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Mattrance
01-05-2012, 05:06 PM
Hi,

Should or are transmission lines within a speaker cabinet be built in order to absorb all of the backward waves from a driver to prevent any phasing issues, or are they more used for turning an out of phase waveform, in phase, to come out of a port/vent adding to the amplitude of the sound. and if this is the case are exact mathematics of the angles through the line essential to get the waveform in-phase?

Im new to this game as you probably figured. As far as i can tell in my research so far there seams to be an argument for both cases which has confused me somewhat. some to get a better/cleaner response from the driver and others to add to its output

Any information would be greatly appreciated

Cheers.

wenn_du_weinst
01-05-2012, 05:11 PM
Well to be 100% both.
One version of t line, and imo the true t line enclosure, has stuffing and is designed to dissipate the rear wave while not interfering with the cone moment or front wave.
The second version, and the most popular on car audio forums, is really a 1/4 length wave guide. This version puts the rear wave 180 out of phase from it's origin to match the front wave and enforce it. To learn how to design check out here (http://www.quarter-wave.com/)

Mattrance
01-05-2012, 05:57 PM
cheers for the information and the link. looks useful from a first read. If the T line were to do both jobs surely it would be counter productive to be absorbing the wave you are trying to invert?

im currently in my final university year and for my audio engineering project im building a speaker to then test in different acoustical environments. in your opinion would you opt for a closed box or ported design over a transmission line cabinet? and is it worth doing for a full range driver or just subs? still confused as to what frequencies will be inverted?

wenn_du_weinst
01-05-2012, 05:59 PM
You understood that wrong.
I meant; That there is no answer to that question as both are excepted as t lines. Not that it does both. There is a huge argument over which is the correct way

Mattrance
01-05-2012, 06:03 PM
o right sorry. i get you now. is it only useful for subs though if your planning to add to the output with your T line, as i woul of thought high end frequencies will just get absorbed. im thinking of using a full range driver but unsure atm.

subzero
01-05-2012, 06:20 PM
Hi,

Should or are transmission lines within a speaker cabinet be built in order to absorb all of the backward waves from a driver to prevent any phasing issues, or are they more used for turning an out of phase waveform, in phase, to come out of a port/vent adding to the amplitude of the sound. and if this is the case are exact mathematics of the angles through the line essential to get the waveform in-phase?

Im new to this game as you probably figured. As far as i can tell in my research so far there seams to be an argument for both cases which has confused me somewhat. some to get a better/cleaner response from the driver and others to add to its output

Any information would be greatly appreciated

Cheers.What is a transmission line enclosure ? (http://www.angelfire.com/biz/davidson/FILE2.html)

The transmission line speaker was first described and patented in the 1960's. In a classic transmission line, the sound wave from the back of the woofer is channeled down a long pathway filled with a fibrous bundle of wool or another synthetic material. In a properly designed line, very low frequencies exit the end of the transmission line that extend the low frequency response one half octave below the fundamental resonance of the driver.

In a transmission line enclosure, the back wave of the woofer does not bounce off an interior wall and radiate back into the room through the thin cone of the woofer as in sealed or ported enclosures. These multiple echoes color the sound and can only be eliminated in a transmission line enclosure.

There is no pressure in a transmission line to excite strong enclosure resonances. In a sealed or ported box, enclosure resonances can usually only be controlled, not eliminated as in a properly designed transmission line enclosure.

Together, the extended low frequency response, the lack of multiple echoes from the inside of the box, and the elimination of wall resonance account for the extremely clean, well controlled and powerful sound of a properly designed transmission line speaker.

Mattrance
01-05-2012, 06:30 PM
cheers man. think i've got it now. whilst were at it though do you know of any good speaker cabinet design websites?

globalminds_ent
01-05-2012, 06:46 PM
I learn something new everyday. Seems like with a t line u could use a harder wood or something since when using MDF a lot of the sound is going through the box because 3/4 mdf is not not going to be to stop a huge 40hz wave. If a t line utilizes all of the low end seems like u would want something more solid to keep the sound from going through it... Is this true ??

hispls
01-05-2012, 07:00 PM
I learn something new everyday. Seems like with a t line u could use a harder wood or something since when using MDF a lot of the sound is going through the box because 3/4 mdf is not not going to be to stop a huge 40hz wave. If a t line utilizes all of the low end seems like u would want something more solid to keep the sound from going through it... Is this true ??



I would say it totally depends on your power requirements. Even 5/8 MDF is adequate with say a 12" sub under 500W. Geting into competition level stuff running multiple killowats, even 2 or 3 layers of 3/4 MDF can and will flex if not properly braced.

