Is the presence of only the bride's guardian, the ma'dhun, and two witnesses at the marriage contract considered a public declaration of the marriage?

A marriage contract is valid with a guardian, even if he does not openly declare it, because it is a contract of exchange, so its declaration is not a condition, just like a sale. The narrations regarding declaration are to be understood as recommending it, as evidenced by the command to beat the drum and make noise during it, which is not obligatory. Ahmad's prohibition is due to dislike (karaha), not prohibition (tahrim). The declaration of marriage and the beating of the drum usually occur after the contract, and if it were a condition, it would have been considered at the time of the contract.