Subjective loudness of sonic-boom: N-wave and minimized ('low-boom') signatures

Uovember, 1977

SUBJECTIVE LOUDNESS OF SONIC-BOOM: U-~IAVE AND MINIMIZED ('LOH-BOm1') SIGNATURES

by

A. Niedzwiecki and H. S. Ribner

\' 1

11

"

TECHNISCHE HOGESCHOOL DELFT

WCHTVAART-EN RUtMTEVAARTIECKNIEK

BIBLIOTHEEK

Kluyverweg

1 -

DELFT

UTIAS Technica1 Uote No. 215 CN ISSN 0082-5263

•

SUBJECTIVE LOUDNESS OF SONIC-BOOM: N-WAVE AND MINIMIZED ('LOW-BOOM') SIGNATURES

by

A. Niedzwiecki and H. S. Ribner

Stibmitted October,

1977

Acknowledgement

This research was supported by fUnds fr om Transport Canada Research and Development Centre (TDC), the National Research Council of Canada, and the United States Air Force Office of Scientif;i.c Research under Grant

AF-AFOSR

75-28088.

Summary

A loudspeaker-driven simulation booth with extended ri se-time

capability (down to 0.22 ms) has been used for subjective loudness tests of

sonic booms. Test series I compared N-waves aver a range of 0.22 to 10 InS

rise time, 100 to 250 ms duration and 0.5 to 2.0 psf (24 to

96

N/rrf!.) peak averpressure • In one sequence, tradeoff between rise time and overpressure was measured for equal loudness; in another, the tradeoff between duration

and averpressure . For equal loudness 10 ms rise time required

8

dB higher

averpressure than for 1 ms rise time. Duration had li ttle effect in. the

range 100 to 200 ms but at 250 ms noticeably enhanced the loudness. These

results confirm those measured by Shepherd and Sutherland, made at 1 InS rise

time and abave (except for the anomalous enhancement at 250 ms duration) , and extend the measurements down to 0.22 ms. There is -also good agreement with theoretical predictions (Johnson-Robinson, Zepler-Harel methods) except for the 10 ms rise time and 250 ms duration cases.

Test series II compared certain 'flat-top' sonic boom signatures

with a reference N-wave (0.5 psf, 1 ms rise time, 150 ms duration). According to current theory, such 'flat top' signatures would be generated by a special family of very long SST aircraft designed for minimized sonic boom; the

front shock (~PSH) is followed by a linear rise to peak amplitude (hpMAX)

followed by the usual linear decay. For equal subjective loudness, flat top

vs. N-wave (peak overpressure ~PN, the peak amplitude of the 'flat top'

sig-nature was substant±ally higher than that of the N-wave; thus for equal

ampli tude the I flat-top' signature was quieter. The results for equal

loud-ness were well fi tted by an empirical law hpSH + 0.11 hpMAX = hpN; the

equivalence shows how the front shock amplitude hpSH dominates the loudness. All this was found compatible with predictions by the method of Johnson and

CONrENTS

Acknowle<4!;ement

Summary

PART I SUBJECTIVE LOUDNESS OF N-WAVE SIGNATURES VS. RISE TIME AND DURATION i i i i i 1 INTRODOCTION 1 EXPERIME:NTAL TECHNIQUE 1

RESULTS AND DISCUSSION

3

CONCLUDING REMARKS

4

PART II SUBJECTIVE LOUDNESS OF 'LOW-BOOM' SIGNATURES VS. WAVE FORM

P~ERS

4

INrRODUCTION

4

TECHNIQUE AND PROCEDURE 5

RESULTS AND DISCUSSION

6

CONCLlIDING REMARKS

8

REFERENCES 9

PART I

SUBJECTIVE LOUDNESS OF N-WAVE SIGNATURES VS. RISE TIME AND DURATION

INTRODUCTION

There is continuing interest in human response to sonic-boom type

pressure waveforms. In particular , the role of the rise time and duration

of the N-wave signatures in controlling the subjective loudness have been

under study. One of the central problems is the prediction of the loudness

given the shape or spectrum of the sonic-boom signature.

To date several investigators have suggested alternative procedures for determining the apparent loudness of such impulsive sounds. Von Port

(Ref.

1)

in a spectral approach, utilized an "effective" continuous sound

concept: he assumed that the ear integrated the signal power over a tiJre duration of 70 milliseconds. In 1969, Johnson and Robinson (Ref. 2) carried out further sonic-boom subjective loudness studies, exam1ning the separate effects of duration and rise time. The technique adopted in this later work follows the earlier work of Von Port in defining an equivalent continuous sound

pressure level. The subjective loudness is then calculated using the

1/3

octave band procedures developed by stevens (Ref. 3) for steady sounds. The

results obtained showed no dep en den ce of the subjective loudness on the

dura-tion of the boom. However, large loudness changes (~out 25 phons) were

pre-dicted for ri se-time and delay-time variations in the range 0-16 milliseconds. Experimental subjective studies with sonic-boom signatures have been conducted by Zepler and Harel (Ref. 4) and also by Shepherd and Sutherland

(Ref.

5).

In the former case subjects compared signals presented by means

of the high-quality earphones, with "practically flat" response between zero

and 1500 Hz, to pure tones at 400 Hz. In the latter study special low frequency

loudspeakers coupled to an airtight chamber (booth) were employed to develop the boom signatures; these were evaluated subjectively using a paired-camparison technique.

The present experiments are very similar in concept to those of Shepherd and Sutherland. However, the simulation booth has been designed for five-fold short er rise time capability. Additionally, a camputer-aided tech-nique has been developed for more faithful wave form simulation.

EXPERIMENrAL TECHNIQUE

The UTIAS Sonic Boom Simulation Booth (Ref. 6) consists of an

air-tight 2.1

m3

volume chamber driven by 12 loudspeakers mounted in apertures in

the wall faced by 'the subject. The booth features a double-wall plywood

construction with inside wall surfaces heavily lined with sound-absorbing fiberglass to minimize reflections and consequent resonanees at the higher

frequencies; the free-air volume is thus reduced to about

1.3

m

3.

