sonic boom generator

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N94- 33501

GEORGIA

TECH

SONIC

BOOM

SIMULATOR

Krish Georgia

K.

Ahuja Technology 30342

Institute of GTRI/ASTL Atlanta, Ga.

First

Annual

High-Speed Williamsburg, May 14-16,

Research Virginia 1991

Workshop

1315 PRECEDING P.,'IGE E;LANK NOT FILMED

GENERAL To examine 3 the 30 building Hz, driver program has test and Georgia system on been house human response to sonic boom in the

range special NASA

Hz to acoustic Langley

Institute of to simulate building extended has been to

Technology is sonic boom. and an made human upper available

building a To support this of Georgia 4

response, frequency by

simulator's KHz. Tech At the drivers assembled. The with following A for

capability residential these tests. time and The

of preparation the associated system pages house has, provide and are

of

this document, electronics not been of of plans

most have fully

of been tested.

the acoustic built and

however, an the overview

the

progress are also

to

date.

The

acoustic the

driver test

systems,

principle Future

their

operation

together

described.

summarized.

Figure

1

Outline

of

presentation

Outline of Presentation

Source requirements Very low frequency source details Test house Future plans1316

MOTIVATION Guidelines are speech due to measures accepted environment emissions, bric-a-brac outdoor There can be response. subsonic indoors ability subsonic to experiments 10 Hz. produce structural as 3 Hz. of is currently for interference the assessment in and the hearing of exposure of damage. flyovers or DNL. the to Further, may be However, interior relative assessed currently in on by aircraft for noise

available

form

methodology

predicting annoyance objective there is no

conventional aircraft such as EPNL, SEL, way such and sonic to where assess reaction

human critically

response depends

an indoor secondary rattling reaction of to

as noise associated booms is

induced building vibrations and acoustic radiations. Human more predictable. to as some booms difference indicate to that sonic the boom

considerable shaped There aircraft than sonic aircraft the The very in such also noise,

evidence a exists sonic This way

signature human to the than done than to and as low

minimize

resulting

indication that are relatively may primarily

in comparison more objectionable be due to response has been of much was both the higher developed human

outdoors. booms noise. building

to induce more structural Although, considerable work response to to noise, most frequencies described here to determine at outdoors 2

examine

controlled

have been restricted sonic boom simulator low frequency both indoors noise

response,

and Figure

frequenciies

Motivation

1. Structural / human response at low frequency 2. Effect of boom shaping

1317

SONIC

BOOM

The actual aircraft are

N-shaped shape design better

disturbance may and understood vary by operation.

shown because The examining

here of effects the a

is the

an on

idealized people and contents

shape. effects of

The and such

atmospheric spectral frequency the duration, at higher that frequency.

structures

waves. The peak the total duration frequency. have longer Larger duration

level takes place at of the boom. Longer airplanes and consists line at and thus planes lower

dependent upon the lower the altitudes As shown are tangent will in

flying peak

this figure, spectrum to a 6-dB-per-octave The system described response in the range

of several convolutions higher frequencies. designed to have

here was 3 Hz - 4 kHz.

flat

frequency

Figure

3

Sonic

Boom

5PL &p

Very 2-

Low 30

30-

LOW 100

Intermediate 100400

High 4004k

""

"" "

N ,.

Response 6 dB/0ctave

N-WAVE

Frequency

(Hz)

1318

VERY Electro-acoustic frequencies low response excess wall phase, Tech described system. of of a frequency in the test 2 psf

LOW

FREQUENCY drivers that 30 was 330 This pressure Hz are

SOURCE generate available to was over taken a It

REQUIREMENTS large produce also 10 required ft x 12 the during amplitudes Our to ft produce area of development flat frequency in the at very

higher

than driver range sound house.

commercially.

required Hz. level figure, of a system frequency

shows the sonic boom later,

dimensions simulator other high

single unit of the driver. Georgia consists of six such units. As speakers are also part of this

Figure

4

'very Low Frequency Source Requirements Flat response 3Hz - 30Hz 2 psf peak pressure on the test house wall

13_9

VERY The system shown

LOW in Figure

FREQUENCY 4 is shown

SPEAKER here in its finished form.

