Thanks for doing the calculation for me. Just shows to go you that my math skills must really suck! 🙂 Anyway this is great news because 118.13% would indeed fit between the 100% to 125% rule that is mentioned here http://www.teresaudio.com/haven/subs/subs.html but still less than 20% to 25% as Jon Risch recommends here. http://www.t-linespeakers.org/design/classic.html In other words, perfect.
That's good news for me on so many levels. The current plan is to get a length of 16" Sonotube and fit it to a box for both drivers in a push-pull out of phase arrangement. The length will be tuned for around 30Hz like you suggested (probably 31.5Hz which is a nice happy medium between 21 and 42Hz).
Unless I've made a terrible oversight, it looks like it's a go for two 12"s in a push-pull out of phase configuration. It'll consist of one pre-fabbed 1ft³ internal volume encloser to house the drivers (because I'm trying to avoid/can't really do any woodworking) with two ~11" holes on opposite ends for driver mounting and one appropriately sized hole on the top to connect the tube (hey, I can cut holes in stuff, but that's about it 🙂 ). One 16" diameter Sonotube and an MDF or particle board spacer will be used to join the tube to the box with sealant, screws etc.
12" woofer Fs 21 Hz × 1.5 = 31.5 Hz optimum TL tuning length. (thanks GM)
For TL length, I'm using this calculation:
1128 ÷ 31.5 Hz = 35.81 × .25 = 8.95' × 12 = 107.428" (almost exactly 9 feet)
For actual tube length, merely subtract one cubic foot.
107.428" - 12(enclosure) = 95.425" (or ÷ 12 = 7.95' = almost exactly 8 feet)
Once constructed, this will give an unstuffed tuning of 31.5 Hz, and with stuffing, should be great down past the woofer's Fs of 21Hz. The CSA of the 16" tube is within the tolerances for both drivers' Sd as specified by people with more TL experience than me, so the only thing left is to acquire the materials and get to work. 😀
Edit: I'll see if the enclosure will support cutting a hole large enough to facilitate installing the backwards-facing driver through the tube hole at the top. That makes more sense than mounting it like an isobaric on the thin perpendicular outer edge. The internal volume will be reduced slightly, but I doubt it matters.
12" woofer Fs 21 Hz × 1.5 = 31.5 Hz optimum TL tuning length. (thanks GM)
For TL length, I'm using this calculation:
1128 ÷ 31.5 Hz = 35.81 × .25 = 8.95' × 12 = 107.428" (almost exactly 9 feet)
For actual tube length, merely subtract one cubic foot.
107.428" - 12(enclosure) = 95.425" (or ÷ 12 = 7.95' = almost exactly 8 feet)
Once constructed, this will give an unstuffed tuning of 31.5 Hz, and with stuffing, should be great down past the woofer's Fs of 21Hz. The CSA of the 16" tube is within the tolerances for both drivers' Sd as specified by people with more TL experience than me, so the only thing left is to acquire the materials and get to work. 😀
Edit: I'll see if the enclosure will support cutting a hole large enough to facilitate installing the backwards-facing driver through the tube hole at the top. That makes more sense than mounting it like an isobaric on the thin perpendicular outer edge. The internal volume will be reduced slightly, but I doubt it matters.
GM, I'm going to bother you just once more. Before I commit any money toward this project, how well do you think a 9' TL (tuned to around 30Hz) with a push-pull set of 40-1350 drivers will work with a 1 cubic foot box connected to a 16" diameter, 8 foot long Sonotube? Do you know of anyone who's ever used these drivers in anything like this before? Thankyou.
Man, if only I would have known about transmission lines back in '90 when I first got these woofers. I would surely have made one instead of those two failed attempts at sealed boxes (I didn't have a clue about internal volumes vs Vas and Fb/F3 type stuff back then, but had plenty of time to experiment). These woofers have gone unused for a decade. At least now I have a little bit of knowledge and hopefully the TL described above will give these woofers a proper alignment for once.
