Aula sobre Delay e Reverberação2

8/2/2019 Aula sobre Delay e Reverberao2

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25 ms 50 ms 75 ms 100 ms0 ms


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25 ms 50 ms 75 ms 100 ms0 ms

echoEfeitos de modulao


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Vsom = 340 m/s

Delay = deslocamento/ Vsom

Delay = 34 metros / 340 m/s

Delay = 0,1 segundos ou 100 milissegundos

17 metros

17 metros


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Se 1 minuto = 60 segundos

e 1 segundo = 1000 ms

Ento:

1 minuto = 60.000 ms

60 beats por minuto (bpm) equivalem a 60 pulsos com a durao de 1 (um)

segundo cada uma.

60.000 60 = 1.000 ms

Portanto, em um andamento de 60 bpm:

Cada semnima ter a durao de 1.000 ms

Cada colcheia ter a durao de 500 ms Cada semicolcheia ter a durao de 250 ms Cada mnima equivaler a um tempo de 2.000 ms E cada semibreve ter 4.000 ms de durao


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bpm semibreve mnima semnima colcheia semicolcheia

54

60

72

86

94

104

112

128

134

Dividindo o nmero 60.000 pelo bpm de uma msica obtemos portanto o

valor de cada nota em milissegundos

Por exemplo:

Se o bpm for equivalente a 84, a semnima ter a durao de 714,28 msSe o bpm for equivalente a 174, a semnima ter a durao de 344,82 ms


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Delay

Delay frequencias canceladas(Hz)

milissegundos

segundos fundamental

2 harmonico3 harmonico4 harmonico5 harmonico 6harmonico

0,25 0,00025 2000 4000 6000 8000 10000 12000

0,35 0,00035 1429 2857 4286 5714 7143 8571

0,5 0,0005 1000 2000 3000 4000 5000 6000

0,75 0,00075 667 1333 2000 2667 3333 4000

1 0,001 500 1000 1500 2000 2500 3000

2 0,002 250 500 750 1000 1250 1500

3 0,003 167 333 500 667 833 1000

4 0,004 125 250 375 500 625 750

5 0,005 100 200 300 400 500 600

6 0,006 83 167 250 333 417 500

7 0,007 71 143 214 286 357 429

8 0,008 63 125 188 250 313 375

9 0,009 56 111 167 222 278 333

10 0,01 50 100 150 200 250 300

11 0,011 45 91 136 182 227 273

12 0,012 42 83 125 167 208 250

13 0,013 38 77 115 154 192 231

14 0,014 36 71 107 143 179 214

15 0,015 33 67 100 133 167 200

16 0,016 31 63 94 125 156 188

17 0,017 29 59 88 118 147 176

18 0,018 28 56 83 111 139 167

19 0,019 26 53 79 105 132 158

20 0,02 25 50 75 100 125 150

21 0,021 24 48 71 95 119 143

22 0,022 23 45 68 91 114 136

23 0,023 22 43 65 87 109 130

24 0,024 21 42 63 83 104 125

25 0,025 20 40 60 80 100 120


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Parmetros:

Delay: Controla o tempo de cada repetio do efeito;

Feedback: Controla a quantidade de sinal processado que reinjetada no efeito. Alguns permitem

determinar se o feedback positivo (em fase, acentua harmnicos pares, som mais metlico) ou

negativo (fora de fase, acentua harmnicos mpares, som mais "quente").

Rate : Controla a velocidade com que o modulador varia o delay. Por exemplo, Rate= 0.1 Hz significa

que o efeito far uma varredura de um ciclo a cada 10 segundos.

Depth: Em geral expresso como uma razo, especifica a relao entre o delay mnimo e mximo. Por

exemplo, 6:1 pode gerar uma varredura de 1 a 6 ms ou de 3 a 18ms.


