How I measured
Everything on this page came from one afternoon and gear anyone can buy. The point of doing it this way is that anyone can repeat it — and correct me.
- Microphone
- miniDSP UMIK-1 measurement microphone, fixed gain
- Recorder
- Voice Memos on a Mac, lossless, 44.1 kHz
- Plucks
- Open low E and low A, six to thirteen plucks each, same flesh rest stroke
- Distances
- 2 feet and 6 feet, slightly off-axis of the soundhole
- Tap tests
- Felt mallet on the body, fifteen to twenty-eight taps per instrument
- Analysis
- Harmonic levels, spectral centroid, decay times, inharmonicity fits and averaged tap spectra, computed in Python
One room, one microphone position per distance, one player, and no calibration file applied. Room reflections can move individual low partials by several decibels, and I can't fully control how hard I plucked from one instrument to the next. The broad patterns below held across repeated plucks and both distances; treat single numbers as approximate.
The five instruments at a glance
“82 Hz output” is the level at 6 feet of the low E’s second harmonic, on a common reference, so the numbers compare directly between instruments. The guitarrón has no low E; its value is its lowest E, an octave higher, whose fundamental lands on the same frequency.
The note isn’t there
Nobody hears the fundamental of a low E from an acoustic bass guitar. On every one I measured, the 41 Hz fundamental sat 20 to 25 dB below the strongest partial — for practical purposes, absent. Yet every one of them plays an unmistakable low E, because the brain reconstructs the note from the harmonics above it. This is the missing fundamental, and it isn’t a trick small instruments play. Even on the upright, the low E’s fundamental sat 20 dB below its own second harmonic.
The body chooses which harmonics escape
As the body gets smaller, its resonances climb, and the instrument’s energy climbs with them. The upright pours its energy into the second harmonic at 82 Hz. The Tario peaks on the third, the Martin on the fourth, and the Kala spreads across the fourth through the seventh. Above about 200 Hz, all four are roughly level. Almost the entire difference between them lives in the bottom three harmonics.
The two instruments that work share one tuning
A tap test shows where a body resonates. The lowest strong peak is the air resonance — the note you get blowing across a bottle — and below it, radiated output falls off a cliff. The strong peaks above it belong to the top.
The three acoustic bass guitars resonate progressively higher as they get smaller: 97 Hz for the Tario, 114 for the Martin, around 175 for the Kala. The upright and the guitarrón both land at 63 Hz, with their main top response between roughly 120 and 145 Hz.
A carved European orchestral instrument and a Mexican folk instrument, built by ear with no theory of hearing, arrived at the same two numbers.
They got there by opposite routes. The upright has roughly twice the guitarrón’s air volume and far larger openings in its top; the guitarrón is smaller, with one modest soundhole. The air resonance rises with the size of the opening and falls with the volume of the box, so each tradition balanced the two differently and landed in the same place. Given the guitarrón’s soundhole, the upright’s body would resonate somewhere near 45 Hz. Neither tradition went there.
Lower air resonance, more 82 Hz
The second harmonic of the low E, at 82 Hz, is the single most valuable partial on a bass: it sits at the bottom of the band the ear relies on, and on most acoustic instruments it falls right at the edge of the body’s cliff. Plot each instrument’s output at 82 Hz against its air resonance and a clear relationship appears.
Between about 115 Hz and 60 Hz, output at 82 Hz rose by roughly half a decibel for every hertz the air resonance came down. Beyond 115 Hz the curve flattens: once 82 Hz is far below the cliff, moving the resonance further away matters less. That makes the move from a guitar-sized body’s resonance down into the 60s the steepest, most rewarding part of the curve.
Loudness and depth are different things
At 6 feet — campfire distance — the Martin is as loud as the Tario on the low E and louder on the low A. Yet it is 7 dB weaker at 82 Hz, and its balance point sits 30 Hz higher. On the low A, the Kala nearly ties the Tario in loudness while sitting 20 dB behind it at 110 Hz. A decibel meter says these instruments are equals. Their spectra say they are giving the listener very different evidence for the note.
The guitarrón makes the point most vividly. Its octave E ties the upright on A-weighted level, a rough stand-in for perceived loudness at moderate volume, while the upright towers over everything on raw level because nearly all its energy sits in the bass. The upright reads deeper. The guitarrón cuts.
Where the balance point sits
The spectral centroid is the balance point of a sound’s energy: weight every partial by how loud it is and find the centre of gravity. It is the best single predictor of whether a sound reads as dark or bright. Dividing it by the note’s fundamental expresses it in harmonics, which makes it independent of pitch — and lets it be compared directly with the dominance region, harmonics two through five.