Figure

5

Very Low Frequency Speaker!

1320

LOW The units The which drive magnets, inherently nonlinear or rotation. input signal driver to be units

AND for

INTERMEDIATE the The low and shown with the a

FREQUENCY intermediate in the Figure very principle

SOURCE frequency 6a low of are some frequency operation motion by noise of of converter means typical that becomes motion to the of of coils, heavy are the the

servo-driven sketch is shafts. and

units. used in in

units 6b It

conjunction shows shows specially design coil motion,

drivers.

Figure to

servo-driven

system. connected Servo-drive

rotary-to-linear strengthened radiators fragile a is voice

eliminates low frequency Unlike motor can

voice response coil

compromised voice large a

weak with

designs.

provide exactly

unlimited proportional

Rotation voltage

in either direction and current. Figure 6

Low and Intermediate Servo driven units

Frequency

Source

BELT

I

TWO RADIATORS DRIVE AR._! TO ONE OF MOTOR DRIVE

BELT MECHANISM SHO_,VN WITH ONE DRIVE ARM REMOVED

J

SHAFT

1321

SPEAKER The complete house ("test the enclosure drawn like a

ENCLOSURE simulator that used made

AND

THE

TEST

HOUSE an

(FRONT)

noise house")

unit is housed in to be a residential out of an awning

enclosure outside a unit. As shown here, which can be

has walls curtain.

material

Figure

7

Speaker

Enclosure and the Test House (Front)

1322

SPEAKER Figure 8 shows

ENCLOSURE the back view

AND

THE

TEST

HOUSE enclosure

(BACK) and the test

of the house. Figure

speaker

8

Speaker

Enclosure and the Test House (Back)

1323

SPEAKER

ENCLOSURE

AND

THE

TEST

HOUSE

(SIDE

VIEW)

Figure

9

shows

the

side

view

of the house. Figure

speaker

enclosure

and

the

test

9

Speaker

Enclosure

and the Test House

(Side View)

1324

VERY LOW FREQUENCY SPEAKER (2 Hz - 30 Hz)Only in one of a Figure the single 10. through unit Figure the of of the 10a the window very shows driver. from low the frequency window 10b the of is Figure inside speaker the a view is house of shown that the here faces driver

openings

opening

house.

Figure

10

Very Low Frequency Speaker (2Hz- 30Hz)

(a)

(b)

_

1325

EASILY The people in diffuser very could 11. is moved Figure low

DISMOUNTABLE speaker dismount bolt the Figure from system various is noise 11

ARRANGEMENT was in designed as unit. Figure so l la that and two here the

frequency mount The and holding away

components producing

shown

undone

Easily Dismountable

Arrangement

J

(b)

(a)

1326

ORIGINAL OF POOR

PAGE 1S QUALITY

VANE It of is the the controlled very force that top and low produces bottom movement frequency needed to the in

MOVEMENT of move sound. this figure. of sides vanes speaker air Each As air located system in and unit shown in the that out has in the of middle provides the two next section the speaker separate figure, two motorTwo vane

fluctuating opening openings,

these vanes help move operated fans placed positions are shown in

large amount on the two Figure 12. Figure

provided by of the vanes.

12

Vane Movement

lIF _l-

"_'---_l

(a) Vanes

closed

(b) Vanes

open

O_k_;NAL OF POOR

PA('_

!S

QUALIYY

1327

PRINCIPLE

OF OPERATION OF THE VERY NOISE SOURCE

LOW

FREQUENCY

As shown in Figure 13a, air mass for each vane is provided by a blower fan. In Figure 13b, the soli

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