Six 15 inch low-frequency loudspeakers and six

8

inch medi~

frequency loudspeakers are used with a crossover network at 500 H~ The

equalizing network to compensate for speaker and booth coloration of the frequency response. The main element of the equalizing network is an Altec Lansing Model 729A "Acousta-Voicette" containing twenty-four one-third octave filters centered at frequencies from 12,000

Hz

down to 63 Hz; each filter is adjustable over a range

±

12 dB. Additional filters utilizing summation circuitry are used to control the response of the system in the frequency range 0.1 Hz to 60 Hz. Careful adjustment of these filters compensates for the major part of the non-uniform frequency response of the basic system, elmininating mu('.h of the waveform di st orti on • The basic scheme of this sonic-boom simulation system is shown in Fig. 1.

In addition, a special noise-squelch circuit decreases the background noise: the system is triggered (using signals recorded on the second channel of the tape recorder) permitting the loudspeakers to be swi tched off during the intervals between the test sounds. The total simulation system has nearly flat response over the frequency range from 0.1 to 5000 Hz and permits a

relatively accurate reproduction of N-wave and other pressure signatures. The test signals used in the experiment were generated in digital form (Fig. 2) by the HP 2100A computer and converted to analogue form wi th

conventional fast D/ A equipment. The computer output was recorded on a Bruel and Kjaer FM tape recorder featuring uniform frequency response from de t 0

5000 Hz. Examples of N-wave sonic-booms reproduced in this facility for the tests of Part I herein are shown in Figs. 3 and

4.

A later improved waveform is exhibited in the top left panel of Fig. 5.* Substantial further improvement in waveform fideli ty (Fig. 5) is afforded by a computer-based "predi stortion " scheme, described and utilized in Part II; this scheme was not yet introduced in the Part I investigation described below.

Two separate series of sonic boom comparisons featuring N-wave

signatures were carried out with twenty subjects (UTIAS male graduate students). I In the first series the boom duration was held constant at 200 milliseconds,

the rise times were varied over the range 0.22 to 10 ms, and the peak over-pressures over the range 0.5 to 2.5 psf (25 to 96 N/mf). For each rise time the overpressure was adjusted until the subject judged the signal to sound just as loud as a reference N-wave with 1 ms rise time, 1 psf (48 N/m2) over-pressure , and 200 ms duration. In this fashion contours of equal loudness vs. rise time were developed.

In the second series of tests the sonic-boom rise time was held constant at 1 millisecond and a second equal-loudness contour (overpressure ratio vs 0 duration) was defined by addi tional comparison tests using the signatures of duration time from 100 to 250 msec and overpressures from 0.5 to 2 psf (24 to 96 N/m2). The reference N-wave was the same as the previous one.

The sonic-boom characteristic parameters were measured from the oscilloscope photographs using a B & K one-inch microphone incorporating a random-incidence corrector mounted in the booth at ~pproximatèly:~th~ subject IS

ear level. In both cases the overpressure steps during the comparison experi-ment were 2 dB.

* Figure 3 represents a substantial deterioration in waveform simulation

compared wi th Figs. 4-9 of Ref. 6. This appears to have been associated wi th faults developing in the compensating filters (Fig. 1). Repairs and adjust-ments led to the improved N\-wave simulation shown in the upper left hand panë1 of Fig. 5.

. (

Audiograms were obtained before and after each experimental session for aJ..l observers. In addition these observers were examined by a quaJ..ified otolaryngologist and found to have normaJ. hearing.

During each 15-20 minute test session sonic-boam signals in pairs were presented to the subjects while seated singly in the booth. They were required to identify which sound in the pair was judged to be the louder and to communicate this verbally through the intercom to the experiment er . Three

judgement scores were used: "louderll

, llmay be louder ll

, and lIequal loudnessll•

Thus a set of five numerical scores was obtained: Test boom louder = -2 Test boom may be 1 oude r = -1 Both equaJ..ly loud = 0 Reference boom may be louder = 1 Reference boom louder 2

The signals were presented to the observers in random order.

The resuli~Lfor each vaJ..ue of rise time or duration (obtained through the series of comparisons) were plotted in the form of graphs - relative loud-ness (in scores) vs. overpressure ratio between the test and reference signals, for every subject. Two typicaJ.. examples are shown in Fig.

6.

From each graph the overpressure ratio for equaJ.. loudness (score

=

0) was determined and the average of these values for all twenty subjects was used to construct the finaJ.. curves.

RESULTS AND DISCUSSION

The two experimentally determined equaJ..-loudness contours for the N-wave signatures are plotted in Figs. 7 and 8, i. e., (i) overpressure ratio vs. rise time, Fig. 7 (duration 200 msec) , (ii) overpressure ratio vs.

duration, Fig. 8 (rise time 1 msec). The overpressure ratio is defined by

~Ptevel ratio where,

4>test 4>test ~Plevel ratio

=

-20 log10 4>

=

-20 log10 1 psf

ref

Each subject carried out approximately 180 judgements during the course of the two test series. The curves drawn in Figs.7 and 8 are based on the averaged data calculated from the experiment al results for each individual subject. The experimentally determined standard deviation for each plotted point is indicated by the vertical bars on the graphs. It was noted that the deviations among the individuaJ..-comparison results increased progressively as the differences between the features of the reference-boom signature and the test-boom signature increased. This reflects the increasing comparison difficulties. The standard deviation is typicaJ..ly 1 dB; for booms with rise times of 10 msec (duration 200 msec) it rises up to 3.5 dB, and for booms having a duration of 250 msec (rise time 1 msec) it is about 1.4 dB.

Along with the present results (labeled Niedzwiecki) Fig.

7

reproduces the experimental results of Zepler and Rarel (Ref.

4)

and Shepherd and Sutherland (Ref.

5),

along with the predictions by Johnson and Robinson

(Ref. 2) (only the first two go down below 1 ms rise time). There is generally good agreement over the cammon range, essentially within the error bars. The predicted decrease in loudness with increasing rise time is very marked above 0.5 ms. At 10

ms

rise time the results are somewhat divergent , but wi th a large experimental uncertainty. The present results séem to agree best wi th the predictions of Johnson and Robinson.

