... Krishan Ahuja, Robert Funk, Jeffrey Hsu, Michael Heiges, and Charles Stancil; Georgia Tech Re... more ... Krishan Ahuja, Robert Funk, Jeffrey Hsu, Michael Heiges, and Charles Stancil; Georgia Tech Research Institute, Atlanta, Georgia; September 1997 Volume 6 DOT/FAA/ND-97/14 Operation Heli-STAR - Aircraft Position Data; Michael Heiges, Shabnam Khan; Georgia Tech ...
*† ‡ This paper documents noise spectra measured in the interior of a large number of automobiles... more *† ‡ This paper documents noise spectra measured in the interior of a large number of automobiles. The original goal was to measure the vehicle interior acoustic amplitudes in the infrasound region, but since the noise was measured in the audible region also, spectra have been analyzed over a frequency range of 0-20 kHz. These experiments were carried out on public roads around Atlanta, Georgia, USA. The tests were performed with various side window openings, from fully closed to fully open. Typical automobile noise spectra analyzed for ∆f of 0.078 Hz and dissected in low, mid, and high frequency regions are discussed. Contributions to the measured noise by tire rotation, engine firing, and apparent source of infrasound are identified. Past examinations of vehicle interior noise are also reviewed. Changes in vehicle interior noise of various automobiles over the last decade are then discussed. The cars tested include Ford Explorer, Dodge Ram Van, Toyota Corolla, Toyota Camry, and Honda Civic. At frequencies higher than 2 kHz, interior noise is found to be around 20 dB for ∆f of 0.078 Hz. In the mid-frequency region of 500-2000 Hz, the spectrum is made up of the harmonics of the lower frequency region superimposed over a broadband spectrum. Comparing the harmonics in this lower frequency region of different cars, old and new, it is found that over the last decade, on the average, the noise from tire has been reduced by 15 dB and that from engine firing has been reduced by 20 dB. Two infrasound humps were noticeable, one in 0-10 Hz region and another in the 10-20 Hz region of the spectrum. The first hump appears to be related to the vehicle wakes and the second hump is related to Helmholtz resonance of the vehicle interior. The amplitude of sound in this region increases by 12-15 dB at the center of the car on opening the driver's side window by as little as 2 inches. Unlike the audible range, it is found that this infrasound hump has remained unchanged during the last decade, in spite of large improvements in the audible region over the same period.
The main objective of this paper is to provide guidelines for designing and calibrating a high qu... more The main objective of this paper is to provide guidelines for designing and calibrating a high quality, static, jet-noise research facility and making high-quality jet noise measurements. Particular emphasis is placed on methodology for determining if internal noise is dominant in the jet noise spectrum. A section of this document is devoted to clarifying the terminology associated with microphone frequency response corrections and providing a step-wise description of other corrections that must be applied to the measured raw spectra before the jet noise data can be considered accurate and ready for use for extrapolation to full-scale jet engine noise.
The effect on normal incidence acoustic impedance of a non-circular orifice shape is examined rel... more The effect on normal incidence acoustic impedance of a non-circular orifice shape is examined relative to a circular orifice. The impedance of an adjustable porosity perforate, formed from two identical perforates sliding over each other, is measured. As the orifice shape becomes more non-circular, the measured impedance is found to deviate from the predicted results for a circular orifice of the same area. Several isolated orifices of the same open area but different shapes are tested and compared with a circular orifice. Both low incident sound pressure levels using broadband noise and high incident sound pressure levels using sinusoidal tones are used to evaluate the impedance performance of these isolated orifices. One orifice mimics the unique shape produced by the adjustable perforate and results in a smaller attached mass (or mass end correction) compared with a round orifice. This is consistent with the perforate impedance results. The unique orifice shape does not appear to...
1St Annual High Speed Research Workshop, Apr 1, 1992
To examine the building and human response to sonic boom in the range 3 Hz to 30 Hz, Georgia Inst... more To examine the building and human response to sonic boom in the range 3 Hz to 30 Hz, Georgia Institute of Technology is building a special acoustic driver system to simulate sonic boom. To support the NASA LaRC program on building and human response, this simulator's capability has been extended to an upper frequency of 4 KHz. A residential test
It is well known that screech tones from supersonic jets are generated by a feedback loop. The lo... more It is well known that screech tones from supersonic jets are generated by a feedback loop. The loop consists of three main components. They are the downstream propagating instability wave, the shock cell structure in the jet plume, and the feedback acoustic waves immediately outside the jet. Evidence will be presented to show that the screech frequency is largely controlled
... Krishan Ahuja, Robert Funk, Jeffrey Hsu, Michael Heiges, and Charles Stancil; Georgia Tech Re... more ... Krishan Ahuja, Robert Funk, Jeffrey Hsu, Michael Heiges, and Charles Stancil; Georgia Tech Research Institute, Atlanta, Georgia; September 1997 Volume 6 DOT/FAA/ND-97/14 Operation Heli-STAR - Aircraft Position Data; Michael Heiges, Shabnam Khan; Georgia Tech ...
