Transmission Line Enclosure's

TL's are unique, in that they are in a class of non-resonant enclosures. The TL acts as a low-pass filter with a 90-degree phase shift. When properly constructed, all of thr rear wave energy is used.

Characteristics
1. Low cabinet Resonance
2. Relatively loud deep bass (below 50-hz)
3. Highly damped impedence peak
4. Decreased cone motion in the 40-Hz range. (Susceptible to subsonic noise)
5. Low degree of mid-bass coloration
6. Low effeciency

No hand calculator design method is available that I am aware of, also I have not been able to mathematically predict performance.

I can supply you with the information that I have if your interested. I have built one using 8 3-1/2-inch drivers, I still have it. It hits pretty low, but it needs a lot of power.

 

That about sumss it up Ranger, you even mentioned a few things i forgot about!!!

I have experimented with them in the past, for home audio use, not car. Had mixed results, did one with 2 old 8 inchers, sounded like poop......did one with a single 6 incher did really good. They take some planning and ewperimentation to get right.

You must have lots of patience and a box design that can be "modified" to adjust and tune, whether it is lengths of the line or the amount of dampning material, etc........

I DONT reccomend them for a beginer!! But if you wanna try, do! you may end up with a nice design.

I would have to do some serious thinking to remember some of the design criteria. Might do a search on these later this week,

 

I'll take a picture of it Monday and post it, its at my shop, on my test bench. I use it to test amps. I've had BD 1000s hooked to it for hours and not one speaker failure. I know now it would have been perfect if the line was about 10-inches longer.

I'll look for my info, I have it in a folder here somewhere, I think its between Abstract Algebra and Mathematics: A Practical Odyssey

Anyway I'll post what I have

And please continue to correct any spelling or gramatical errors that you may find

 

1. Make the line 6-8 feet long (impractical in a car), this should correspond to 35-45Hz

2. The cross sectional area of the line behind the woofer should be 25% greater than that of the woofers Sd. If you start at 100% greater than Sd bass will be lower. You can go as high as 250% over woofer Sd

3. The port opening (The end of the line) should have a cross sectional area equal to the woofers Sd.

Turns in the line are not added to the total lenght of the line. You didn't know math was involved did you?

 

It can have turns in it, no problem. Just be sure to maintain area and radius all the internal edges.

 

Quarter wave enclosure.....never heard that term


But the idea "sounds" similiar

 

Quarter Wave is another term for a Transmission Line. Do you want to know why?

You can say NO, but I'm gonna tell you anyway. In a previous post I said that the line needs to be 6-8 feet long. We will look at the middle length, 7 feet, which is 84 inches

Now take the speed of sound (in inches) which is about 13560 inches per second. Now lets divide that by 40 Hz. The result will be the length of a 40 Hz wave. The length of the wave shoud be 339 inches

While we can build a line that long it would be impracticle. The question that you have to ask yourself is "what other lengths correspond to that 40 Hz frequency?" (do you still have that Sine Wave Chart I E-Mailed you)

The same reason that we can make a car loud just by adjusting box size and tuning works here. Any octave above or below this length will correspond to this frequency.

Take our 339 inch long Transmission line and divide by 4, the result will be 84.75- inches. Close enough to the 84 inches that I wanted to get to any way. Because we divided by 4, we have a quarter of the original length of the wave. ( for octave we can only divide or multiply by 2 raised to some power.)

Now if you next question is "why can we not just divide by 8 (which is 2 to the third power) and get a shorter line?" I can answer that, but put some thought into it first, see if you can come up with the answer.

 

One thing you have to be carefull with tl boxes are they can destroy a woofer if its being overpowered even if its built perfectly. I built one in 1994 that was for 3 10w6s. posted a 150.5 on the dash with iasca disc and windows up. in a regular cab ranger cut through. Now remember meters only went to 160 back then . no one had broke 160 yet. and i think that was on the dash. i wish i still had the dimentions. It seems like dez and dave from music systems in el paso helped me figure some of it out back then . i had been installing for about 3 years at the time. and they were gods to me. I picked up the phone and called them way to much.

its probaly why i am so patient with people now when they ask for my advice. these guys were class acts. and great installers.Have not seen either one in years .