T line build for Megalomaniac

[rollerdj 10+ year member]

how much power is it seeing?

 

[Megalomaniac 5,000+ posts]

not much right now. maybe 40 watts off a plate amp. I have not decided on what amp to buy.

Im thinking about doing 3 way towers. the eu's will be still Tlined, and use a B&G planar and an Adire Extremis for the mids and highs.

 

[rollerdj 10+ year member]

yumm. i've been thinking about doing another build for HT using planar tweets. but god are they pricey.

 

[mobeious 10+ year member]

thats not a a T-line just a ported box with a really long port... good try looks good

 

[IDSkoT 5,000+ posts]

thats not a a T-line just a ported box with a really long port... good try looks good

That's basically what T-lines are. Though, I have to agree it doesn't look very T-liney.

 

[mokedaddy 5,000+ posts]

It depends on who you ask whether it is a t-line or not.

By definition it isnt since the port appears to be uniform width across the whole port, but it will still, for the most part, act as a t-line does.

Nice build tho. Craftsmanship looks top notch.

 

[Megalomaniac 5,000+ posts]

it is a tline //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

the qts of the eu is .28, its a bit low for a tline, so you have 2 obvious options either add a compression chamber or tune higher (no more than 5-10hz above fs).This design needed both if I wanted to keep it a straight line. Polyfil will help the response curve substantially, its a matter of trial and error now for me.

btw its a straight tline not a tapered tline(which is why the port is uniform accross)

 

[mokedaddy 5,000+ posts]

Its a hybrid t-line if you want to get specific. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

1/4 wave does not necessarily equal a t-line.

 

[rollerdj 10+ year member]

lawl, i don't care what it's called. looks cool to me.

 

[Megalomaniac 5,000+ posts]

Its a hybrid t-line if you want to get specific. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
1/4 wave does not necessarily equal a t-line.

you can thank eD for having silly specs on the driver //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

 

[mokedaddy 5,000+ posts]

you can thank eD for having silly specs on the driver //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

Old school t-lines are crazy stupid to design and just about impossible to model. Thus the reason hardly anyone uses them anymore. That is why there are now variations in 1/4 wave designs such as the uniform width ports and compression chambers.

I would love to hear it though and see how that particular design would compare to a more traditional t-line that I made long ago.

 

[RAM_Designs 5,000+ posts]

^^^I'm curious how it sounds too.

 

[Immacomputer 10+ year member]

Old school t-lines are crazy stupid to design and just about impossible to model. Thus the reason hardly anyone uses them anymore. That is why there are now variations in 1/4 wave designs such as the uniform width ports and compression chambers.
I would love to hear it though and see how that particular design would compare to a more traditional t-line that I made long ago.

They're really not too difficult to design and to model. Martin J. King has done excellent work in the area of transmission lines and horns and has uncovered much of their mystery. His matlab simulations are pretty good at modeling transmission line behavior. I was able to get accurate models of not only the transmission line enclosure for my sub, but I was also able to get an accurate model of the sub when in my vehicle. It predicted one peak at 22hz and a dip at 30hz with a passband of 15-70hz and that's very similar to what I measured.

Transmission lines are not mysterious and they're not uncommon. They have been used for thousands of years. And transmission lines do NOT have to have a taper for them to act like a transmission line. The changing of line area from the open end to the closed end is a way of limiting the upper order harmonics of the 1/4 wave resonance to smooth out peaks and valleys in the frequency response.

thats not a a T-line just a ported box with a really long port... good try looks good

If that is the case, then there has to be reduced cone movement at tuning right? The enclosure on my sub is very similar to this one in that it is a transmission line with a compression chamber. The tuning frequency if you were to calculate it as a ported enclosure would be around 35hz like this one. The problem is that I actually have a maximum of cone movement around 35hz and a minimum around 22hz. The sub also doesn't come anywhere near to unloading below 35hz and on the contrary, has quite a bit of acoustic loading controlling the cone below 35hz. Doesn't sound like a ported enclosure with a long port to me. Something else interesting is that when I model it using Martin J. King's t-line sections mathcad file, it tells me there should a cone movement minimum at 22hz and line velocity max at 22hz as well but it doesn't when trying to model it like a ported enclosure with his ported enclosure mathcad file.

