Richard A. Carman

Modeling noise from motocross facility with complex terrain

The authors prepared a study for an existing motocross facility under new ownership. The study was required by the county for a continued use permit. The facility is in a rural setting and will host weekend races and practice activity. The terrain of the motocross track is complex with a hill and flat section with jumps. To conduct the study, an empirical noise model was constructed for future track activity using noise measurements performed at selected locations at the facility’s property line during simulated race and practice activity. A model of the future dirt bike noise was created by scaling the measured race and practice activity based on the level of future bike activity anticipated by the owner. The data were scaled using the number of bike rider hours to account for the time riders spend riding, the number of riders per activity, and the number of different activities per day. Long-term noise was measured at the same locations to obtain typical ambient levels during hours with no bike activity...

Considerations to Establish Ground-Borne Noise Criteria to Define Mitigation for Noise-Sensitive Spaces

FTA provides guidance for the evaluation of impacts to a variety of noise- and vibration-sensitive uses along a rail transit system. Included under the category of special buildings are concert halls or sound-recording facilities and auditoriums. The impact criteria for ground-borne noise from the transit systems into such spaces are maximum noise levels of 25 or 30 dBA, respectively, far more restrictive than for any other category considered in the FTA Guidance Manual. Conformance with these impact criteria is necessary to avoid significant impact during environmental analysis but may not be a sufficient evaluation of the effect of the transit systems. Some special parameters that should be considered for any rail transportation project that seeks to become a close neighbor of such facilities are discussed.

Area-wide infrasound measurements for two wind turbine facilities

Area-wide measurements of low frequency wind turbine noise were conducted in residential areas adjacent to two different wind turbine facilities in Southern California. The residential measurement location distances ranged from 615 m to 9 km from wind turbines. Additional measurements were also conducted at distances as close as 125 m from the wind turbines. To obtain the residential measurement data, simultaneous digital recordings were made inside and outside residences using microphones designed to achieve a linear response down to 0.07 Hz. The outdoor measurements were conducted with a ground board and two windscreens. The recorded data at residences were analyzed using a cross-spectral technique to minimize the effects of wind acting on the microphone. The data clearly show the presence of infrasound at the blade passage frequency of the wind turbines as well as at the associated harmonics. The primary range of interest is frequencies between 0 and 10 Hz. The residential data in some instances indicate higher levels of infrasound indoors compared to outdoors, indicating a potential amplification of very low frequency sound energy by the residential structure. Representative infrasound data for both facilities are presented and discussed.

Measuring wind turbine infrasound in the presence of wind

A windscreen enables noise measurements to be made as accurately as possible under typical field conditions. Measuring wind turbine noise presents a greater level of difficulty than normal. For there to be wind turbine noise, there needs to be wind for the turbines to operate. Greater wind turbine noise is generally associated with higher wind speeds. Multiple windscreens have been found to significantly reduce artificial wind noise in the range of hearing of 20 to 20 kHz, but cannot reduce the very low frequency pressure fluctuations associated with the movement of air during gusts of wind or in the case of interior measurements fluctuations due to wind pressurizing the building. Wind turbines have been demonstrated by others to produce infrasound in the range of 0.5 to 10 Hz. Measuring infrasound in the presence of local wind is a challenge, since finding a less windy time is not an option. Area-wide measurements of wind turbine noise were conducted at two wind turbine facilities. In analyzing the recor...

Potential noise impacts associated with concert sound from a proposed football stadium.

A proposed new stadium for a national league football team was the subject of a recent Environmental Impact Report prepared for a major redevelopment of a former industrial site in San Francisco, CA. The development will include commercial and residential components, which would be adjacent to existing residential and industrial land. Consequently, potential noise impacts were evaluated for existing and future residential receptors. San Francisco recently revised its noise ordinance adopting relatively low limits for community noise, thus posing interesting challenges for new noise sources. The concept for the new outdoor stadium included a fixed sound system for football games that could result in noise impacts as well as those from crowd noise. This paper, however, will focus on the potential for community noise impacts from outdoor concerts that could be held in the stadium using the performer’s sound system as is typical in this situation. A three‐dimensional acoustical model, which included the local...

