ततः शङ्खाश्च भेर्यश्च पणवानकगोमुखाः।सहसैवाभ्यहन्यन्त स शब्दस्तुमुलोऽभवत्॥
tataḥ śaṅkhāśca bheryaśca paṇavānaka-gomukhāḥsahasaivābhyahanyanta sa śabdastumulo ’bhavat
Word by word
The verse says
Then conches and kettledrums, tabors, drums and horns suddenly blared out, and the sound was a tumult.
In plain words
The whole army answers at once. Every instrument, all together.
One conch became a hundred. The sound is described simply as tumult - tumulaḥ - a word that means noise without shape, the kind you cannot pick anything out of.
After eleven verses of careful naming and counting, everything turns into undifferentiated noise.
Where you've felt this · in community
You are in a stadium when the noise stops being separate voices and becomes one wall of sound. For a few seconds you cannot hear yourself think. You notice that you have stopped thinking, and that it comes as a relief.
Going deeper
This is a hinge in the chapter, and it works by sound.
Until now everything has been counted and named - this warrior, that rank, our side, theirs. Now it collapses into one noise that belongs to nobody. The counting stops mattering because it cannot be heard.
Something similar happens to Arjuna a few verses from now. His careful sense of who is who - my teacher, my cousin, my side - is about to break down into something he cannot sort at all.
The poem prepares you for that with this noise. War is introduced first as a sound that makes distinctions impossible, and only then as a field full of relatives. By the time Arjuna looks across in verse 26, we have already been told, in the language of drums, what is about to happen to his mind.