t-line box?

[bbeljefe]

I'm considering a quarter wave tline for one of my subs. The problem is most of my subs have a low FS and I don't think I have room for a low tune. Why is it bad to tune above the drivers FS?
Subs I currently possess:

15" RE XXX v2 (FS of 19hz, probably not even an option for a tline in a vehicle. Will likely become a H/T sub)

2006/2007 15" FI BL Dual 2 ohm. FS of ~30hz.

2 12" RF Power HX2. FS of 26hz.

15" Mach 5 SPL. FS is high 30's or even low 40's.

Tuning above Fs can cause the driver to unload below Fs. There isn't much acoustical suspension in a t-line to begin with and when you tune high there is even less. I would do the Mach 5 at ~35Hz.

 

[negolien]

Meh I talked to a guy I had doing install work and he quoted me a regular box at $300 just for parts and build labor not any install in the vehicle I was like //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif .

 

[Immacomputer 10+ year member]

Tuning above Fs can cause the driver to unload below Fs. There isn't much acoustical suspension in a t-line to begin with and when you tune high there is even less. I would do the Mach 5 at ~35Hz.

I disagree here as well. You should focus your 1/4 wave length based around the sub's resonance in a sealed enclosure of the equivalent size that you're planning on using. There is PLENTY of pressure build up in a transmission line enclosure as the very nature of a transmission line is to transfer a high pressure area into a high velocity area. Think about how a transmission in a car takes torque and turns it into velocity. A transmission line enclosure works just the same way! My AE av12 had like a 24hz Fs and yet it had beautiful control well below tuning and Fs, even with 1200rms (though around 30hz excursion got a little scary with that kind of power but hey, it was only rated at 500rms to begin with!). I tuned to my line to 35hz because it was about 3 cubic feet total. That sub modeled to have an Fc of around 35hz in a 3ft^3 enclosure. And at 22hz, I had a 3dB peak and minimal excursion (though if you modeled the box as a ported enclosure, as it had a compression chamber, it would have also been tuned to 35hz). Pretty interesting stuff... that box got **** loud, **** low, and ridiculously musical and clean.

So you CAN tune above Fs without an issue but you REALLY need to use Martin J King's alignment tables PDF to calculate your line area. Too much line area and too high of a tuning with give you a ******, peaky, and uncontrolled enclosure. Also, tapping/self loading an enclosure can help reduce enclosure size and add more cone control. Google "tapped horn" or "tapped transmission line enclosure" for more information on that.

I'm not trying to be argumentative -- I just want to clear up some things that I've found to be different in my experiences with transmission lines. I find them interesting, beautiful, efficient, and best of all, low end monsters. Nothing tickles me more than playing low and flat below 30hz, no matter what output levels lol. I also want other people to experience these types of enclosures with their best face so I get bothered when I see inefficient designs or just poorly done (steve meade forum style: Fs/Sd ghettoness) enclosures because they turn people off to the type instead of continuing to play around with them and find new things that work!

 

[snoopysnooper 10+ year member]

im obsessed with tlines, its all i used to run. i have one being built now for 4 sundown sa8s

 

[bbeljefe]

I disagree here as well. You should focus your 1/4 wave length based around the sub's resonance in a sealed enclosure of the equivalent size that you're planning on using. There is PLENTY of pressure build up in a transmission line enclosure as the very nature of a transmission line is to transfer a high pressure area into a high velocity area. Think about how a transmission in a car takes torque and turns it into velocity. A transmission line enclosure works just the same way! My AE av12 had like a 24hz Fs and yet it had beautiful control well below tuning and Fs, even with 1200rms (though around 30hz excursion got a little scary with that kind of power but hey, it was only rated at 500rms to begin with!). I tuned to my line to 35hz because it was about 3 cubic feet total. That sub modeled to have an Fc of around 35hz in a 3ft^3 enclosure. And at 22hz, I had a 3dB peak and minimal excursion (though if you modeled the box as a ported enclosure, as it had a compression chamber, it would have also been tuned to 35hz). Pretty interesting stuff... that box got **** loud, **** low, and ridiculously musical and clean.
So you CAN tune above Fs without an issue but you REALLY need to use Martin J King's alignment tables PDF to calculate your line area. Too much line area and too high of a tuning with give you a ******, peaky, and uncontrolled enclosure. Also, tapping/self loading an enclosure can help reduce enclosure size and add more cone control. Google "tapped horn" or "tapped transmission line enclosure" for more information on that.

I'm not trying to be argumentative -- I just want to clear up some things that I've found to be different in my experiences with transmission lines. I find them interesting, beautiful, efficient, and best of all, low end monsters. Nothing tickles me more than playing low and flat below 30hz, no matter what output levels lol. I also want other people to experience these types of enclosures with their best face so I get bothered when I see inefficient designs or just poorly done (steve meade forum style: Fs/Sd ghettoness) enclosures because they turn people off to the type instead of continuing to play around with them and find new things that work!

That's interesting man. Thanks for the info.

