In this research, some of audio signal properties have been studied according to the speaker's vocal tract shape. A database of audio files has been recorded. These files belong to 57 men whose age between 35 and 45. All speakers came from the same academic and social culture. Furthermore, they don't suffer from any problems in hearings and utterance. The vowel database was created in perfect recording conditions. The spent time needed for recording process was about five minutes for each speaker who said the Arabic word " سألتمُونِيهَا " three times. That word is very rich of vowel letters. It composes of the whole Arabic long vowel. Based on the analysis study of the recorded audio signals, the relationship between the formant frequencies and the length of speaker's vocal tract has been studied. The results show an inverse proportion for the first three frequencies F1, f2, F3 and no clear relationship for the two other frequencies F4, F5.