Narrative.ly Sensing-The-city Silencing-The-subway

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If youve ever stood in the Spring Street subway station in

Manhattan and asked yourself, Hmm, I wonder if standing here

Thu, Jan 31, 2013

by Christopher Maag

Inside a high-tech effort to minimize the maddening racet in the !e" #or underground$

SILENCING THE

SUBWAY

%hotos by &mon 'assan

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is a terrible idea? then a !ui"k "onsultation of the noise e#posure

standards promulgated in $une %&&' by the (ational Institute for

)""upational Safety and Health will show that, indeed, standing

there is a terrible idea* +uring the lull between trains, the station is

a !uiet enough pla"e* ou "an hear a womans boot heel "la"king

against the "on"rete platform, the Metro-ard readers pier"ing

ele"troni" beep, the "li"k."li"k."li"k of spinning turnstiles, a train

in an ad/a"ent tunnel shaking the walls with te"toni" rumble*

0his is the rush hours !uietest moment, when noise levels inside

the station drop to a low of seventy.one de"ibels* 0he hush, on a0hursday morning in $anuary, lasts eight se"onds*

1n uptown 2 lo"al train arrives* Its doors open with a staggered

thunk.unk.unk3 the fans inside the trains twenty roof.mounted,

si#.and.a.half.ton 4ombardier heating and "ooling units spool up3

and the stations noise level /umps to ninety de"ibels* 0hats as loud

as an idling semi tru"k* 1""ording to (ational Institute for

)""upational Safety and Health 5(I)SH6 rules, workers e#posed to

ninety de"ibels of noise for eight hours a day must wear prote"tive

gear to prevent ear damage and eventual deafness*

7rom there, the sound piles on* Spring Street station is built on a

"onve# "urve of subway tra"k shaped like the tail of a parenthesis,

and when the downtown 8 e#press rolls over the middle tra"k, its

hard.fi#ed wheels shriek and bark as they struggle to make the

turn, emitting this horrible 99:ee999:ee:9999::: that stabs your

brain*

1 man on the platform s"run"hes up his fa"e and sti"ks fingers in

both ears* 0he doors on the uptown 2 wha"k "losed and the trainsthree.phase, %8;*


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a""elerate* (ow someones pushed the "rash bar on the emergen"y

door, whi"h s"ree"hes its bi.tonal alarm like a 4ritish poli"e siren

on helium, and theres some loud ele"tri"al b======== from

somepla"e you "ant even tell* 1bove all this noise is a little

re"orded announ"ement piped through the loudspeakers to inform

you in a friendly but all.business female voi"e that 0he ne#t

uptown2 trainwill arrive 4ut you know this more from

memory than from hearing, be"ause you "ant a"tually hear any of

it* 0he noise in the station "limbs to %>2 de"ibels, and sin"e youve

already "onsulted the handy "hart on page two of the (I)SH noise

e#posure report, you know for "ertain that your inner ears "an takeonly three minutes and forty.five se"onds of this hell before they

start to suffer permanent damage, and the noise burrows past your

eardrums into that part of your brain where you es"ape fearful

things and hide, its invading even that soft pea"eful spa"e, yes, oh

od its terrible why did I ever leave St* @ouis where its !uiet I hate

(ew ork make it stopA

Bhi"h is to say that, a"ousti"ally speaking, the (ew ork -ity

subway system is a "ra=y.making hells"ape* 0he Metropolitan

0ransit 1uthority knows this, and perhaps even more surprising,

theyre about to spend CD2*2 million dollars to fi# it*

E E E

Bhen the M01 started planning the Se"ond 1venue subwayline, the first ma/or e#tension of (ew ork -itys subwaygrid in fifty.three years, its engineers thought about ways to

redu"e sound levels inside the new stations* 0he goal the authority

set for itself was modest* It would not try to make the new stations

whisper !uiet, like +*-*s Metro* It would not "onsider how peoplerespond to the a"ousti"s holisti"ally as they "ome into the subway

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from the urban street, says $oe Solway, the M01s lead a"ousti"al

engineering "ontra"tor on the pro/e"t, who prefers to think in su"h

terms* (or would it bother fitting the sounds of the subway into

what Solway "alls (ew orks ama=ing urban soundtra"k*

0he M01 does not "are about ama=ing urban soundtra"ks* 0he

main thing the authority does "are about when it "omes to sounds

is making sure people "an hear the publi" address loudspeakers*0his might make the agen"y seem unimaginative, but theres a good

reason for the agen"ys a"ousti" "onservatismF thirty.one people

died in a fire in the @ondon Gndergrounds ings -ross station in

%&';, partially be"ause they "ouldnt hear eva"uation instru"tions*

(o deaths have been dire"tly attributed to subway noise in (ew

ork in re"ent years, although new tra"ks along the + train in4ensonhurst, 4rooklyn, prompted noise "omplaints in D>%> from

( presentation by (rup engineering company )oos at noise a)ong the *econd (enue sub"ay

)ine

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business owners underneath the elevated line* @ast year, -ity

-oun"il member eter 7* Jallone $r* mailed a letter to the M01

about the sound of air brakes along the K and ( lines near the

+itmars 1venue stop in 1storia, Kueens, whi"h he "ompared to

standing ne#t to a (1S1 laun"h site*

4esides, making a sound system people "an a"tually hear is !uite a

bit more "ompli"ated than it seems* It re!uires engineers to isolate

and "apture two different kinds of vibration* 0he first "omes from

the trains wheels spinning on the steel tra"k, whi"h reverberates

for blo"ks and even miles and turns our buildings, sidewalks andstreets into speakers* 0his is "alled stru"ture.borne vibration* 0he

other kind is "alled airborne vibration, whi"h in"ludes all the higher

fre!uen"y stuff like ele"tri"al e!uipment hums and the e"hoing

sound of human voi"es 5whi"h, even with seven million daily riders,

plays a surprisingly modest role in the field of subway a"ousti"s*6

7or the M01, figuring out how to tame all these unwanted noises

and amplify the only sound they really want started with one basi"

!uestionF Bhats the best way to float a train?

The Problem in Harvey Weinsteins Basement

Sometime after Harvey Beinstein, the movie produ"er, bought

his eight.bedroom, five.story Best Jillage townhouse for

C%8*& million in D>>2, he dis"overed a little problem* He wanted to

build a movie theater in the basement, but his house sits so "lose to

the %LDL subway line that every passing train shakes the

foundation like a tea"up on the San 1ndreas 7ault*

So Beinstein hired 4onnie S"hnitta* 7ive.foot.two with girlish,white.blond bangs that "over her forehead and dire"t attention to

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her bright blue eyes, Schnitta is the kind of genius-type who makes

her incredibly complex work sound fun. As founder and president

of SoundSense, an acoustical consulting and engineering company,

shes helped clients including Ralph Lauren and eter !ennings with

their airborne and structure-borne "ibration abatement needs. She

once helped a baker who tried to stop his e#uipment from "ibrating

by placing a giant mixing machine on springs.

$So the neighbor in the ad%acent building was trying to sleep, and

he heard this ca-tunk ca-tunk ca-tunk of the mixing machine

walking around the floor,& says Schnitta, '(, who has a bachelorsdegree in math, a bachelors and a masters degree in mechanical

engineering, and a doctorate in math, engineering and ocean

physics with a specialty in signal processing. She sol"ed the

problem by replacing the bakers springs with s#uishy synthetic

rubber pads. $)ts ama*ing what a little neoprene can accomplish+&

Schnittas fix for einsteins basement was rather more in"ol"ed.

hat she built was a theater that floats, with the interior space

suspended from the rest of the house using springs along the

ceiling, neoprene decouplers along the walls, and a combination of

neoprene and decoupler feet under the floor. orking together,

these tools isolate, or decouple, the theater from the foundation so

that energy wa"es radiating down the track, through the groundand into the foundation get absorbed by the s#uishy barrier, lea"ing

the screening room #uiet and motionless.

$hen it didnt ha"e a direct connection to the rest of the building

so that e"erything was acting as a shock absorber,& Schnitta said.

he As new subway line will operate along the same principle.hen most of /ew 0orks lines were built in the early twentieth

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century, the engineers focused on securing track tightly to the

ground. his made the system hardy, but it also created a direct

pathway for "ibrations to radiate in e"ery direction.

1nlike the last time /ew 0ork built a ma%or subway line, howe"er,

the line train that the A plans to build underneath Second

A"enue is being constructed in a place thats already hea"ily

populated. 2ngineering it the old way would cause #ui"ers and

shakes in hundreds of existing buildings.

