T-S parameters for Linkwitz transform

chrish · 29th March 2005, 03:48 AM

Hello everyone,

I am interested in building the Linkwitz transform curcuit described here http://sound.westhost.com/project71.htm and here http://www.linkwitzlab.com/filters.htm#9 for a pair of subwoofers I am about to build. The sub woofers are the ones described by Lynn Olson here http://www.nutshellhifi.com/ME2txt.html#swactive for use with his Ariel speakers. The sub woofers boxes are two 90 litre enclosures each with two scan speak 25W/8565-01 drivers.

With the Linkwitz transform curcuit described in the Elliot Sound Products link above, you must provide some Theile-Small values to place into a spread sheet to obtain the correct component values for the circuit. The spread sheet ( http://sound.westhost.com/linkxfrm.zip ) has inputs for the values Fs ( 19Hz ), Qts ( 0.34 ), Vas ( 229 litres ), Vb (desired box volume) ( 90 litres ). The spreadsheet then calculates Qtc, Fsc and F3. My problem is that the calculated Qtc is 0.64, yet Lynn Olson states that the Qtc for this setup is 0.77. I am assuming that this is the difference between having one an two drivers in the same enclosure. Can someone help point me in the right direction to make the correct calculations for the use of two drivers in one enclosure. Can I simply "fudge" the Qts figure to give the Qtc of 0.77?

Don't expect anybody to do all the work for me, but it would be a great help if someone could just point me in the right direction.

Thanks for your help,

Chris

justinc · 29th March 2005, 03:57 AM

try modeling it with the enclosure have the size you may get the qtc you are looking for then. I assume this is the starting qtc not the final one once the transform circuit has been applied

chrish · 29th March 2005, 04:16 AM

Thanks Justin, not quite sure what you are saying. The Qtc is what the spreadsheet calculates the system has (with no transform) using the parameters you supply (Fs, Qts, Vas and your enclosure size). You then can nominate the frequency you want to roll off (20 Hz is default) and the desired Q (0.8 default on the spreadsheet). If I fudge the Qts (total Q of driver) in the input parameters from 0.34 to 0.41 the spreadsheet gives a Qtc (Q total System) of 0.77, the value Olson says he has calculated. I am not sure if this will screw up some of the other parameters or not. I am happy to modify the spreadsheet to take into account multiple drivers, but I am not sure where to look to get the formula.

Thanks,

Chris

mike.e · 29th March 2005, 04:17 AM

I simply used winisd pro + patch, LT filters available. Assuming their correct...

www.linearteam.dk

justinc · 29th March 2005, 04:41 AM

It looks like the spreadsheet will only figure 1 driver in the enclosure. So if you are going to use 2 drivers in the enclosure, just put the Vb half as what it would be for the 2 drivers. so 45l instead of 90l. This should give you the qtc you are looking for

chrish · 29th March 2005, 05:33 AM

Thank you very much for that! Qtc comes in at 0.84 with the half volume figure. I guess this is pretty close to the 0.77 calculated by Olson...

Oh, and that winisd program looks very interesting too, thanks.

Chris

mike.e · 2nd April 2005, 07:35 AM

bear in mind winisd pro is free,but if you know what the bugs are its fine

29th March 2005, 03:48 AM	#1
chrish diyAudio Member Join Date: Oct 2003 Location: Sydney	T-S parameters for Linkwitz transform Hello everyone, I am interested in building the Linkwitz transform curcuit described here http://sound.westhost.com/project71.htm and here http://www.linkwitzlab.com/filters.htm#9 for a pair of subwoofers I am about to build. The sub woofers are the ones described by Lynn Olson here http://www.nutshellhifi.com/ME2txt.html#swactive for use with his Ariel speakers. The sub woofers boxes are two 90 litre enclosures each with two scan speak 25W/8565-01 drivers. With the Linkwitz transform curcuit described in the Elliot Sound Products link above, you must provide some Theile-Small values to place into a spread sheet to obtain the correct component values for the circuit. The spread sheet ( http://sound.westhost.com/linkxfrm.zip ) has inputs for the values Fs ( 19Hz ), Qts ( 0.34 ), Vas ( 229 litres ), Vb (desired box volume) ( 90 litres ). The spreadsheet then calculates Qtc, Fsc and F3. My problem is that the calculated Qtc is 0.64, yet Lynn Olson states that the Qtc for this setup is 0.77. I am assuming that this is the difference between having one an two drivers in the same enclosure. Can someone help point me in the right direction to make the correct calculations for the use of two drivers in one enclosure. Can I simply "fudge" the Qts figure to give the Qtc of 0.77? Don't expect anybody to do all the work for me, but it would be a great help if someone could just point me in the right direction. Thanks for your help, Chris

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29th March 2005, 03:57 AM	#2
justinc diyAudio Member Join Date: Jan 2005 Location: boston	try modeling it with the enclosure have the size you may get the qtc you are looking for then. I assume this is the starting qtc not the final one once the transform circuit has been applied

29th March 2005, 04:16 AM	#3
chrish diyAudio Member Join Date: Oct 2003 Location: Sydney	Thanks Justin, not quite sure what you are saying. The Qtc is what the spreadsheet calculates the system has (with no transform) using the parameters you supply (Fs, Qts, Vas and your enclosure size). You then can nominate the frequency you want to roll off (20 Hz is default) and the desired Q (0.8 default on the spreadsheet). If I fudge the Qts (total Q of driver) in the input parameters from 0.34 to 0.41 the spreadsheet gives a Qtc (Q total System) of 0.77, the value Olson says he has calculated. I am not sure if this will screw up some of the other parameters or not. I am happy to modify the spreadsheet to take into account multiple drivers, but I am not sure where to look to get the formula. Thanks, Chris

29th March 2005, 04:17 AM	#4
mike.e diyAudio Member Join Date: Sep 2004 Location: NZ	I simply used winisd pro + patch, LT filters available. Assuming their correct... www.linearteam.dk

29th March 2005, 04:41 AM	#5
justinc diyAudio Member Join Date: Jan 2005 Location: boston	It looks like the spreadsheet will only figure 1 driver in the enclosure. So if you are going to use 2 drivers in the enclosure, just put the Vb half as what it would be for the 2 drivers. so 45l instead of 90l. This should give you the qtc you are looking for

29th March 2005, 05:33 AM	#6
chrish diyAudio Member Join Date: Oct 2003 Location: Sydney	Thank you very much for that! Qtc comes in at 0.84 with the half volume figure. I guess this is pretty close to the 0.77 calculated by Olson... Oh, and that winisd program looks very interesting too, thanks. Chris

2nd April 2005, 07:35 AM	#7
mike.e diyAudio Member Join Date: Sep 2004 Location: NZ	bear in mind winisd pro is free,but if you know what the bugs are its fine

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