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10 ms

20 ms

30 ms

50 ms

75 ms

100 ms

200 ms

500 ms

1000 ms

No referencias:

http://estadodearte.wordpress.com/2011/05/08/flanger-e-

phaser/


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2 - Phase

Os perodos das oscilaes em ondas sonoras na faixa audvel (20Hz - 20kHz) varia entre 50ms e 0,05ms. Portanto,

defasagens nessa faixa de tempo iro interferir nas oscilaes de frequncias peridicas (cancelamento de fase). Esse

atraso relacionado s frequncias sonoras a base para 3 tipos de efeito: phase, flange, chorus (a diferena entre eles

est ligada ao tempo de delay).

Descrio:

O efeito de phase emprega atrasos muito curtos na faixa de 1 a 10 ms. Quando o sinal original atrasado em relao

ao sinal repetido ocorre um efeito conhecido por comb filter no qual as frequncias cujos perodos esto diretamente

relacionados ao tempo de atraso so atenuadas e reforadas devido ao cancelamento de fase. Efeitos de phase

utilizam um determinado nmero de filtros para gerar o efeito comb. Usando um modulador (LFO) para mover esse filtro

dentro de uma determinada regio do espectro causa um cancelamento de fases varivel dependente das frequncias

usadas. Esse efeito conhecido como phase.

Parmetros:

Rate (ou speed): determina a velocidade com o que o modulador ir varrer ciclicamente a faixa de espectro

determinada.

Range : determina essa faixa do espectro a ser varrida pelo modulador.

Outros : filtros, feedback loop.


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Range: de 500 Hz

at 1Khz

Rate: (speed): 2 Hz

(2 ciclos porsegundo ou seja 2

varreduras por

segundo)

Range: de 500 Hz

at 9,5Khz

Rate: (speed): 2 Hz

(2 ciclos por

segundo ou seja 2varreduras por

segundo)

Phaser


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3 - Flange:

Descrio:

Esse efeito semelhante ao phase e foi usado pela primeira vez em uma gravao pelo inovador guitarrista Les Paul. O

efeito era alcanado com dois gravadores magnticos contendo o mesmo material sonoro fazendo com que um dos

gravadores diminuisse ocasionalmente a rotao para gerar uma diferena de fase entre os sinais. Nos sistemas digitais, o

flanger obtido de modo semelhante ao pahser, com atrasos de 1 a 20ms e um modulador que varia o atraso (regular ourandomicamente).

A diferena entre phase e flange que neste ltimo a atenuao e o reforo das frequncias ocorrem em intervalos

regulares enquanto que no phase isso depende da disposio dos filtros. Alm disso, no phase o espaamento, a

largura e a intensidade (depth) podem ser variveis. Em geral, flange tem um efeito no campo das alturas mais

pronunciado que o phase.

Figura: Diagrama de Efeito Flanger

Parmetros:

Delay: Controla o tempo de delay

Feedback: Controla a quantidade de sinal processado que reinjetada no efeito. Alguns permitem determinar se o

feedback positivo (em fase, acentua harmnicos pares, som mais metlico) ou negativo (fora de fase, acentua

harmnicos mpares, som mais "quente").

Rate : Controla a velocidade com que o modulador varia a o delay. Por exemplo, Rate= 0.1 Hz significa que o efeito far

uma varredura de um ciclo a cada 10 segundos.

Depth: Em geral expresso como uma razo, especifica a relao entre o delay mnimo e mximo. Por exemplo, 6:1 pode

gerar uma varredura de 1 a 6 ms ou de 3 a 18ms.

Outros : tipo de onda moduladora


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Na figura abaixo temos um DELAY. Trata-se de um plug-in que serve para gerar um ATRASO no sinal de udio que

passar por ele.

MIX: balano entre o

sinal de entrada e o sinal

processado por este

plug-in.

LPF: filtro passa

baixas, controla o

corte de agudos

DELAY: controla o

tempo de atraso do

sinal

DEPTH: controla o

montante de sinal que ser

adicionado pelos controles

moduladores.

