See also : aircraft noise • effective perceived-noise level • judged perceived noise level • maximum perceived noise level • noise and number index • noise exposure forecast • perceived noise level • tone-corrected perceived noise level
See also sound speed gradient
The cut-off frequencies have a ratio of 21/6 for example a 1 kHz third-octave band filter has a centre frequency of 1000 Hz with lower and upper frequencies of 891 Hz and 1122 Hz respectively
Third Octave Band Filters centred at one of the preferred frequencies, should meet the IEC and ANSI standardised attenuation characteristics.
See also audible range • audible sound definition • auditory masking • masked threshold • threshold shift
Threshold of Speech Intelligibility
It is usually assumed that the following components are additive, at least for small values of the components.
Noise Induced Permanent Threshold Shift (NIPTS) is the component of permanent threshold shift associated with a noise exposure.
Permanent Threshold Shift (PTS) the component of threshold shift that shows no progressive recovery with the passage of time when the apparent cause has been removed.
Temporary Threshold Shift (TTS) an upward shift in the threshold of human hearing. Usually caused by being subjected to a loud sound. When the noise abates the hearing usually returns to normal. However continual exposure will cause the shift to be permanent.
See also hearing loss and noise induced hearing loss
Timbre Definition (IEC 801-29-09) that attribute of auditory sensation which enables a listener to judge that two non-identical sounds having the same loudness and pitch are dissimilar.
Note : Timbre depends primarily upon the waveform, but also upon the sound pressure and the temporal characteristics of the sound.
See also loudness and related terms
See also time domain averaging and time series.
Time-average Sound Energy Density
Time-average Sound Level
Time-average Sound Pressure Level
A time domain graph shows how a signal changes over time, whereas a frequency domain graph shows how much of the signal lies within each given frequency band over a range of frequencies.
Time Domain Averaging also known as time synchronous averaging is often used in machinery monitoring. It requires a tachometer connected to the trigger input of the analyser to synchronise each snapshot of the signal to the running speed of the machine.
Time Domain Averaging is very useful in reducing the random noise components in a spectrum, or in reducing the effect of other interfering signals such as components from a nearby machine.
See also other types of averaging
See also time average • time domain averaging • time series
See also noise dose and sound exposure
See also sound level time weightings and time constants
This is exactly what we do when we apply a weighting function or time window to a specified period of time record. Examples are rectangular, hanning, etc.
See also windowing
BS 7445 suggests that if the level in a 1/3-octave band is 5 dB or more higher then the adjacent two frequency bands then it's likely to constitute a nuisance and should be rated accordingly.
Tone Assessment Measurements, some meters include software to make measurements directly.
Tone Assessment Parameters include :
Kt : the value added to the LAeq to give the tone-corrected rating level
Lta : the audibility of all tones found in the same critical band as the selected tone
Lpn : the total level of the masking noise in the band containing the selected tone
Lpti : the level of the selected tone
Lpt : the total level of all tones in the critical band containing the prominent tone
Tone-corrected Perceived Noise Level Definition (IEC 801-29-14) a sound pressure level in decibels, obtained by adding to perceived noise level an adjustment that is related to the degree of irregularity that may occur among contiguous one-third-octave band sound pressure levels of an aircraft noise
Note 1 : the adjustment is described in ISO 3891-1978 ; it may vary from 0 dB to 6,7 dB.
Note 2 : the adjustment purports to account for the extra subjective noisiness caused by pronounced audible tones such as may be generated by propellers, compressors, turbines or fans.
See also aircraft noise • effective perceived-noise level • judged perceived noise level • maximum perceived noise level • noise and number index • noise exposure forecast • perceived noise level • T10
The unit is the N·m (newton metre)
TNI = 4 (LA10 - LA90) + (LA90 - 30) dB
Transfer Impedance Definition (IEC 801-25-18) quotient of a dynamic field quantity at one point in a system by the corresponding kinematic field quantity at another point in the same system
See also acoustic impedance and related terms
Transient Definition (IEC 161-02-01) pertaining to or designating a phenomenon or a quantity which varies between two consecutive steady states during a time interval short compared with the timescale of interest. Applies to an adjective and noun
See also maximum transient vibration valueTransient Oscillation Definition (IEC 801-24-03) oscillation that results from a change in external excitation
See also other oscillation terms
Transmission Impedance and Radiation when acoustic waves pass from one medium to another, part is reflected back. The transmission and reflection factors are determined by the relative impedances of the two materials.
See also acoustic impedance and related terms
Transmission Loss Definition (IEC 801-23-39) reduction in sound pressure level between two designated locations in a sound transmission system, one location often being at a reference distance from the source.
Also known as propagation loss, but should not to be confused with sound insulation transmission loss IEC 801-31-39.
Type 1 precision grade sound level meters for laboratory and field use - renamed Class 1.
Type 2 general grade sound level meters for field use - renamed Class 2.
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