Both Shepherd and Sutherland (experiment), and Johnson and Robinson (theory) find a negligible influence of the sonic-boom duration on the subjective loudness. The results of the present study, on the other hand, indica:te an

abrupt rise in the equal-loudness curve of the overpressure vs. duration (Fig. 8) for duration of 250 msec (rise time 1 msec) .

CONCLUDING REMARKS

Tentative conclusions based on the above indicate reasonably consistent trends with the earlier theoretical and experimental subjective boom data, except for the effects of the longer boom durations (in excess of 250 msec) shown in Fig.

8.

The substantial rise in the equal-loudness contour in this case remains unexplained. The present experimental data adds addi tional confidence to the existing theoretical methods of predicting the subjective loudness of sanic boom N-wave signatures (especially the Johnson and Robinson procedure) in an expanded parameter range gi ven by

Risetime Duration Peak overpressure, 0.22 to 10 msec 100 to 250 msec l5p { 25 to 50

Njrrfl-1 to 2 psf PART II

SUBJECTIVE LOUDNESS OF 'LOW-BOOM' SIGNATURES VS. WAVE FORM PARAMETERS INTRODUCTION

One of the major problems that has limited development of supersonic civil aviation is the human annoyance caused by the sonic-boom. Therefore a prominent averue of research has been the exploration of sonic boom minimization te chniques • A promising approach suggested by McLean (Ref.

7)

(which requires very long aircraft) has been developed by Seebass and George (Ref. 8) for flight in an isothermal atmosphere. The mathematical theory has been extended to the real atmosphere by Darden (Refs.

9,

10). This theory permits minimization of either the initial shock of the signature or the maximum overpressure by means of a specially tailored distribution of the aircraft cross-section and lift.

By neans of such tailoring Dar..den computed a family of minimized

signatures associa:ted with certain proposed "second generation" SST configurations

4

(Fig.

9).

The expectation was that for a given aircraft volume, weight, flight alti tude and Mach mmlber, these signatures should sound less loud than

normal N-waves. This inspired the present investigation aimed at simulating

these signatures in the UTIAS loudspeaker-driven booth and conducting jury tests of the subjective loudness.

Darden' s signatures don ot exhibit full fore-and-aft symmetry (cf

Fig.

9).

However, the Johnson-Robinson method (Ref. 2) for predic"ting

loud-ness is predicated on fore-aft synnnetry. For this and other reasons of a practical nature it was decided to replace Darden's signatures by symmetric

ones in the tests, the relationship being as in Fig.

9.

The differences are

not great, and it is thought their effect on the subjective loudness should be minimal.

In the present investigation it has been attempted to establish

experimentally the relationship between the subject~ve loudness of these

'low-boom' signatures and their characteristic parameters, Le. ,the flat top

duration Dl' and the ratio shock overpressure/peak overpressure (x =

LPSH!4JMAX;

~ cf Fig.

9).

In the last section of the report the Johnson and Robinson theoretical

loudness prediction procedure (Ref.

2)

has been verified and extended to the "new

'low-boom' family of signatures.

TECHNIQUE AND PROCEDURE

The paired-comparison observations with the 'low-boom' signatures were carried out in the same UTIAS facility as for Part I (N-wave signatures). However, it was found that the simulation technique had to be further refined to reproduce properly these "flat top" waves; the inadequacy of the basic

scheme of reproduction is shown in the top right-hand trace of Fig.

5.

A

sub-stantial effort led to a scheme for predistorting the electrical input signal

to counter the loudspeaker-booth distortion. The bottom curves in Figs.

5

and

10 show the very satisfactory N-wave and flat-top signatures resulting from such a predi storted input.

The scheme of this predistortion is outlined in Fig. 11. The complex

frequency response af the simulator is designated r(w); if this were a real

constant (flat response) there would be no distortion.* The essence of the idea is to alter the electrical input signal spectrum by the inverse of r(w). Then r(w) cancels out; the predistortion r(w) precisely counteracts the real distortion r(w). Note that this cancellation is effected by working in the frequency domain; the appealing but naive notion that one can cancel a distor-tion "bump" by a predistordistor-tion "valley" in the time-domain input signal is a crude oversimplification.

N-wave simulation is likewise greatly improved by use of the predis-tortion technique for the electrical input signal. This is shown on the

left-hand panels of Fig.

5.

It is unfortunate that the scheme had not yet been

perfected for the Par"t I experiments.

*

_{More generally, a form roe} -iwto _{for r w would imply no distortion, but the} ( ) signature would be delayed by a time to'

The steps of the predistortion procedure of Fig. 11 are implemented

as follows: Fl(t) is a test input signal (e.g., N-wave) and F2(t) the

corre-'sponding output signal from a microphone in the booth. F3(t) is the signal to

he simulated: the desired microphone signal 0 The HP 2l00A computer applies

the standard Fast Fourier Transform procedure to derive the corresponding

spectra: Fl(W),

F2(W),

F3(W). Th~p the two spe ct ral ratios in the centre box

of Fig. 11 are evaluatedto yield

F4(W);

this is a 'predistorted' input spectrum

which will yield the desired output spectrum

F3{w)

according to (c) of Fig.

11-As predistorted input signal F4(t) in the time domain, the computer evaluates

the inverse Fourier transform of

'4(W).

F4(t) is the correct predistorted

electrical input signal that will yield thedesired microphone signal F3(t) in

the booth. Examples of F4(t) are shown in the upper panels of Fig. 10.

The whole process is done by a single Fortran program in the HP 2l00A

computer wi th 24K memory, Fast Fourier Transform hardware, and AID and DIA

converters. The compu."'cer-generated "predistorted" signatures are recorded on

the Bruel a.l1.d K..jaer FM tape recorder and played back into the amplifiers of

the UTIAS Sonic-Boom Simulator. It is worth mention toot the predistortion

method can be applied to improve the reproduction of any type of impulsi ve

sound, subject to bandwidth and amplitude limitations.