RATE: indica a velocidade de

atuao dos moduladores de

sinal ao fazer a varredura de

freqncias. (quo rpido oudevagar a variao do sinal

ser feita pelos moduladores).

FEEDBACK: indica o nmero de

repeties que so reintroduzidas no

delay. Grosso modo indica o numero

de repeties do sinal que passoupelos moduladores.

GROOVE: controle que gera uma

pequena variao no tempo do

delay, humanizando um pouco o

efeito mecnico das repeties.

METER: est sintonizado ao

tempo e ao delay escolhido.

Extremamente til para se

fazer retardos estritamentesintonizados com o

andamento da msica.

TEMPO: o andamento damsica, funciona somente

quando a msica foi colocada

corretamente no grid.

Controles MODULADORES de sinal, que causam um efeito de comb filter (filtro pente)no sinal que passa pelo delay .Esse efeito

um sweeping (varredura) de freqncias que gera alguns cancelamentos de fase conforme o a varredura sobe ou desce as

freqncias (est associado aos efeitos chamados FLANGER e PHASER)


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Reflexes em ambientes fechados


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Algumas consideraes a respeito da reverberao

Reverberao um fenmeno que ocorre EM AMBIENTES FECHADOS OU SEMI-FECHADOS devido s mltiplas

reflexes sonoras que decorrem do choque das frentes de onda com as superfcies a contidas . Essas reflexes

ocorrem em todas as direes, em intervalos de tempo to curtos (milissegundos) que torna-se impossvel para o

crebro separar uma reflexo da outra. Esse campo de reverberao - campo reverberante - ocorre logo aps a

ocorrncia das reflexes primrias (early reflections) e acontece de forma to difusa que no se percebe mais uma

separao de uma reflexo para outra.

4) http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/reverb.html#c1

3) http://www.soundonsound.com/sos/jul08/articles/reverb1.htm

Fontes para pesquisa:

1) VALLE, Slon do. Manual prtico de acstica.(captulo 8 - pp. 93 at 103) So Paulo: Editora Msica & Tecnologia, 2006

2) HENRIQUE, Lus L.Acstica Musical. (captulo 19 - pp. 758 at 808) Lisboa: Calouste Gulbenkian, 2002.

Som

origi

nal

Early

reflections

Reverberao

Pr delay

Som

direto

(sem

refle

xo)
http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/reverb.htmlhttp://www.soundonsound.com/sos/jul08/articles/reverb1.htmhttp://www.soundonsound.com/sos/jul08/articles/reverb1.htmhttp://www.soundonsound.com/sos/jul08/articles/reverb1.htmhttp://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/reverb.html


17/27

Algumas consideraes a respeito da reverberao

Som direto

Refle

xesprim

rias Campo de reverberaes

ITD ( initial time delay) = o tempo decorrido entre o som original e a primeira de todas as reflexes, incluindo as early reflections.

Pr delay = o tempo decorrido entre o som original e o inicio da reverberao propriamente dita, quando o som difuso comea a seespalhar por todo o ambiente. No deve, portanto, ser confundido com o ITD, que definido pelaprimeira de todas as reflexes.

Early reflections (reflexes primrias) = Antes de o som se tornar difuso, espalhando-se por igual por todo o ambiente, ouvem-se

algumas reflexes localizadas e bastante distantes entre si no tempo e no espao. Estas primeiras reflexes so chamadas early

reflections ou reflexes primrias, e podem existir mesmo em ambientes com pouqussima reverberao

ITD


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Densidade = a quantidade de reflexes contidas dentro do campo reverberante. Quanto maior a quantidade de reflexes,

maior ser a densidade ou seja, a difuso. Quanto menor a quantidade de reflexes, menor ser a densidade ou difuso.

A densidade da reverberao a quantidade de reflexes que formam o campo reverberante. Uma alta densidade produz uma

reverberao muito macia, regular soando como um suave prolongamento do som original.

