I am working on ''Active noise cancellation for air vent'' project. I am using NI myRIO1900, Audio Technica ATR 3350 omni directional microphones and Tevion Loudspeakers. I have done the programming using LabVIEW and I have used FPGA module.
I am using sinusoidal noise source of (200-500 Hz) as test noise signal.
I have implemented LMS 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.
I know I have to consider secondary path modelling and feedback modelling. I have actually completed the coding of FBFxLMS also but I don't have any reasonable results with this also.
But my question is how to improve the acoustical design of my setup.
What are the problems using just cardboard material to simulate the environment of air vent?
I have read in 2-3 places (here in 2nd answer) that without proper acoustical design it is not possible to reduce the noise effectively.
Quoting from a paper
If the acoustical design of the system is not optimized,the digital controller may not be able to attenuate the undesired noise adequately.
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 find the limitations of how much a DSP will affect and how much the actual acoustic design. If anyone can provide some reasonable resources to go through, it will be highly appreciated.