As for the previous N-wave experiments, the paired-comparison

tech-niClue was employed. Two separate test-sessions were carried out. In the first

set the flat top duration of the signatures was held constant (Dl

=

30 msec)

and the ratio x

=

~sHl~ (front shock overpressure/maximum overpressure

ratio) varied within the range of 0.2 to l.O. The eClual-loudness contour

(overpressure ratios vs. x) was defined through the camparison of these

signa-tures wi th an N-wave reference signature having the same rise time (1 msec)

and duration (150 msec), and overpressure ~

=

0.5 psf. Ten observers , all

illIAS male graduate student s , took part in this experiment.

In the second test-series the overpressure ratio x

=

6'PsH./A'PMAx

was

held constant at x

=

0.5 and the equal-loudness contour (overpressure ratio vs.

flat top duration) was determined for the 'low-boom' signa:tures having the flat

top duration within the range of 10 msec to

60

msec at the duration 150 msec

(Le., from 0.0667 to 0.4 of' the duration). The reference N-wave had the same duration (150 msec) and rise time (1 msec) as the previous one but the over-pressure &PN was fixed at 1 psf. Eight ob servers , illIAS male graduate students,

took part in this experiment. In both cases the overpressure steps during the

comparison tests were 2 dB.

Audiograms were obtained before and after each session for all test

observers and each of them was found to have norma.l .. 'hearing .by the qualified

otolaryngologist.

The experimental procedure, the judgement scores and the manner of

obtaining the equal-loudness curves were the same as inthe previous N-wave

e..xperiment (see Part I for details). RESULTS AND DISCUSSION

Two eClual-loudness contours derived from the experimental results

for the r low-boom' signatures are illustrated in Figs. 12 and 13. The first

one shows the overpressure level ratio vs. x

=

LWSW

ÖP.MAx" . where the

over-pressure level ratio is defined by,

~level

ratio

=

-20 loglO &MAX/4>N

=

-20 loglO 4>MAX/l psf

The second graph shows the overpressure level ratio vs. flat top duration Dl of the flow-boom' signature.

Theplotted e~ual-loudness curves are based on the averaged values

calculated from the experiment al results for each subject. The vertical bars indicate the experimentally determined standard deviation. The standard

deviation of the e~ual-loudness contour based on the ratio X. is within the

range 0.8 dB to 1.3 dB and in case of the curve based on the flat top duration

Dl it is between

0.6

dB and 1.1 dB.

It was found in the experiment (Fig. 12) that for e~ual loudness

the overpressure level ratio increases by 11.7 dB for an increase of the value of the parameter 'x' from 0.2 to l.O. The actual properly scaled waveforms

judged as e~ually loud are shown in Fig.

14.

The comparison suggests that

the subjective loudness of the flow-boom' type of signature depends mainly

upon the front shock. .

More specifically, the results are well approximated by the empirical formula (Fig. 15),

.. DPN-wave

=

4l

_SH + 0.11

fP

_MAX (low boo~ sigIl:ature)

for e~ual loudness (at e~ual duration and rise time). This tells us that the

peak pressure ~MAX contributes only one ninth as much to the loudness as the

front shock (and similarly for the rear half of the wave); that is, the front (and rear) shock amplitudes (for fixed rise time) dominate the loudness, as indicated earlier.

The effect on the subjective loudness of the flat top duration Dl

was shown in Fig. 13. The overpressure level ratio for e~ual loudness varies

less than 1 dBwith the increase of the duration Dl from

0.667

to

0.4

of the

total duration. This change is within the range of the error of the

experi-mental methode Therefore, we can infer that the duration of the flat top of

the flow-boom' signature has negligible influence on the subjective loudness. The experimental results of the flow-boom' comparison tests were

supported by theoretical loudness calculations . The loudness of each

signa-ture, judged as e~ually loud as the reference N-wave, was calculated from

the energy spectrum obtained by FFT procedure. The Johnson and Robinson (Ref. 2) procedure for N-waves, based on the stevens Mark VI method for

continuous sounds (Ref.

3),

was followed in the calculations . The loudness

was calculated for the positive parts of the signatures only with adoubling to allow for the mirror-image negative part. Johnson and Robinson justify this on the ground that the separation between the front and rear shock is sufficiently long compared to the auditory critical time.

The results of these calculations are compared with the calculated loudness of the reference N-wave in Figs. 16 and 17. The calculated loudness

(in phons) for all stu<lied flow-boom signatures' diffèrs from the calculated loudness of the reference N-wave whiCh sounds equally loud by less than l phon. This very good agreement of the empirical and theoretical results supports the viability of the Johnson and Robinson (Ref. 2) loudness comparisons between N-waves and the flow-boom' family of signatures within the range of parameters given by

0.0667 ::: (Dl duration

=

D

2 duration)

<

0.4

0.2

<

<

l.0

CONCLUDING REMARKS

A series of jury tests of the perceived loudness of flow-boom' sonic boom signatures have been carried out and compared with theoretical predictions. The results indicate that the loudness is dominated by the amplitude &SH and rise time of the front and rear shocks. The peak amplitude can thus be much larger than that of an N-wave that sotmd equally loud. Put another way, an N-wave of the same peak amplitude will sound much louder than some of the low boom signatureS:--Based on Darden's (Refs.

9,

10) calculations of possible

flow boom' signatures for realizable aircraft, the attainable loudness reduc-tions are roughly equivalent to those resulting from halving the present N-wave amplitudes.

The relative loudness predictions of the Johnson-Robinson theory

conformed very well to the measurements. Thus their potential for applicability to a much broader range of transient sounds is indicated. In view of the uncer-tainty of the role of impulsive sound on hearing loss, further research to establish the applicability should be made. It is already clear that the rise time of impulsive sounds is a major parameter aJ..ong with the peak amplitude.

1. Von Port, E. 2. Johnson, D. R. Robinson, D. W.

3

.

stevens, S. S. 4. Zep1er, E. E. Harel, J. R. P. 5. Shepherd, L. J. Suther1and, W. W. 6. G1ass, 1. 1. Ribner, H. S. Gott1ieb, J. J. 7. McLean, F. E. 8. Seebass, R. George, A. R.

9.

Darden, C. M. 10. Darden, C. M. Mack, R. J. REFERENCES

(1963) "Uber die Lautstarke Einzelner Kurzer Schal1impulse", Acoustica 13, 211.