Uma baixa densidade produz uma reverberao mais spera, mais semelhante sonoridade das early reflections.

Dica: Para instrumentos de ataque forte, como bateria, percusso, solos de violo, etc., prefervel uma densidade mais alta,

para que no se ouam reflexes isoladas do ataque - a no ser claro, que se deseje isso!

Para instrumentos de ataque suave, como cordas (arco), obo, clarinete, rgo, etc.., uma reverberao de baixa densidade

pode valorizar o instrumento, criando dobras e aumentando sua textura. (Slon do Valle)

Reverberao muito densa e difusa Reverberao menos densa e difusa

Reverberao com pouca

densidade e difuso

Reverberao com muito

pouca densidade e difuso

Densidade a 100% Densidade a 66%

Densidade a 33% Densidade a 15%

Na figura abaixo temos um Processador de ambincia sonora chamado REVERBER Trata se de um plug in para se


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Na figura abaixo temos um Processador de ambincia sonora chamado REVERBER. Trata-se de um plug-in para se

processar a quantidade de reflexes sonoras que sero adicionadas ao som original, dando a impresso de que ele

est soando em um ambiente maior do que o ambiente original onde ele foi gravado.

Diffusion = a quantidade de reflexes contidas

dentro do campo reverberante. Quanto maior a

quantidade de reflexes, maior ser a

densidade ou seja, a difuso. Quanto menor aquantidade de reflexes, menor ser a

densidade ou difuso.

Decay = O tempo de durao do campo

reverberante. O intervalo de tempo em que

ocorrem as reverberaes, desde o seu inicio -

enquanto campo difuso - at o final das

reflexes.

Pr delay = O tempo que decorre entre o som

direto e o comeo do campo reverberante. O

pr delay o intervalo de tempo onde ocorrem

as early reflections.

HF CUT = corte de agudos do

sinal que entra no equipamento

LP FILTER = filtro passa baixas

que atua no sinal j processado

por este equipamento.

O Tamanho da

sala pode ser

selecionado

entre pequena,

mdia ougrande

Seleciona o tipo

de algoritmo a

partir do qual foi

desenvolvido o

tipo dereverberao

Seleciona o montante de sinal processado que ser

mixado ao som original. Se for 0% nenhum sinal

processado pelo reverber ser adicionado. Se for100% , somente o sinal processado ser escutado.

Se for 50%, o volume tanto do sinal original quanto

do sinal processado ser igual


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Campo reverberanteEarly Reflections

Som direto

Pr delay Decay

density

Difuso = Densidade

Reverber pouco difuso

Reverber muito difuso

Diffusion = a quantidade de reflexescontidas dentro do campo reverberante.

Quanto maior a quantidade de reflexes,

maior ser a densidade ou seja, a

difuso. Quanto menor a quantidade de

reflexes, menor ser a densidade ou

difuso.

Decay = O tempo de durao do campo

reverberante. O intervalo de tempo emque ocorrem as reverberaes, desde o

seu inicio - enquanto campo difuso - at o

final das reflexes.

Pr delay = O tempo que decorre entre o

som direto e o comeo do campo

reverberante. O pr delay o intervalo de

tempo onde ocorrem as early reflections.


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Na maior parte dos ambientes fechados as freqncias agudas sofrem um decaimento mais rpido que as freqncias

mais graves, sendo assim, a maioria dos pug-ins de reverberao fornecem um filtro de agudos para que seja possvel a

simulao desse corte de agudos. No existe obrigatoriedade de uso, porm quando se deseja um ambiente de

reverberao mais natural sua utilizao bastante til

Numa sala de concerto de grandes dimenses, um ouvinte recebe cerca de 8000 reflexes durante 1 segundo de som

direto. A cada reflexo est associado um atraso no tempo, uma diferente direo e um certo nvel sonoro. Desse

excesso de informao o ouvinte seleciona o que lhe interessa. (Lus L. Henrique: Acstica Musical, pgina 787)


