Sealed or TL

[time]

I have a pair of Lab 12 Generation II Drivers I bought a couple years ago to try in TL subs. seperate enclosures. I'm planning on a pair of Bash 500 amps to drive them.

I have built TL subs as a learning project with inexpensive(okay,cheap) drivers and was very impressed with the results given the limitation of the drivers. Basically I'm second guessing putting these in a TL. They really don't need enclosure help to play the tight clean bass I'm looking for and the Bash amps have plenty of power. But, I'm having a hard time dropping the project and going sealed. Call it the fun facter.

The numbers I ran for a TL gives me a 80" long pipe, 10' diameter(if round), resulting in 3.636 cu ft of internal volume. That is the volume I believe I'd use in a sealed system.

My wrist is broken at present so I can't draw to design the enclosure for awhile(Any folds I may use, ect) so I thought I'd get some opinions.

Oh, listening room is about 15'X25'. No size restrictions. Ugly is even okay. In other words, the wife will not provide any input.

[Pete Schumacher ®]

I have a pair of Lab 12 Generation II Drivers I bought a couple years ago to try in TL subs. seperate enclosures. I'm planning on a pair of Bash 500 amps to drive them.

I have built TL subs as a learning project with inexpensive(okay,cheap) drivers and was very impressed with the results given the limitation of the drivers. Basically I'm second guessing putting these in a TL. They really don't need enclosure help to play the tight clean bass I'm looking for and the Bash amps have plenty of power. But, I'm having a hard time dropping the project and going sealed. Call it the fun facter.

The numbers I ran for a TL gives me a 80" long pipe, 10' diameter(if round), resulting in 3.636 cu ft of internal volume. That is the volume I believe I'd use in a sealed system.

My wrist is broken at present so I can't draw to design the enclosure for awhile(Any folds I may use, ect) so I thought I'd get some opinions.

Oh, listening room is about 15'X25'. No size restrictions. Ugly is even okay. In other words, the wife will not provide any input.

A TL will work just fine with the LAB12. However, a simple, straight line isn't what you really want. You really want a tapered transmission line, with the first half of the line stuffed with fiber, and tapering at least 10:1 ratio of the start area of the line vs. the terminus end.

[billfitzmaurice]

The numbers I ran for a TL gives me a 80" long pipe, 10' diameter(if round), resulting in 3.636 cu ft of internal volume. That is the volume I believe I'd use in a sealed system.

Depending on topology an 80" pipe is good for an Fp in the vicinity of 45 Hz. That's roughly the same as F3 in 1.9 cu ft sealed with a .7 Q. In 3.5 cu ft vented the Lab 12 is good for a 22Hz F3, so I'd go sealed for music, vented for HT. TL doesn't show me any advantages with this driver using less than a 10 foot pipe.

[Pete Schumacher ®]

Depending on topology an 80" pipe is good for an Fp in the vicinity of 45 Hz. That's roughly the same as F3 in 1.9 cu ft sealed with a .7 Q. In 3.5 cu ft vented the Lab 12 is good for a 22Hz F3, so I'd go sealed for music, vented for HT. TL doesn't show me any advantages with this driver using less than a 10 foot pipe.

I can guarantee that if it models well in 3.5 cubic foot vented enclosure, then it will model very well in a tapered (15:1) TL of perhaps 15% more overall volume.

[time]

I can guarantee that if it models well in 3.5 cubic foot vented enclosure, then it will model very well in a tapered (15:1) TL of perhaps 15% more overall volume.

I did taper my first project and am not sure why I was not planning on tapering this one. Some thing I read somewhere but............ I do prefer tapering, don't know what I was thinking.

I should have mentioned that I will be effectively lengthening the line with stuffing. 80" is short but stuffing it will get me where I want to be. It will also increase the volume, a balancing act for sure.

The subs will be used for music.

I found out this morning that I have another six weeks in a cast, so I can take my time thinking this out.

[Pete Schumacher ®]

I did taper my first project and am not sure why I was not planning on tapering this one. Some thing I read somewhere but............ I do prefer tapering, don't know what I was thinking.

I should have mentioned that I will be effectively lengthening the line with stuffing. 80" is short but stuffing it will get me where I want to be. It will also increase the volume, a balancing act for sure.

The subs will be used for music.

I found out this morning that I have another six weeks in a cast, so I can take my time thinking this out.

Have you seen Martin King's quarter wave website? http://www.quarter-wave.com/

Check out this spreadsheet:
http://www.quarter-wave.com/TLs/Alig...tor_3_3_09.xls

I plugged in the 15:1 ratio for the line and used PE's data for the LAB12.

Line length is 83.85"
Starting area (closed end) 137.12 sq. in.
terminus area (open end) 9.14 sq. in.

Mount driver 20% along the line from the closed end. Stuff the 1st half of the line length with about 1 pound per cubic foot.

Line volume = 3.54 cubic feet . . .

Go figure.

[diy speaker guy]

A 9 sq inch terminus for a high(ish) excursion 12 inch subwoofer application? I didn't model it but it sounds way way way too small to me. What's the terminus air velocity at xmax? Just off the top of my head, I'd imagine audible chuffing with possibly as little as 10 watts.

[Deward Hastings]

A 9 sq inch terminus

Sure sounds more like a port loaded reflex box than it does like a "transmission line".

[Pete Schumacher ®]

A 9 sq inch terminus for a high(ish) excursion 12 inch subwoofer application? I didn't model it but it sounds way way way too small to me. What's the terminus air velocity at xmax? Just off the top of my head, I'd imagine audible chuffing with possibly as little as 10 watts.