Man, if only I would have known about transmission lines back in '90 when I first got these woofers. I would surely have made one instead of those two failed attempts at sealed boxes (I didn't have a clue about internal volumes vs Vas and Fb/F3 type stuff back then, but had plenty of time to experiment). These woofers have gone unused for a decade. At least now I have a little bit of knowledge and hopefully the TL described above will give these woofers a proper alignment for once.
I'll say this for GM....
the design is fine, you have learned enough to get you started.... the rest will come with your experience in doing it yourself. Build it.... You wont be dissapointed
the design is fine, you have learned enough to get you started.... the rest will come with your experience in doing it yourself. Build it.... You wont be dissapointed
Greets!
====
>Awesome! Thanks for spending lots of time helping me. You've answered more questions than you've raised, and that's a good thing.
====
You're welcome, but judging from scanning your later posts, I don't appear to be getting through to you on some key design considerations.
====
>My uncle did something like that in the late '80s or early '90s with a 4" driver and a short length of tube in front and a long length in back. He said the resonances of the tube were a little strange at first, but then got used to it. It appearantly sounded very amazing for its size. I think the driver was in the first 1/3 or 1/4 of the total length. It was just straight PVC pipe if I recall correctly. I don't think he stuffed it with anything.
====
Sounds like a B*** Wave Cannon 'clone' with 1/4-3/4 WL pipes. With this design, the driver ideally needs to have a 0.3-0.4 Qts, so this would be an option if you ever wanted to try it. The total pipe length needs to be ~1/4WL of the driver's Fs, so 13560/4/21 = ~161", with one piece being 161/4 = ~40".
The patent says that ideally the pipe's CSA should be 50% of Sd for a 2:1 compression ratio, but most folks just use a pipe closest to the driver size, like 12" dia. for a 12" driver, etc. and are pleased with the results.
Their biggest problem is supporting a long straight pipe since they usually wind up having to suspend it overhead to fit in the room, so building a folded labryinth out of no-void plywood is the 'Hot Ticket'.
====
>Is there any way to know if a 14" or 16" tube will have enough volume for a Vb of 5.4ft³ if it were compared to a sealed box? The Vas of the speaker being 13.3ft³ and the F3 at 39.08Hz equals a Qtc of .707 (which is what I'd like if possible).
====
?? Vb of a cylinder = (CSA*L). Divide this by 1728 to get (ft^3) if the answer is in (in^3).
You're comparing apples n' oranges though. 5.4 ft^3 won't be nearly enough Vb for an optimized TL. Anyway, if you want this alignment, then go sealed as it will protect the driver much better since the pipe will have to be tuned to ~39*1.4142 = ~55 Hz, kind of a waste of a low Fs driver, and even then the net Vb needs to be ~15ft^3 for one driver. When I reduce it to 5.4ft^3, it requires a lot more stuffing to approximate a 0.7 Qtc sealed.
====
>To get the ÷ I used the character map. The alt code is alt+0247. × is alt+0215 (I'd been using the letter x).
====
Cool! Thanks! I had to do a search since I'd never noticed it in the 'System Tools' folder. How pathetic is that? Anyway, what's an 'alt code'? In the character map window all I do is select the symbol, click 'copy', then paste it into the doc: ÷
OK, I had the window a bit below the taskbar, now I see that when I highlight the symbol it shows the code at the bottom........ duh!
GM
====
>Awesome! Thanks for spending lots of time helping me. You've answered more questions than you've raised, and that's a good thing.
====
You're welcome, but judging from scanning your later posts, I don't appear to be getting through to you on some key design considerations.
====
>My uncle did something like that in the late '80s or early '90s with a 4" driver and a short length of tube in front and a long length in back. He said the resonances of the tube were a little strange at first, but then got used to it. It appearantly sounded very amazing for its size. I think the driver was in the first 1/3 or 1/4 of the total length. It was just straight PVC pipe if I recall correctly. I don't think he stuffed it with anything.
====
Sounds like a B*** Wave Cannon 'clone' with 1/4-3/4 WL pipes. With this design, the driver ideally needs to have a 0.3-0.4 Qts, so this would be an option if you ever wanted to try it. The total pipe length needs to be ~1/4WL of the driver's Fs, so 13560/4/21 = ~161", with one piece being 161/4 = ~40".
