Perancangan Suara Terarah Menggunakan Parametric Array Ultrasonik

Mengarahkan dan memfokuskan gelombang suara belum menjadi hal yang lumrah. Padahal manfaat aplikasi dari sistem audio terarah sangat beragam, salah satunya informasi terfokus dalam suatu ruang bagi seseorang yang melintasi spot tertentu, ataupun manfaat yang lain. Salah satu metode pengarahan suara adalah dengan memodulasi suara audio ke gelombang berfrekuensi ultrasonik yang memiliki keterarahan yang baik. Gelombang ultrasonik juga dapat dibelokkan dengan mengatur beda fase antar elemennya. Pada penelitian ini, digabungkan antara metode pemfokusan suara ultrasonik termodulasi melalui parametric array dan metode pengarahan suara phase-shift array. Dalam implementasinya, sinyal audio diinputkan ke pre-amp untuk diumpankan ke ADC Arduino. Hasil pembacaan ADC digunakan untuk memvariasi duty cycle sinyal PWM 40 kHz yang juga dihasilkan oleh Arduino. Sinyal PWM termodulasi kemudian diteruskan ke serangkaian penguat kelas D untuk kemudian diteruskan ke serangkaian parametric array untuk memancarkan gelombang suara. Hasil menunjukkan frekuensi suara audio dapat dimodulasi secara PWM ke frekuensi ultrasonik untuk lalu dipancarkan dan mengalami demodulasi kembali ke frekuensi audio. Fokus main lobe memiliki lebar sudut sebesar 30° dengan level suara sekitar 10 dB nyaris tanpa side lobe. Kualitas reproduksi suara relatif baik meskipun dengan noise. Sementara itu, terdapat batas sudut pengarahan yang sempit sehingga kurang efektif. Hal ini sebagai efek kompromi rancangan antara fokus dan keterarahan. Diharapkan lanjutan dari penelitian ini dapat menyeimbangkan rancangan keterarahan dan pengarahan gelombang suara. ================================================================= Directing and focusing sound waves is yet a common thing. Whereas there are several usage of a directional sound, one of those being a focused information source in a room for a particular people that passed a certain spot, among other usage and benefits. One method to focusing a sound waves is by modulating an audio sound into ultrasound waves which has a good beam focus and a non-linear characteristic. Ultrasound beam could also be redirected by adjusting phase differences between their elements. This study wish to try to combine beam focusing method of using modulated ultrasound by parametric array and beam steering method of using phase-shift array. For the implementation, audio signal is passed into a pre amp before being fed into Arduino. ADC converts the signal and used its value to vary the duty cycle of a 40 kHz signal which also generated by Arduino. Modulated PWM signal then was fed into a series of class-D amplifier before being passed into parametric array for beaming the sound waves. The results show that audio frequency could be modulated using PWM into ultrasound frequency for later being beamed and undergo a demodulation back into audio frequency. Main lobe focus covers an area of about 30° with sound level of about 10 dB nearly without side lobes. The sound reproduction quality itself is relatively good with addition of noises. Meanwhile, there is a sound directivity angle limitation which is relatively narrow thus being not effective and couldn’t be perceived by listener. This was the effect of design tradeoff between sound focus and directivity. It is expected that any continuation of this study will be able to develop a design that balances beam focus and directivity