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Ruido en el casco

hollerosholleros MegaForero ✭✭✭
Un ingeniero vigués demuestra con ecuaciones por qué el ruido del casco de moto es mayor dentro que fuera

grafico.jpg

Un motorista que circula a una velocidad de 120 kilómetros/hora soporta en el interior de su casco niveles de ruido similares a los que se registran en la cabina de un caza. Aunque para la gran mayoría este hecho resulte sorprendente, los expertos lo conocen desde hace décadas, pero ha sido un investigador de la Universidad de Vigo el primero en determinar las causas por las que el nivel sonoro es más alto dentro de este elemento protector que en el exterior.
La originalidad de la tesis realizada por José Luis González Cespón, profesor de la Escuela de Ingeniería Industrial en su sede ciudad, radica en la consideración del casco como un "componente activo" en la generación del ruido. De hecho, es la principal causa. Para poder demostrar esta teoría diseñó un nuevo protocolo de medición y, fruto de los experimentos realizados, desarrolló unas ecuaciones hasta hoy inexistentes para predecir el comportamiento del casco según la velocidad de la motocicleta.

Las elevadas cifras de usuarios –seis millones entre pilotos y copilotos, solo en España, según los cálculos de Cespón– contrastan con la escasa decena de artículos científicos publicados en todo el mundo desde 1973 hasta la actualidad y con el hecho de que el concepto estructural apenas ha variado desde el modelo patentado en 1953 por Charles F. Lombard, miembro de las fuerzas aéreas estadounidenses.
El experto vigués aplica la teoría de los recintos pequeños para explicar que el casco amplifica las bajas frecuencias en su interior ya que éstas, dada su mayor longitud de onda, no pueden escapar. Si nos colocásemos este elemento de protección en una habitación en la que dos personas mantienen una conversación, lo que equivale a unos 50 decibelios, nosotros llegaríamos a soportar 60, dependiendo de la frecuencia.

"Y esta resonancia que tiene el casco de por sí se agudiza, cuando la moto está en marcha, por el efecto del aire que circula bajo la barbilla y la golpea. Cuanto más veloz llega el aire mayor es la vibración y mayor el ruido que se genera en el interior", revela.
En términos técnicos, el casco equivaldría a un filtro paso-bajo. Enunciada la teoría, el investigador desarrolló una serie de ensayos con una medida diferente al decibelio A, el que se utiliza habitualmente, porque "esta ponderación no es representativa de la realidad que percibe el piloto".
Cespón utilizó cinco cascos integrales de gama media-alta –de entre 400 y 800 euros– y una motocicleta sin pantalla de protección que condujo un alumno voluntario en la misma posición –manos rectas y mirada al frente– durante las 700 mediciones realizadas en un tramo recto de la A-55 entre Porriño y Tui.

El investigador acumuló 150 horas de grabaciones del nivel sonoro que soportaba el piloto en el interior de cada casco circulando a diferentes velocidades –50, 80, 100 y 120km/h– y alternando las posiciones de las tomas de ventilación, considerando el visor como tal, y con la protección o no del cuello del motorista.
Los menores registros de ruido se produjeron cuanto todas las ventilaciones estaban abiertas y el cuello cerrado, puesto que se rebajaba la presión y, por tanto, el nivel sonoro.

Cada medición se repitió tres veces en días y horas diferentes y todas dieron resultados muy parecidos, lo que demuestra la validez de la hipótesis del casco como elemento generador del ruido y echa por tierra las tres teorías que hasta ahora intentaban explicar este fenómeno sin tener en cuenta su papel.
El ingeniero vigués, que ha desarrollado una ecuación por cada una de las velocidades analizadas, se esforzará ahora en alcanzar una única fórmula que permita predecir el comportamiento de un casco.