(1969) "Procedure for Calculating the Loudness of Sonic Bangs", Acoustica 29, 307.

(1961) "Procedure for Calculating Loudness: Mark VI", J. Acoust. Soc. of AJnerica, Vol. 30, No. 11, 1577.

(1965) "The Loudness of Sonic Booms and other Impulsi ve Sounds", J. Sound Vob., 2, 249.

(1968) "Re1ative Annoyance and Loudness Judgements of Various Simulated Sonie Boom Waveforms", Rept. No. CR-1192, NASA, Washington, D.C.

(1972) "Canadian Sonic-Boom Simulation Faci1ities", Canadian Aeronautics

&

Space Journa1, Vol. 18, No. 8, 235.

(1965) "Some Nonasymptotic Effects on Sonic Boom of Large Airplanes" , TN D-2877, NASA.

(1972) "Sonic-Boom Minimization", J. Acoust. Soc. of America, Vol. 51, No. 2 (Part 3), 686.

(1975) "Minimization of Sonic-Boom Parameters in Real and Isothermal Atmospheres", Rept. No. TN D-7842, NASA, Washington, D.C.

(1976) "Current Research in Sonic Boom Minimization", Proceedings of the SCAR Conference, Part I, NASA CP-001, 5~5.

PREDISTORTED ELECTRICAL

INPUT

TAPE RECORDER COMPENSATING FILTERS

AMPLIFIERS LOUDSPEAKERS BOOTH SOUND IN BOOTH

Jy

t

N-WAVE Fig. 1 Schematic arrangement of UTIAS loudspeaker-driven sonic boom simulation

booth. Compensatory "predistortion" of electrical input signal (see text) was used for Part II, but not for part 1.

( A)

100 ms

( B)

200 m

Fig. 2 Ideal N-wave signature generated by computer (rise time exaggerated).

(a) Test signature: duration

=

100 ros; rise time

=

1 ros; overpressure

=

2 psf (96 N/m2); (b) Reference signature: duration

=

200 ma; rise

CA)

..

I'

"-

_~

"-

I~

r

,-(e)

~

Î\

r\

-"

,~

\J

(C)

~

"

'\

~,."

'\.

~

L .

Fig.

3

Reproduetion of N-wave sonie boom signatures

by UTIAS simulation booth as used in Part I

(no predistortion). (a) Rise time

=

0.22 ms;

duration

=

200 ma; overpressure

=

1

psf

(48

N/~);

(b) Rise time

=

10 ma; duration

=

200

ma; overpressure

=

2

psf

(96 N/~);

(e) Rise

(A)

~ liIIo..

If

--

. -

-.4

/

~

"

(B)

-..-

~ ~

V

./

~

Fig.

4

Front shocks of Figure

3

to expanded seale.

(a) Rise time

=

0.22 ma; overpressure

=

1

psf

(48 N/~);

(b) Rise time

=

3

ms;

over-pressure

=

1 psf

(48 N/~).

• ~

~

_~

"

ho.

"

~ ..I

"

~

-

"-

I\..

-..

,...

....

~

'"

~

..

I'-.

_r-... ~ I\.. I"'"

_'\

I--~

....

~

_i'..

_I"

1-

~

_{r-.... l-.}

"-

_l

-~

_r-....

_"

_~ ...

'"

...

~

Fig.

5

Examples of pressure signals recorded by microphone in UI'IAS simulation

booth without (top) and wi th (bottom) predistortion of input signal.

(See text concerning improvement over rigure

3.)

L _{(A) L (8)} 2 2 1 0 0 -I -I -2 -2 ₁ 6 4 2 0 -2 -4 -6 AP [dB] 6 4 2 0 -2 -4 -6 AP [dB]

Fig.

6

Relati ve loudness scores vs overpressure ratio between reference and

test boom. (a) Subject No.

4 -

duration

=

200 ms; rise time

=

1 ms;

6

4

2

0

-2

-4

-6

-8

.

-10

-12

-14

6P level ratio

[dB]

0.22

0.5 • NIEDZWIECKI expo

o SHEPHERD. SUTHERLAND expo

6 JOHNSON. ROBINSON theo. o ZEPLER. HAREL theo.

3.

Cl o

10

rise time [ma]

Fig. 7 Equal loudness curve.

Trade~ff

between

ove~ressure

level ratio (20 loglO

6p

_re

f /6

_.

pt

_es

t) and rise tilOO for 200

ms

duration N-waves.

!!p

_re

.

f

= 1

psf

(48

N/~), Tref

=

1 InS.

- . NIEDZWIECKI expo

t.p level ratio • SHEPHERD. SUTHERLA.ND expo

[dB]

4 3 2

o

-I -2 duration 100

150

200

250 [ma]

Fig.

8

Equal loudness curve. Tradeoff between overpressure level ratio (20 loglO

ÄPref/4Ptest) and duration for

1 ms

rise time N-waves.

!!Pref = 1

psf

PRESSURE

t.P_MAX

RT - Rise Time

DI - Front Flat Top Duration 0- Duration

t.P_{MAX -} Maximum Overpressure t.P_{SH -} Front Shock Overpressure

--

_TIME

Fig.

9

Idealized vs attainable "low boom" sonic boom signatures. "Attainable"

signifies realizaQle via aircraft design and flight procedure.

ttv

V

~

~

....

I

,""-

1"-t:-...

""

...

r--...

"-""

I'--"

'"

~I---

r....

-...

~

I

i'-

...

""'~

r

...

""-

,.,

~ ...

'"

"

...-

-1

... ~

Fig. 10 Effect of "predistortion" of electrical input signals (top) to amplifiers driving UTIAS sonic boom simulation booth in achieving

®

SIMULATOR

f"tJ

R

(w)

f"tJ

r(W)

f"tJ

F

₂

(w)=F,

' "

(w)x

' "

r(w)

®

F.

