INTERIOR NOISE

[daveklepper]

A pair of papers in the December 2015 issue of the Journal of the Acoustical Society of America addresses the issiue.  One is:

Speech privacy and annoyance considerations in the acoustics environment of passenger cars of high-speed trains

Jin Yong Jeon, Joo Young Hong, Hyung Suk Jang, and JaeHyeon Kim

 

Dept. of Arch.Eng., HanyangU. Saeol 133-791, South Korea

The other paper, same authors, addresses noise levels that can be annoying.

The conclusion is that A-Scale noise levels between 59dB and 63dB are optimimum.  Higher levels are annoying, and lower levels reduce speech privacy, limiting ability to converse comfortably with one's seat-mate.

The car inteior resembles a regular coach, two-by-two, seat spacing approximating Amfleet 1.

Recommend finding the issue and articles in your libraries.  Or write the authors.

An important former employer, Bolt Beranek and Newman, Inc, (BBN) did a similar study for Pullman around 1958, and came to similar conclusions. 

 

[Dragoman]

Interesting. Is it possible to use modern noise-cancelling or noise-shaping technology to achieve the desired levels? I recently was at a restaurant which has tended to be rather noisy, due (apparently) to bad acoustics in the architectural design. Well, now they advertise some sort of sound-neutralizing equipment which is supposed to make it "sound" quieter. Is something like that possible on trains/planes? I know Bose makes sound-cancelling headphones

[daveklepper]

Yes, the technology is available, but in most applications it is more expensive than simpler use of sound-absorbing material, avaialble in a wide variety of forms and finishes,as well as broad-band and selective-frequency-band versions/

The particular problem with active cancillation is avoiding its working in one location and making things worse nearby.

 

However, if a room is too quiet, a subtle background noise system can help privacy, and my firm designed possible as many as forty or fifty such systems, inlcuding one for Chessie System HQ in Clevelalnd, and one for a millionare's bedroom to mask exterior weather-related and traffic noise..

 

[Wizlish]

Out of curiosity, has anyone done a study on acceptable perceived levels of noise based on relative power of annoying frequencies (not just power-spectrum weighting or the assumptions made for A weighting) or noise that has a complex timbre or periodic modulation that would be alarming, annoying, or intrusive?

I would think that even very quiet truck clatter, or high=frequency squeaking as in Amfleet car 'giggling', might be significant in this respect.  Surely Dave knows some references.

[daveklepper]

Yes.   Textbooks on Noise Control by Cyril Harris and L.L. Beranek, and general architectural acoustics textbooks by Marshall Long and David Egan discuss the subject.  It is also discussed in the two Korean study passenger train papers.  In a nutshell, the A-scale insures a lower level of high-and-mid-frequency noise that low-frequency (bass) noise, which is less annoyinhg and pure-tone annoyance is about ten decibels more annoying than random noise in any frequency band, the spread being even greater at higher frequencies.  Certain kinds of modulation of a continuing white or pink (random with different frequency weighting) noise can be pleasant, simulating mild waves breaking on a seacoast, and other modulation can be annoying, like the beating of engine noise in a Lockeed Electra..  Screech is mostly pure-tone, and the gigling sound is beating one, with pure-tone components.

[daveklepper]

For a combination of random noise with pure tones:    "It is also important to avoid pure tones in the noise spectrum.   For frequencies above 500 Hz,  it is reasonable to require  the  toes  to  be  inaudible,  which requires  their  Sound Pressure Level to be below the third–octave-band level of the other noise in the band.  In practice, these results in tones needing to be at least five decBels below the rest of the noisse in the octave band."  Third par. p. 121, Worship Space Acoustics, Kleiner-Klepper-Torres, jrosspub.org., Fort Lauderdale, 2010.  Note that the Amtrak coach jiggle is also vibration, and there are also criteria for vibration, not discussed in detail in our WSA book.  The whole topic with regard to transportation vehicle noise is better addressed in: Handbook of Acoustical Measurements and Noise Control, Cyril M. Harris, McGraw Hill, New York, 1998, and Leo L. Beranek, Noise and Vibration Control, Institute of Noise Control ering, Washinigton, 1988.www.ince.usa.org..........