Exposure to noise is a one of the common problems in any industrial places. Many solutions have been introduced to overcome the deleterious effects of noise pollution maintaining and repairing systems in the equipments, environmental control and hearing conservation systems are some of these solutions that could be mentioned.
There are various types of Hearing protection devices and each one is useful under special circumstances. Commonly, different Hearing protection devices have a particular brochure to introduce information about the manufacturers and the quality of noise reduction in that special production.
Three different methods are commonly used to determine the noise reduction factor in various Hearing protection devices. All these methods have been presented based on the mathematical evaluations and according to the spectral features of the sound existing in the environment and then the sound pressure level is determined in dBA. In the current article we will have a look on the mentioned arithmetic models and their special characteristics.

Background and Aim: Temporal resolution refers to the ability of perceiving changes over time. This study was conducted to prepare Persian version of the temporal resolution test, which was first introduced by Phillips (1994) and Stuart (1996), and to obtain its results in 18 to 25 year old normal individuals of both genders.
Methods: To construct the Persian version of the temporal resolution test, like the original version, speech stimuli, continuous and interrupted noises were used. Speech stimuli comprised four lists of fifty words-monosyllabic lists, which were presented to the right ears first in quietness and then with continuous and interrupted noises on S/Ns of -20, -10, 0, +10 dB. The test was performed on thirty three right handed healthy individuals (14 male and 19 female with the mean age 21.02, SD=1.7 year old) in written response mode.
Results: Significant difference was shown between test scores in quiet with each of the continuous (p<0.0001) and interrupted (p≤0.0001) noises in four signal to noise ratios, and also between test scores of continuous and interrupted noise presentations (p<0.0001). No significant correlation was revealed between gender and test scores and age and test score and age in +10 dB S/N ratio.
Conclusion: Conducting this test on a group of healthy individuals showed its application for measuring temporal resolution with speech stimuli.