(t)

COMPUTE

F

2

_(w)

=

F

_(w)

FI

(w)

R

~

" >< ...

t

F

3

_(w)

=

F

4(W)

F

(w)

>< . .

t

©

, , >< , ...

t

'"

f"tJ f"tJ

~(w)

_r(w)

F

₃

(w)

f"tJ

SIMULATOR

- F

4

(w}

X

r

(w)

Fig. 11 The predistortion procedure:

(a) Transfer function measurement using signal !het) (see RH inset)

(b) Computation of transfer function of system r~w) and "predistortion" of test signal F

₃

(t) (c) Reproduction of IIpredistorted" signal F4 (t) through the sYstem

<I

.1P

MAX

level ratio

(dB)

4

2

0

-2

_jD1f.-

_!

-4

6PsH-:-~

-6

_o

~I

-8

Ol

_o

= 30 ms = 150 ms RT = 1 ms

-10

_{6PN = 0.5 pst}

-12

~

1'v-

_~

0

.2

.4

.6

.8

1.0

X

=

.1PSH

.1P

_MAX

N-wave amplitude vs low-boom signature amplitude (dB) for same sub-Fig. 12 jective loudness: effect of ratio of front shock pressure to maximum

pressure for fixed flat top duration.

4

2

o

-2

-4

-6

-8

.1PMAX

level ratio

(dB)

o

la

20

30

~PN = I psf

o

=

150 ms RT

=

I ms 6PSH - 5 6PMAX -. t-I' - -

D

- - - + i

40

50

60

Fig.

13

N-wave amplitude vs low-boom signature amplitude (dB) for same

(psf)

1.5

1

6PMAX

0.5

O '

_ ..

I!

::=--.

~

,

I

(psf)

0.5

0 ' "

=::::",~

(psf)

0.5

0 ' "

---""

-=

x

= 1.0 6 PSH

=

0.433 psf

Fig.

14

Shapes of some pairs (low-boom and

N-wave) judged equally loud.

0.6

6PSH (psf)

0.5~-

_ _ _ _ _

~N-WAVE

- - - - -~

0.4

0.3

o

0.2

0.4

o

0.6

o.s

1.0

6PSH X = 6PMAX

Fig. 15 Low-boom signature front shoCk overpressure for same subjective loudness as N-'>fave with over-pressure ~N = 0.5 psf: (circles) effect of ratio front shock overpressure/maximum over-pressure for fixed flat top duration; (triangles)

caJ..culated vaJ..ues of "effective overpressure" of

99

98

97

LOUDNESS

(phons)

N-WAVE

- -- -- - - _1_

~p

=

0.5

pst

•

•

..

~

f\r

.2

.4

.6

~

.8

1.0

RT

=

1

ms

0=

150

ms

x=

~Ps

PMAX

Fig. 16 Calculated loudness of signatures judged equal1y loud. Solid line: loudness of 10lv-boom signatures vs ratio front shock overpressure/

maximum overpressure.

105

104

103

LOUONESS

(phons)

10

20

30

40

50

60

/lP

=

I pst

RT

=

1 ms

0=

150 ms

(ms)

01= 02

Fig. 17 Calculated loudness signatures judged equally loud. Solid 1ine: loudness of 10'lv-boom signatures vs flat top duration.

UNCLASSJli'IED

SECURITY CLASSIFICATION OF TH IS PAGE (Wh en Data Entered)

.

REPORT DOCUMENT ATION PAGE _{BEFORE COMPLETING FORM} READ INSTRUCTIONS

1. REPORT NUMBER

r

GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

4. TlTLE (end Subtltle) 5. TYPE OF REPORT & PERIOD COVERED

StJB.JEarIVE LOUDNESS OF SONIC BOOM:

N-WAVE AND

INI'ERIM

MINDfiZED ('LOW-BOOM') SIGNATURES

Jan. 1 - Dec. 31, 1977

6. PERFORMING ORG. REPORT NUMBER urIAS

TN NO. 215

7. AUTHOR(a) 8. CONTRACT OR GRANT NUMBER(a)

A. NIEDZWIECKI

AFOSR 75-2808

H. S. RIBNER

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK AREA & WORK UNIT NUMBERS

UNIVERSITY OF TORONTO,

2307A2

INSTITUTE FOR AEROSPACE STUDIES,

61102F

4925 DUFFERIN ST.,DOWNSVIEW,ONTARIO,CANADA M3H 5T6

11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

AIR FORCE OFFICE OF SCIEN.l'IFIC RESEARCH/NA

₁₉₇₇

BLDG. 410,

_{13. NUMBER OF PAGES}

BOLLING

AIR

FORCE BASE, D.C. 20332

₃₃

14. MONITORING AGENCY NAME a. ADDRESS(1l dIllerent Irom Controlling Oflice) 15. SECURITY CLASS. (ol thla report)

UNCLASSIFIED

ISa. DECL ASSI FICATION/ DOWNGRADING SCHEDULE

16. OISTRIBUTION STATEMENT (ol thls Report)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (ol the abstract entered In Block 20, /I dIllerent Irom Report)

18. SUPPLEMENTARY NOTES

19. KEY WORDS (Cont/nue on reverse Blde 11 necea"ary end Identlly by block number)

ACOUSTICS

SONIC BOOM

AERO-ACOUSTICS

PSYCHOACOUSTICS

20. ABSTRACT (Continue on reverae alde 11 nece".ary end Identlly by block number)

A loudspeaker-driven simulation booth with extended rise-time capability

(down to 0.22 ms) has been used for subjective loudness tests of sonie booms.

Test series I campared N-waves over a range of 0.22 to 10 ms rise time, 100 to

250 ms duration and 0.5 to 2.0 psf (24 to 96

N/~)

peak overpressure. In one

sequence, tradeoff between rise time and overpressure was measured for equal

loudness; in another, the tradeoff between duration and ove rp re s sure . For

equal loudness 10 ms rise time required 8 dB higher overpressure than for 1 ms

UN'CLASS!F'IED

SECURITY CLASSIFICATION OF THIS PAGE(When Data Entered)

rise time. Duration had little effect in the range 100 to 200 ros but at 250 ms noticeably enhanced the loudness. These results confirm those measured by Shepherd and Sutherland, made at 1 ros rise time and above (except for the anomalous enhancement at 250 ms duration), and extend the measurements down to 0.22 ms. There is also good agreement with theoretical predictions (Johnson-Robinson, Zepler-Harel methods) except for the 10 ros rise time and 250 ros duration cases.