That's between a 3" diameter and 4" diameter port area.

The line can simply be sized up slightly to offer a slightly larger terminus if you feel that's a bit shy, or you can simply open up the terminus a bit more, at the cost of more passband ripple, which may not be a concern depending on where you cross.

Remember, this is not some large slug of air moving in a port. Calculate the size of a port required to tune 3.5 cubic feet to 22Hz, and then remember that there is no "port" in the tapered TL, but a uniformly changing line gradually reducing to that size.

[Pete Schumacher ®]

Sure sounds more like a port loaded reflex box than it does like a "transmission line".

Then you have no concept of a tapered transmission line.

[time]

Yes, I have read all of Martin Kings stuff.

I had not seen that spread sheet though. Kings own spreadsheet was difficult to use. This one is much more freindly for a newbie like me.

Thanks.

I'm surprized the numbers are so close to mine without the taper. Gives me a bit of a confidence boost.

[Pete Schumacher ®]

Yes, I have read all of Martin Kings stuff.

I had not seen that spread sheet though. Kings own spreadsheet was difficult to use. This one is much more freindly for a newbie like me.

Thanks.

I'm surprized the numbers are so close to mine without the taper. Gives me a bit of a confidence boost.

If 15:1 taper seems a bit steep, then just reduce to around 10:1. The line just gets a little longer and the box slightly larger.

[Deward Hastings]

Then you have no concept of a tapered transmission line.

Or perhaps you just want to appropriate the mythos associated with the name "transmission line" to variants of the "quarter wave" resonant enclosure designs, where I see significant enough difference to warrant calling different things by different names.

[time]

If 15:1 taper seems a bit steep, then just reduce to around 10:1. The line just gets a little longer and the box slightly larger.

Okay, I'll work with the spreadsheet and see what I come up with.

Do you think it would chuff at 9 sq inches? I know I get allot of air out of my other build with considerably larger terminus. But its a 12' line and a low excursion driver.

[martin]

Remember, this is not some large slug of air moving in a port. Calculate the size of a port required to tune 3.5 cubic feet to 22Hz, and then remember that there is no "port" in the tapered TL, but a uniformly changing line gradually reducing to that size.

I think that is a key observation. I have often wondered if port chuffing was really sound wave reflections in the port tube due to the sudden changes in acoustic impedance at each end of the tube. I wonder if the constant taper to a small opening would remove that concern. I know Paul K and e-mailed each other about this when he was considering building a severly tapered TL with a small terminus, I believe his design worked just fine.

[Pete Schumacher ®]

Or perhaps you just want to appropriate the mythos associated with the name "transmission line" to variants of the "quarter wave" resonant enclosure designs, where I see significant enough difference to warrant calling different things by different names.

Non tapered TLs and tapered TLs both work on the same principle with the notable improvement in passband response offered by a tapered TL over it's non tapered sibling.

I'm not applying any "mythos" of TL, as there really isn't one to me. Just another way of augmenting bass using the enclosure. It's just that for low tuned enclosures, tapered TLs are far easier to implement vs vented counterparts due to port dimensions getting ridiculous.

You tell me then, what's the difference between the operation of a tapered and non-tapered TL? Please, I'd like to know. You don't seem to be able to differentiate between a tapered TL and a ported box, so let's see you expound on the differences between tapered TL and non tapered.

If you don't think a tapered TL is a TL, please explain why.

[Pete Schumacher ®]

I think that is a key observation. I have often wondered if port chuffing was really sound wave reflections in the port tube due to the sudden changes in acoustic impedance at each end of the tube. I wonder if the constant taper to a small opening would remove that concern. I know Paul K and e-mailed each other about this when he was considering building a severly tapered TL with a small terminus, I believe his design worked just fine.

Dan Neubecker's HOSS is one example of a significant taper and small terminus and no audible problems. I do believe Paul modeled that enclosure.

I'll be doing a 3 cubic foot tapered TL with a slot terminus for a pair of RSS210HF-4. Overall taper is right around 15:1. I'm looking forward to hearing the results.

[Pete Schumacher ®]

Okay, I'll work with the spreadsheet and see what I come up with.

Do you think it would chuff at 9 sq inches? I know I get allot of air out of my other build with considerably larger terminus. But its a 12' line and a low excursion driver.

9 inches may be on the edge. And since you're not using this beyond sub frequencies for the most part, response ripple up high isn't a concern, so going with a shallower taper is probably just fine. Pushing it to 12 sq inches has the same area as a 4" port, but one that is very short.

[diy speaker guy]

I think that is a key observation. I have often wondered if port chuffing was really sound wave reflections in the port tube due to the sudden changes in acoustic impedance at each end of the tube. I wonder if the constant taper to a small opening would remove that concern. I know Paul K and e-mailed each other about this when he was considering building a severly tapered TL with a small terminus, I believe his design worked just fine.

If this turns out to be true it would be a big deal and this definitely should be investigated further. I'd certainly be pleased if there was a bit more flexibility than you would see in a ported alignment. I'll keep an open mind on this one and hope to see somebody do some real research. Until then though, even though I don't have anything planned at the moment I'll still be using large ports in my own projects just in case.

[time]

Okay,

Line lenght 91.17"
closed end 127.97 sq inch
open end 12 sq inch

If I had the ability to test I would build a 9 sq inch version to get some answers. But I would prove little to this crowd if all I could say is "it doesn't chuff". So.........................................

I appreciate everyones input.