One of the consequences of the progress of science and technology in recent decades is the immediate recording and dissemination of film and sound from various social events. A clear example of this claim is the observation of various videos and sounds from crime scenes in the media. Sometimes sound is the only clue left by criminals at crime scenes. This has prompted forensic experts to seek precise and scientific analysis of sound in order to determine the identity of the speaker and confirm or refute their hypotheses. In forensic phonetics, paying attention to the phonetic characteristics of vowels in different manifestations of spoken language such as dialects, styles, etc. is of great importance. In this study, the vowel space of two speech styles, readable and clear, in Persian has been investigated and compared within the framework of phonetic phonetics. The main objective is to analyze the phonological differences between these two styles for use in forensic applications such as speaker identification, speech reconstruction, or criminal analysis. The research is descriptive-analytical, and the data were obtained by analyzing the first and second structural frequencies of vowels extracted from audio samples. The audio samples included the speech of 25 Persian speakers (male and female) in two speech styles: readable and clear, which were recorded and collected using a microphone. Python and R software were used to extract and analyze the data. The results showed that clear speech has a wider vowel space than readable speech and provides greater accuracy for forensic purposes. It was also found that in both readable and clear styles, women have a larger vowel space than men, and the ability to identify women's voices is greater than that of men. In the study of inter-speaker variation, it was also found that there is greater coherence in women's vowel production and greater dispersion in men's vowel production, and that clear style enhances this dispersion in men and weakens it in women. Therefore, gender and speech style interactively affect the amount of inter-speaker variation, and round vowels, especially /u/, show the greatest sensitivity to these factors.