Test series II xampared certain 'flat-top' sonic boom signatures with a reference N-wave (0.5 psf, 1 ros rise time, 150 ros duration). According to current theory, such 'flat top' signatures would be generated by a special

family of very long SST aircraf't designed for minimized sonic boom: the

front shock (llPSH) is followed by a linear rise to peak amplitude

(4)MAx)

followed by the usual linear decay. For equal subjective loudness, flat top vs N-wave (peak overpressure APN) the peak amplitude of the 'flat top'

sig-nature was substantially higher than that of the N-wave; thus' for equal

amplitude the 'flat-top' signature was quieter. The results for equal

loud-ness were well ntted by an empirical law 4>SH + O.ll~"=

4>N;

the

equivalence shows how the f.ront shock amplitude APSH do~nates the loudness.

All this was found compatible wi th predictions by the method of Johnson and Robinson.

UNCLASSIFIED

I1UAS TEX:IIIIICAL N<1rE NO. 215

Institute for Aerospace studies, University or Torollto 4925 Duf't'erin street, Downsview , Ont eri 0 , Canada, lot3H 5T6

SUIlJECTIVE LOUDNESS Ol" BONIC-BOOM: N-WAVE AND MINIMIZEIl (, LOW-BOOM' )

NiedzW1eck1, A., Ribner, H. S. 30 pages 17 figures

1. AeoUBties 2. Socie boom 3. Aero-&Cousties 4. Psycho&cousties

SIGNATUREB

~

I. Niedzwieck1, A., Ribner, H. S. 11. t7rIAS Techn1eal Note No. 215

A 10udapeaker-dr1ven simul .. tion booth wUh extended riae-time ea.pobllity (down to 0.22 ma) has been

used for subjective loudness tests or sonic booms. Test series I eompa.red N-waves over a range of 0.22

to 10 InS rise time, 100 to 250 InS duration end 0.5 to 2.0 psf (24 to 96 N/uJ.) peak overpressure . In

one sequence, tradeoff between rise time and overpressure was XDea8ured for equal loudnesB; in another,

tbe tra.deoff between duration a.nd overpressure • l"or equal loudness 10 ma rise time required 8 dB higher

overpressure than for 1 InS rise time. Duration hed little effect in the range 100 to 200 ma but at 250

InS notieeobly enhaneed the loudness. Tbese results eonfirm those measured by Shepherd and Sutherland, made .. t 1 InS rise tilDe and above (except for the anomalous enhaneement at 250 ms duration), and extend tbe mea.surements down to 0.22 ma. Tbere is also good agreement with theoretieal predictions (Johnson-Robinson, Zepler-Herel methods) exeept for the 10 ma rise tilDe and 250 ms duration cases.

Test series II compared certain 1 nat-top , sonie boom s1gnatw-es with a reference N-wave (0.5 pef, 1

ma rise time, 150 ms duration) • According to current theory, BUch I flat top I signatures would be

genel'o-ated by .. special family of very long SST a.ireraft designed for min1m1zed socie boom; the front shock

(lIpSH) is followed by a linea.r rise to peak amplitude (lIpMAJC) fo11owed by the usual linea.r deeay. For

equal subjeetive loudness, fl .. t top vs. N-wave (peak overpressure 4>N, the peak amplitude of the 'flat

top' a.ignature w&s substantially higher than toot of the N-wa.ve; thus for equal nntitude the 'flat-top' sign .. ture was quieter. Tbe results for equal loudness were well fitted by an emp r cal law 4>SH + 0.11

l\pMAJC = ~; the equivalenee shows how tbe front shock amplitude lIpSH domina.tes the loudness. All this

" ... found eaap .. tible witb predictiona by tbe method of Johnson and Robinson.

•

t7rIAS TEXlHNICAL NCIrE NO. 215

Institute tor Aeroapace studies, tJnivers1ty of Torollto 4925 Dufterin Street, Downsview, Onta.rio, Canada, lot3H 5T6

SllBJECTIVE LOUDNESS Ol" SONIO-BOOM: N-WAVE AND MINDIIZED (, LOW-BOOM') SIGNATUREB

Niedzwieck1, A., Ribner, H. S. 30 page. 17 t1gures

1. AeoUBties 2. Socie ·boom 3. Aero-&Coustie. 4. Psycho&Cousties I. N1edzwieck1, A., R1bner, H. S. Il. t7rIAS Techn1eal Note No. 215

~

A 10udapeaker-dr1ven simul .. tion booth with extended rise-time eapob111ty (down to 0.22 ma) has been used for subjective loudness tests or sonie booms. Test series I eompa.red N-waves <Ner a range of 0.22

to 10 ms rise time, 100 to 250 ma duration and 0.5 to 2.0 psr (24 to 96 N/uJ.) peak overpressure • In

one aequence, tradeoff between rise time and averpressure was measured -ror equaJ.. loudness; in another, the tra.deoff between durat10n a.nd overpressure • l"or equal loudness 10 ma rise tilDe required 8 dB higher

overpressure than for 1 ma rise time. Duration hed little effect in the range 100 to 200 ma but at 250 ms notieeobly enhaneed the loudness. These results eonfirm those measured by Shepherd and Butherland,

mede at 1 ma rise time and obove (except for the a.nomalous enhaneement at 250 ma duration). and extend

the measurements down to 0.22 ma. Tbere is also good agreement with theoretieal predictions (Johnson-Robinson, Zepler-Ha.rel methods) exeept for the 10 ma rise time and 250 ma duration cases.

Test series Il eompa.red eerta.in 'flat-top' socie boom Bignatures with .. referenee N-w .. ve (0.5 psf, 1

ma rise time, 150 ms duration). According to eurrent theory, such 'fl .. t top' signatures would be

geneI'-ated by a special family of very long SST a.ireraft designed for min1m1zed sonie boom; the front shock (lIPSH) is followed by .. linea.r rise to peak amplitude (lIpIWC) followed by the usual l1nea.r deeay. For

equal subjeetive ~, flat top vs. N-wave (peak overpreBsure 4>N, the peak amplitude of the 'flat top' signature was SubBta.ntially higher than toot of the N-wave; thus for equal nnlitUde the 'n .. t-top' signature was quieter. Tbe results for equal loudness were well fitted by an emp rieal 1 .. " 4>SH + 0.11

lIpMAX ~ ~; the equivalenee shows how tbe frollt shock amplitude lIpSH dominates the 10udnesB. All this

w ... found eaap .. tible wi tb predictions by the method of Johnson and Robinson.

