Background and objectives: This article is aimed at: 1.studying the relationship between Bone conduction pure tone thresholds and speech reception thresholds via bone conduction in normal patients 2.studying the stability and repeatability of the speech reception thresholds via bone conduction and 3. Comparing the characteristics of the function of the speech gain via bone conduction with that of air conduction.
Method: 60 normal hearing subjects (30 males and 30 females) were evaluated by air conduction pure tone audiometry, bone conduction pure tone audiometry and speech reception thresholds.
Results: Findings for the mentioned tests in all subjects were statistically insignificant. The results are prepared in tables and charts.
Conclusion: Pure tone thresholds and speech reception thresholds acquired by means of air conduction testing and bone conduction testing and the stability and repeatability were similar in both evaluations.

Materials and Methods: It is for the first time in Iran that designing and construction of phase-shifter instrument for performing Masking Level Difference have been studied. For reducing limitations of MLD test in middle ear pathologies, new methods of performing MLD has been considered.
In this method noise is conducted by bone vibrator, located on forehead. The comparison between standard method and proposed method has been obtained.Forty 20-25 year-old men referring to the Faculty of Rehabilitation Science in Iran university of Medical Sciences have been tested in the period of time between 10.30.1998 to 12.21.1998.The MLD test was performed in both method at frequencies of 250, 500, 1000, 2000 & 4000 Hz.
Results: The mean of MLD results n the standard method was 11.175 dB ranging from 10 to 13 dB that is in accordance with normative data.
- There was no significant difference between the means obtained in the methods for performing MLD.
- In both methods the MLD means decreased with frequency increments.
Conclusion: It is preferable to use proposal method in middle ear disorders due to normal cochlear sensitivity and subsequently enough noise that is conducted by bone conduction (60 dB SPL).