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The Loudspeaker Study

Eric Moskus&

Nathan Sibon, Zach Bruin, TJ Kallaher, Mike Capello

November 6th, !"#

$coustical Testin% '

(r) (omini*ue Ch+enne

(r) auren -onsse

"

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Abstract:

n The Loudspeaker Study,the polar patterns, .re*uenc/ response, an0 crossover cut1o..

.re*uenc/ o. a bi1ampe0 Event T-23 po4ere0 lou0speaker 4ere all calculate0 in Columbia Colle%e

Chica%o5s anechoic chamber usin% TE!) The .re*uenc/ response o. the lou0speaker 4as also

calculate0 insi0e Columbia Colle%e Chica%o5s acoustic lab 7a non1anechoic environment8) The results

o. the anechoic an0 non1anechoic .re*uenc/ response tests sho4 a relativel/ hi%h 0e%ree o. similarit/)

The Event lou0speaker has a .airl/ colore0 .re*uenc/ response, especiall/ belo4 !! 9: an0 above

;k9:) The crossover cut1o.. .re*uenc/ 4as .oun0 to be at "2be%ins to take on a car0ioi0 pattern, an0 at "=,=2>9: the response becomes nearl/ h/percar0ioi0)

Introduction:

The Loudspeaker Study4as the secon0 o. three pro?ects to be complete0 .or the $coustical

Testin% course at Columbia Colle%e Chica%o) The aim o. the stu0/ 4as to 0etermine the .re*uenc/

response, polar pattern, an0 crossover cut1o.. .re*uenc/ o. an Event T-23 lou0speaker usin% TE!

insi0e o. Columbia Colle%e Chica%o5s anechoic chamber) The .re*uenc/ response o. the lou0speaker

4as also to be measure0 in a non1anechoic environment)

Signal Flow & Preparation:

The Event T-23 lou0speaker 4as place0 onto an @utline ET1ST electronic turntable 4hich

itsel. 4as place0 onto an elevate0 table insi0e the anechoic chamber 7see i%) $1" in $ppen0iA $8) The

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bottom o. the lou0speaker cabinet 4as ## inches o.. the %roun0) The Electro1oice -E;; microphone,

4hich 4as the microphone use0 .or all testin%, 4as place0 into a microphone stan0 an0 positione0 >!);

inches a4a/ .rom the lou0speaker an0 ># inches o.. the %roun0) The microphone 4as pointe0 0irectl/

bet4een the t4o 0rivers o. the lou0speaker) T4o $uraleA "55 Sonoiber absorptive panels 4ere place0

over the three le%s o. the microphone stan0 to prevent an/ potential re.lections .rom marrin% our 0ata)

roper si%nal .lo4 to an0 .rom the anechoic

chamber necessitate0 that si%nal output be sent

.rom the TE! unit into the Event lou0speaker,

an0 that the input at the microphone be sent into

the computer) Si%nals 4ere route0 in an0 out o. the

anechoic chamber via a snake boA, 4hich

penetrate0 throu%h a hole in the 4all near the

ceilin% o. the anechoic chamber) The hole

appeare0 to be su..icientl/ covere0 as to prevent

soun0 leaka%e) The .ull si%nal .lo4 bet4een

components can be seen in i%) ") $ more 0etaile0

eAplanation o. si%nal .lo4, as 4ell as photos, can

be .oun0 in $ppen0iA $)

$ Time -esponse 7ETC8 test 4as

per.orme0 throu%h the TE! so.t4are to veri./

correct si%nal .lo4) To per.orm this test, TE!

%enerates a .re*uenc/ s4eep 4hich is then sent to

the Event lou0speaker) This preliminar/ test not onl/ con.irme0 si%nal .lo4 but also sho4e0 that the

si%nal1to1noise ratio in the anechoic chamber 4as a0e*uate .or testin% 7aroun0 >! 0B relative8) The test

#

Fig. 1:This chart shows the signal flow between componentsused during tests in the anechoic chamber. The signal flow of

the TEF20 unit output into the Eent loudspeaker, as well as

the signal flow of the microphone input into the computer, are

represented in the chart. The wall bordering the anechoicchamber and the acoustics lab is represented by the dashed

orange lines. !omponents below the dashed lines were

located inside the anechoic chamber, while components aboethe lines were located inside the acoustics lab. For imagesand e"planations of the physical connections between these

components see #ppendi" #.

