paulspencer said:
ok, ..
slight practical difficulty, .. hard to fit large sonotubes in a compact car, .. i decided to make do with 2 home-depot type 12" x 4' sonotubes (the good stuff is too far away from me - whitecap, dallas), .. which i plan to fit together (maybe sacrifice 6" of one of them to make an internal coupler). i can always get more tube, depending on how low i want to tune this thing. i wish i could get 13' tube but it just isn't available.
i mish mashed this 8ft arrangement together as seen in pic (sans active crossover and amplification)
1. i haven't sealed or stuffed anything together,. crossinng over as low as 40-50Hz. i notice uncontrolled woofer motion on some tracks, .. even at normal volume playing relatively light dire straits stuff (even when i have the 25Hz low cut filter enabled), .. is this what paulspencer means, ..or is the woofer junk (worked fine when i had it in a sealed box in the car , .. but that doesn't count for much in home audio) or is it just my "extremely tardy preliminary setup, .. what's a person to do about this.?
if i make this arrangement permanent, .. i do plan to build a proper box to seat the woofer front firing and couple to the tube
2. forgive me for asking again, .. but from this post
i still can't see how less than a pound of polyfill can fill more than 8 cubic feet, ..even teased out.
advice appreciated
vin
Attachments
Vin,
I'm sure that if both sonotubes are well connected, that you should be able to get it to work well regarding coupling them. While the driver has a little less output than what most would use, it is not that far behind the Shiva if you don't ask too much down low. Based on the xmax of 9mm compared to the Shiva 15mm, you could expect it to be theoretically within say 3db.
2 x xmax ~ +6db
as a first order HP filter keeps excursion constant, excursion will normally double for each octave lower you wish to go.
Therefore to match the output of the Shiva at 20 Hz with another driver playing at 40 Hz, you need half the xmax ~ 8mm.
If you used a second of the same driver mounted push pull like the TL example you linked at the start, you could then expect a little more output than the Shiva above fs.
Perhaps to limit excursion you need the HP filter at 30 Hz. Perhaps you also need a higher order filter to limit overexcursion.
It could also be that you have problems with vertical room modes. If you find significantly less bass in a room that is not significantly bigger, then either the room has less stored energy (less solid construction that absorbs the bass energy as well as allows it to pass through the walls) or you have room mode issues.
Normally I'd expect room mode issues to be in the range covered by your main speakers, which with their dipole radiation should deal with them much better than a monopole. You are crossing to a monopole below what is most likely the modal range of the room. This approach should work well and is recommended by both Thorsten Loesch and Linkwitz.
I'm sure that if both sonotubes are well connected, that you should be able to get it to work well regarding coupling them. While the driver has a little less output than what most would use, it is not that far behind the Shiva if you don't ask too much down low. Based on the xmax of 9mm compared to the Shiva 15mm, you could expect it to be theoretically within say 3db.
2 x xmax ~ +6db
as a first order HP filter keeps excursion constant, excursion will normally double for each octave lower you wish to go.
Therefore to match the output of the Shiva at 20 Hz with another driver playing at 40 Hz, you need half the xmax ~ 8mm.
If you used a second of the same driver mounted push pull like the TL example you linked at the start, you could then expect a little more output than the Shiva above fs.
Perhaps to limit excursion you need the HP filter at 30 Hz. Perhaps you also need a higher order filter to limit overexcursion.
It could also be that you have problems with vertical room modes. If you find significantly less bass in a room that is not significantly bigger, then either the room has less stored energy (less solid construction that absorbs the bass energy as well as allows it to pass through the walls) or you have room mode issues.
Normally I'd expect room mode issues to be in the range covered by your main speakers, which with their dipole radiation should deal with them much better than a monopole. You are crossing to a monopole below what is most likely the modal range of the room. This approach should work well and is recommended by both Thorsten Loesch and Linkwitz.
Hi,
progress report:
glued two 4 ft tubes together for a total of 7.5 ft at this point (can always buy more tube cheap if I need to) ,
Having some time over the long weekend, I decided to try and understand the underlying design principles and was poring through John Risch's calculations as per http://www.t-linespeakers.org/design/classic.html and specifically http://www.audioasylum.com/audio/speakers/messages/11476.html
couple of naive questions:
question 1:
i tried using winisd to model the sealed equivalent (entering the params of the mtx 4000 12" 4ohm driver) , .. not sure how exactly to determine Fb from here,
.. using winisd, Qtc seems to vary somewhat . .. plugging in values for Johns scanspeak example, the -6dB values seem close to what John gets, .. except that in my case, they don't seem to vary even when I change the volume. Help
question 2:
is it better to design the transmission line above, equal, or below the Fs of the driver.
