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T line boxes

 

Silver Member
Username: Alexv305

Tavernier, FL USA

Post Number: 590
Registered: Oct-05
Pete from Team Toxic Bass puts the sub half way between the port and the chamber. i saw another box that said t line and it was one huge port. there was no chamber, the rear end of the sub was entirely in the port.

What is the exact definition of a t line box? Also does anyone know how to make them and are the better for SPL? SQ? SQL?
 

Gold Member
Username: Killerzracing71

Fredericksburg, Virginia United states

Post Number: 1215
Registered: Aug-05
i saw this on steave meades website..... i want to know more about it.... from whut i read it will make the sub an octave below whut its tuned to just as loud as a convinetial setup..... but they take alot of room..... a whole lot....
 

Gold Member
Username: Cenus

Hicksville, Ohio

Post Number: 2863
Registered: Jan-05
Because an Electrostatic Loudspeaker is incapable of producing low frequencies, a tradeoff must be made. Therefore, for a standard dynamic loudspeaker is used. It is then of paramount importance to design the enclosure for the dynamic subwoofer to be as accurate as possible to match the ESL. There are three main speaker enclosure types for the general consumer: acoustic suspension (sealed), bass reflex (vented), and compound (bandpass). Each one of these designs has variations but are similar enough to be ignored for our purposes. Each type of enclosure makes tradeoffs between efficiency, frequency response and accuracy.

By far, an acoustic suspension yields the very best accuracy. The air in the box acts like a spring, and counteracts the motion of the diaphragm. This helps to decrease the amount of over and under shoot giving the sealed enclosure very tight and defined bass. It also tends to protect the speaker from extreme excursion that would cause the cone or voice coil to "bottom out" or hit the frame, damaging the speaker. However, like any spring system, there is a resonance, and below this resonance, the output falls away at about 6db per octave. Also, due to the speaker having to fight the air spring or compliance of the box, the efficiency is low.

The bass reflex or vented enclosure has a greater efficiency. The back wave (sound from the back of the speaker diaphragm) that would normally be dissipated as heat in the enclosure is channeled out through a tuned vent to add with the front wave. In this way, the system is more efficient, but does not have the protection of the air spring. The frequency response tends to be not as flat as sealed. Furthermore, the tuned resonant system has very poor response below the resonance point and can be easily damaged, as the diaphragm decouples from the air and can bottom out with no air spring protection.

The compound or bandpass enclosure is composed of mounting the loudspeaker in a combination of vented and or sealed enclosures in front and behind. The most used is the 4th order bandpass enclosure, where one side of the speaker is in a sealed box and one side is in a vented box. This allows for a double tuned system that has very high efficiency in its pass-band range. However, like the vented box, anything outside of the range is severely attenuated. Also it is difficult to design properly and easy to abuse. The bandpass enclosure is not for audiophiles and tends to give the "one-note-thumper" sound of teenage car audio systems.

For more information on speaker enclosure types, please refer to The Subwoofer DIY Page v1.1

Transmission Line Basics

A Transmission Line (TL) is not like any of these three enclosure designs. The Transmission line is an old design, but as it turns out, is almost a perfect system. For example, the Bose Wave Radio uses a TL enclosure to produce its award winning sound. As the name implies, a transmission line is a long tube that expends from the back of the loudspeaker. By tapering the line, there is NO possible way in which sound can reflect back and forth and therefore standing waves and resonances common to standard speaker enclosures are eliminated. By eliminating back-wave reflections, the driver is also protected from having the back-wave re-radiate through the diaphragm, causing distortion and diaphragm breakup. The purpose of the transmission line is to eliminate the phase cancellation that would occur if the driver was in free air. Because of the length of the line, there is not enough time for air to travel through the line and cancel the front-wave. The magic of the system is what happens to the back-wave. The length of the line creates a tuned chamber much like an open ended pipe from a pipe organ. This causes a phase shift depending on the frequency and the length of the line. Through proper design, this causes the wave from the end of the TL to reinforce the front-wave at the frequencies where the front-wave begins to decrease due to increased air resistance at lower frequencies. Also, the tuned aspect of the TL strongly effects the fundamental resonance of the loudspeaker. It causes a very heavy dampening effect, which also helps to eliminate the overshoot and undershoot of the massive bass driver diaphragm. But this dampening is unlike the air spring of a sealed box and the diaphragm does not have to fight for motion. As a result, the efficiency is better than bass-reflex enclosures, the accuracy is better than acoustic suspension, and the frequency response and linearity is better than all systems.

The line length is usually tuned to be 1/4 of the fundamental resonance of the driver loudspeaker. The TL can be folded, or in other words curved. If stuffed properly with damping material such as wool, the actual length can be decreased due to the resistive effect of the material on the air. The construction and design of a TL bass system may be more difficult, but the result is a dynamic driver than can truly complement an electrostatic loudspeaker.



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Bronze Member
Username: Hgihkcin

Lincoln, NE

Post Number: 68
Registered: Sep-05
amazing post dustin, very informative, i wanna build one now..... does anybody have diagrams and calculations for it?
 

Gold Member
Username: 54danny54

KY More Wang Th...

Post Number: 3312
Registered: Nov-04
nick.
i used to have the forumula fora 1/4 wave. i dont remember wha it was but let me tell u, the enclosure is HUGE and the formula is hard
 

Silver Member
Username: Alexv305

Tavernier, FL USA

Post Number: 591
Registered: Oct-05
Very amazing post dustin. Good thing I brought this topic up. Ive been reading on TL boxes and to the car audio industry, they are very impracticle. They are truely amazing designs, but take up massive amounts of space also. Fortunately Pete from team toxic bass has figured out a way to create a hybrid between bass reflex and a t line. it is much smaller and has around the same output, but i think less.

anyways dustin, how do horn loaded enclosures fit into this and what does tapering do? I read something like it speeds up turbulence causing the air in the horn to move more rapidly drastically increasing SPL... how do people come about building these?
 

Gold Member
Username: Nyyfan13

Fi SSD USA

Post Number: 3135
Registered: Jul-06
copy and paste dustin? lol

either way, good post...plus one for your
 

Gold Member
Username: Sploosh56

Ohio

Post Number: 1614
Registered: May-04
that post reminded me of glasswolf. anyway i have formula for a T Line at home so i'll psot it when i get home
 

Gold Member
Username: Cenus

Hicksville, Ohio

Post Number: 2864
Registered: Jan-05
LOL ya i'll admit i copyied and pasted, but still its very informitive, t-line are very hard to build correctly, and are useally very big insize, perfect fot HT but not so much car audio.
 

Gold Member
Username: Nyyfan13

Fi SSD USA

Post Number: 3149
Registered: Jul-06
lol...the post was too perfect...good find anyway tho...very informative
 

Gold Member
Username: Cenus

Hicksville, Ohio

Post Number: 2866
Registered: Jan-05
http://www.freepatentsonline.com/5266752.html heres another good site for info, i would of just copyied and pasted but its kinda long.
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