Dept. for Speech, Music and Hearing

Quarterly Progress andStatus Report

Experiments on flutesFransson, F.

journal: STL-QPSRvolume: 13number: 4year: 1972pages: 029-033

http://www.speech.kth.se/qpsr

STL-QPSR 4/1972

B. EXPERIMENTS ON FLUTES"

F. Fransson

Abstract

The a i r velocity distribution and sound field a t the embouchure of a played experimental flute i s studied by means of the STL-iono- phone. The measurements show that the sound i s radiated in lobes, the directions of which change slightly with the fundamental f r e - quency of the tone played. By measuring the sound spectrum in different positions, it i s shown that optimal positions regarding the signal to noise rat io can be found. Studie s of the importance of the embouchure edge angle showed that a smaller edge angle in- c reased the dynamic range. However, alterations of this angle a r e accompanied by considerable change s in the spectrum, which may increase the loudness of the tone even if i t s sound p res su re level r e - mains constant.

I. Air velocity distribution and sound field a t the embouchure

The sound of a flute i s generated when the laminar a i r s t r eam from

the player i s converted to a turbulent s t r eam a t the embouchure edge (193)

Although a good deal of scientific work has been devoted to the acoustics

of the flute, little i s known about the propert ies of the a i r s t ream. In

this paper a method for registration of some of these propert ies will be

p r e sented.

A cylindrical head joint with reform plate was studied (Fig. 111-B - I).

It could be inserted into three cylindrical tubes of different lengths. In v.. this way the total length of the flute from the cork to the open end could

be chosen to be 36, 44, or 63 cm. The embouchure edge angle OJ , de - fined in Fig. 111-B-2a was 30°. In modern flutes it appears to vary be - tween 27O and 37O.

.Cis the receiver the STL-ionophone i s a suitable device for measure -

ments on oscillating a i r s t reams. A s a t ransmi t te r i t i s practical for

measuring of the resonance propert ies of wind instruments. The e lec-

t r ica l c i rcui t diagram of the STL-ionophone i s given in Fig. 111-B-3.

The a i r velocity, i. e. the DC component of the a i r s t r eam, i s proportional

t o t h e l o w p a s s f i l t e r e d i o n o p h o n e c u r r e n t i Therap idve loc i tyosc i l l a - 0'

t ions, i. e. the sound of the a i r s t r eam, i s obtained f rom the ionophone

voltage V n '

>< This ar t ic le was written by F r a n s Fransson in 1970. It was accepted for publication in a journal that however ceased before printing Fransson ' s ar t ic le . It can be mentioned that more information a - bout the STL-ionophone a s a microphone i s given in Fransson-Jansson: STL-QPSR 2 -3/i97 I , pp. 43-52.

Fig. 111-B-2a. Section through center of embouchure on the experimental flute.

b. Polar diagram of the a i r velocity distribution near the embouchure.

TRANSMITTER

RECEIVER

Fig. 111-B-3. E l e c t r i c c i r cu i t d i ag ram of the STL-ionophone.

STL-QPSR 4/1972 30.

During the experiments the ionophone was attached to the flute in

front of the embouchure center (a t I on Fig. 111-B-I). It could be turned

around the flute on the periphery of a c ircle with a radius of 7 cm nor-

m a l to the flute length axis and with the center a t the embouchure edge.

The position of the ionophone was defined by means of the location

angle cn a s shown in Fig. 111-B-2a.

The a i r velocity, the locatioq angle rn, and the sound level a t the

open end picked up by a microphone were simultaneously regis tered on

three channels on a mingograph. The rapid velocity oscillations and

the sound a t the open end were recorded on tape.

The flute was blown by a trained flutist in the normal way. Record-

ings were taken in blowing the fundamcntzl and the octave. Thereby

the sound level controlled with a microphone a t the open end was kept

constant. In order to study the importance of the damping of the fun-

damental resonan.ce, a small amount of cotton wool was inserted into

the open end. The cotton wool was adjusted to the l imit just suppressing

the tone production.

Some resul t s f rom experiments with the flute length of 63 cm a r e

given in Fig. 111-B -2b showing how the a i r velocity a t constant distance

f rom the embouchure edge varies a s a function of the ionophone loca-

tion angle m . The a i r velocity distribution has the shape of a lobe. The lobe of

the fundamental is much l a rge r than that of the octave. The sound level

a t the open end was in both cases kept constant. According to theory,

the sound level increases 6 d ~ / o c t if the source level i s kept constant.

This means that the source level of the higher tone must be reduced

6 dB if the sound level a t the open end shall be the same a s for the tone

one octave lower. This appears to be a plausible explanation to the dif - ferent lobe - size s for the fundamental and the octave.

The lobe of the damped fundamental i s somewhat l a rge r than that of

the undamped fundamental. This means that the a i r s t r eam i s more

diffuse in the case when the flute does not sound. A possible reason i s

that the damping has some influence on the shape of the a i r s t r eam in

view of the fact that there i s a strong reaction betweer, resonator and

source.

STL-QPSR 4/1972 31,

F r o m the shape of the lobe the angle of maximum velocity may be

defined, This angle appears to depend on the blowing. When the fun-

damental i s blown the a i r s t ream i s directed m o r e downwards than

when the octave i s blown. This resul t i s likely in view of the well-

known fact the overblowing is accompanied by a slight change in the

shape and position of the l ips (39 4).