The patent says that ideally the pipe's CSA should be 50% of Sd for a 2:1 compression ratio, but most folks just use a pipe closest to the driver size, like 12" dia. for a 12" driver, etc. and are pleased with the results.
Their biggest problem is supporting a long straight pipe since they usually wind up having to suspend it overhead to fit in the room, so building a folded labryinth out of no-void plywood is the 'Hot Ticket'.
====
>Is there any way to know if a 14" or 16" tube will have enough volume for a Vb of 5.4ft³ if it were compared to a sealed box? The Vas of the speaker being 13.3ft³ and the F3 at 39.08Hz equals a Qtc of .707 (which is what I'd like if possible).
====
?? Vb of a cylinder = (CSA*L). Divide this by 1728 to get (ft^3) if the answer is in (in^3).
You're comparing apples n' oranges though. 5.4 ft^3 won't be nearly enough Vb for an optimized TL. Anyway, if you want this alignment, then go sealed as it will protect the driver much better since the pipe will have to be tuned to ~39*1.4142 = ~55 Hz, kind of a waste of a low Fs driver, and even then the net Vb needs to be ~15ft^3 for one driver. When I reduce it to 5.4ft^3, it requires a lot more stuffing to approximate a 0.7 Qtc sealed.
====
>To get the ÷ I used the character map. The alt code is alt+0247. × is alt+0215 (I'd been using the letter x).
====
Cool! Thanks! I had to do a search since I'd never noticed it in the 'System Tools' folder. How pathetic is that? Anyway, what's an 'alt code'? In the character map window all I do is select the symbol, click 'copy', then paste it into the doc: ÷
OK, I had the window a bit below the taskbar, now I see that when I highlight the symbol it shows the code at the bottom........ duh!
GM
Greets!
====
>Thanks for doing the calculation for me.
Anyway this is great news because 118.13% would indeed fit between the 100% to 125% rule that is mentioned here http://www.teresaudio.com/haven/subs/subs.html but still less than 20% to 25% as Jon Risch recommends.............
The current plan is to get a length of 16" Sonotube and fit it to a box for both drivers in a push-pull out of phase arrangement. The length will be tuned for around 30Hz like you suggested (probably 31.5Hz which is a nice happy medium between 21 and 42Hz).
====
You're welcome! I answered your Q on the percentage problem, but that's not to imply I agree with using JR's rule of thumb (ROT) for determining CSA, so how many times do I have to say that basing it on Sd isn't the 'Hot Ticket' for best performance? Your driver's Vas is way too high for two of them driving only a single 16" dia. pipe. Makes for a ~billiard table flat impedance though. To say the bass will be 'tight' is a gross understatement. At minimum you'll need a 16" dia. pipe/driver to get it up to ~an IB response down to ~30 Hz before it starts rolling off at a faster rate (~2.363x Sd).
You really need to model these in MathCad to see the theoretical results of your actions.
GM
====
>Thanks for doing the calculation for me.
Anyway this is great news because 118.13% would indeed fit between the 100% to 125% rule that is mentioned here http://www.teresaudio.com/haven/subs/subs.html but still less than 20% to 25% as Jon Risch recommends.............
The current plan is to get a length of 16" Sonotube and fit it to a box for both drivers in a push-pull out of phase arrangement. The length will be tuned for around 30Hz like you suggested (probably 31.5Hz which is a nice happy medium between 21 and 42Hz).
====
You're welcome! I answered your Q on the percentage problem, but that's not to imply I agree with using JR's rule of thumb (ROT) for determining CSA, so how many times do I have to say that basing it on Sd isn't the 'Hot Ticket' for best performance? Your driver's Vas is way too high for two of them driving only a single 16" dia. pipe. Makes for a ~billiard table flat impedance though. To say the bass will be 'tight' is a gross understatement. At minimum you'll need a 16" dia. pipe/driver to get it up to ~an IB response down to ~30 Hz before it starts rolling off at a faster rate (~2.363x Sd).
