Subject: Re: Sensitivity of Directional Microphones From: Chirag Patel <cpatel(at)NCA.UWO.CA> Date: Mon, 26 Jan 2004 16:33:13 -0500Hello all, I have a question regarding hearing aid micropohones. I am looking at the Knowles website, more specifically at one of their directional hearing aids. I am trying to predict the response (polar plot) of a 2 mic based directional hearing aid. I came across a paper which showed that I would need the sensitivities of each microphone, like so: The polar pattern for two mics separated by a distance "d" is equal to: S1 = Sensitivity of Mic#1 S2 = Sensitivity of Mic#2 k = 2*pi*f/c theta = angle between line joining the microphone and the propogation direction of the incoming front R(theta) = (S1 + S2) + (j*k*d/2)*(S2-S1)*cos(theta) Now, I can easily calculate (or have fixed in my testing) all the parameters except the sensitivites of the mics. I know data sheets provide the sensitivites at different frequencies, but since S1 and S2 are complex numbers, can I recover the phase information from those graphs provided by the hearing aid manufacture (as given on the following link http://www.knowleselectronics.com/images/products/pdf/Thin%20Mic%20data%20sh eet%20-%20Issue%2003.pdf --> Using a plot like the one on the first page of this pdf file). It appears to be only the "magnitude" response associated with typical Bode plots. Does any one have any suggestions how I can model the sensitivities with the given limitations? Also, can someone confirm that the term (S2-S1) will not be equal to 0, are the values (being complex in nature) accounting for the internal time delay between the two mics? Thanks guys, Chirag Patel ****************************** || || |||||||| /( (at) (at) )\ ------------oOOo-(_)-oOOo------------- Chirag Patel National Centre for Audiology cpatel(at)nca.uwo.ca -------------------------------------- Oooo oooO ( ) ( ) ) / \ ( (_/ \_) --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.559 / Virus Database: 351 - Release Date: 07/01/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.559 / Virus Database: 351 - Release Date: 07/01/2004