Thanks, Vin
-----------------------------------------------------------------------
iteration 1
length of line = 1.83m (6 ft long, 1 ft diameter sonotube)
therefore, ..
unstuffed line => 330 / (1.83 * 4 ) = 45 Hz
stuffed line => 45 / 0.5 = 23 Hz
V_unstuffed = 4.7 cu.ft = 133 l (0.786 * l (ft)
for Qtc of 0.74, .. (using winisd and MTX datasheet)
unstuffed Fb (box resonant freq.) = 27 Hz
factor in apparant inc. in vol by stuffing
stuffed Fb = 27 / 1.35 = 20Hz
-----------------------------------------------------------------------
iteration2
length of line = 2.3m (7.5 ft long, 1 ft diameter sonotube)
therefore, ..
unstuffed line => 330 / (2.3 * 4 ) = 36 Hz
stuffed line => 45 / 0.5 = 28 Hz
V_unstuffed = 5.9 cu.ft = 168 l
for Qtc of 0.70, .. (using winisd and MTX datasheet)
unstuffed Fb (box resonant freq.) = 27 Hz
factor in apparant inc. in vol by stuffing
stuffed Fb = 27 / 1.35 = 20Hz
progress report:
glued two 4 ft tubes together for a total of 7.5 ft at this point (can always buy more tube cheap if I need to) ,
Having some time over the long weekend, I decided to try and understand the underlying design principles and was poring through John Risch's calculations as per http://www.t-linespeakers.org/design/classic.html and specifically http://www.audioasylum.com/audio/speakers/messages/11476.html
couple of naive questions:
question 1:
i tried using winisd to model the sealed equivalent (entering the params of the mtx 4000 12" 4ohm driver) , .. not sure how exactly to determine Fb from here,
.. using winisd, Qtc seems to vary somewhat . .. plugging in values for Johns scanspeak example, the -6dB values seem close to what John gets, .. except that in my case, they don't seem to vary even when I change the volume. Help
question 2:
is it better to design the transmission line above, equal, or below the Fs of the driver.
Thanks, Vin
-----------------------------------------------------------------------
iteration 1
length of line = 1.83m (6 ft long, 1 ft diameter sonotube)
therefore, ..
unstuffed line => 330 / (1.83 * 4 ) = 45 Hz
stuffed line => 45 / 0.5 = 23 Hz
V_unstuffed = 4.7 cu.ft = 133 l (0.786 * l (ft)
for Qtc of 0.74, .. (using winisd and MTX datasheet)
unstuffed Fb (box resonant freq.) = 27 Hz
factor in apparant inc. in vol by stuffing
stuffed Fb = 27 / 1.35 = 20Hz
-----------------------------------------------------------------------
iteration2
length of line = 2.3m (7.5 ft long, 1 ft diameter sonotube)
therefore, ..
unstuffed line => 330 / (2.3 * 4 ) = 36 Hz
stuffed line => 45 / 0.5 = 28 Hz
V_unstuffed = 5.9 cu.ft = 168 l
for Qtc of 0.70, .. (using winisd and MTX datasheet)
unstuffed Fb (box resonant freq.) = 27 Hz
factor in apparant inc. in vol by stuffing
stuffed Fb = 27 / 1.35 = 20Hz
According to the AlphaTL xls kindly posted on this forum by GM -- using your driver's specs and a length of 7.5' will give you ...
30HZ using Fibreglass stuffing of .463 lbs per cubic ft
36HZ using Polyfil stuffing of .885 lbs per cubic ft
The research you did ("the old way") has been supplanted by more recent very intensive computer modeling work by Martin J King and also Augspurger.
The AlphaTL xls is based on Augspurger's work (Planet10 has "had good results with it").
Bose spent "13 years and million of dollars" researching this area for the Bose Cannon. They claim you should tune no lower than 1/2 the driver's fs (22HZ in your case) -- a 11.5' tube and about 1/3 lb of Fibreglass per cubic ft.
I built a 20' Bose Cannon and it models VERY CLOSELY to the AlphaTL predictions (using a tuning of 18HZ).
