Verse 17

आकाशभावनामच्छां शब्दबीजरसोन्मुखीम् ।ततस्तां घनतां यातं घनस्पन्दक्रमान्मनः

In plain words

the clear conceiving of ākāśa, inclined toward the seed-essence of sound. Then mind, having gone on to that density by the sequence of dense vibration,