Ok for paralel sided duct...
driver Fs is 38 Hz so a 1/4 wave of that is 2.25 metres and if you wanted to use a secondary 1/4 wave duct to address the first harmonic (76 Hz) that duct would be 1.125 metres long. I would not worry about the Sd of the ducts just make them have as large a cross section as will comportably fit into the cabinet. I have used ducts as small in CSA (cross sectional area) as 1/4 of driver Sd and the still work fine.
I am just guessing here but my take would be that using a Karlson taper at the end of the line(s) would due to increading volume of coupler make the duct seem to expand in size somewhat from the speakers perspective. If that is in fact the case then you might want to make the lines a little longer. For a first kick at the cat I would not worry too much about it as this is more of a proof of concept trial run of things.
As I saif before I would calculate the length of the front coupler section (from top to mid point of the driver) as part of each duct lengths total length. You will have to do a scale drawing to see how best to fudge it/them (the duct(s)) into the back side of the cabinet and then go from there. I think that it will work well. Let me know if you ever get up the gusto to give it a try. Regards Moray James.
PS I think that you will want to use drivers with as Le as low as possible.
driver Fs is 38 Hz so a 1/4 wave of that is 2.25 metres and if you wanted to use a secondary 1/4 wave duct to address the first harmonic (76 Hz) that duct would be 1.125 metres long. I would not worry about the Sd of the ducts just make them have as large a cross section as will comportably fit into the cabinet. I have used ducts as small in CSA (cross sectional area) as 1/4 of driver Sd and the still work fine.
I am just guessing here but my take would be that using a Karlson taper at the end of the line(s) would due to increading volume of coupler make the duct seem to expand in size somewhat from the speakers perspective. If that is in fact the case then you might want to make the lines a little longer. For a first kick at the cat I would not worry too much about it as this is more of a proof of concept trial run of things.
As I saif before I would calculate the length of the front coupler section (from top to mid point of the driver) as part of each duct lengths total length. You will have to do a scale drawing to see how best to fudge it/them (the duct(s)) into the back side of the cabinet and then go from there. I think that it will work well. Let me know if you ever get up the gusto to give it a try. Regards Moray James.
PS I think that you will want to use drivers with as Le as low as possible.
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