I am working on ''Active noise cancellation for air vent'' project. I am using NI myRIO1900 it has FPGA module(Xylinx Z-7010) , Audio Technica ATR 3350 omni directional microphones and Tevion Loudspeakers. I have done the programming using LabVIEW . I am using sinusoidal noise source of (200-500 Hz) as test noise signal to simulate the noise.
I have implemented LMS(least mean squares) algorithm on LabVIEW, as a preliminary results I am getting around 8dB noise reduction but these results are pretty random in a sense only at certain volume levels( if I adjust very carefully), the noise cancellation is happening and the variation in step size is not giving any decent change ( again I have to make volume level changes to see some results).
Over all, I am getting some results but I don't have control over the results.
This is my set up
[the pipe length is 1 meter] I know I have to consider secondary path modelling and feedback modelling. I have actually completed the coding of FBFxLMS(Feedback Filtered x LMS Algorithm) also but I don't have any reasonable results with this also.
I have read in 2-3 places that without proper acoustical design it is not possible to reduce the noise effectively. Quoting from this paper page 5
''If the acoustical design of the system is not optimized,the digital controller may not be able to attenuate the undesired noise adequately.''
I am using this paper as my major reference.
The only point I am aware of is using low frequency noises (<= 500Hz) to consider the sound wave propagation as plane acoustic wave. I am completely unaware of any other details on how to better my acoustical design.
I am wondering how to improve the acoustical design of my setup for effective noise cancellation?
What are the problems using just cardboard material to simulate the environment of air vent ?
Please help me if some one has experience with ANC or Acoustical design.
I am just using this model as prototype to demonstrate effective and controlled Active Noise cancellation.I don't have any practical model to compare to(right now!).
I am looking for some useful references or previous works dealing with acoustical design of Active Noise Cancellation(ANC).
1.In the picture the Anti noise speaker has just been inserted without proper sealing.