*† ‡ This paper documents noise spectra measured in the interior of a large number of automobiles... more *† ‡ This paper documents noise spectra measured in the interior of a large number of automobiles. The original goal was to measure the vehicle interior acoustic amplitudes in the infrasound region, but since the noise was measured in the audible region also, spectra have been analyzed over a frequency range of 0-20 kHz. These experiments were carried out on public roads around Atlanta, Georgia, USA. The tests were performed with various side window openings, from fully closed to fully open. Typical automobile noise spectra analyzed for ∆f of 0.078 Hz and dissected in low, mid, and high frequency regions are discussed. Contributions to the measured noise by tire rotation, engine firing, and apparent source of infrasound are identified. Past examinations of vehicle interior noise are also reviewed. Changes in vehicle interior noise of various automobiles over the last decade are then discussed. The cars tested include Ford Explorer, Dodge Ram Van, Toyota Corolla, Toyota Camry, and Honda Civic. At frequencies higher than 2 kHz, interior noise is found to be around 20 dB for ∆f of 0.078 Hz. In the mid-frequency region of 500-2000 Hz, the spectrum is made up of the harmonics of the lower frequency region superimposed over a broadband spectrum. Comparing the harmonics in this lower frequency region of different cars, old and new, it is found that over the last decade, on the average, the noise from tire has been reduced by 15 dB and that from engine firing has been reduced by 20 dB. Two infrasound humps were noticeable, one in 0-10 Hz region and another in the 10-20 Hz region of the spectrum. The first hump appears to be related to the vehicle wakes and the second hump is related to Helmholtz resonance of the vehicle interior. The amplitude of sound in this region increases by 12-15 dB at the center of the car on opening the driver's side window by as little as 2 inches. Unlike the audible range, it is found that this infrasound hump has remained unchanged during the last decade, in spite of large improvements in the audible region over the same period.
The main objective of this paper is to provide guidelines for designing and calibrating a high qu... more The main objective of this paper is to provide guidelines for designing and calibrating a high quality, static, jet-noise research facility and making high-quality jet noise measurements. Particular emphasis is placed on methodology for determining if internal noise is dominant in the jet noise spectrum. A section of this document is devoted to clarifying the terminology associated with microphone frequency response corrections and providing a step-wise description of other corrections that must be applied to the measured raw spectra before the jet noise data can be considered accurate and ready for use for extrapolation to full-scale jet engine noise.
The effect on normal incidence acoustic impedance of a non-circular orifice shape is examined rel... more The effect on normal incidence acoustic impedance of a non-circular orifice shape is examined relative to a circular orifice. The impedance of an adjustable porosity perforate, formed from two identical perforates sliding over each other, is measured. As the orifice shape becomes more non-circular, the measured impedance is found to deviate from the predicted results for a circular orifice of the same area. Several isolated orifices of the same open area but different shapes are tested and compared with a circular orifice. Both low incident sound pressure levels using broadband noise and high incident sound pressure levels using sinusoidal tones are used to evaluate the impedance performance of these isolated orifices. One orifice mimics the unique shape produced by the adjustable perforate and results in a smaller attached mass (or mass end correction) compared with a round orifice. This is consistent with the perforate impedance results. The unique orifice shape does not appear to...
1St Annual High Speed Research Workshop, Apr 1, 1992
To examine the building and human response to sonic boom in the range 3 Hz to 30 Hz, Georgia Inst... more To examine the building and human response to sonic boom in the range 3 Hz to 30 Hz, Georgia Institute of Technology is building a special acoustic driver system to simulate sonic boom. To support the NASA LaRC program on building and human response, this simulator's capability has been extended to an upper frequency of 4 KHz. A residential test
It is well known that screech tones from supersonic jets are generated by a feedback loop. The lo... more It is well known that screech tones from supersonic jets are generated by a feedback loop. The loop consists of three main components. They are the downstream propagating instability wave, the shock cell structure in the jet plume, and the feedback acoustic waves immediately outside the jet. Evidence will be presented to show that the screech frequency is largely controlled
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