T-line sounds spectacular if done properly.

wenn_du_weinst
01-05-2012, 07:05 PM
he isn't talking flex, he means pressure loss. I'd use bamboo plywood

Mattrance
01-11-2012, 12:37 PM
would only bamboo plywood or MDF and not ordinary plywood keep the low end sound pressure within the T line?

duanebro
01-11-2012, 02:55 PM
I don't think this is correct, pro audio use 1/4" plywood to build horns, (braced every 4") If they can do 130db @ 50hz without cabin gain, then I don't think that you need crazy wood to build a spl box. Just make sure that the panels can't flex and you will be fine. (That can be a challenge though!)

its_bacon12
01-11-2012, 06:28 PM
Hi,

Should or are transmission lines within a speaker cabinet be built in order to absorb all of the backward waves from a driver to prevent any phasing issues, or are they more used for turning an out of phase waveform, in phase, to come out of a port/vent adding to the amplitude of the sound. and if this is the case are exact mathematics of the angles through the line essential to get the waveform in-phase?

Im new to this game as you probably figured. As far as i can tell in my research so far there seams to be an argument for both cases which has confused me somewhat. some to get a better/cleaner response from the driver and others to add to its output

Any information would be greatly appreciated

Cheers.

From my understanding, a transmission line is used to manipulate the back wave in different ways depending on the design, but it is never used to cancel the back wave. That would just be a large sealed box essentially. Again, this is my understanding of them, as I don't have much experience with TLs. TQWT is the one I've seen most of, which uses a tapered tube (port) in the same way a horn works, to manipulate the back wave to greater output.

wenn_du_weinst
01-11-2012, 06:32 PM
I don't think this is correct, pro audio use 1/4" plywood to build horns, (braced every 4") If they can do 130db @ 50hz without cabin gain, then I don't think that you need crazy wood to build a spl box. Just make sure that the panels can't flex and you will be fine. (That can be a challenge though!)

it's not for deterring flex, it's to eliminate resonance.

wenn_du_weinst
01-11-2012, 06:39 PM
would only bamboo plywood or MDF and not ordinary plywood keep the low end sound pressure within the T line?

you can use mdf/plywood if you want.
Mdf I would use resin to seal it inside though.

Moble Enclosurs
01-11-2012, 08:35 PM
tline questions. So many of them. And for a good reason. A tline can work in multiple ways to create the response you are looking for and it involves much more than what will likely be explained in this thread. Around the internet, there are many papers and views on these designs and some are great, some are completely bias, and some are just plain incorrect. It seems that everyone needs to understand sound before getting into understanding designs, which is the right way to learn any of this. If you want to figure out a specific design type, you need to know all of the variables involved. And not even understanding how the thickness of material effects the response is saying to me that the definitions of sound are not yet understood here. You need to learn about absorption, rarefaction, refelction effects(all of them), resonances, nodes, propagation paths, time delays, db losses based on distance, phase, etc. many many other factors before understanding a design. So, though some of these answers are great information, a lot needs to be figured out not just by forum answers, but by school, trail and error, experimentation, experience, etc.
Im sorry, I had to mention this to you in hopes that if you are serious about figuring out a design, you know what to look for rather than getting random answers about certain aspects. Here is a hint..........do not rely on quarter wave theory all the time. There is a time a place for it, and is can be very inconsistent depending on the requested response needed. So much can be involved, and most of the answers will not be here. My recommendation is to get an education in acoustics rather than answers from others who only know certain answers. Because even if you find out a lot of those answers over time by asking questions, applying them will be inefficient without knowing all of the effects involved. It has taken me over 10 years to get where I am with acoustics and designing and I am still writing formulas or manipulating them to get more accuracy from them even today.
If the question about thickness of material is still a concern, then knowledge of sound is highly recommended before trying to figure how a design works.

Reverend Mayhem
06-14-2012, 02:17 AM
I get the whole point of making the making the face of the encloser stronger but just making that stronger wont get you there. You want to calculate the quarter wave and match that by tuning your encloser to that frequency. The calculation is the distance from the encloser to the windshield in feet times 4 then divide by 1132 which is the speed of sound at see level. Then that will give your frequency you will want to tune your encloser to. That way the pressure in the cab and the encloser are the same. When you get to that point your sub-woofers will be able to withstand more power because it isn't working against itself. This all applies when building a walled system but im not entirely sure with anything else.

Flex68
06-14-2012, 02:23 AM
holy dead thread resurrection, batman!

lmfao