You really need to model these in MathCad to see the theoretical results of your actions.
GM
Greets!
====
>Unless I've made a terrible oversight.......
====
See my previous post.
====
>12" woofer Fs 21 Hz × 1.5 = 31.5 Hz optimum TL tuning length. (thanks GM)
====
That's not what I posted.
====
>For TL length, I'm using this calculation:
1128 ÷ 31.5 Hz = 35.81 × .25 = 8.95' × 12 = 107.428" (almost exactly 9 feet)
For actual tube length, merely subtract one cubic foot.
107.428" - 12(enclosure) = 95.425" (or ÷ 12 = 7.95' = almost exactly 8 feet)
====
Subtract 1 ft.......
====
>Once constructed, this will give an unstuffed tuning of 31.5 Hz, and with stuffing, should be great down past the woofer's Fs of 21Hz. The CSA of the 16" tube is within the tolerances for both drivers' Sd as specified by people with more TL experience than me, so the only thing left is to acquire the materials and get to work.
====
Not so IMO! See my previous responses!
GM
====
>Unless I've made a terrible oversight.......
====
See my previous post.
====
>12" woofer Fs 21 Hz × 1.5 = 31.5 Hz optimum TL tuning length. (thanks GM)
====
That's not what I posted.
====
>For TL length, I'm using this calculation:
1128 ÷ 31.5 Hz = 35.81 × .25 = 8.95' × 12 = 107.428" (almost exactly 9 feet)
For actual tube length, merely subtract one cubic foot.
107.428" - 12(enclosure) = 95.425" (or ÷ 12 = 7.95' = almost exactly 8 feet)
====
Subtract 1 ft.......
====
>Once constructed, this will give an unstuffed tuning of 31.5 Hz, and with stuffing, should be great down past the woofer's Fs of 21Hz. The CSA of the 16" tube is within the tolerances for both drivers' Sd as specified by people with more TL experience than me, so the only thing left is to acquire the materials and get to work.
====
Not so IMO! See my previous responses!
GM
Greets!
====
>I'll say this for GM....
the design is fine, you have learned enough to get you started.... the rest will come with your experience in doing it yourself. Build it.... You wont be dissapointed
====
Speak for yourself! Per my previous comments I flat don't agree! As always though YMMV.
GM
====
>I'll say this for GM....
the design is fine, you have learned enough to get you started.... the rest will come with your experience in doing it yourself. Build it.... You wont be dissapointed
====
Speak for yourself! Per my previous comments I flat don't agree! As always though YMMV.
GM
An alt code is where you hold down the Alt key and type four numbers, then lift the alt key.
I keep confusing myself reading conflicting information from several sources. Mainly those tube TL pages. To be honest, I'm very glad that you have been putting up with me during my growing pains, as it were.
I'll check out that MathCad program.
So you said 29 or 30 Hz and not 31.5Hz. 😀 The updated plan so far is to get two 9 foot long 16" diameter Sonotubes for 29 or 30Hz and a set of 12" to 16" particle board or MDF adapters.
I keep confusing myself reading conflicting information from several sources. Mainly those tube TL pages. To be honest, I'm very glad that you have been putting up with me during my growing pains, as it were.
A single driver per tube will actually cost less than the dual drivers in a box idea. That sounds a lot better for a first time project. I just hope it literally sounds better than when they were in incorrectly sized enclosures.
I'll check out that MathCad program.
So you said 29 or 30 Hz and not 31.5Hz. 😀 The updated plan so far is to get two 9 foot long 16" diameter Sonotubes for 29 or 30Hz and a set of 12" to 16" particle board or MDF adapters.
I checked out the MathCad program but I'm having trouble using it. I suck at software as well as math. 🙁
How about this idea. To keep it simple (because I'm stupid), could you tell me if one 16" diameter 9 foot long tube will work with one 40-1350 driver? If so, I'll get two tubes and call it a day. Thank you.