30HZ using Fibreglass stuffing of .463 lbs per cubic ft
36HZ using Polyfil stuffing of .885 lbs per cubic ft
The research you did ("the old way") has been supplanted by more recent very intensive computer modeling work by Martin J King and also Augspurger.
The AlphaTL xls is based on Augspurger's work (Planet10 has "had good results with it").
Bose spent "13 years and million of dollars" researching this area for the Bose Cannon. They claim you should tune no lower than 1/2 the driver's fs (22HZ in your case) -- a 11.5' tube and about 1/3 lb of Fibreglass per cubic ft.
I built a 20' Bose Cannon and it models VERY CLOSELY to the AlphaTL predictions (using a tuning of 18HZ).
qi, .. thank you for the advice
downloaded the spreadsheet and plugged in the values,.. i see how you predict Fb by trial and error substitutions of Fb values till the L value for the stuffing type matches with the AVAILABLE length of tube
two questions (hopefully not too dense):
1.(minor),.. naive question,.. but how is the stuffing calculated from these results.
i'm guessing
weight of polyfill / cuft = 0.269 * 1.041 = 0.28 lb /cuft
vol of 1 linear ft of 12" sonotube = 3.14 cuft
therefore, .. wt (lb).of polyfill per linear ft of sonotube = 0.28 * 3.14 = 0.88
2. (little less minor) , ... okay, .. so we know how to predict the response for a given length. i'm in the process of building this thing today, .. but given that i have the mundane capability to cut off or splice more tube on to this beast, .. my question is a bit more fundamental what would the OPTIMUM length of the tube be, given a particular driver? From your last 2 statements,.. you indicate that tuning the line lower than the driver is the way to go. My driver's Fs is 29Hz, .. half of that is aruond 15hz, .. how do you determine 22Hz?
Thanks for all the help so far
GM's spreadsheet results for Polyfill
Lp (in) 89.928 =======>(output) current length of tube
So/SL (in^2) 154.725
alpha 1.288
Z stuffing factor 0.269
Dp 1.041
Qts 0.540
Vas 4.030
Fs 29.500
Fb 36.000 =======> (trial and error input) Fs
downloaded the spreadsheet and plugged in the values,.. i see how you predict Fb by trial and error substitutions of Fb values till the L value for the stuffing type matches with the AVAILABLE length of tube
two questions (hopefully not too dense):
1.(minor),.. naive question,.. but how is the stuffing calculated from these results.
i'm guessing
weight of polyfill / cuft = 0.269 * 1.041 = 0.28 lb /cuft
vol of 1 linear ft of 12" sonotube = 3.14 cuft
therefore, .. wt (lb).of polyfill per linear ft of sonotube = 0.28 * 3.14 = 0.88
2. (little less minor) , ... okay, .. so we know how to predict the response for a given length. i'm in the process of building this thing today, .. but given that i have the mundane capability to cut off or splice more tube on to this beast, .. my question is a bit more fundamental what would the OPTIMUM length of the tube be, given a particular driver? From your last 2 statements,.. you indicate that tuning the line lower than the driver is the way to go. My driver's Fs is 29Hz, .. half of that is aruond 15hz, .. how do you determine 22Hz?
Thanks for all the help so far
GM's spreadsheet results for Polyfill
Lp (in) 89.928 =======>(output) current length of tube
So/SL (in^2) 154.725
alpha 1.288
Z stuffing factor 0.269
Dp 1.041
Qts 0.540
Vas 4.030
Fs 29.500
Fb 36.000 =======> (trial and error input) Fs
Sorry, guy. I made the same mistake as Planet10. I am building a shed in the back yard so the boss is keeping a sharp eye on me
I just took the wriong (8" driver) numbers from the AlphaTL xls. Yours are correct. The stuffing comes right off the xls with no further calcs.
I wouldn't go much below 22HZ which is around a 12' tube since you are already concerend about over driving that MTX4000.
As Dave already mentioned, the room should get also help out.
Good luck and I hope I have helped in some way
>1.(minor),.. naive question,.. but how is the stuffing calculated from these results.
i'm guessing
weight of polyfill / cuft = 0.269 * 1.041 = 0.28 lb /cuft
vol of 1 linear ft of 12" sonotube = 3.14 cuft
therefore, .. wt (lb).of polyfill per linear ft of sonotube = 0.28 * 3.14 = 0.88
====
I posted the spreadsheet for a specific thread and noted that it was set up for easy transfer of values into MJK's TL worksheet, so the calc'd stuffing is in lbs/ft^3. The alpha cab and Z stuffing factors are just calc'd variables used to calc the cab So/SL and Df or Dp, so Vb in ft^3*Dp is the total number of lbs of polyfil theoretically required to yield a ~IB response down to whatever Fb is, though of course if it sounds too overdamped, some can be removed.
Sorry about the confusion, when I noticed that Dave P10 had made a similar mistake last week, I told him I would post a more user friendly version soon. I guess not soon enough.
====
>2. (little less minor) , ... okay, .. so we know how to predict the response for a given length. i'm in the process of building this thing today, .. but given that i have the mundane capability to cut off or splice more tube on to this beast, .. my question is a bit more fundamental what would the OPTIMUM length of the tube be, given a particular driver? From your last 2 statements,.. you indicate that tuning the line lower than the driver is the way to go. My driver's Fs is 29Hz, .. half of that is aruond 15hz, .. how do you determine 22Hz?
====
Like Rick (Alpha TL's designer), I don't think in terms of a fixed length, but the desired Fb. WRT choosing it, until Qts is >1, the theoretical ideal is Fb = Fs, or no lower than 0.707*Fs assuming the driver has sufficient Xmax for the intended app. With Qts >1, then tuning it above Fs by whatever amount causes the peaking at Fb to 'fill in' with the high Q 'hump' in the response to extend it.
GM
i'm guessing
weight of polyfill / cuft = 0.269 * 1.041 = 0.28 lb /cuft
vol of 1 linear ft of 12" sonotube = 3.14 cuft
therefore, .. wt (lb).of polyfill per linear ft of sonotube = 0.28 * 3.14 = 0.88
====
I posted the spreadsheet for a specific thread and noted that it was set up for easy transfer of values into MJK's TL worksheet, so the calc'd stuffing is in lbs/ft^3. The alpha cab and Z stuffing factors are just calc'd variables used to calc the cab So/SL and Df or Dp, so Vb in ft^3*Dp is the total number of lbs of polyfil theoretically required to yield a ~IB response down to whatever Fb is, though of course if it sounds too overdamped, some can be removed.
Sorry about the confusion, when I noticed that Dave P10 had made a similar mistake last week, I told him I would post a more user friendly version soon. I guess not soon enough.
====
>2. (little less minor) , ... okay, .. so we know how to predict the response for a given length. i'm in the process of building this thing today, .. but given that i have the mundane capability to cut off or splice more tube on to this beast, .. my question is a bit more fundamental what would the OPTIMUM length of the tube be, given a particular driver? From your last 2 statements,.. you indicate that tuning the line lower than the driver is the way to go. My driver's Fs is 29Hz, .. half of that is aruond 15hz, .. how do you determine 22Hz?
====
Like Rick (Alpha TL's designer), I don't think in terms of a fixed length, but the desired Fb. WRT choosing it, until Qts is >1, the theoretical ideal is Fb = Fs, or no lower than 0.707*Fs assuming the driver has sufficient Xmax for the intended app. With Qts >1, then tuning it above Fs by whatever amount causes the peaking at Fb to 'fill in' with the high Q 'hump' in the response to extend it.
GM
GM:
The Bose Cannon patent states that fb may be as low as .5*Fs. You are saying no lower than .707*Fs. Could you please elaborate?
Also, is there a way to modify the AlphaTL xls to iteratively determine for the condition Qts > 1 using the solve feature? Do we currently have enough information to do so? Will MJK's MathCad calcs give us this optimum?
The Bose Cannon patent states that fb may be as low as .5*Fs. You are saying no lower than .707*Fs. Could you please elaborate?