Its a hybrid t-line if you want to get specific. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
1/4 wave does not necessarily equal a t-line.

Both of you have a fundamental flaw in your understanding of transmission lines. Every port in every enclosure has transmission line characteristics at certain frequencies. It's effects aren't normally noticed in subwoofer enclosures because they need to be very long to have transmission line characteristics (over 60" to get a 1/4 wave of 60hz... when is the last time you've used a 60" long port?). In this case, there will be some effects of a ported enclosure but the ported tuning frequency is equal to the 1/4 wave frequency which will dampen the oscillation of the port. Also, the air mass ratio of the port to net volume is far too large for the net air mass to effectively drive the port. Instead, the compression chamber will rise in pressure and try to drive the port. As the pressure from the chamber starts to compress the port, the inertia of the port air mass will reject this change and the pressure heading down the line will decrease but the velocity of the air will increase. That's also the exact same thing that happens in a transmission line enclosure.

 

[sqhertz 5,000+ posts]

i poop t-lines. //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

btw, it looks good.

 

[mokedaddy 5,000+ posts]

They're really not too difficult to design and to model. Martin J. King has done excellent work in the area of transmission lines and horns and has uncovered much of their mystery. His matlab simulations are pretty good at modeling transmission line behavior. I was able to get accurate models of not only the transmission line enclosure for my sub, but I was also able to get an accurate model of the sub when in my vehicle. It predicted one peak at 22hz and a dip at 30hz with a passband of 15-70hz and that's very similar to what I measured.
Transmission lines are not mysterious and they're not uncommon. They have been used for thousands of years. And transmission lines do NOT have to have a taper for them to act like a transmission line. The changing of line area from the open end to the closed end is a way of limiting the upper order harmonics of the 1/4 wave resonance to smooth out peaks and valleys in the frequency response.

If that is the case, then there has to be reduced cone movement at tuning right? The enclosure on my sub is very similar to this one in that it is a transmission line with a compression chamber. The tuning frequency if you were to calculate it as a ported enclosure would be around 35hz like this one. The problem is that I actually have a maximum of cone movement around 35hz and a minimum around 22hz. The sub also doesn't come anywhere near to unloading below 35hz and on the contrary, has quite a bit of acoustic loading controlling the cone below 35hz. Doesn't sound like a ported enclosure with a long port to me. Something else interesting is that when I model it using Martin J. King's t-line sections matlab file, it tells me there should a cone movement minimum at 22hz and line velocity max at 22hz as well but it doesn't when trying to model it like a ported enclosure with his ported enclosure matlab file.

Both of you have a fundamental flaw in your understanding of transmission lines. Every port in every enclosure has transmission line characteristics at certain frequencies. It's effects aren't normally noticed in subwoofer enclosures because they need to be very long to have transmission line characteristics (over 60" to get a 1/4 wave of 60hz... when is the last time you've used a 60" long port?). In this case, there will be some effects of a ported enclosure but the ported tuning frequency is equal to the 1/4 wave frequency which will dampen the oscillation of the port. Also, the air mass ratio of the port to net volume is far too large for the net air mass to effectively drive the port. Instead, the compression chamber will rise in pressure and try to drive the port. As the pressure from the chamber starts to compress the port, the inertia of the port air mass will reject this change and the pressure heading down the line will decrease but the velocity of the air will increase. That's also the exact same thing that happens in a transmission line enclosure.

He has done great work, I have read a couple of his articles. And no they arent nearly as complicated as designing horns but it does take a great deal of trial and error to get the most of out them.

So have you ever frequency tested a compression chamber and a traditional tline in a vehicle? I would be willing to bet they arent the same. Most likely close but due to differences in driver vs port placement they will vary. That was my only point. It may 'act' the same but wont be the exact same. Thus the variations of 1/4 wave enclosures.

To me its like saying ap would be the same thing as id since in theory they produce the same results, but arent necessarily the same thing. Yes its semantics but im bored. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif