Sennheiser AR 2011

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    2011 Annual Report

    IN THE DEPTHS

    OF SOUND

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    08

    0 20 Hz

    To use a metaphor, sound like light can be visible

    or invisible; it can be audible or sneak by completely

    unnoticed. Whereas one listener might find a sound

    loud, another may not. At the other end of the spectrum, an

    animal can hear sounds that would go completely undetect-

    ed by the human ear, such as a rogue wave, miles out at sea.

    Infrasound and ultrasound are just such sounds.

    Simply put, acoustics is the study of sound. Its scien-

    tists, or acousticians, measure how sound waves are gener-

    ated, transmitted and received. An acoustics engineer then

    uses this information, for instance, to improve the sound

    quality of a concert hall. To decrease the noise level in a

    building, he can lower the level to reduce generation, put

    barriers in place to hinder transmission, and increase back-

    ground noise or suggest earplugs to block out reception.

    Sometimes, an acoustician is simply interested in studying

    the loss of generation and reception in order to predict the

    strength of generation.

    Psychoacoustics studies the psychological and

    physiological responses associated with sound its

    emotions and associations to better understand how

    sound is perceived. For instance, what is it about the sound

    of a Harley that makes it seem powerful or expensive?

    To unravel this mystery, the acoustician may have to factor

    in inaudible components such as its vibrations and very low-

    frequency sounds.

    It may seem like a paradox after all, acoustics is

    generally involved in measuring sounds we can actually hear

    but infrasonic and ultrasonic acoustics measures sounds

    that have little or no acoustic perception, generally those

    within the frequency range of 20 Hz to 20 KHz (cycles per

    second). Frequencies outside this range are either ultrason-

    ic (above 20 KHz) or infrasonic (below 20 Hz) and though

    generally considered inaudible, this is open to debate. For in-

    stance, the frequency range of infrasound can vary accord-

    ing to its intensity and rate, and factors such as age, gender

    and noise exposure can also play a role.

    Infrasound is often accompanied by audible sound

    emitted from the same source. Lets take the boom box

    car as a case in point. The reason we can hear it coming

    down the road for miles is that air does not absorb low-fre-

    quency sounds as well as it does high-frequency sounds.

    Thats also why a plane produces white sound (a mixture of

    sound waves over a wide frequency) when flying directly

    overhead, and more bass (low f requency) as it moves away.

    Low-frequency sounds not only travel further through air

    than high-frequency sounds, they penetrate physical struc-

    tures. The reason why a plane flying over your house will

    sound very low and rumbling is because the building has

    filtered out the middle- and high-frequency sounds.

    Although virtually inaudible, infrasound and infra-

    sound vibrations can have a dramatic physical impact. As

    intensity and frequency increases, infrasound and its vibra-

    tions can cause symptoms similar to what divers call the

    rapture of the deep: nausea, dizziness, a loss of equilibrium

    and disorientation, impaired judgment, speech and vision.

    Infrasound can also increase blood pressure and heart

    rate, or give an adrenaline rush. Theres good reason why

    national and international standards have been put in place

    to specify permissible levels of whole-body vibration and

    infrasound.

    Tossing and turning at night? Could be infrasound.

    For instance, research is being conducted on the infrasonic

    effect of wind generation. Though initial findings would

    09

    ESSAY

    INAUDIBLE WORLDMEASURING THE

    We may not be able to hear sound frequencies below 20 Hz, but we can feel

    them. Sometimes they rob us of sleep, sometimes they drive us into a frenzyand sometimes they save our lives. An essay on infrasound.

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    10

    0 20 Hz

    found that infrasound can im-

    pair whales hearing.

    In building acoustics,

    we normally measure frequen-

    cies between 100 Hz and 5,000

    Hz. My company tests the

    Sound Transmission Class (STC)

    of all types of architectural

    materials from walls, to

    doors, windows, building fa-

    ades and special barriers. Even though our own state-of-

    the-art, 200-cubic-meter reverberation chamber is accred-

    ited to 80 Hz, thats still way above the infrasound range.

    Clearly, new procedures are needed to measure infrasound

    in buildings.

    Scientists and governments have long been looking

    into whether infrasound can be used to detect weather pat-

    terns and predict natural disasters, such as volcanoes and

    tsunamis. By studying the invisible in this case, the

    inaudible we might better understand our environment

    and save lives.

    argue that the impact is likely low, there is some evidence

    that wind farms may cause insomnia.

    We went to the Metrodome in Minneapolis to better

    understand the effects of subwoofers and their low-

    frequency sounds at major concert venues. Pink Floyd and

    the Steve Miller Band, for instance, have their sound cranked

    up as high as 130 dBA peak. The tremendous volume makes

    it hard to hear so the musicians have to rely on feedback to

    feel the low-frequency sounds so that they can s tay togeth-

    er. And its the infrasound and vibration blasting from the

    subwoofers that makes the crowd feel the music.

    Animals are tremendously sensitive to sound, and

    there are some fascinating studies being carried out in or-

    der to understand acoustic communication between mam-

    mals. Elephants and whales, for instance, can hear over im-

    mense distances. Following the Indonesian tsunami in

    2004, researchers wanted to find out whether the ele-

    phants were able to sense the coming disaster and then

    communicate it onward as they tried to break free of their

    chains. Important research on the impact of infrasound

    that is generated by naval submarines on whales has

    t

    HD 700The HD 700 uses its amazing frequency range topaint soundscapes on widescreen.

    Frequency response 8-44,000 Hz (-3 dB)

    Transducer principle Dynamic, open

    Total harmonicdistortion

    0.03 % (1kHz,1Vrms)

    Weight 270 g

    Sennheiser HD 700Reference Audiophile Headphones

    AUGMENTEDREALITY

    AUTHOR STEVEN J. ORFIELD

    9.4Steven J.

    Orfield is

    the found-

    er of Or-

    field Laboratories (OL) in Minneapolis,

    USA. OL provides design, research and

    testing services for the architectural

    and research communities. OL designed

    the first American Sound Quality analy-

    sis system, which included evaluation of

    major professional audio headphones.

    After conducting thorough tests, OL de-

    cided to use Sennheiser headphones for

    all its studies on sound. Currently, Or-

    field is using the new Sennheiser HD 700

    whose specially tuned, high-

    efficiency converters deliver high

    sound-pressure levels and a vented

    magnet system that minimizes air tur-

    bulence and, with it, distortion. The

    American is also known for his anechoic

    chamber, which was awarded The Qui-

    etest Place on Earth by the 2005 Guin-

    ness Book of World Records. The sound

    level in this chamber is -9.4 dBA.

    ESSAY

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    12 13

    0.0000000000000016 Hz

    BLACK-HOLE ACOUSTICS

    THE DAY I HEARD THE

    SOUND IN THE UNIVERSE

    LOWEST SOUND

    British-born Andrew Fabian is one of the foremost astronomers inthe world. His specialty? Listening to the murmurs of the universe and

    observing its black holes. In doing so, he has discovered sound wavesa million times below the limits of the human ear.

    As an X-ray astronomer, Im interested in studying

    processes in the universe that release tremendous

    amounts of energy energy whose electromagnetic

    radiation is dispersed across the universe to be recorded on

    Earth after its long cosmic journey. Though it might seem

    similar to the study of stars, there is a huge difference be-

    tween stars and the heavenly bodies I observe. The radia-

    tion sources I study have temperatures in excess of 1,000

    times that of stars. Using the law of physics, we know the

    radiation they emit also has a frequency of more than 1,000

    times that of stars. Whereas the electromagnetic waves

    emitted from a stars hot surface make it possible for us to

    admire them against the dark expanse of the universe, the

    shift in frequencies takes black holes out of the visible spec-

    trum and into the range of invisible X-rays.

    One possible source of such X-ray radiation is giant

    gas clouds, which become extremely hot as they are drawn

    into black holes. Black holes are the remnants of stars that,

    after having consumed all their combustible fuel, collapse

    under their own weight, as it were, into an extremely con-

    centrated mass. If the same thing happened to the Earth,