$)f its a deep foundation thats sitting on the rock, you"e got a "eryefficient transfer of "ibrations into your building,& Solway says.

So the As new train tracks will float. here are different ways to

accomplish this. 3ne way is to spread a layer of neoprene and

springs along the tunnel floor, so the entire track slab is decoupled

from the ground. his system is the best in terms of isolating

"ibrations, since it spreads the weight of the train across a long,spongy bed.

)ts also the most expensi"e. 4eeping with its mission to build

something better, but not perfect, the transit authority went with a

Low 5ibration rack 6L57 system. Like existing tracks, this new

one will be secured with steel plates bolted to concrete ties. 8ut

each tie will sit on a rubber boot embedded into the concrete track

bed like a tooth in a %aw. rains tra"eling the track will send

"ibrations down into the rubber boots, which will isolate some 6but

not all7 of the energy before it escapes into the subways concrete

foundation and then out into the surrounding ground. :ompared

to current trains, the result will be weaker "ibrations radiating

shorter distances.

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;uring the pro%ects first phase, the two-mile section from 2ast

' million.

$0ou can either sol"e the problem at the tracks or you can float all

the apartments,& says Schnitta, who also consulted with the A

about its track choice. $3b"iously its better to stop it at the

source.&

he floating track will reduce the really long-wa"elength, low-

fre#uency "ibrations that subway trains send radiating out throughthe ground. 2nergy wa"es with higher fre#uencies and shorter

wa"elengths cant tra"el through the walls, so they get stuck inside

subway stations, where they bounce around and create the

aforementioned acoustic hellscapeBwhich engenders the As

second acoustic sticky wicketC Dow to make a big subway train

sound like a little subway trainE

The Train Sandwich

! oe Solway is an engineer who likes his toys, and right now hescommanding a "ery expensi"e toy. )ts the listening lab insidethe new ater Street offices of Arup, the global engineering

company hired as the As consultant on the acoustics and

"ibrations pro%ects along the Second A"enue line. he rooms walls

are padded in black sound-absorbing materials, which make it

sound like a radio studio. heres a big cur"ed pro%ection screen in

front, and a circle of eighteen speakers at "arious heights plus four

subwoofers arranged in a circle facing the middle of the room.

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Solway, a reser"ed character with a 8ritish accent, wire rim glasses,

buttoned-down shirt collar and blond hair combed into a classic

news anchor wa"e, can barely contain his delight.

$he listening lab was completely a game-changer in the way that

we do our design,& he says, gi"ing clients $the sub%ecti"e feel of how

you will experience a space.&

Sitting at a bank of computer screens in the back of the room,

Solway proceeds to layer sound as one might place slices of turkey

breast on a piece of bread. De starts by playing the indi"idual sound

that his client, the A, really cares aboutC

$A 8rooklyn-bound R train is approaching the station. All express

trains are currently running on local tracks.&

he female announcers "oice is loud, professional and precisely

annunciated. )n his methodical way, Solway proceeds to screw it

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up. 8y changing the settings on his computer, he filters the original

recording through a crappy A microphone, which constrains the

womans "oice to its highest fre#uencies and makes it sound

scratchy.

Since most subway announcements are recorded in open booths

without soundproofing, Solway layers typical station sounds in the

background. Suddenly, the announcers "oice fades into the middle

distance. After that comes the bu** from unshielded electrical

cables, which makes the woman sound as if shes using a hair dryer.

)n his next slice, Solway plays this whole recorded mess throughthe stations band-limited speakers, turning the "oice brittle and

tinny, and then he factors in the stations lousy acoustics. Lost in

sonic backwash, the announcers "oice is almost entirely swallowed

up.

$/ow, of course theres one thing were missing,& Solway says.

A final keyboard tap brings in the whooshing air rush of a train. he

perky-but-professional public address announcerE lease. Der

"oice might as well not exist.