Lo importante es que, resuelto el misterio, los fabricantes ya disponen de un protocolo de medición para ensayar nuevos diseños que protejan la salud auditiva de los motociclistas. Cespón ofrece algunas pistas: "La solución podría pasar por una evolución del casco de bicicleta, con su misma estructura pero más resistente, o por un modelo más poroso"
Nunca discutas con un idi0ta, te rebajará a su nivel y te ganará por su experiencia.

http://www.zzr.es/
h2ufstorv7i9.gif
http://www.zzr.es/

Comentarios

  • TaiTai MegaForero ✭✭✭
    Verás tu como nos sacan cascos con bufanda cuando lean el artículo alguno de los ingenieros listos de alguna compañía... image




    image






    Pd: muy interesante, yo si he notado diferencia de ruido de ir con buff a no llevar nada, lo de las ventilaciones no lo he probado, aún imageimage
    Rua + F5, por siempre Azua...
    SECTOR PATANEGRA socio nº 96
    Whats-App-Image-2017-11-22-at-23-57-08.jpg
    Toqué rodilla, tb estribera y bota, y el 100.000 es mio

    Que si, que ya vendí la 9R
  • HardcorEHardcorE MegaForero ✭✭✭
    -Honda ST1300 ABS Paneuropean
    -Kymco Grand Dink 300 ABS (Xtown 300)
  • pepe palotespepe palotes Forero Master ✭✭✭
    Llevar pañuelo sí disminuye el sonido...pero me llama la atención que abriendo las ventilaciones suene menos. Tendré q probarlo
  • adrieriadrieri Forero Master ✭✭✭
    Yo las llevo siempre abiertas, incluso en invierno
    ¿Para qué corres? Si delante también llueve...image

    Mis rutas en https://sinhorizontealavista.blogspot.com.es/
  • HarperHarper Forero Senior ✭✭✭
    En el Qwest de shoei tengo puesto el [FONT=&amp]WHISPER STRIP y la barbillera. la reducción del ruido es enorme. ¿la desventaja? pues que cuesta algo mas ponerse el casco, pero compensa.

    [/FONT]shoei-whisper-kit.jpg


    Digo yo que podrá ponerse en la mayoría de cascos, ademas parece que existen unos genericos y mas extremos:

    0_big.jpg
  • adrieriadrieri Forero Master ✭✭✭
    Harper escribió : »
    En el Qwest de shoei tengo puesto el [FONT=&amp]WHISPER STRIP y la barbillera. la reducción del ruido es enorme. ¿la desventaja? pues que cuesta algo mas ponerse el casco, pero compensa.

    [/FONT]shoei-whisper-kit.jpg


    Digo yo que podrá ponerse en la mayoría de cascos, ademas parece que existen unos genericos y mas extremos:

    0_big.jpg
    Lo malo es que eso en verano te puedes morir... Yo ando por Sevilla...
    ¿Para qué corres? Si delante también llueve...image

    Mis rutas en https://sinhorizontealavista.blogspot.com.es/
  • HarperHarper Forero Senior ✭✭✭
    adrieri escribió : »
    Lo malo es que eso en verano te puedes morir... Yo ando por Sevilla...

    Yo lo utilizo todo el año, El calor lo llevo fatal, aun sin el whisper me asaría, asi que .. ya puestos... me ahorro el ruido.
  • hollerosholleros MegaForero ✭✭✭
    Harper escribió : »
    Digo yo que podrá ponerse en la mayoría de cascos, ademas parece que existen unos genericos y mas extremos:

    0_big.jpg

    Enlace ?
    Nunca discutas con un idi0ta, te rebajará a su nivel y te ganará por su experiencia.

    http://www.zzr.es/
    h2ufstorv7i9.gif
    http://www.zzr.es/
  • seisverdeseisverde MegaForero ✭✭✭✭✭
    Interesante, sabes si está publicada la investigación?
    Lo que no tengo muy claro es a que se refieren en el artículo a bajas frecuencias porque por las dimensiones típicas de una calota la primera frecuencia fundamental está en torno a los 1000Hz, que ya no es baja frecuencia y que es una frecuencia fácilmente absorbible con las espumas del interior del casco.
    También tengo curiosidad por saber como hicieron las medidas en marcha, típicamente los fabricantes usan un dummie como este para las pruebas:

    [SIGPIC][/SIGPIC]
  • seisverdeseisverde MegaForero ✭✭✭✭✭
    UVIGO | 22 julio 2011 09:37 [...]
    En este proyecto, patrocinado por la empresa Tekplus, colaboran tres grupos de investigación de la Universidad de Vigo, el Centro de Ingeniería Mecánica y Automoción, CIMA, y el CFD Simulation Group y Sonitum. En el transcurso del trabajo se desarrolló un casco que recogía alguna mejora de otros grupos. “En lo tocante al ruido y, a pesar de ser de los menos ruidosos, no se pudieron aplicar las conclusiones de la tesis, fundamentalmente por el modo en que se fabrican los cascos en la actualidad”. Con todo, presenta una mejora que consiste en disminuir el espacio por donde entra el aire bajo la barbilla.


    La noticia es antigua, y por lo que aparece en otro artículo parece que ha descubierto la pólvora...
    [SIGPIC][/SIGPIC]
  • sesmerosesmero Forero Master ✭✭✭
    también depende el tipo de moto porque la cabeza no tiene la misma inclinación en una r que en un wc
  • seisverdeseisverde MegaForero ✭✭✭✭✭
    https://www.insidescience.org/content/lowering-volume-motorcyclists/714

    Helmet and acoustics research might offer riders a quieter trip.


