Al-Hāfidh Ibn Hajr (rahimahullāh) said:
عَنْ عَامِرِ بْنِ عَبْدِ اللَّهِ بْنِ الزُّبَيْرِ عَنْ أَبِيهِ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ أَعْلِنُوا النِّكَاحَ
979: Narrated ‘Āmir Ibn ‘Abdillah ibn Zubair from his father (radiyallāhu ‘anhum) that Allah’s Messenger (salallāhu alaihi wasallam) said:
“Announce the marriages.”
Reported by Ahmad and declared Saheeh by al-Hākim. 
 Ahmad no. 16130, Al-Hākim 2/183, and the hadeeth is “Hasan li-ghairihi” (Good due to other chains of narration).
Shaikh Saalih al-Fawzān (hafidhahullāh) said:
‘Āmir Ibn Abdillāh Ibn Az-Zubair Ibn Al-‘Awwaam: then he is a Tābi’ee, his father is ‘Abdullāh Ibn Az-Zubair (a Companion), and his grandfather is Az-Zubair Ibn Al-‘Awwām (a Companion) – may Allāh be pleased with them both, they were both Companions.
عَنْ عَائِشَةَ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ أَعْلِنُوا هَذَا النِّكَاحَ وَاضْرِبُوا عَلَيْهِ بِالْغِرْبَالِ
The Prophet (salallaahu `alaihi wassallam) said:
“Announce this marriage and strike the drum for it.”
Reported by at-Tirmidhee 1089, Ibn Maajah 1895, from ‘Ā’ishah (radiyallāhu ‘anhā).
This hadeeth proves the obligation of announcing the marriages, and they should not be a secret. So they are announced to distinguish them from fornication. And the announcing is done by various means:
The beating of the “duff” (drum) by the women is a type of announcing because whoever hears it, comes to know that a marriage has taken place. It is not accompanied by music and other musical instruments. All of this is forbidden. As for specifically playing the drum, then it is allowed on the occasions of marriage for the purpose of announcing the marriage (nikāh).
Also from the conditions of marriage (nikāh) is the witnessing of it, and this will be discussed, and it is a condition from the conditions of marriage (that is necessary for its validity).
From the types of announcing is to carry out a “waleemah” (a meal for invited guests), either upon the contract of the marriage or upon the consummation of the marriage due to the saying of the Prophet (salallāhu ‘alaihi wasallam) to ‘Abdur-Rahmān Ibn ‘Awf on the occasion of his marriage:
عَنْ أَنَسٍ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ رَأَى عَلَى عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ أَثَرَ صُفْرَةٍ فَقَالَ مَا هَذَا فَقَالَ إِنِّي تَزَوَّجْتُ امْرَأَةً عَلَى وَزْنِ نَوَاةٍ مِنْ ذَهَبٍ فَقَالَ بَارَكَ اللَّهُ لَكَ أَوْلِمْ وَلَوْ بِشَاةٍ
“Perform a waleemah even if it is with one sheep.”
(Bukhāri, no. 2048, 3937. Muslim 1428)
So by way of these means the marriage is announced, so if the marriage is not announced through one of these means, the nikāh is not sound, rather it is void.
Adapted from volume 4, Kitābun-Nikāh (The Book of Marriage) from Shaikh Sālih al-Fawzān’s explanation of Bulūgh Al-Marām min Adillatil-Ahkām of Al-Hāfidh Ahmad Ibn ‘Ali Ibn Hajr Al-Asqalāni (born 773H, died 852H), entitled Tas-heel al-Ilmām bi-fiqhil-Ahādeeth min Bulūghil-Marām and is printed in seven volumes.