It is not clear whether this gallant sound filled Duryōdhana with enthusiasm or not. The Kaurava army however was inspired and they were all set for the war, as stated in the next ślōka –
ततः शङ्खाश्च भेर्यश्च पणवानकगोमुखाः |
सहसैवाभ्यहन्यन्त स शब्दस्तुमुलोऽभवत्  ||१३||
tataḥ śaṅkhāśca bhēryaśca paṇavānakagōmukhāḥ | sahasaivābhyahan’yanta sa śabdastumulō̕bhavat ||13||
[Next, conches, kettledrums, tabors, drums and clarions blared out in unison. What emerged was a tumultuous din].
There is a description here, of the army’s reaction to the commander’s orders. On hearing the sound of Bhīṣma’s conch, the chiefs of the sub-divisions, heads of akṣōhiṇis, replied to Bhīṣma by blowing their conches, indicating their readiness. Likewise, in order to instruct their soldiers to be in prepared, they messaged their sub-unit leaders: ततः शङ्खाश्च (tataḥ śaṅkhāśca).
Later on, across each unit of the army, spanning its rank and file, kettledrums situated here and there were played out. भेरि(bhēri) were large drums used from the ramparts of forts to convey messages.
When the sound from a bhēri touched their ears, soldiers scattered all over the camp, stood in readiness to receive the next instruction. Wearing their armours and carrying their arms (weapons).
Soon the पणव(paṇava) would be heard too. पणव(paṇava) might probably mean tabor. Tabor is a small drum (instrument) made of hide, played to attract attention of the people around while trying to convey a public message. In the earlier times, whenever a royal message was to be conveyed, this process would be followed. On hearing the sound of a tabor, people would assemble in the streets. The royal messenger would then read out the message to them. This instrument is also called ‘tom-tom.’ This is how the usage of ‘tom-tom’ for messages publicized on the streets, came into vogue. According to some, पणव(paṇava) is a ढोल(dhōl) – a double sided barrel drum, with animal hide stretched & fastened over its open ends.
When the tabor was sounded, soldiers would be ‘all ears,’ waiting attentively for the forthcoming instructions. It would also signify that they would have to follow their pre-assigned positions in the battle front formations. In line with this, soldiers would march ahead to the focal point of the battle, to the frontal regions. In sync with their march would be the rhythmic beats of the drums.
Just as how a band is played to match a ‘march past,’ so is this. Conches – kettledrums – tabors were played out like marching orders. The drums were
background instruments, to inspire the ryhtm of a march. The drum was a large sized hide covered instrument, that was sounded from one place, beating ‘dum-dum’ to the rhythmic march of the soldiers. According to some the drum was a tabor.
In this series of sounds, the last to be sounded was a गोमुख(gōmukha). Gomukha was nothing but a horn or clarion. The horn – clarion was sounded when the army’s march had ended and the soldiers were ready to plunge into battle.
Not just five. But all war related instruments. Five are auspiciously described here.
The instruments listed in this ślōka are laid out in such an order in this verse that it signifies the state of readiness of the Kaurava army. Hundreds of conches, kettledrums, tabors, drums, clarions – one-upon another – as they were sounded loudly, how the entire environment drowned in confusion, is picturised in the fourth quadrant of the verse: स शब्दस्तुमुलोऽभवत् (sa śabdastumulō̕bhavat).
That sound spread tumultuously in all directions, to all corners. There are two intents behind this tumultuous sound – one to inspire their soldiers, second to put the opponent in a state of panic.
ततः (tataḥ) – post the sounding of Bhīṣma’s conch; सहसा +ऐव (sahasā+aiva) – immendiately; शङ्खाः(śaṅkhāḥ) – the conches of other troop members; च(ca) – and; पणव+ अनक+गोमुखाः (paṇava +anaka+gōmukhāḥ) – tabor, rhythmically beaten drums, clarions; अभ्यहन्यन्त(abhyahan’yanta) – played out; सः(saḥ) – those; शब्दः(śabdaḥ) – noise; तुमुलः(tumulaḥ) – blaring to the ears; अभवत्(abhavat) – took place.
* * *
Bhīṣma tried to cheer Duryōdhana through the sounding of his conch. He signalled his army to be ready for the war. At the same time, to the Pāndava army he indicated, ‘We are ready. The moment we get your response, the war commences.’ The response of the Pāndavas to this is brought out in the following ślōkas of the Gītā.
The essence of these two slokas is elucidated by by Śrī Rāmānuja in this way –
Śrī Rāmānuja’s Commentary
Noticing Duryōdhana’s grief Bhīṣma, to cheer him, produced a lion’s roar and the conch sound and made them sound the conches and kettledrums to signify the sound of victory.
* * *
 According to some, the Gita text should be ‘स शब्दस्तुमुलो महान्(sa śabdastumulō mahān)’