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Gol Gumbaz, Bijapur

Gol Gumbaz, the mausoleum of Muhammad Adil Shah (AD 1626 56) located in Bijapur, District Bijapur, Karnataka State is an

important monument of Indo-Islamic architecture aptly known for its amazing dimensions and unique acoustic features. The

construction of this building was completed and the deceased king was interred in this building in 1034 AH (AD 1656) and

contains the sepulcher containing the tombs of Muhammad Adil Shah (AD 1626-1656), the seventh Sultan of the Adil Shahi

dynasty, his wives and daughters. Soon after his accession to the throne in AD 1626, the Sultan started constructing this

edifice for burying his mortal remains. He was buried in the vast vault beneath the floor along with other family members. The

exact position of the real tomb is indicated by the wooden canopy kept on the high platform at the middle of the floor of the

hall.

The foundation of this mausoleum rests on the bedrock, which has prevented any unequal settlement. Above the basement

this building is a huge cube with each sidewall decorated with three arches. The central arch, wider than the side ones, has

doorways except on the north, where a semi-octagonal chamber buttresses the wall. At the corners of this great cube are

added seven tiered towers octagonal in cross-section. After the death of its builder further decoration of the structure appears

to have been given up.

This edifice ranks among the most imposing ones in India for the sheer monumentality of its massive dome and its floor area.

The hemispherical masonry dome has an internal diameter of 37.92 m. The thickness of the dome varies from 3.05 m. near

the base to 2.74 m. near the top. The floor area of the monument is 1703.56 sq. m.

At a height of 33.22 m from the floor of the hall, projects a 3.25 m wide gallery, all round the inner periphery of the dome. This

gallery is called the Whispering Gallery, because even the finest whisper or sound made in it is heard from side to side and

even a single loud clap is distinctly echoed over ten times.

http://www.audioease.com/promotion/Gol-Gumbaz-

Whispering-Gallery.jpg

http://www.audioease.com/IR/golgumbaz/gol-gumbaz-outside.jpg http://www.ne.jp/asahi/arc/ind/1_primer/indoislam/

gol.jpg

http://www.audioease.com/IR/golgumbaz/golgumbaz.html

On August 20 2005 a letter reached Audio Ease It said:
http://www.audioease.com/IR/golgumbaz/golgumbaz.htmlhttp://www.audioease.com/IR/golgumbaz/golgumbaz.htmlhttp://www.audioease.com/IR/golgumbaz/golgumbaz.html


23/27

On August 20 2005, a letter reached Audio Ease. It said:

" Dear Sir, I would like to enlighten you that since you have captured the greatest impulses and have made plugins with the best of reverbs. I thereby would urge you to build a

plugin with perhaps the richest ever reverbs that any one has ever heard. Hold your heart ...I really mean what I say. As you are aware India is a Country that has rich heritage

monuments & these buildings are among the wonders of the world. The monuments have been built with great acoustic conditions & have examples of genius brilliant

mathematics of sound reverberations and acoustic conditions.. In eyes and ears of an Audio engineer It could only be the GOL GUMBZ of Bijapur in INDIA as an acoustic

wonder of the world which has the richest acoustic reverb ever in the universe. "

I was taken by the tone of this letter from Mr Rahul Atul, a recording engineer of Solapur India, that at the time was involved in audio and music for film. I Googled up the

building and it's history and the pictures and descriptions that I found were so powerful, that there was no question that we needed to do our best to obtain Gol Gumbaz for our

sampling library.

After numerous letters to the government of India, with the help of Rahul, we finally obtained enough stamps to gamble on a shipment of gear. A huge flight case, including a 90pound Genelec 1037, was flown over to Delhi where it got stuck in bureaucracy right away. Many months were necessary to locate the gear, safeguard it and finally get it back

to the Netherlands, where it arrived a year later.

