Good idea, but it also adds mass to the cone right? Aren't there any laser reflection measurement methods?
The Eminence Lab 12 speakers in post #15 exhibit 180 degrees of phase shift from 16 Hz to 250 Hz, about the same as your simulation in #14.
That's about as good as it gets without FIR, which would delay the signal to achieve a flatter phase response. The amount of delay would increase depending on the LF response desired, the lower, the longer.
That delay would only be apparent if you were comparing it to the original signal, which would not happen in a playback system.
Why do you perceive the phase shift that all loudspeakers normally exhibit a problem?
Why is the delay required in a FIR which could correct the phase shift a problem?
It's a problem because it's for a near-field active noise cancellation application for low frequencies up to 200Hz. I wasn't aware of the properties of low-frequency speakers so I guess I have to take a different approach. The noise itself is also picked up near the speaker so there is no way to "predict" the noise once it gets to the place where it has to be cancelled. Therefore any phase shift from microphone through electronics and then to speaker is a problem.
Thanks for all the comments.
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