On the low E, each instrument lands in a distinct place, and each position matches the word players reach for. The upright sits at the bottom edge: enormous depth, not much definition — muddy. The Tario sits near the centre: deep and clear. The Martin sits in the upper half: present, cutting. The Kala sits above the band entirely: throaty.
Close-up measurements flatter bass
Moving the microphone from 2 feet to 6 cost the Tario 12 to 14 dB — about 3 to 4 dB more than distance alone predicts — and the lowest partials fell fastest. Below the air resonance, the top and the soundhole move against each other and partly cancel; close to the instrument you still catch some of that bass, and a few feet away the cancellation wins.
Bigger bodies are flattered most. The Kala lost 9 to 10 dB over the same distance, close to what simple spreading predicts. Part of the Tario’s dramatic lead at 2 feet had evaporated by 6. Any fair comparison of acoustic bass instruments has to specify a distance, and it should be at least a metre.
Reading a body from its decays
Before the tap test, the Tario’s own notes had already sketched its body. A partial that dies fast is losing its energy somewhere, and on an instrument the main place for it to go is into the body and out into the room. Plotting how long each partial rang, across both strings, grouped the partials by frequency rather than by harmonic number: long-ringing below 60 Hz and between about 110 and 125 Hz, fast-dying near 82 Hz and from 160 to 220 Hz.
The tap test confirmed the shape — an air resonance, a trough, a cluster of top resonances — and corrected the number: I had estimated the air resonance near 80 Hz, and it measured 97. The shape was right; the measurement fixed the value.
Strings: clean, even the steel one
Every synthetic-core string in this set came out essentially harmonic: partials within a few cents of whole-number multiples, with no sign of the steadily growing sharpness that string stiffness produces. So did the upright’s steel rope-core Spirocores — at a 41-inch scale, which is exactly the medicine steel needs. That is consistent with the argument that long scale lengths exist to tame steel’s stiffness.
It also means the villain of my manifesto — steel strings at the scale lengths acoustic bass guitars actually use — was not in this dataset. Among these five instruments, the body explains almost everything the measurements could see. The next measurement is a steel-strung acoustic bass guitar under the same protocol.
Why the little Kala won anyway
Head to head, the Kala U-Bass with Galli black nylon strings is the weakest of the five. Yet it hung with a hand-built resonator tenor guitar in front of a crowd of strangers at a hostel in the Tetons, and held its own under Micaela Kingslight’s voice and nylon-string guitar in Costa Rica. The measurements explain why.
- It competed on pitch, not frequency. Its energy overlaps the guitars’ register, but its harmonics are cleanly spaced at 41 Hz, so the ear groups them into one voice far below anything else playing. Clean harmonics don’t just sound deeper; they are easier to pick out of a mix.
- Its energy sits where hearing is keen. At 165 to 290 Hz, it is far more audible at moderate volume than 41 or 82 Hz would be. It lacked depth, not audibility.
- Listeners were close, where even the Kala came within about 6 dB of the Tario.
- The competition was gentle. A nylon-string guitar and a singer leave the low register open.
- Expectations were zero. A ukulele-sized instrument producing an unmistakable bass line violates everyone’s prior at once. “That little thing sounds like a bass” is the sound of it happening.
What I got wrong
The measurements corrected me four times in one afternoon. Each time the prediction had the right shape and the wrong number.
- I wrote that an upright and an acoustic bass guitar radiate nearly the same amount of 41 Hz. The upright radiates about 20 dB more.
- I argued that small bodies are an advantage. They trade depth for presence, which wins some rooms and loses others.
- I read a notch in the Tario’s sixth harmonic as a quirk of my plucking position. Moving the microphone made it vanish; it was a dead spot in the room.
- I estimated the Tario’s air resonance at 80 Hz from its decay times. It is 97.
What it means for building one
The Tario — the best acoustic bass guitar I own — has its air resonance nearly 30 Hz too high and a trough in its response right where the low E’s third harmonic lives. The targets for my own instrument land on both weaknesses, and on the tuning the upright and guitarrón already share.
The realistic goal is not the upright; a carryable body cannot match its radiating area. It is the guitarrón’s body tuning, under a bass that reaches the low E the guitarrón cannot.
What to measure next
- A steel-strung acoustic bass guitar under the identical protocol — the missing control, and the direct test of the claim that steel is the biggest single problem.
- Rest strokes against free strokes on the same instrument, to test whether a bigger stroke measurably produces more second harmonic.
- The Tario’s open G, which sits almost exactly on its 97 Hz air resonance and should sound noticeably boomier than its neighbours.
- The first prototype of my own design, tapped before the strings go on.