But I wanted to go, so we decided to make it a lower profile session. We re-worked the portable speaker sampling method, and made an aluminum spider to mount the trusted

DPA microphones on. It enabled me to double the VR camera stand as a microphone stand. And so I got a recording set together that was portable and could be taken as

luggage on my flight.

A final two days at the Indian Embassy in the Hague got me my visa, and I received a cocktail of anti viral shots in both my shoulders that was threatening to either make me go

bald or turn yellow. Finally, almost 18 months later, in February 2007 me and my gear were ready to embark for India where my faithful help had arranged a string of

transportation that would bump me through the next night and the best part of the following day.

I was allowed a 6 hour crash before we took off again to Bijapur, to explore the actual building and decide on locations for sampling the next day. It was then that i found out

what the magnitude of this building was, and how lucky i was that our Genelec 1037 never made it to the spot. There would have been no way to get the 1037 up the hundreds

of tiny steps of this spectacle.

The most stunning feature (apart from the sheer size of the building, the staggering number of suicides that take place inside the building, and 20 + seconds of reverb from walls

made of mud) was undoubtedly the whispering gallery.

Right below the rim of a dome that is second largest in the world (second to St. Peter's Basilica in Rome) is a gallery in which even whispering can clearly be heard at a 37

meter distance, and each sound gets repeated 10 times over.

Superintending Archaeologist. Mr Venkateshiah himself had travelled to Bijapur to be present at the our sampling gig, and in the early morning of februari 23 we took him andhis delegation of security people from the gallery in the top to the shah's tombs below ground level.

Busloads of people were held at the gates so we could have silence. And when temperatures were approaching 40 degrees celcius our job was done after 7 strenuous hours of

work.

During my stay we also managed to obtain a good set of samples of the 16th century Ibrahim Roza, a tomb that served as an inspiration for the Taj Mahal. More about that

session later.

Back home, in the dark, in our surround studio, the samples turned out to be great successes, and comparison to our reference samples

(tabla's played back through our set in the Gol Gumbaz) revealed no artifacts. It seemed like we had been able to capture the "...acoustic wonder of the world which has the

richest acoustic reverb ever in the universe...."

Arjen van der SchootJune 2007.
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24/27

Golconda Fort: Architectural and Acoustic wonder in Hyderabad

Submitted by Lisha on Sun, 2010-12-12 16:40 Monuments

In the 16th century, Golkonda was the capital and fortress city of the QutbShahi kingdom, near Hyderabad. The city was home to one of the most powerful Muslim sultanates in the region

and was the center of a flourishing diamond trade. According to a legend, the fort derives its name from GollaKonda, which is a Telugu word for Shepherd's Hill. It is believed that a

shepherd boy came across an idol on the hill. This led to the construction of a mud fort by the then Kakatiya dynasty ruler of the kingdom around the site.

The city and fortress are built on a granite hill that is 120 meters (400 ft) high and is surrounded by massive crenelated ramparts. The beginnings of the fort date to 1143, when the HinduKakatiya dynasty ruled the area. The Kakatiya dynasty was followed by the state of Warangal, which was later conquered by the Islamic Bahmani Sultanat. The fort became the capital of a

major province in the Sultanate and after its collapse it became the capital of the QutbShahi kings. The fort f inally fell into ruins after a siege and its fall to Mughal emperor Aurangazeb.

After the collapse of the Bahmani Sultanat, Golkonda rose to prominence as the seat of the QutbShahi dynasty around 1507. Over a period of 62 years the mud fort was expanded by the

first three QutbShahi kings into a massive fort of granite, extending around 5 km in circumference. It remained the capital of the QutbShahi dynasty until 1590 when the capital was shifted

to Hyderabad. The QutbShahis expanded the fort, whose 7 km outer wall enclosed the city. The state became a focal point for Shia Islam in India, for instance in the 17th century Bahrainiclerics, Sheikh Ja`far bin Kamal al-Din and Sheikh Salih Al-Karzakani both emigrated to Golkonda.

