes bloom and overhang slightly, the low midrange is fatter, and the whole thing feels a fraction slower to respond than a matched rig. The amplifier is a valve head at high volume, sagging under hard attacks, and the speaker's own impedance peak just above 100 Hz is exaggerated by the high source impedance, giving a pronounced resonant thump on every low note. Playing is slow and heavy: sustained power chords with lots of space between them, allowed to bloom and decay fully. The cabinet is closed-back with real cone breakup around 2 to 3 kHz and nothing above 5 kHz. Drums are slow, enormous and slightly behind the beat. Bass is deep and simple. There are no effects at all beyond the room. It ends on a low chord left to feed back and slowly rise in pitch.

27. THE BACK PANEL IS A FILTER

Amp head → Open-back or closed-back cab — The blackface clean rig, Plexi at full volume, no pedals

• Mechanisms: Open back vs closed back, Multiple drivers, Band-limiting, Sensitivity, Mechanical non-linearity
• The move: The same head into two cabinets that differ only in whether the rear is sealed.
• The friction: Front and rear waves interfere below the dipole peak, rolling off at about 6 dB per octave, and sealing the back raises the driver's resonance by roughly two and a half semitones. So the choice is not a preference between two flavours, it is a genuine change in low-frequency response and in how directional the rig is in the room.
• The recipe: Open back for clean and mid-forward tones and for filling a small room; closed back for tight low end, projection and anything downtuned. If a rig sounds huge on stage and thin out front, that is an open back radiating backwards. And note that the cabinet choice interacts with everything upstream — a scooped preamp into an open back has almost nothing left in the middle.

The same guitar part played twice through two cabinets, five minutes, 100 BPM, illustrative and warm. First half: an open-backed combo, where the front and rear waves partially cancel below the dipole peak so the deep low end is missing, but the low midrange is generous and punchy and the sound spreads omnidirectionally around the room rather than beaming forward. It is airy at the top and feels close and enveloping. Second half: the identical amplifier into a sealed cabinet, where the driver's resonance sits higher and nothing radiates backwards — the low end is tighter, deeper and far more directional, the tone is more focused and forward, and the airiness is gone. The guitar is mid-gain throughout, played with dynamic chord work and single-note lines so the difference in low-frequency behaviour is obvious on both. The amplifier settings never change between halves. Recording is one microphone at a fixed distance, so the cabinet is the only variable. Bass and drums are steady and unremarkable by design. It ends with both cabinets running together on a final chord.

28. TWO SPEAKERS, ONE PHASE PROBLEM

One head → Two different cabs — The two-amp grunge rig, The rack rig and buffered loop switching

• Mechanisms: Multiple drivers, Mic placement, Impulse response, Published speaker specs, Sensitivity
• The move: A single amplifier driving two dissimilar cabinets at once, which is a recording trick and a live problem.
• The friction: Two drivers with different resonances and different distances to a microphone will partially cancel each other. That is exactly what an impulse response captures as inter-speaker cancellation — and it can be a gorgeous comb-filtered thickening or a hole in the midrange, depending entirely on placement, with nothing on the amplifier able to fix it.
• The recipe: Mic each cabinet separately and check the sum in mono before committing; if the low end disappears, flip the polarity on one and check again. Keep the microphone distances equal or deliberately unequal, not accidentally so. Live, two dissimilar cabinets in one room is a lottery — the audience hears a different sum at every seat.

Enormous layered guitar tone built from two different speaker cabinets running from one amplifier, five minutes, 112 BPM, wide and complex. The head drives a closed-back cabinet with a modern high-sensitivity driver and an open-backed cabinet with a low-powered vintage-voiced one at the same time, and each is captured with its own microphone. Because the two drivers have different resonances and their microphones sit at slightly different distances, the sum has a distinct comb-filtered character — certain narrow bands reinforced, others partially cancelled — that gives the tone a hollow, three-dimensional quality no single cabinet produces. The vintage driver breaks up early and adds ragged cone distortion on top of the amplifier's own; the modern one stays composed and supplies the low end and the top. Together they read as one very large, slightly unstable guitar sound. Playing is mid-gain riff-based rock with a heavy pick attack and open ringing strings. Drums are live and roomy; bass is thick. The two cabinet signals are panned slightly apart rather than hard, so the width is subtle. It ends on a chord where the two cabinets decay at visibly different rates.

29. DOPPLER YOU CANNOT SIMULATE

Amp → Rotating baffle — The Texas blues rig, The jangle rig

• Mechanisms: Rotating baffle, Chorus, Stages to notches, Vibrato, Uni-Vibe stagger
• The move: A real speaker mechanically moved, rather than a circuit imitating the result.
• The friction: A rotating baffle Doppler-shifts an actual sound source, so pitch, amplitude and radiation pattern all change together and the room becomes part of the effect. A phaser produces notches, a chorus produces detuning, and neither produces the physical three-dimensional movement — which is why every phase-shift approximation is recognisable as one.
• The recipe: Mic it in stereo, at least two microphones at different angles, and let the room in — a close mono mic throws away most of what makes it work. Speed changes are the effect, so use the ramp between slow and fast rather than parking it. And expect the recorded version to be far more convincing than the in-room version to anyone not standing in front of it.

Clean and lightly overdriven guitar through a physically rotating speaker baffle, five minutes, 76 BPM, three-dimensional and unmistakably mechanical. The sound source itself is moving, so every note is Doppler-shifted in pitch as well as swept in amplitude, and the room's reflections move with it — the effect surrounds the listener rather than sitting in the stereo field. Two microphones at different angles capture it, giving genuine width that is not a delay or a phase trick. The rotation speed changes during the piece, ramping slowly from a lazy sway up to a fast shimmer and back down, and the ramp itself is the most expressive gesture in the arrangement. The guitar underneath is warm and mid-focused, played with sustained chords and slow melodic lines so there is time for the rotation to work on each note. The amplifier is only just breaking up. A small amount of natural room reverb, nothing electronic. Bass is simple and warm; drums are brushed and quiet. It ends with the rotation slowing to a stop over a final held chord, the pitch wobble getting slower and wider until it settles.