Also, is there a way to modify the AlphaTL xls to iteratively determine for the condition Qts > 1 using the solve feature? Do we currently have enough information to do so? Will MJK's MathCad calcs give us this optimum?
still haven't sealed in the baffle,.. want to paint it first
i stuffed the 7.5 ft line with 0.7 to 0.8 lb polyfill / cubic ft (equivalent to around 0.5 lb polyfil per linear ft of 12"ID sonotube)
maybe it's because i haven't sealed the tube (currently just a snug fit) but still, i see a few problems
1. i see and hear the woofer bottoming out / behaving badly (even at low volumes with not very intense music). bass below 25Hz is cut (fixed low-cut on my crossover) and crossover point at around 45 Hz
2. not much volume at all (even though the 100 W x 2 (bridged to 200Watts amp is getting fairly warm )
3. bad woofer? not sealing it ? line too short?
i stuffed the 7.5 ft line with 0.7 to 0.8 lb polyfill / cubic ft (equivalent to around 0.5 lb polyfil per linear ft of 12"ID sonotube)
maybe it's because i haven't sealed the tube (currently just a snug fit) but still, i see a few problems
1. i see and hear the woofer bottoming out / behaving badly (even at low volumes with not very intense music). bass below 25Hz is cut (fixed low-cut on my crossover) and crossover point at around 45 Hz
2. not much volume at all (even though the 100 W x 2 (bridged to 200Watts amp is getting fairly warm )
3. bad woofer? not sealing it ? line too short?
Attachments
>The Bose Cannon patent states that fb may be as low as .5*Fs. You are saying no lower than .707*Fs. Could you please elaborate?
====
Look at those two points on a driver's free air impedance curve and think about what a cab's primary function is, damping Fs, and it's secondary function, increasing gain above Fs.
Understand that patents have nothing to do with what's technically correct, but are intended to 'lock out' anyone from offering anything remotely close to what they might ultimately market, not to mention obfuscate as much as legally possible to keep folks from figuring out what they're really up to. I haven't read it so don't know all the 'ifs, ands, or buts', but another reason for covering to 0.5*Fs in a patent is some designs acoustically load the driver down to a lower effective Fs, which I gather would allow for a legal loophole around it if all practical/useful variants are to be included.
But then there's the ELF system, so it's really just a matter of what tradeoffs you're willing to accept. When dealing with vented designs though, there's not enough to be gained by going below this point to offset the performance losses IMO, so don't recommend it. As always, YMMV, etc..
====
>Also, is there a way to modify the AlphaTL xls to iteratively determine for the condition Qts > 1 using the solve feature? Do we currently have enough information to do so?
====
I'm sure there is, but between my lack of math skills and Excel programming knowledge, it won't be by me. Sure would be nice to have though.
====
>Will MJK's MathCad calcs give us this optimum?
====
Not unless he adds this feature to the worksheet he released to the public. At least some of his personal worksheets have additional features, so this may be one of them. Then again, I haven't played with his revised 'Classic' TL alignments, which may take this into account.
====
>1. i see and hear the woofer bottoming out / behaving badly (even at low volumes with not very intense music). bass below 25Hz is cut (fixed low-cut on my crossover) and crossover point at around 45 Hz
2. not much volume at all (even though the 100 W x 2 (bridged to 200Watts amp is getting fairly warm )
====
Even a very minor leak is enough to severely limit output, and due to the limited Xmax won't play very low even if properly sealed, with only a ~25W power handling capability down low in half space, so depending on the location, it could be only half this.
Anyway, just doing a sim of a 90" long x 12" diameter A-TL with 1.082lbs/ft^3 of polyfil (~5.88ft^3*1.082 = ~6.362 lbs total) yields a ~IB response to ~21Hz with a ~1dB dip centered around ~105Hz, so I wouldn't go any longer since it will just increase the depth/BW of it, but instead shorter if more gain in desired.
Bumping it up to the reciprocal of minimum Fb, or 1.414*Fb = ~61Hz and increasing stuffing 25% to ~1.3525 lbs/ft^3 to offset it a bit, then I get a nice ~2dB bump in the response centered around 79Hz with the tradeoff being a quicker rolloff below Fs, a good plan IMO considering the limited Xmax/XO point.
Then again, am I misunderstanding the BW this is being used for? I mean "....bass below 25Hz is cut (fixed low-cut on my crossover) and crossover point at around 45 Hz" could mean that this is its BW. If so, then an ELF sub is the way to go, though you'll need several drivers to get any real output.
GM
====
Look at those two points on a driver's free air impedance curve and think about what a cab's primary function is, damping Fs, and it's secondary function, increasing gain above Fs.
Understand that patents have nothing to do with what's technically correct, but are intended to 'lock out' anyone from offering anything remotely close to what they might ultimately market, not to mention obfuscate as much as legally possible to keep folks from figuring out what they're really up to. I haven't read it so don't know all the 'ifs, ands, or buts', but another reason for covering to 0.5*Fs in a patent is some designs acoustically load the driver down to a lower effective Fs, which I gather would allow for a legal loophole around it if all practical/useful variants are to be included.