 

[Jroo 10+ year member]

I disagree here as well. You should focus your 1/4 wave length based around the sub's resonance in a sealed enclosure of the equivalent size that you're planning on using. There is PLENTY of pressure build up in a transmission line enclosure as the very nature of a transmission line is to transfer a high pressure area into a high velocity area. Think about how a transmission in a car takes torque and turns it into velocity. A transmission line enclosure works just the same way! My AE av12 had like a 24hz Fs and yet it had beautiful control well below tuning and Fs, even with 1200rms (though around 30hz excursion got a little scary with that kind of power but hey, it was only rated at 500rms to begin with!). I tuned to my line to 35hz because it was about 3 cubic feet total. That sub modeled to have an Fc of around 35hz in a 3ft^3 enclosure. And at 22hz, I had a 3dB peak and minimal excursion (though if you modeled the box as a ported enclosure, as it had a compression chamber, it would have also been tuned to 35hz). Pretty interesting stuff... that box got **** loud, **** low, and ridiculously musical and clean.
So you CAN tune above Fs without an issue but you REALLY need to use Martin J King's alignment tables PDF to calculate your line area. Too much line area and too high of a tuning with give you a ******, peaky, and uncontrolled enclosure. Also, tapping/self loading an enclosure can help reduce enclosure size and add more cone control. Google "tapped horn" or "tapped transmission line enclosure" for more information on that.

I'm not trying to be argumentative -- I just want to clear up some things that I've found to be different in my experiences with transmission lines. I find them interesting, beautiful, efficient, and best of all, low end monsters. Nothing tickles me more than playing low and flat below 30hz, no matter what output levels lol. I also want other people to experience these types of enclosures with their best face so I get bothered when I see inefficient designs or just poorly done (steve meade forum style: Fs/Sd ghettoness) enclosures because they turn people off to the type instead of continuing to play around with them and find new things that work!

Certainly said some things that are new to me or I havent heard anyone say. I will say the tuning above Fs I was told is a huge no no, but seems to work for you. Im going to go look at the Martin J alignment table and see how much difference it gives me and some of the stuff I have done on paper. I would say 90% of the lines I see on forums are following the steve meade formula. There are a few guys that seem to have some magic T line juice and do some funky things with compression chambers, increasing and decreasing line size, but the average joes seem to follow the Fs/Sd model.

 

[Jroo 10+ year member]

im obsessed with tlines, its all i used to run. i have one being built now for 4 sundown sa8s

How big is a line for 4 SA8s? I guess that works because you drive a caravan.

 

[Immacomputer 10+ year member]

Certainly said some things that are new to me or I havent heard anyone say. I will say the tuning above Fs I was told is a huge no no, but seems to work for you. Im going to go look at the Martin J alignment table and see how much difference it gives me and some of the stuff I have done on paper. I would say 90% of the lines I see on forums are following the steve meade formula. There are a few guys that seem to have some magic T line juice and do some funky things with compression chambers, increasing and decreasing line size, but the average joes seem to follow the Fs/Sd model.

I would suggest reading everything on Quarter Wavelength Loudspeaker Design but there is a ton of good information in the Alignment Tables PDF. He also has MathCad worksheets that are ******* amazing for enclosure design whether it's ported, transmission line, or even horn type enclosures. I think they're like $25 though, sadly. You can even take your interior dimensions of your vehicle and get a rough estimate of what your cabin gain response looks like. I modified my files (he's locked them now it seems) back in the day and I was able to fully simulate what a box would look like with my cabin gain applied and it matched the meter with frightening accuracy. I wasn't able to get it to work as accurately with trunk vehicles but it did work out ok when I filled my trunk with expanding foam and fired the subs forward.

I die a little inside when I see a steve meade style transmission line. They're not all terrible and sometimes they might be very close to what they should be but most of the time they're just not the most efficient design. It's like sonotube tlines... the only way those can usually sound great is in a large room or to mass load them like a Voigt Pipe (putting a port at the end of the line basically).

 

[Jroo 10+ year member]

I would suggest reading everything on Quarter Wavelength Loudspeaker Design but there is a ton of good information in the Alignment Tables PDF. He also has MathCad worksheets that are ******* amazing for enclosure design whether it's ported, transmission line, or even horn type enclosures.
I die a little inside when I see a steve meade style transmission line. They're not all terrible and sometimes they might be very close to what they should be but most of the time they're just not the most efficient design. It's like sonotube tlines... the only way those can usually sound great is in a large room or to mass load them like a Voigt Pipe (putting a port at the end of the line basically).

After reading through some of the info you posted, I see why **** near everyone uses the Steve Meade method. After reading a couple of pages I was trying to figure out if the guy was designing a box or helping me apply to NASA to launch a rocket. Light reading it is not.

 

[Immacomputer 10+ year member]

Haha, yea it's pretty in depth. It helped quite a bit that I was reading it while going to school for electrical engineering and studying electrical transmission lines at the same time (tons of the same math involved). I would suggest taking note of the Alignment Tables pdf on page 3 at the bottom where he has the boxed equation for line area. Then you need to note the Dr and Dz charts on page 11 and 12. Page 13 has a sample problem where he calculates line area for a driver which helps make application make sense. Every time I've used his method for line area, it's worked out and usually helps make the line smaller and more manageable. Also, the table for effective line length given taper and expansion is very nice and can be useful if ever making a line that varies in line area.