Available copies of this report are limited. Return this card to UTIAS, if you require a copy. Available copies of this report are limited. Return this card to UTIAS, i. you require a copy. t7rIAS TEX:HNICAL NOTE NO. 215

Institute for Aerospaee studies, tJnivers1ty of Toronto

4925 Dufferin Street, Downsview, Onta.rio, Canada, M3H 5T6

SUIlJECTIVE LOUDNESS OF SONIC-BOOM: N-WAVE AND MINlXIZED (, LOW-BOOM') SIGNATURES

Niedzwiecki, A., R1bner, H. S. 30 pages 17 figures

1. Acoustics 2. Sonie boom 3. Aero-acoUstics 4. Psychoacoustics

1. Niedzwieck1, A., Ribner, H. S. Il. t7rIAS Techn1eal Note No. 215

~

A 10udapeaker-dr1ven simulation booth with extended ri se-time eapobility (down to 0.22 ms) has been used for subjective loudness tests of socie booms. Test series I eompa.red N-waves over a range of 0.22

to 10 InS rise time, 100 to 250 ms dur .. t10n and 0.5 to 2.0 psf (24 to 96 N/uJ.) peak overpreBsure. In

one sequence, tradeoff bet\-leen rise time ,and overpressure was measured for equal loudneBs; in another,

the tradeoff between duration and overpressure . l"or equal loudness 10 ms rise time required 8 dB higher

overpressure than ror 1. ros rise time. Duration had 11 ttle effect in the range 100 to 200 ma but at 250 ms noticeabl.y enhanced the loudness. These results confirm. those measured bl' Shepherd and Sutherland,

made at 1. ma rise time and above (except for the anamalous enhancement at 250 ms duration), and extend

the :oeasurements down to 0.22 ms. There is also goed agreement with theoretical predictions (Johnson-Robinson, Zepler-Ha.rel methode) except for the 10 ma rise time and 250 ms duration cases.

Test series II compared certain 'fiat-top' sonie boom signatures with a referenee N-wave (0.5 psf, 1

m.s rise time, 150 ma duration). Aeeording to eurrent theory, sueh 'flat top' signatures wo\Ûd be

gene1\-ated by a special family of very long SST a.ireraft designed for min1m1zed sonie boom; the front shock

(lIpSH) is fo11owed by a .linea.r rise to peak amplitude (lIpMAJC) fo11owed by the usual linea.r deeay. For

equal subjeetive loudness, flat top vs. N-wave (peak overpressure 4>N, the peak amplitude of the 'flat

top' signature was substantially higher than toot of the N-wave; thus for equal amplitude the 'flat-top'

signa.ture was quieter. The results for equaJ.. loudness were well fitted by all elI!Pirieal law 4>SH + 0.11

L'>PMAJC = ""PH; the equivalence shows how tbe front shock amplitude lIpSH d=inates the loudness. All thia

was fO\Uld eOOlpatible with predictioos by the method o-r Johnson and Robinson.

t7rIAS TmHNICAL NClrE NO. 215

Inst1tute for Aerospace Studies, tJniversity of Torollto

4925 Dufferin Street, Downsview, Onta.rio, Canada, M3H 5T6

SUBJECTIVE LOUDNESS Ol" SONIC-BOOM: N-WAVE AND MINDm:ED (, LOW-BOOM') SIGNATURES

Niedzwieck1, A., Ribner, H. S. 30 pages 17 figures 1. Acoustics 2. Socie boom 3. Aero-acousties 4. Psychoaeousties 1. Niedzwieck1, A., Ribner, H. S. Ir. t7rIAS Techn1eal Note No. 215

~

A loudapeaker-driven simul .. tion booth with extended ri se-time eapability (down to 0.22 ma) has been used for subjecti ve loudness tests of sonie booms. Test series I eompa.red N-waves over a range of 0.22

to 10 ma rise time, 100 to 250 ma duration and 0.5 to 2.0 psf (24 to 96 N/uJ.) peak overpressure. In

one sequenee, tradeoff between rise time and overpre66ure was measured for equal loudneasj in another, the tradeoff between duration and overpressure . P'or equal loUdnesa 10 ma rise time reqJ.ired 8 dB higher

overpressure the.n 'lor 1 ma ri6e time. Duration had 1ittle e:f'fect in the range 100 to 200 ma but at 250

ma noticeably enhanced the loudnes8. These results conf'irm those measured by Shepherd and Suther1and,

made at 1 ma rise time and &hove (except :for tbe anomalous enhancement at 250 ma duration), and extend

the measurements down to 0.22 ms. There 1s also goed agreement with theoretical predictions

(Johnson-Rob1nson, Zepler-Harel.methods) except tor the 10 ma rise time and 250 ma duration cases.

Test series U eompared certain ''flat-top' sonie boom signatures with a referenee N-wave (0.5 psf, 1 ms rise tilDe, 150 ms duration). According to eurrent theory, such 'flat top' signatures would be gene

l'-ated by a special family of very long SST a.ireraft designed for micimized sonie boom; the front shock (lIpSH) is followed by a linea.r rise to peak amplitude (lIpIWC) followed by the usual linea.r decay. For

equal subjeetive loudness, flat top vs. N-wave (peak overpressure 4>N, the peak amplitude of the 'flat

top' signa.ture wa'S"Sübiitäntially higher than toot of the N-wave; thus for equal amplitude the 'flat- top'

signature was quieter. The resUlts for equaJ.. loudness were ,",ell :fitted by an empirical 1aw 4>SH + 0.11

l\pMAJC = ~; the equivalenee shows how the frollt shock amplitude 4>SH domina.tes the loudness. All this

was f'o\Uld compatible with predietions by the method of' Jobnson and Robinson.