The QutbShahi sultanate lasted until its conquest by Mughal emperor Aurangzeb in 1687. The fortress held out against Aurangzeb for nine months, falling to the Mughals through

treachery. Kancharla Gopanna, popularly known as Bhaktha Ramadaasu, a devout Hindu who constructed Bhadrachalm temple without informing the sultan at that time Tana Shah, was

kept in a jail located inside the fort.

The most important builder of Golkonda was Ibrahim QuliQutb Shah Wali, the fourth Qutb king. Ibrahim was following in the spirit of his ancestors, the QutubShahi kings, a great family ofbuilders who had ruled the kingdom of Golkonda from 1512. Their first capital, the fortress citadel of Golkonda, was rebuilt for defense from invading Mughals from the north. Golkonda

consists of four distinct forts with a 10 km long outer wall with 87 semicircular bastions (some still mounted with cannons), eight gateways, and four drawbridges, with a number of royal

apartments & halls, temples, mosques, magazines, stables, etc. inside. The lowest of these is the outermost enclosure into which we enter by the "Fateh Darwaza" (Victory gate, so called

after Aurangzebs triumphant army marched in through this gate) studded with giant iron spikes (to prevent elephants from battering them down) near the south-eastern corner. At Fateh

Darwaza can be experienced a fantastic acoustic effect, characteristic of the engineering marvels at Golkonda. A hand clap at a certain point below the dome at the entrance reverberatesand can be heard clearly at the 'Bala Hisar' pavilion, the highest point almost a kilometre away. This worked as a warning note to the royals in case of an attack.

The graceful gardens of the fort may have lost their fragrance, for which they were known 400 years ago, yet a walk in these former gardens should be in your schedule when exploring the

past glories of Golconda Fort.

Bala Hissar Gate is the main entrance to the fort located on the eastern side. It has a pointed arch bordered by rows of scroll work. The spandrels have yalis and decorated roundels. The

area above the door has peacocks with ornate tails flanking an ornamental arched niche. The granite block lintel below has sculpted yalis flanking a disc. The design of peacocks and lions

is a blend of Hindu - Muslim architecture.

Toli Masjid, situated at Karwan, about 2 km from the Golkonda fort, was built in 1671 by Mir Musa Khan Mahaldar, royal architect of Abdullah Qutb Shah. The facade consists of five

arches, each with lotus medallions in the spandrels. It is here that the saying Walls have ears can be seen. Any whispering in the chamber was easily carried to the chambers above

which have now been ruined. The central arch is slightly wider and more ornate. The mosque inside is divided into two halls, a transverse outer hall and an inner hall entered through triple

arches. At the end of the corridor there is the Kings Durbar where the Kings men and the Courtiers gathered to give judgement for the accused. The chamber acoustics is such that any

noise from the movement of clothes to attack the King or people is echoed multiple times.

It is believed that there is a secret underground tunnel that leads from the "Durbar Hall" and ends in one of the palaces at the foot of the hi ll. The fort also contains the tombs of the

QutubShahi kings. These tombs have Islamic architecture and are located about 1 km north of the outer wall of Golconda. They are encircled by beautiful gardens and numerous

exquisitely carved stones. It is also believed that there was a secret tunnel to Charminar.

The two individual pavilions on the outer side of Golconda are also major attractions of the fort. It is built on a point which is quite rocky. The "Kala Mandir" is also located in the fort. It can

be seen from the king's durbar (king's court) which was on top of the Golconda Fort.

This majestic structure has beautiful palaces and an ingenious water supply system. The Queens chambers had no mirrors or so but a water pit. It was believed that looking into the mirrorrepeatedly would increase dark spots on the skin of the Queens. Thus water pit was used to look at the images. Sadly, the unique architecture of the fort is now losing its charm. The

ventilation of the fort is absolutely fabulous having exotic designs. They were so intricately designed that cool breeze could reach the interiors of the fort, providing a respite from the heat of

summer.

