IR Measurement: Tongue Steel Tongue Drum!!Ruben Brovida - 1 Feb 2014

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Introduction!The Tongue Drum is my measurement subject for a few reason.!Since it is easy to find quality IR for rooms, churches, halls, I decided to measure a system that proves to me more interesting, and has qualities that can be used for sound design & composition.!Metallic objects often have resonatingcharacteristics that fascinating me, given the similarity with sounds that only digital synthesis model can reproduce.!!

The Tongue Drum!

The Tongue Drum, Tank Drum or Hank Drum is a round steel slit/tongue drum originally fashioned form a propane tank.!The Tongue can be tuned by the player by varying the length of the cuts. The steel tongue drum is often tuned to pentatonic scales but can be tuned to the diatonic scale, the chromatic scale, or any set of notes the maker chooses. The instrument is played with the fingers or with mallets.!It uses some of the same basic physical principles as a steel pan, but modified in such a way as to act as aHelmholtzresonator.!Helmholtz resonanceis the phenomenon of air resonance!in a cavity, such as when one blows across the top of an !empty bottle.!! !

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Material List:!

Audio interface M-Audio Profire 610! Macbook Pro! AKG C411! !

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Yamaha monitor speaker MSP 5! Praat! Ableton !

Helmholtz Resonators

Hang Drum

Tongue Drum

Generating & verifying the sweep:!

I used the Praat script form Peters website to generate the sweep.!!startFreq=10!endFreq=12800!lnRange=ln(endFreq/startFreq)!periodT=10!multFact=lnRange/periodT!Create Sound... ExpSweep 0 periodT 44100 exp(multFact*0.5*(x-periodT))*sin(2*pi*startFreq/multFact*exp(multFact*x))!!and after I applied fade -in and -out.!!! !!!!

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Frequency (Hz)10 100 1000 10420 200 200050 500 5000

Soun

d pr

essu

re le

vel (

dB/H

z)

-60

-40

-20

with a flat spectrum.

Convolving the sweep with fades !and a time-reversed !

one give as result animpulse

Measurement!!To have the instrument resonating properly with the sweep, the speaker was in direct contact with it, so physical vibrations from the speaker cone were transmitted; furthermore the Tongue was displaced on a soft blanket to avoid hard surface blocking the resonance.!!After a few trials to find the sweet spot for audio interface playback level & preamp gain, !I measured 10 points in the Tongue.!!!!!!!!!!!!!!!!! !!!

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2. the center!3. the root note G!4. A!5. B!6. D!7. E!8. the root note one octave higher!9. A!10. B

Second, measurement: on the Tongue

1. the bottom

First measurement: under the Tongue

Thoughts!!The IR 1 & 2 have almost the same spectrum except for the lowest partials amp, with frequency matching the G pentatonic scale.!There is no frequency component with an amplitude greater than the other sufficiently to give the impression of a clear and definite pitch. !!!!!!!!!!!!!!!!!The IR from 3 to 10, measured on the keys of the tongue, have the resonance of the note in question, plus various harmonics that occur across the spectrum.!!IR 3 - G ! ! ! ! ! ! IR 4 - A!!!!!!!!!IR 5 - B! ! ! IR 6 - D!!!!!!!!!

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Frequency (Hz)10 100 1000 10420 200 200050 500 5000

Soun

d pr

essu

re le

vel (

dB/H

z)

-20

0

20

Frequency (Hz)10 100 1000 10420 200 200050 500 5000

Soun

d pr

essu

re le

vel (

dB/H

z)

0

20

40

IR 7 - E! ! ! ! ! ! IR 8 - G!!!!!!!!!!!IR 9 - A! ! ! ! ! ! IR 10 - B!!!!!!!!!!!!They all share the same spectrum, but each impulse has got more power in the related frequency band. This is generating a more clear root frequency and so the impression of pitch.!! !

Conclusion:!

!This process has allowed me to verify the Tongue tuning, and I found that has slight imperfections, as well as some partial enharmonic, but these probably contribute to the bell-like sound. !!The IR technique is a powerful tool, in reverberation, but especially in sound design & composition; to be able to play creatively with materials, space & system, and to collect them, to store them inside your pc, open a new field of experimentation.!!!!!!

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!!Measurement

Pictures!

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