Modeling ground response functions in rock: A comparison of multiple methods.

Rail transit operations often produce groundborne vibration with energy that extends into the audible frequency range. It is often necessary to predict potential ground/structure‐borne vibration and noise transmission in the design of new buildings in close proximity to existing rail lines or for new rail facilities/alignments. In a detailed analysis, key factors include source vibration characteristics (spectral force input to soil and/or track structure), ground vibration propagation characteristics (spreading and material damping losses), building foundation type (soil/structure interaction and coupling losses), and structural design of upper floors (floor and wall resonances and attenuation through the building). This paper focuses on methods for obtaining vibration propagation characteristics in rock which is an efficient transmitter of vibration at audible frequencies. Three methods for obtaining one‐third octave band response functions are compared: empirical methods, finite element analysis, and s...

Predicting structure‐borne noise for new construction adjacent to medical facilities.

When new building construction is conducted in close proximity to existing medical or medical research facilities, structure‐borne noise due to construction activities generating vibration can cause impacts to the occupants of the existing building. Theoretical modeling of structure‐borne noise is very complicated and can be extremely time consuming. The feasibility of the two primary candidates (i.e., FEA and SEA) for modeling this phenomenon is questionable, at least at this point, for a number of reasons that are discussed. It is possible that the time will come when a theoretical method can be used reliably to predict structure‐borne noise transmission. In the meantime, using an empirical approach seems to be the most viable. A case study is presented of a facility for medical research involving mice. Preconstruction projections of structure‐borne noise and vibration are compared to those measured with an extensive monitoring program employed during construction.

Correlation of field measurements for footstep force pulse with finite element analysis model for determining vibration response of a building floor

An idealized force pulse that simulates footsteps was developed by Galbraith and Barton. Their proposed forcing function was determined from direct force measurements using walkers of different weights walking at various speeds. Unger and White used this idealized footstep pulse to determine the maximum dynamic deflection of a floor for the purpose of building design calculations. These basic concepts were used to revisit the characteristics of the idealized forcing function. During the design phase of an academic research facility, extensive vibration measurements were obtained using an exemplar floor similar in design to that proposed for the new research building. The exemplar floor was modeled using FEA. Its modal characteristics were compared to the field test results and found to be in reasonable agreement. Upon having established confidence in the basic FEA model, the field measurement results of two walkers on the exemplar floor were compared with the FEA results predicted using the Galbraith‐Bart...

An evaluation of the accuracy of the Federal Transit Administration approved, groundborne noise and vibration prediction model for rail transit systems; a case study for a new subway line using post construction, transit operation measurements

The groundborne noise and vibration model developed by Nelson and Saurenman in 1984, now recognized by the Federal Transit Administration as the approved model for new transit system facilities, is entering its third decade of use by engineers and consultants in the transit industry. The accuracy of the model has been explored in the past (e.g., Carman and Wolfe). New data obtained for a recently completed extension to a major heavy rail transit system provides an opportunity to evaluate the accuracy of the model once more. During the engineering design phase of the project, noise and vibration predictions were performed for numerous buildings adjacent to the new subway line. The values predicted by the model were used to determine the need for and type of noise and/or vibration control measures. After the start of transit operations on the new line, noise and vibration measurements were made inside several of the buildings to determine whether the criteria were in fact achieved. The measurement results a...

Community noise model for train warning horn

For public safety, freight and passenger trains are required to have audible warning devices to signal the approach of trains at grade crossings, and in case of an emergency, where there is a shared right‐of‐way or other possible public access to railroad tracks. Some communities have expressed a desire to reduce the need for sounding warning horns at grade crossings. Although very expensive, grade‐separated railroad crossings are one means by which communities and railroads can reduce the need for horn blowing in populated areas. Efforts are being made to develop new grade crossing safety devices that reduce the need for horn blowing. However, use of warning devices such as horns or whistles to signal the approach of trains, especially at grade crossings, will probably remain a major source of railroad noise in most communities through which railroads pass. A noise prediction model is presented and compared with noise data measured for freight train locomotive horns at grade crossings. Horn sounding dura...