This is the optional Forum header for the Suggestion Box.
 Page:12345

# TOPIC:

## Re:Linkwitz transform 11 years 8 months ago #3667

 knuisje Offline Senior Member Posts: 48 Thank you received: 4 I'm back from my holiday. I guess everything is solved now? Please Log in or Create an account to join the conversation.

## Re:Linkwitz transform 11 years 8 months ago #3668

 dreite Offline Platinum Member Posts: 1784 Thank you received: 777 Charlie, I will most likely be at the Burning Amp festival this year. If you find me we can touch base and maybe I can help you with miniDSP-related items. Dave. Please Log in or Create an account to join the conversation.

## Re: Linkwitz transform 11 years 5 months ago #4191

 CharlieLaub Offline Premium Member Posts: 113 Thank you received: 8 You can calculate the magnitude and phase responses versus frequency in Excel. Here is how to do it: 1. Calculate z^-1 versus frequency 2. use the biquad coefficients to calculate the transfer function using Excel's complex number functions. See "digital crossovers" in the Applications menu on this web site for info on the IIR transfer function 3. Calculate the magnitude (use IMABS) and phase (IMARGUMENT) of the transfer function for each z^-1 I do this in a loudspeaker crossover design spreadsheet that I have recently put together, which I will be releasing early next year in order to plot the response of the filters for the MiniDSP and compare them to analog filter functions. -Charlie The following user(s) said Thank You: Crumboo Please Log in or Create an account to join the conversation.

## Re: Linkwitz transform 11 years 5 months ago #4195

 Crumboo Offline Premium Member Posts: 144 Thank you received: 14 Thank you, I think that it is the first step that is wrong in my calculations. How do you express z^-1 vs. frequency? I have used z=exp(j*2*PI*f/f_sample). I believe the frequency should be corrected for frequency warping, but the result I get is wrong I'm afraid. Interesting about your spreadsheet, are you releasing it for free? Please Log in or Create an account to join the conversation.

## Re: Linkwitz transform 11 years 5 months ago #4207

 CharlieLaub Offline Premium Member Posts: 113 Thank you received: 8 Here is how to computer the filter response, given the "biquad coefficients": First, define the digital frequency (omega) as w = 2*pi*f*T where f is the frequency in Hertz, and T is the sampling interval, T = (sampling frequency)^-1 Then z = EXP( 0 + iw ) where i is (-1)^0.5. Note that z is a complex number. To get other powers of z, use exponentiation. For instance in Excel: z^-1 = IMPOWER(IMEXP(COMPLEX(0,w)),-1) z^-2 = IMPOWER(IMEXP(COMPLEX(0,w)),-2) In the above Excel formulas, I have inserted "w" in place of a cell reference to w. After computing these quantities, use the definition of the transfer function, the coefficients of each term, and Excel's complex number functions IMDIV, IMSUM, and IMPRODUCT to compute the quantity H(z) shown below: Finally, compute the magnitude and phase response from the transfer function using IMABS And IMARGUMENT, noting that the phase angle computed by IMARGUMENT will be in radians. -Charlie The following user(s) said Thank You: Crumboo Please Log in or Create an account to join the conversation. Last edit: by CharlieLaub.

## Re: Linkwitz transform 11 years 5 months ago #4209

 Crumboo Offline Premium Member Posts: 144 Thank you received: 14 Hi again, As for specifying the distance between speakers I meant in the vertical direction (not the "depth"). While measured data is needed for the actual filter calculations, it could be useful to simulate the combined response in different directions as well. The tools you are developing will be very useful! Please Log in or Create an account to join the conversation.

## Re: Linkwitz transform 11 years 5 months ago #4210

 Crumboo Offline Premium Member Posts: 144 Thank you received: 14 I followed the steps you wrote in order to calculate the response, and I now get the correct result! Thank you so much CharlieLaub! Please Log in or Create an account to join the conversation.

## Re: Linkwitz transform 11 years 5 months ago #4211

 CharlieLaub Offline Premium Member Posts: 113 Thank you received: 8 If you really want to calculate the off-axis response of a loudspeaker, you need to know the positions in space for all the drivers, not just the x,y position on the baffle, but also the z position (distance in front of or behind the baffle plane, or from some reference point/plane). There are some tools that you can use to calculate off-axis responses, such as the Baffle Response Simulator . Doing these calculations correctly is not trivial, because you need to use a good directivity model of the driver. If you download and try out the BRS, you will see that it takes some time to calculate the response. In the end, it's still a model of a rigid piston, and off axis measurements would be more accurate. The approach that I have taken with my crossover design tool is intended to keep things simple. You start with the on-axis response using measurements taken there. If you want to know the off-axis response, you need to supply different measurements, or at least change the acoustic delays in each driver response spreadsheet to reflect the different pathlengths to the off-axis position(s). -Charlie Please Log in or Create an account to join the conversation.
 Page:12345
Moderators: devteam