- Tension sets pitch
- Overtones set colour
- Weight can tune them
- Strike, listen, retune
PLAIN HEAD
Why most drums thud
A stretched skin vibrates in many patterns at once, and their frequencies do not line up as harmonics.
See the numbersTHE PHYSICS OF PERCUSSION
Strike it.
Hear the physics.
Every drum is a stretched skin deciding which notes to keep.
Most drums give a thud, not a note. A few, like timpani and tabla, are built to sing in tune, and the talking drum can bend its pitch mid-phrase. Here is how a drumhead makes its sound, in plain English.
Plain English, with the sources linked.
TENSION sets the pitch
Try the drum check
THE SHORT ANSWER
A thud or a note?
It depends on whether the drumhead's
overtones line up with each other.
KETTLE DRUM
How timpani find a note
The sealed kettle and the air around the head pull the overtones into line, giving a pitch an orchestra can use.
Listen closer
LOADED HEAD
Drums that sing in tune
Indian drums such as the tabla carry a weighted central patch that turns their overtones into harmonics.
Read the factsA QUICK DRUM CHECK
Does your drum
play a note?
Pick a kind of drum to see what its head does with its overtones. The descriptions come from university physics teaching material, a 1920 paper in Nature and a Smithsonian museum record.
No pitch is not a fault. A thud with clashing overtones is exactly what a snare or bass drum is meant to give.
TWO DRUMHEADS COMPARED
Same skin,
different maths.
Overtones written as multiples
of the lowest frequency.
1 : 1.59 : 2.14 : 2.30
First four vibration modes
An ideal circular membrane's overtones fall at awkward ratios. None is a whole-number multiple of the lowest, so the modes are inharmonic and the drum gives no firm pitch.
PLAIN, EVEN HEAD
1 : 2 : 3 : 4 : 5
Tones the head can give
With a weighted central patch, an Indian drumhead gave five tones in harmonic sequence, counting the fundamental. Raman later described the head dividing into one to five sections to produce them.
LOADED HEAD · RAMAN AND KUMAR, 1920
Raman and Kumar opened their 1920 note by observing that percussion instruments, as a class, give inharmonic overtones. These drums were the exception they set out to explain.
LISTEN CLOSER
Four ways to
hear the physics.
Move the strike point
Hit a drum dead centre, then part-way to the rim. Timpani players aim about halfway to three quarters of the way out, where the useful modes ring.
Change the tension
Press gently on the head with one hand while tapping with the other. More tension raises the pitch, the same idea the talking drum uses.
Listen above the note
On timpani, try to pick out the fifth and the octave sounding above the main note. They are what make it a tuned drum.
Mind the volume
Noise adds up. NIOSH sets its limit at 85 dBA over eight hours and halves the time for every 3 dBA more, so long loud sessions count.
DRUM FACTS
Five things worth
hearing about.
Tighter means higher
Like a string, a drumhead rises in pitch as its tension increases. Its frequencies also depend on its size and on how heavy the membrane is for its area.
Overtones that do not line up
On an ideal circular head, the next modes above the lowest sit at about 1.59, 2.14 and 2.30 times its frequency. Physicists call such modes inharmonic.
The timpani skip their lowest mode
On timpani the true fundamental is heavily damped and not generally used in music. Players strike about halfway to three quarters of the way out to excite the preferred modes.
There is iron in the patch
Raman and Kumar described the central load on the Indian drumhead as a flexible composition containing finely divided iron, laid unevenly so the head gives harmonic tones.
A drum that talks
The Yoruba talking drum mimics the tones and cadence of speech. The player squeezes the ties joining its two heads between arm and torso while striking it with a curved stick.
QUICK QUESTIONS
Drums, answered.
Short answers to the questions people ask most.
Why does a drum not play a clear note like a guitar?
A plain circular drumhead vibrates in several patterns at once, and their frequencies are about 1.59, 2.14 and 2.30 times the lowest one. Because these overtones are not whole-number multiples, the ear hears a thud rather than a definite pitch.
How do timpani play definite notes?
The head sits over a sealed kettle. The enclosed air and air damping shift the preferred vibration modes into a near-harmonic series, so the drum sounds a main note with a fifth and an octave above it. Its true lowest mode is heavily damped and not used.
What makes the tabla and mridangam sound so musical?
Indian drums of this kind carry a weighted patch on the head. In 1920 C. V. Raman and Sivakali Kumar reported that this loading lets the head give five tones in harmonic sequence, counting the fundamental, much like a string.
How does a talking drum change pitch?
The Yoruba talking drum has two heads joined by cords. The player squeezes the cords between arm and body while striking, which tightens the heads and raises the pitch, letting the drum follow the tones of spoken Yoruba.
How loud is too loud when playing?
The US National Institute for Occupational Safety and Health recommends a limit of 85 A-weighted decibels averaged over an eight-hour day, and halving the time for every 3 dBA increase. Bars and nightclubs often reach 95 dBA or more.
References
- PHY 103 Physics of Music: drums and membrane modesUniversity of Rochester
- The timpaniHyperPhysics, Georgia State University
- Musical drums with harmonic overtones (Raman and Kumar)Nature, 1920 (Indian Academy of Sciences repository)
- The Indian musical drums (C. V. Raman)Proceedings of the Indian Academy of Sciences, 1934
- Object of the day: Yoruba talking drumSmithsonian Music
- Noise and occupational hearing lossCDC / NIOSH