How about this idea. To keep it simple (because I'm stupid), could you tell me if one 16" diameter 9 foot long tube will work with one 40-1350 driver? If so, I'll get two tubes and call it a day. Thank you.
According to Rick Shultz' Alpha TL spreadsheet (which GM kindly posted on this forum), your driver requires a 20" diameter tube 9' long.
With 1/3 lbs of fibreglass stuffing per cubic foot of tube you will get a tuning of 26HZ.
BTW, read GM's posts carefully. They are of great value...
With 1/3 lbs of fibreglass stuffing per cubic foot of tube you will get a tuning of 26HZ.
BTW, read GM's posts carefully. They are of great value...
GM:
Actually, the short pipe is 1/3 the length of the long pipe -- 54" in this case (not ~40"). Maybe that's why the one you built sounded like a "boom-tube" (as you put it).😀
Actually, the short pipe is 1/3 the length of the long pipe -- 54" in this case (not ~40"). Maybe that's why the one you built sounded like a "boom-tube" (as you put it).😀
Greets!
?! Actually, ~40" IS 1/3 the length of the long pipe, ergo the long pipe is ~40" x 3 = ~120" + ~40" for the other pipe = ~161", i.e. a 1:3 ratio, not 1/3 the 1/4 WL of Fs you calc'd. Remember, these are 1/4 WL resonators so it's a lot simpler IMO to just divide the total length required by four to find the driver offset point.
Regardless, the difference should only affect BW/gain due to the phase offset, whereas it's the undamped pipe action that makes it a 'boom-tube', like any other underdamped bandbass alignment.
GM
?! Actually, ~40" IS 1/3 the length of the long pipe, ergo the long pipe is ~40" x 3 = ~120" + ~40" for the other pipe = ~161", i.e. a 1:3 ratio, not 1/3 the 1/4 WL of Fs you calc'd. Remember, these are 1/4 WL resonators so it's a lot simpler IMO to just divide the total length required by four to find the driver offset point.
Regardless, the difference should only affect BW/gain due to the phase offset, whereas it's the undamped pipe action that makes it a 'boom-tube', like any other underdamped bandbass alignment.
GM
GM
Not so. The patent actually says that the longer pipe can be tuned to 1/2 the driver's Fs. If the longer pipe is tuned to 20hz, the driver's fs can be as high as 40...
Not so. The patent actually says that the longer pipe can be tuned to 1/2 the driver's Fs. If the longer pipe is tuned to 20hz, the driver's fs can be as high as 40...
Greets!
It's been a long time since I picked the patent apart and don't recall all the particulars, so maybe I'm confusing my experience with what I recall of the patent. Anyway, according to my proof-of-concept notes, for low Fs drivers the total pipe length needs to be 1/4WL of Fs. For higher Fs drivers they can be tuned as low as (0.375*Fs), but you'll probably hit its excursions limits at such a low SPL that in a HI-Fi app you're better off using bass shakers IMO.
Obviously, any combination of 1:3 ratios can be used regardless of the driver's Fs since they are 1/4WL resonators, but for this driver I don't recommend going any lower than 1/4WL total, especially since I seriously doubt Jeff or most other DIYers would make the effort to build a proper 2:1 compression ratio front and rear chamber that's required to properly load the pipes.
As alway though YMMV.
GM
It's been a long time since I picked the patent apart and don't recall all the particulars, so maybe I'm confusing my experience with what I recall of the patent. Anyway, according to my proof-of-concept notes, for low Fs drivers the total pipe length needs to be 1/4WL of Fs. For higher Fs drivers they can be tuned as low as (0.375*Fs), but you'll probably hit its excursions limits at such a low SPL that in a HI-Fi app you're better off using bass shakers IMO.
Obviously, any combination of 1:3 ratios can be used regardless of the driver's Fs since they are 1/4WL resonators, but for this driver I don't recommend going any lower than 1/4WL total, especially since I seriously doubt Jeff or most other DIYers would make the effort to build a proper 2:1 compression ratio front and rear chamber that's required to properly load the pipes.
As alway though YMMV.
GM
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