    Originally published:
    Aug 2 2011 - 1:00pm


    By:
    Chris Gorski


    (ISNS) -- Before hopping on his motorcycle, Michael Carley puts on earplugs, followed by his helmet. It's a step many riders take. After accelerating, most of the sound that a rider can hear isn't from the bike engine or other vehicles on the road, but from the air rushing over and around his helmet.
    The helmet Carley wears is designed and tested for comfort and impact protection -- but not for sound protection. Noise inside the helmet can reach rock-concert levels when traveling at highway speeds.
    Carley, a mechanical engineer, has gathered a group of engineers and psychologists to study how to minimize helmet noise. The group includes researchers from two U.K. universities, the University of Bath, where Carley works, and nearby Bath Spa University. They are studying how to protect riders from hearing damage and reduce the potential distraction that noise poses to riders.
    "Riding a motorcycle is a very noisy endeavor," said Rick Korchak, editor of webBikeWorld, a popular motorcycle website that carries detailed helmet reviews. "There are no quiet motorcycles and there are no quiet helmets."
    While riders and others recognize that noise can be a problem, many U.S. jurisdictions prohibit the use of earplugs or other noise-reducing devices. One long road trip could take a rider through numerous changes in local laws.
    "A lot of people, they just do what they're comfortable with, irrespective of what the jurisdiction says is the law," said Charles Brown, a psychologist specializing in sound perception from the University of South Alabama in Mobile.
    "We strongly advocate the use of high-quality, correctly inserted earplugs when riding a motorcycle," said Korchak. He added that good earplugs will not eliminate all noises, allowing sirens and traffic to be heard.
    Sound Research
    Riders experience noise from multiple sources.
    First is the engine noise, which is a relatively insignificant factor once riders accelerate to highway speeds. Audible wind noise can reach volumes as high as 115 decibels or more, roughly equivalent to what power saw operators without ear protection would hear. The Occupational Safety and Health Administration recommends limiting such exposure to 15 minutes or less per day.
    Most initial academic research in motorcycle sound focused on long term hearing damage. The group from Bath began researching the topic by establishing reliable measurements of what happens to air passing over a helmet in a wind tunnel. Then, on roads and test tracks, they studied the relative placement of the rider and the motorcycle. They studied how all the important variables interact, such as the height of the windshield, the location of the helmet and the size of the rider.
    Turbulent air buffeting off the motorcycle windshield is one problem. The researchers found that small differences in air flow patterns can cause large variations in sound level. Subsequently, the Bath group took their experiments to wind tunnels to measure in detail what riders experience.
    The Bath group's most recent paper, accepted for publication by The Journal of the Acoustical Society of America, details the way airflow around the helmet creates noise. They found that for the type of helmets with a full shield and visor covering the face, the largest component of noise comes from air rushing around the chin bar, which wraps around the jaw.
    There's another type of sound experienced by riders, but it's more difficult to quantify, and not affected by earplugs. It's called body conducted sound. Aboard a motorcycle, this process transmits engine vibrations and the percussive force of the wind through the flesh and bone to the ear. Earplugs don't stop it, and it can be significant.
    "It's why your voice sounds different when you hear a recording of your voice versus what you experience as your own voice," said Carley.
    Limiting Sound's Impact
    Reducing the amount of sound that reaches riders can benefit more than motorcyclists' hearing. Riders have to process the sound of riding, the sound conducted through their bones, and a wide variety of visual stimuli as well, all while responding to the situation around them.
    Another topic under investigation by the Bath group is how sound impacts attention. Nigel Holt, a member of that team and a psychologist at Bath Spa University, said that one experiment measured how different volumes of sound impaired a test subject's peripheral vision.
    Cutting down the amount of sound reaching riders is a complicated task.
    "Bone and body transmitted sound bypasses the ear canal entirely," said Holt.
    The Bath group found that lower frequency sounds, including body conducted sound, travel efficiently through the body. The researchers found that a helmet's structure may actually amplify that noise.
    Helmet designers are primarily focusing on designs that will best protect the head against impact, said John Kennedy, an engineer at the University of Bath. "I suppose the acoustic performance of the linings and the various materials doesn't necessarily enter into the design process."
    The shape of helmets could be changed to become more aerodynamic and therefore quieter, but a sleek, sweeping wedge like a racing bicycling helmet might fail to match the current shapes for impact protection and also make it more difficult to hold the head steady when peering over the shoulder before changing lanes.
    Both the Bath group and Brown believe consistent sound rating standards for helmets are needed and that other systems should be developed to reduce the amount of noise that reaches riders. That might require new research on materials that both protect against impact and limit the transmission of acoustic signals.
    Brown, working with Michael Gordon, a psychologist at William Patterson University in Wayne, N.J., performed an experiment to see how much noise canceling technology could diminish noise on a motorcycle. These devices produce frequencies that interfere with incoming noise so that the wearer is protected from potentially damaging sound levels.
    They attached a large set of noise-canceling earmuffs to a motorcycle helmet and placed the assembly atop an acoustically engineered dummy head. Their helmet covered the top and back of the head, but did not have a face shield. After driving the rig around at different speeds, they found that the device reduced sound by as much as 26 decibels, roughly equivalent to the difference in sound between a normal conversation and a busy roadway.
    A Fit for the Future
    Even without earplugs or noise-canceling, riders can make many minor adjustments to substantially reduce the amount of sound to which they are exposed.
    Kennedy said that small movements in riding position can change the volume of sound by more than 10 decibels, and that wearing a scarf around the neck can seal off the cavity around aerodynamically-tricky chin bar.
    "The most important thing that motorcycle owners can do is to make sure their helmet fits their head shape," said Korchak.
    Korchak said that there are five general helmet shapes. Getting the right size and right shape is important, so that the helmet fits snugly around the head and neck, along with jacket collars and the part of the helmet that fits around the neck.
    Carley said that it’s important that helmets be well-ventilated, so that riders travel with the visor closed. Riding with an open visor can create additional wind noise. He also believes that a change in motorcycle design could help, such as building windshields that allow air to flow through them. This would change the aerodynamics so that less air is pushed over the windshield and thrown onto the helmet, he said.
    Using active noise reduction is one potential method to protect riders, but it hasn't been successfully integrated into a production helmet. Brown and Gordon's next experiment investigates a smaller set of headphones that can fit inside a helmet.
    "We think that smart helmets that reduce the wind noise and are designed to transfer a reasonable amount of environmental noise is the way to go," said Brown. "We think that's potentially in the grasp of the technology today."
    The Bath researchers are currently focusing on passive noise reduction techniques such as acoustically absorbent materials. They are concerned about how the necessary protective materials and sufficient noise-canceling equipment can both fit in an effective helmet, as well as the lack of protection offered against body conducted sound.