But then there's the ELF system, so it's really just a matter of what tradeoffs you're willing to accept. When dealing with vented designs though, there's not enough to be gained by going below this point to offset the performance losses IMO, so don't recommend it. As always, YMMV, etc..
====
>Also, is there a way to modify the AlphaTL xls to iteratively determine for the condition Qts > 1 using the solve feature? Do we currently have enough information to do so?
====
I'm sure there is, but between my lack of math skills and Excel programming knowledge, it won't be by me. Sure would be nice to have though.
====
>Will MJK's MathCad calcs give us this optimum?
====
Not unless he adds this feature to the worksheet he released to the public. At least some of his personal worksheets have additional features, so this may be one of them. Then again, I haven't played with his revised 'Classic' TL alignments, which may take this into account.
====
>1. i see and hear the woofer bottoming out / behaving badly (even at low volumes with not very intense music). bass below 25Hz is cut (fixed low-cut on my crossover) and crossover point at around 45 Hz
2. not much volume at all (even though the 100 W x 2 (bridged to 200Watts amp is getting fairly warm )
====
Even a very minor leak is enough to severely limit output, and due to the limited Xmax won't play very low even if properly sealed, with only a ~25W power handling capability down low in half space, so depending on the location, it could be only half this.
Anyway, just doing a sim of a 90" long x 12" diameter A-TL with 1.082lbs/ft^3 of polyfil (~5.88ft^3*1.082 = ~6.362 lbs total) yields a ~IB response to ~21Hz with a ~1dB dip centered around ~105Hz, so I wouldn't go any longer since it will just increase the depth/BW of it, but instead shorter if more gain in desired.
Bumping it up to the reciprocal of minimum Fb, or 1.414*Fb = ~61Hz and increasing stuffing 25% to ~1.3525 lbs/ft^3 to offset it a bit, then I get a nice ~2dB bump in the response centered around 79Hz with the tradeoff being a quicker rolloff below Fs, a good plan IMO considering the limited Xmax/XO point.
Then again, am I misunderstanding the BW this is being used for? I mean "....bass below 25Hz is cut (fixed low-cut on my crossover) and crossover point at around 45 Hz" could mean that this is its BW. If so, then an ELF sub is the way to go, though you'll need several drivers to get any real output.
GM
GM said:
I limited sub 25 Hz based upon an earlier suggestion in this thread (paulspencer, i think) , .. but no difference even if i turn off the cut., .. realistically, i don't need this tube to work any higher than 40 - 50Hz as my mains can take it from there
i'll seal the baffle in later today or tomorrow and report on progress
considering xmax limitations, .. i should have an adire shiva in next week to address that issue
should be interesting to see what happens if i ever plug my dayton MTM TLs in this system (cabs done 6 months ago, .. too lazy to buy the drivers and build the crossover )
thanks, vin
GM:
AlphaTL calcs an fb of 36HZ at 90" using polyfil. I believe Vin wants to go much lower than that and is willing to replace the driver if necessary (to an Adire Shiva) to do so -- hence my recommendation of going to 11' (25HZ).
Am I missing something here?
Vin:
Nice pics and I love your Maggies!
AlphaTL calcs an fb of 36HZ at 90" using polyfil. I believe Vin wants to go much lower than that and is willing to replace the driver if necessary (to an Adire Shiva) to do so -- hence my recommendation of going to 11' (25HZ).
Am I missing something here?
Vin:
Nice pics and I love your Maggies!
>I limited sub 25 Hz based upon an earlier suggestion in this thread (paulspencer, i think) , .. but no difference even if i turn off the cut., .. realistically, i don't need this tube to work any higher than 40 - 50Hz as my mains can take it from there
====
In this case, add the extra length and only stuff it with ~0.2 lbs/ft^3, or however little you can get by with before it begins peaking at Fb and the first null around 95Hz. If the sim is accurate, it should yield a rising response at >89dB/2.83V/m sensitivity above 25Hz in half space, rolling off at ~24dB/octave below ~20Hz to cross the IB response around 15Hz. If stuck in a well constructed/damped corner, it theoretically will peak out around 100dB/m before going non-linear.