(Acoustics Lab)

(Anechoic Chamber)

Anechoic Chamber

Wall

Electro-oice!E"" #icrophone

$ittree Patch $ay

TEF%&

E'ent T!()LLoudspeaker

*o+puter

*o+puter Station Patch $ay

Snake $o,

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also sho4e0 that the environment is not per.ectl/ anechoic, as re.lections coul0 be seen in the time

response curves) 9o4ever, the soun0 levels o. the re.lections 4ere more than ! 0B belo4 the level o.

the 0irect soun0) $n eAample o. an ETC test in the anechoic chamber can be seen in i%) )

Freuency !esponse in Anechoic *ha+ber:

$n ETC test 4as per.orme0 to ac*uire the 0ela/ time parameter nee0e0 .or the .re*uenc/

response test) This test calculate0 that the 0irect soun0 arrive0 at the microphone ) ms a.ter the

si%nal onset) This 0ela/ time 4as then importe0 into the receive 0ela/ time parameter o. TE!5s Time

(omain Spectrometr/ 7T(S8 test, 4hich 4as the test use0 to calculate the .re*uenc/ response o. the

lou0speaker) $ number o. trial T(S tests 4ere per.orme0 at various settin%s in or0er to 0etermine

4hich settin%s 4oul0 be most appropriate .or calculatin% the .re*uenc/ response)

The TE! unit ha0 a ten0enc/ to .ail in operation 0urin% tests 4ith lon% .re*uenc/ s4eeps an0

hi%h .re*uenc/ resolution) $ 4a/ aroun0 this problem 4as to per.orm several T(S tests usin% a ver/

>

Fig. 2:This is a sample Time $esponse %ET!& Test performed at '02( samples with a )0 second 20*+20k*+ sweep. The direct sound arries at the microphone ).0- ms after the onset, at '.)/ d. The

relatiely high noise floor was due to electrical noise from the system. $egardless, there was still about a

(0 d signaltonoise ratio. The sound leels of reflections are also all more than 20d less than the leel

of the direct sound.

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hi%h .re*uenc/ resolution 7D ;9:8 but 4ith smaller ban04i0ths) The results .rom the multiple T(S

tests coul0 then be inte%rate0 into one .re*uenc/ response %raph coverin% the entire .re*uenc/ ran%e

.rom !9:1!k9:) Several tests 4ere per.orme0 usin% this metho0, but the 0ata 0i0 not 0eviate

si%ni.icantl/ .rom 0ata %athere0 usin% a sin%le T(S test at a lo4er .re*uenc/ resolution) ltimatel/, the

settin%s outline0 in i%) # an0 i%) B1" in $ppen0iA B 4ere use0 in the T(S test to 0etermine the

lou0speaker5s .re*uenc/ response) i%) # also sho4s the .re*uenc/ response o. the Event T-23 as

measure0 in the anechoic chamber)

The .re*uenc/ response o. the lou0speaker is .airl/ colore0 throu%hout the .re*uenc/ ran%e

teste0) 9o4ever, 0ata belo4 "!!9: appears particularl/ unreliable, likel/ because o. limitations in the

0esi%n o. the anechoic chamber) o4 .re*uenc/ rumble 4as also hear0 leakin% out o. the anechoic

chamber 0urin% testin% 4hich ma/ have contribute0 to this unreliabilit/) re*uencies above ;k9: are

;

Fig. 3: This is the fre1uency response graph of the Eent T$L loudspeaker, as measured in the anechoic chamber. The

test was performed at '02( samples with a '0*+ fre1uency resolution, //./( ms time resolution, and using a single '//.3

second 20*+20k*+ fre1uency sweep. The full settings for this test can be seen in Fig. ' in #ppendi" .

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si%ni.icantl/ colore0 b/ the lou0speaker)

Freuency !esponse in Acoustics Lab:

The .re*uenc/ response o. the Event T-23 lou0speaker 4as to be remeasure0 in a non1

anechoic environment 7Columbia Colle%e5s acoustics lab8 so that it coul0 be compare0 4ith the

response ac*uire0 in the anechoic chamber)The Event T-23 lou0speaker an0 Electro1oice -E;;

microphone 4ere positione0 in the acoustics lab in a similar manner to ho4 the/ 4ere positione0 insi0e

the anechoic chamber 7see i%) $1; in $ppen0iA $8) The 0istance bet4een the Electro1oice -E;;

microphone an0 the Event lou0speaker 4as >!); inches) The microphone an0 lou0speaker 4ere

connecte0 0irectl/ to the TE! unit usin% 3- eAtension cables) hotos o. the setup 0urin% the

.re*uenc/ response tests in the non1anechoic acoustics lab can be seen in $ppen0iA $)