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Regular Article

ACOUSTIC COUPLING EFFECTS IN ST PAUL'S CATHEDRAL, LONDON

J.S. ANDERSON, M. BRATOS-ANDERSON

Purchase

Department of Mechanical Engineering and Aeronautics, City University, Northampton Square,

London, EC1V 0HB, England

Received 20 July 1999; Accepted 8 November 1999. Available online 19 March 2002.

Abstract

In St Paul's Cathedral there are many arches, columns and cornices which enable the internal

space to be divided into subspaces. The subspaces may be considered to be acoustically coupled

via areas which connect the rooms. Two of the most acoustically important subspaces in the

Cathedral are the choir and the space under the dome. The choir, the space within the wooden

choir stalls, has more sound absorption than the rest of the building, which is mostly marble and

Portland stone. In the model of coupled subspaces an acoustic energy balance equation, appliedto a diffuse field, is derived for each subspace. In St Paul's Cathedral the internal space is divided

into 70 acoustical subspaces. The initial-value problem which is formulated by the system of 70

acoustic energy balance equations with initial conditions has been reduced to the eigenvalue

problem. The decay of sound energy density has been obtained for different locations in the

Cathedral and for different positions of the sound source. Experimentally obtained sound decay

curves are in good agreement with numerical results. Both the experimental and numerical results

demonstrate the fine structure of reverberation.

Purchase

Copyright 2000 Academic Press. All rights reserved.

http://www.sciencedirect.com/science/article/pii/S0022460X99929887

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Whispering Gallery Modes
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St Pauls cathedal and the Whispering Gallery, also shown electric field in a micro sphere The whispering gallery is located in the

dome of St Paul's Cathedral, London, and has the curious property that if two people stand at opposite sides of the gallery, at a

distance of 42 meters, and one whispers into the wall of the dome, then the other person can hear what is being said. Interestingly

the effect does not work if one speaks normally, giving the gallery its name. The reason for this strange effect is that the sound

bounces along the wall of the gallery with very little loss, and so can be heard at a great distance. The reason it does not work if

you speak normally is that the increased amplitude of the noise allows it to circulate the gallery multiple times, and so the sounds

all get mixed up and can no longer be heard properly. It can be viewed that there is a narrow region near the edge of the domewhere the waves propagate most efficiently, and this is known as a 'whispering gallery mode' in honour of gallery where it was

discovered.

In recent times whispering gallery modes have found new fame with the development of nano-optics. In the modern version of this

effect light is made to bounce around the edge of a glass sphere. This setup appears to be very similar to that already depicted,

although there are some subtle differences. Under normal conditions when light reaches an interface some of it will be reflected

and some will be transmitted. However, if the light is in glass and is travelling back into air there is an angle at which the light can

no longer be transmitted and it suffers total internal reflection - exactly 100% of the light is reflected, a very useful effect to reducelosses. When light is travelling around the edge of a sphere it will be total reflected at each bounce, and so propagate with little

loss (in fact a very small amount of light leaks out with each bounce due to the curved surface, but this get very complicated so it

will be ignored for now). Since the light will make many millions of circulations of the sphere before being absorbed it will undergo

interference with itself. This means that only whole numbers of wavelengths of light can 'fit' around the edge of the sphere. This

selectivity causes discrete modes, known as whispering gallery modes, to exist in the cavity, and these modes are of the lowest

loss anywhere in existence.

The problem when studying whispering gallery modes is that the low loss makes it very hard to get light into- or out of- these

modes. In our work we placed light emitters around the edges of the sphere, when pumped with a laser these emit light directlyinto the whispering gallery cavity mode, so no coupling is required. To observe the output light we rely on the fact the spheres are

not quite perfect and so some light is scattered out. From the spectra of this light we discover that only certain wavelengths are

strongly present, as expected, each corresponding to a different number of bounces around the spheres circumference.
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