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Since he started working in the Second Avenue project in 2002,

Solways job has been to fix this war of sounds, or, more accurately,

to arrange a negotiated truce

!is first step was to build a computer model of a hollowed"out tube

with all the dimensions of a Second Avenue subway stop #nto this

virtual space he sent a sound called an electronic handclap, but

which sounds like a gun fired in an empty warehouse $y measuring

the speed, strength and direction of this noise as it bounced

through the space, Solway created a sonic snapshot %ike a

computer"generated photo that shows how a planned subway

Behind the scenes in the sound lab (Audio by Emon Hassan)

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station will appear to the eye, this one uses acoustic data to

recreate how it will sound to the ear

&'his is like an acoustic fingerprint that has all the elements of all

the different reflections of all the surfaces,( he says

'he fingerprint allowed Solway to experiment, placing different

types of soundproofing in different places inside the virtual station

to see which variations do the best job )uelling the noise !e

started by thinking up ways to seal the trains acoustically from the

rest of the station *any airport trams accomplish this by lining theplatform edge with sliding doors 'his wont work along Second

Avenue, however, because + and ' trains with different car lengths

will use the same track, making it impossible for them both to align

with a single set of entrances

So what Solway and the *'A created is a sonic enclosure that

wraps around the train like a submarine sandwich roll 'he ceilingover the tracks will curve down toward the train A separate tube

running the length of the station that contains speakers, security

cameras and air ducts, and which is called the service carrier, will

hang from the ceiling beside the tracks #ts shape will have a similar

arc as the ceiling, and both will be lined with sound"absorbing

materials orking together, the service carrier and the ceiling will

reflect noise back at the train and shrink the gap between train and

platform, limiting how much noise can escape

&Sound can be shaped #t can be tuned,( says Solway &-ompared to

current stations, this is going to be a much more controlled

environment(

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'rains will still make lots of

noise, of course, and so will

electrical e)uipment and crowds

of people 'o limit these sounds,

many interior station walls will

be covered with sound"

absorbing panels that resemble

modern house insulation 'he stuff Solway recommended has a

noise reduction coefficient of 0., meaning it soaks up eighty

percent of the sounds that strike it /'hat efficiency will be lessened

somewhat by an outside layer of grey perforated ceramic tiles thatwill be exposed to the public and used to protect the soft sound

absorber from damage

#f everything works the way Solways computer model suggests,

most sounds inside the station will get one bounce off a reflective

surface, like the floor, before getting trapped by the absorptive

panels

&So the public gets the direct sound of the speakers firing down,

and then they get an early reflection off the floor,( he says &$ut

then once that energy is gone, you want to absorb it as )uickly as

you can(

'he last sound Solway will try to control is fan noise *any existing

1ew ork subway stations sit so close to street level that they

receive ventilation through grates built directly into the sidewalk

-onstruction on the Second Avenue line is boring through bedrock

one hundred feet below ground, however, so it re)uires fans to

push air into the stations and tunnels and suck it out the other side

3ach station will have four fans at its south end and another four atthe north

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'hese fans are big 'ogether with their blast shafts, they re)uire so

much space that the *'A is building separate townhouse"si4ed

buildings at either end of some stations to house them 5n both

sides of every fan will be a silencer that functions like a muffler on acar $uilt with sound"absorbing mineral wool or fiberglass clad in a

wall of perforated metal, each silencer will soak up twenty to thirty

decibels of noise Some fans will also be enclosed in separate

soundproofed rooms $y the time the Second Avenue subway is

complete in 2026, fan roar from these shaft buildings will be

&insignificant and imperceptible( to neighbors and people walking

by on the street, according to the *'As environmental impact

statementfor the project

$ack in Arups sound lab, Solway replays the original recording8 &A

$rooklyn"bound A train( 'his time, he layers in everything the

*'A plans to improve8 a good microphone, a soundproof booth,

shielded cables, decent speakers, fan splitters, and a station with9:00,000 worth of sound"absorbing acoustic panels 'he result is

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!E"T #EE$

%U&P TO 'URRE!T #EE$

PREVIOUS #EE$

#EE$LY THE&E

OF ()*+)*,(- . SE!SI!/ THE 'ITY

significantly less crappy !onestly, thats the best one can say for it

'heres still plenty of background noise 'he announcer sounds

echo"y and distant $ut she is audible 5n the speech intelligibility

index, which ranges from inaudible at 4ero to perfect clarity at one,

the final result lands perfectly in the middle, at 06

&e didnt want to over design and make it too )uiet,( Solway says

&e could have made it )uieter $ut we didnt because it wouldve

been more cost, and really we just wanted it to work(

#ts comforting to know that in 1ew ork even the *etropolitan'ransit Authority, which moves seven million people every day, rips

giant holes in Second Avenue and channels enough force to shake

us in our homes;even this powerful entity struggles mightily to be

just barely heard

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Narrative.ly Sensing-The-city Silencing-The-subway