The Q -value gives a quantitative measure of the damping. The Q - values of the r e sonator for the undamped and damped fundamental

resonance and for the undamped second resonance (i. e. the octave)

were measured , with the ionophone a s sound source inserted into the

embouchure,

The embouchure inductance i s increased wheil the flute i s blown.

Mainly this i s an effect of the covering of the embouchure by the

lip s ( 3 2 5). A s the sca le i s ascended, the l ips a r e m o r e and more pro- (5) truded, and thus the embouchure inductance i s increased .

Consequently, in measuring the Q-values for the undamped and

damped fundamental and for the undamped octave, the embouchure

was part ly covered. In each case the covering was adjusted so that

the resonance frequency of the flute coincided with the blown frequen-

c Y (39 4)

The Q -values in the different cases a s well a s the corresponding

maximum velocity angles cn a r e l isted in Table 111-B-I. The table

shows the general trend of the maxiinuin velocity angles to increase

with the blown frequency. Probably this is an effect of the different

degrees of lip shape and p r ~ t r u s i o n .

TABLE 111-B -I. - - -- - -- -- - - - - - - - - - - --

L Fundamental -- - - - - - - - --. - -

undamped damped 1 - -- - - - --1 - - - - --

- -- ----- - - -- -, Octave

undamped

, Blown Length t frequen-

cm j b y , H z i

-

Blown frequen- cy, Hz

52 1

7 2 9

8 58

rr7

Id o 'id

m 1 o

-

m o

2

45-50

53-57

55-60

Q1 * 2

53

53

48

63

44

35-40

40-44

2 62

3 67 1 36 435 1 4 2 - 4 7 i i

33

30 j 30-45 -

32-42 15

31 35-45 15

STL-QPSR 4/1972 32.

The rapid velocity oscillations of the a i r s t r eam recorded on tape,

were analyzed by means of a Rodhe 6r Schwarz spectrograph. Some

resul t s a r e shown in Fig. 111-B-4 refer r ing to the case when the un-

damped fundamental was blown on the flute with the length of 63 cm.

The different spectrograms refer to various location angles 9. It i s

seen that near the maximum velocity angle the noise i s very strong,

especially in the low frequency region. The tone spectrum i s masked

almost entirely. Fur ther away from this angle some part ia ls appear

and the noise level a t low frequencies decreases .

11. Influence of the embouchure shape on the sound

The edge angle " was found to have some influence on the facility

of blowing and on the dynamic range of the flute. The edge angle of an 0

old flute with a wooderl head joint was found to be about 70 (Fig. ' 111-B--5,

angle " ). On some flutes with wooden head joints this angle was r e - 1

duced by undercutting of the embouchure ( ~ i g . 111-B-5, angle 'V2) and

on a modern piccolo flute made by Hans Rainer in Germany the edge

angle r" was reduced by undercutting and fur thermore by straightcut - 0

ting on the outside to an angle oi 30 (Fig. 111-B -5, angle N ~ ) . An ex-

per iment was therefore made on a flute with a wooden head joint and 0 the angle = 70 . The flute was blown in the low regis te r and the

maximum sound level noted. Oscillogram and spectrogram of the tone

G4 a t maximum sound level i s shown in Fig. 111-B-6a. The embouchure

was thereaf ter cut in a s imilar way a s the above-mentioned piccolo

flute.

The edge angle was now reduced from 70° to 40° and tones in the

low regis te r could now be blown with an increase in the sound level of

4 to 7 dB. Oscillogram and spectrogram of the tone G4 blown to the

same sound level a s by 'V = 70' a r e shown in Fig. 111-B-6b.

As indicated by the spectrograms, the t imbre of the flute tone has

changed considerably and the general impression from a listening t e s t

was that the tone on the modified embouchure was stronger although

the sound level was the same(2). The difference in sharpness of the

STL-QPSR 4/1972 3 3 .

edge angle on old and mode rn flutes i s probably one reason for the di f -

fe rence in t imbre , especia l ly pronounced in the low r eg i s t e r .

Refe rences

(1) Benade, A. H. : Horns , S t r ings , and Harmony (Garden City, N. Y. 1960).

( 2 ) Castellengo, M. : "Rule du Musicien dans l e s S i g n a w Rayon& s p a r l a Flute T rave r s i e r e " , The 6th Internationai Congress on Acous t ics , Tokyo 1968, paper N-2-7.

(3) Coltman, J. W . : 9'Acoustics of the Flute", Phys i c s Today No. 11, 2 1 (1968), pp. 25-32. -

(4) Coltman, J . W. : "Sounding Mechanism of the Flute and Organ Pipe", J .Acoust . Soc. l~n-1. - 44 (1968), pp. 983-992.

(5) F r a n s s o n . F. : "Measurements of the Head-Joint Per tu rba t ion and the Embouchure Reactance of Flutes" , STL-QPSR 4/1968, pp. 15-22.

( 6 ) Yoshimaro , A. : "influence of the l i i r Beam Direct ion upon Acoust ical P rope r t i e s of Flute Tone s f ' , The 6th International Congress on f icoust ics , Tokyo 1968, paper IT-2 -6.