====
>AlphaTL calcs an fb of 36HZ at 90" using polyfil. I believe Vin wants to go much lower than that and is willing to replace the driver if necessary (to an Adire Shiva) to do so -- hence my recommendation of going to 11' (25HZ).
Am I missing something here?
====
Yes, and no. In retrospect I guess I should have labeled it a 'TL' in lieu of 'A-TL' since I just used the A-TL spreadsheet to get a starting point for stuffing density, then plugged it and Vin's tube dims into MJK's TL worksheet. Also, if you do a sim, you'll see that the high stuffing density causes the response to extend somewhat below Fb before finally rolling off >12dB/octave.
Anyway, now that I understand what the app is it's all moot, so the extra length and much less stuffing is the way to go since it's to be used only below its 3rd harmonic.
GM
====
In this case, add the extra length and only stuff it with ~0.2 lbs/ft^3, or however little you can get by with before it begins peaking at Fb and the first null around 95Hz. If the sim is accurate, it should yield a rising response at >89dB/2.83V/m sensitivity above 25Hz in half space, rolling off at ~24dB/octave below ~20Hz to cross the IB response around 15Hz. If stuck in a well constructed/damped corner, it theoretically will peak out around 100dB/m before going non-linear.
====
>AlphaTL calcs an fb of 36HZ at 90" using polyfil. I believe Vin wants to go much lower than that and is willing to replace the driver if necessary (to an Adire Shiva) to do so -- hence my recommendation of going to 11' (25HZ).
Am I missing something here?
====
Yes, and no. In retrospect I guess I should have labeled it a 'TL' in lieu of 'A-TL' since I just used the A-TL spreadsheet to get a starting point for stuffing density, then plugged it and Vin's tube dims into MJK's TL worksheet. Also, if you do a sim, you'll see that the high stuffing density causes the response to extend somewhat below Fb before finally rolling off >12dB/octave.
Anyway, now that I understand what the app is it's all moot, so the extra length and much less stuffing is the way to go since it's to be used only below its 3rd harmonic.
GM
progress so far
baffle painted and set up "flexy style" (will allow me to later on optimize distance between driver and bottom plate)
baffle mated to tube with liquid nails and sealed with silicone sealant
attached driver.
tube still at 7 ft 8" (want to see how things work out with the shiva due to come in next monday)
see attached pix.
results
..............................................................................................
tube was booming badly when empty
for a quick test stuffed about 5 lb of stuffing in the tube, ..much better. the seal seems to have worked wonders on tube performance, .. the woofer is no longer misbehaving, . when i set this up permanently, i will tease out the polyfill better
subjectively, .. fairly good, though nothing really low, .. i'm hoping for good things with the shiva and when i (possibly) extend the length of the sub by another 4 ft for a total of 11.5 ft.
need to hide this project in progress for the next few days, .. have some old aunts visiting for the weekend and don't wished to be scandalized by this monstrosity before i beautify it
baffle painted and set up "flexy style" (will allow me to later on optimize distance between driver and bottom plate)
baffle mated to tube with liquid nails and sealed with silicone sealant
attached driver.
tube still at 7 ft 8" (want to see how things work out with the shiva due to come in next monday)
see attached pix.
results
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tube was booming badly when empty
for a quick test stuffed about 5 lb of stuffing in the tube, ..much better. the seal seems to have worked wonders on tube performance, .. the woofer is no longer misbehaving, . when i set this up permanently, i will tease out the polyfill better
subjectively, .. fairly good, though nothing really low, .. i'm hoping for good things with the shiva and when i (possibly) extend the length of the sub by another 4 ft for a total of 11.5 ft.
need to hide this project in progress for the next few days, .. have some old aunts visiting for the weekend and don't wished to be scandalized by this monstrosity before i beautify it
Attachments
You have lots of options:
1. For more bass (and SPL) at your current length you can go ML TL by capping off the open end and adding a port (one of GM's favourites, I believe).
2. Otherwise, if you want to get to 25HZ and below you need to add the extra 4' length -- the Shiva sims almost exactly the same as your current driver (as I am sure you already know).
3. With the extra length you'll also have the option to go aperiodic (IB) by stuffing the end of the tube and still have reasonable bass (you may find this to be the best 'fit' with the maggies.
4. And guess what? For another ten bucks you can attach a 4' tube to the other end and have a Bose Cannon!
So many options ... so little time
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