$n ETC test 4as per.orme0 an0 the results sho4e0 several si%ni.icant re.lections reachin% the

microphone input 7see i%) C1" in $ppen0iA C8) $ particularl/ troublesome re.lection occurre0 =)"" ms

a.ter onset an0 it 4as 0etermine0 to be the .irst or0er re.lection o.. the %roun0) This re.lection 4as

eliminate0 manuall/ b/ la/in% several absorptive panels on the .loor bet4een the lou0speaker an0

microphone) $n ima%e o. this setup is sho4n in i%) $16 in $ppen0iA $, an0 the e..ect o. a00in% the

absorption to the .loor can be seen in i%) C1 in $ppen0iA C) -a/ tracin% techni*ues 4ere use0 to

0etermine the times at 4hich .irst or0er re.lections o.. o. prominent boun0aries in the room 4oul0

arrive at the microphone 7see i%) (1" in $ppen0iA (8)

n or0er to re0uce the a0verse e..ects o. testin% in a re.lective environment the 0istance

parameter in T(S settin%s 0ispla/ 4as set to >)"; .eet) This means that an/ re.lection occurrin% over

>)"; .eet .rom our measurement 4ill be attenuate0 b/ ";0B) The 0ra4back to this .eature is that

.re*uenc/ resolution is sacri.ice0) The .re*uenc/ response o. the Event lou0speaker in the non1

anechoic environment can be seen in i%) >) The .re*uenc/ response %raph calculate0 in the non1

6

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anechoic environment is ver/ similar to the .re*uenc/ response %raph calculate0 earlier in the anechoic

chamber) The lack o. .re*uenc/ resolution available in the non1anechoic environment, ho4ever, %ave

the .re*uenc/ response a much .latter contour, especiall/ in the lo4er .re*uencies)

Loudspeaker *rosso'er *ut-.// Freuency Test

The tests use0 to 0etermine the crossover cut1o.. .re*uenc/ bet4een the t4o 0rivers o. the

Event lou0speaker 4ere per.orme0 in the anechoic chamber) n or0er to narro4 the ran%e o.

.re*uencies in 4hich to test .or the crossover, the t4eeter an0 4oo.er 4ere separatel/ isolate0 an0 the

.re*uenc/ response o. each in0ivi0ual 0river 4as measure0) The t4eeter o. the lou0speaker 4as

covere0 4ith a thin la/er o. insulation 4hich 4as hel0 in place 4ith 0uct tape) The .re*uenc/ response

o. the 4oo.er alone 4as then measure0 usin% a T(S test, 4ith the microphone approAimatel/ one inch

.rom the center o. the 4oo.er) $n ima%e o. this setup can be seen in i%) $1> in $ppen0iA $) n a

similar .ashion, the 4oo.er 4as then 0ampe0 4ith the same insulation an0 tape, an0 the port hole 4as

=

Fig. 4:This is the fre1uency response graph of the Eent T$L loudspeaker in the nonanechoic

enironment. The fre1uency response here is ery similar to the fre1uency response graph found in

the anechoic chamber, e"cept that the response is much smoother here%especially at lowfre1uencies& because of the lower fre1uency resolution used. The sweep was ran from 20*+20k*+

for /. seconds with '02( samples. The fre1uency resolution was set at 242 *+ in order to attain a

time resolution of ).3 ms %or (.'- feet&.

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plu%%e0 4ith a scar. to prevent lo4 .re*uenc/ leaka%e) The response o. the t4eeter 4as measure0, 4ith

the microphone approAimatel/ one inch .rom the center o. the t4eeter) Complete isolation o. the

0rivers usin% the insulation an0 tape 4as not possible 7especiall/ .or the 4oo.er8, thou%h the/ 4ere

isolate0 enou%h that the 0ata in0icate0 the crossover cuto.. .re*uenc/) -esults o. the t4o .re*uenc/

response tests are overla/e0 an0 sho4n in i%) E1" in $ppen0iA E) The overla/ o. the .re*uenc/

responses o. the t4o 0rivers sho4s a crossover in the re%ion o. k9:)

The insulation, 0uct tape, an0 scar. 4ere all remove0 .rom the lou0speaker be.ore the .inal

crossover test) The microphone 4as positione0 approAimatel/ one inch .rom the lou0speaker, pointe0

in the space bet4een the the 4oo.er an0 t4eeter) $ T(S test 4as per.orme0 4ith an 29: .re*uenc/

resolution an0 the results can be seen in i%) ; an0 i%) 6) The phase 4as overla/e0 4ith the .re*uenc/

response, an0 the crossover ran%e 4as 0etermine0 b/ markin% the minimum an0 maAimum points in

the 7semi8linear portion o. the phase response bet4een about "2;!9:1"

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