The provision of section 170 says that the provisions of sections from 171 to 186 will be applicable to all public and private company. But if your company's articles provide the some other compliance or other thing then company comply article provisions.
For Example: Regarding Quorum:
If your articles says that for proper conducting general meeting minimum 3 members should be present for private company, then as per article 3 members is mandatory. However 2 members is required for minimum quorum for conducting general meeting of private company.
Sir according to section 171 a general meeting is called by giving not less than 21 days notice then in case if articles of private and public company provide for notice not less than 7 days . then it will be valid to call general meeting by not less than 7 days notice both in case of public and private company
In this case your article permit for more than 21 days notice for general meeting but not less than 21 days. You can not overrule the provisions of Companies Act, 1956. Please read section 9 of the Companies Act.
you can not over rule the minimum requirement of Companies Act, requirement in your articles.