    Science category:
    Acoustics
    Engineering
    Environment


    News section:
    Inside Science News Service




    https://quietridehelmets.com/template/images/sales_sheet2.pdf

    https://www.sena.com/product/noise-control-helmet/


    [SIGPIC][/SIGPIC]
  • seisverdeseisverde MegaForero ✭✭✭✭✭
    [h=1]https://www.isvr.co.uk/at_work/m_cycle.htm

    Noise levels under motorcycle helmets[/h]Noise levels under motorcycle helmets can be very high. Above about 65 km/h or 40 mph the wind noise generated by the airflow over a motorcycle and rider exceeds the noise from the motorcycle itself. Daily noise exposures of working motorcyclists without hearing protection may regularly exceed 90 dB(A).
    What does the noise under a police motorcyclist’s helmet sound like?

    We have measured noise levels at the ears of police motorcyclists in a wind tunnel and on the road, with several different helmets and motorcycles. Noise levels in the wind tunnel were similar to those on the road.
    mcyclkph.gif
    The graph above shows some examples of noise levels measured under motorcycle helmets during our tests on the roads. Although both BMW motorcycles were ridden by the same person wearing the same helmet, the noise levels differed. The BMW 1100LT has a windscreen which can be raised and lowered, and the noise levels varied with the height of the windscreen. The Kawasaki was ridden by a different person with a different helmet.
    motorcycle_wind_tunnel.jpg Police motorcycle in the wind tunnel

    The measurements in the wind tunnel showed the main source of noise to be the turbulence at the edge of the windscreen’s wake acting on the helmet. The rank ordering of helmets by the noise level depended upon the motorcycle and in particular the windscreen height - a helmet which is relatively quiet on one motorcycle can be relatively noisy on another and vice-versa. Low windscreens direct the turbulence to the base of the helmet, and modifications to improve the helmet seal around the neck can reduce noise levels on motorcycles with low windscreens. High windscreens direct the turbulence to the helmet visor and forehead, and modifications to improve the sealing of the visor to the helmet shell are then effective. Such simple modifications to helmets can reduce noise levels by between 5 dB and 8 dB at the ear.
    Wind tunnel tests with a flying helmet containing active noise reduction earmuffs demonstrated that noise levels as low as 70 dB(A) at 80 km/h and 80 dB(A) at 115 km/h were achievable at the ear. Similar systems within a motorcyclist’s helmet suggest that this potential will not be realised unless the earmuffs are well isolated from the helmet shell and liner. Another method of achieving similarly low levels is to wear good earplugs. Many police forces in the UK are now providing these for their motorcyclists.
    If you ride a motorcycle and your hearing sounds muffled afterwards, or if your ears ring, then you are suffering temporary hearing damage, which, if repeated regularly, may become permanent hearing damage. We recommend you consider wearing earplugs under the helmet. Because the earplugs reduce the noise, you may seem to be travelling more slowly, so take extra care to check your speed until you get used to the earplugs.
    This project was carried out for the Home Office by ISVR Consulting, the Department of Aeronautics and Astronautics, the Wolfson Unit for Marine Technology and Industrial Dynamics, and Hampshire Constabulary.

    We have also measured the noise exposures of motorcycle patrols for one of the motorist breakdown rescue services. The measurements were carried out during the motorcyclists’ normal duties to determine whether their full-day noise exposures were below the limits of the UK regulations.
    References in the open literature:
    M.C. Lower, D.W. Hurst, A.R. Claughton and A. Thomas, 1994; Sources and levels of noise under motorcyclists' helmets. Proceedings of the Institute of Acoustics, 16, pt 2, 319-326. ISBN 1 873082 59 2.
    M.C. Lower, D.W. Hurst and A. Thomas, 1996; Noise levels and noise reduction under motorcycle helmets. Proceedings of Internoise '96, Book 2, 979 - 982.
    [SIGPIC][/SIGPIC]
  • jvidocqjvidocq MegaForero ✭✭✭
    Muy interesanteimage


    *ORIGINALS NEVER FIT*
  • Fran_CISCFran_CISC MegaForero ✭✭✭
    Ostias, muy muy interesante. Me lo apunto y me lo leo con detenimiento.
    Muchas gracias por compartirlo! image
    Mis viajes en moto: https://franturista.wordpress.com
    A ver si lo actualizo :#

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