T-Line box with a sealed side?

[Chris Hammer]

Cool I understand what your saying...

My only question is how does a sealed side work ina 4th? I could be totally off here but my thought process is a 4th is a combo betweena ported and sealed box. The ported is tuned to a desired frequency and the sealed is there to keep cone control and let you play lower than tuning? Why would a sealed side be so detrimental to a transmission line but work so well in a 4th?

Im sure my newbtastic understanding of 4ths and other encosures has me completely off here.

[the_garynator]

Cool I understand what your saying...

My only question is how does a sealed side work ina 4th? I could be totally off here but my thought process is a 4th is a combo betweena ported and sealed box. The ported is tuned to a desired frequency and the sealed is there to keep cone control and let you play lower than tuning? Why would a sealed side be so detrimental to a transmission line but work so well in a 4th?

Im sure my newbtastic understanding of 4ths and other encosures has me completely off here.

4th orders are a trade off. Output is lower than a standard vented enclosure, but they have better transient response and better power handling. This is good for music but sacrifices spl, hence why you see 4th orders generally used in ground pounders and musical systems. The vented side acts as an acoustic filter, which lowers the cutoff frequency (i.e. sealed boxes have great frequency response, but they lack "the lows", the ported side makes up for that). The ported side also provides additional loading at low frequencies that would normally cause the subwoofer to bottom out in a standard sealed box.

Here is a good reference that will give you a basic understanding of 4th order enclosures http://www.diysubwoo...nd/4thorder.htm (this site is a good resource for getting a basic understanding of pros and cons of many enclosure types as well).

The reason it doesn't work the same with T-Lines is because a T-Line enclosure design has a completely different goal/theory behind it than most enclosures. It actually isn't really an enclosure, it's more of a wave guide with the goal being to invert the sound wave coming from the back of the sub to prevent cancellation. Think of it as having 2 speakers in sealed enclosures, one has the phase swapped (i.e. you have the negative and positive wires swapped on one). They will cancel each other out and you will have extremely low output. Using this analogy, a T-Line attempts to reverse the phase of the out of phase driver so that it matches the other one. (note: this is a simplified description, 1/4 wave T-Lines only invert it 1/4 phase, but for simplicity purposes we'll assume it is a full wave). Now that the two woofers in sealed boxes are working in phase, you are getting output from both vs having them working against each other.

The main "sound" goal of a T-Line is not SPL, nor is it power handling, it's SQ. It actually has very similar "sound" goals as a sealed box, flat response. They just have different ways of doing it. A sealed box attempts to completely remove the rear soundwave, there-by eliminating any interferance. The draw back is that the pass-band is usually higher than what many of us like (i.e. poor "low-end" output/less output overall). A T-Line attempts the same thing, except it tries to utilize the rear wave as well as allowing the subwoofer to have high output on the "low-end". Adding a sealed box to one side of a T-Line completely defeats the purpose of a T-Line. Think of it like putting a sealed box on the front and back of a sub, it's kind of like that.

Cliff notes: Turning a T-Line into a 4th order of sorts is not possible since the T-Line side no longer functions as a T-Line. If you have a perfect T-Line on one side, and a sealed on the other, the T-Line would basically do nothing. So in escense these two enclosure designs are incompatible. Most likely there will be a bit of port resonance at certain frequencies but would probably function almost identically as a standard sealed box, with a possible decrease in output depending on how the T-Line side is designed.

[the_garynator]

On a side note, the enclosure type that has the benefits and versatility that you're probably looking for is a Horn enclosure. (Horns can be used in a 4th order design and provide increased output, etc.)

[Chris Hammer]

Ok thanks for the explanation. Mind blown lol.

I think I understand it alot better now though. Feel like diving a little into the basics of designing a 4th Horn if thatswhat you call it? or even some other style horns..I would like to build one simply because I have time to waste in woodshop lab and several sheets of MDF.

Is it possible to get more output with a Horn than a T-line

IDK if you see my sig but I am only running about 18w right now on a 9$ woofer and it surprises the shit outta my friends who are part of the Keeker comps=loudest ever group. If a horn will have some more output than the t-line that would be even better...even if the frequency response is more peaky and less musical I don't really care....its all for shits and giggles right now just trying different enclosures to use on my next build. I am going to buy a 10" in the 600-1k rms range with low fs and build either a t-line for it or something else different than a standard ported enclosure.

[the_garynator]

Ok thanks for the explanation. Mind blown lol.

I think I understand it alot better now though. Feel like diving a little into the basics of designing a 4th Horn if thatswhat you call it? or even some other style horns..I would like to build one simple because I have time to waste in woodshop lab and several sheets of MDF. Is it possible to get more output with a Horn than a T-line. IDK if you see my sig but I am only running about 18w right now on a 9$ woofer and it surprises the shit outta my friends who are part of the Keeker comps=loudest ever group. If a horn will have some more output than the t-line that would be even better...even if the frequency response is more peaky and less musical I don't really care....its all for shits and giggles right now just trying different enclosures to use on my next build.

I would love to, but unfortunately I have yet to dive into horn enclosure design. While T-Line theory is much more complicated than most people realize (unless you're doing a tube-type), Horn design is basically 1 level more complex, similar design formula for length but you have to calculate for throat area, throat mouth, etc. The calculators out there are also not very user friendly (from my research, using one is about the only way to design one successfully). For example, Hornresp has a lot of parameters that need to be entered and it is very cryptic as to what needs to be entered.

I look at it this way, there is a reason that very few people outside of the small enthusiast groups build and design them. I plan on diving more into horn design but haven't had the time.

Basically, unless you plan on being dedicated enough to do A LOT (and I mean A LOT) of research, and a lot of work, I would stick with ported designs. Otherwise from what I can tell so far is that getting a good grasp on T-Line Theory is a good start prior to getting into horns. Martin J King has a great site, and has about the only information regarding reliably being able to design a good functioning T-Line out there. If you don't believe me on T-Lines being more complicated than they seam, Martin had to remove his worksheets and a lot of information from the public internet and is now charging $25 for access to it because some large speaker manufacturers were using his work to design transmission lines for their speakers.

The disclaimer on his website: "The contents of this website are intended for personal use and not for any commercial venture or gain. Using the MathCad worksheets to study, design, and build quarter wavelength loudspeaker systems for your own enjoyment is encouraged. Selling these speaker systems, or the designs, for profit is prohibited without a license agreement in place. Because of continued use of the MathCad worksheets for personal gain, by a few individuals and small groups, I have reassessed how I will release more advanced versions of the worksheets."

Sadly these worksheets and other information are no longer available for free.

I've currently got a license to his site, but unfortunately haven't had time to play around with his worksheets (my life got real busy a few days after purchasing the license and hasn't slowed down since then lol)

For what it's worth, your best bet for researching further is to start looking at the home speaker crowd. They have the most information on these enclosure types. Anything I've run across on Car Audio sites regarding t-lines or horns is pretty basic, and many times misinformed information. (not putting down car audio types, it's just that horns and t-lines are much more established in the home speaker circles due to the large size being less of a downside in the home.)

[Pro7]

What about a tline on each side? Haha just wondering what that would do

[Chris Hammer]

What about a tline on each side? Haha just wondering what that would do

I thought he same thing...but if you read his explanation above I think it would work against itself and lose againts just a standard t-line and not only that take up double the space lol.

Build it though..see for yourself I've though about doing a couple weird ass things before just to see...Usually they sound like ass..but you might get lucky

[the_garynator]

What about a tline on each side? Haha just wondering what that would do

Running the same length on each side would not work as you'd be effectively cancelling out the 1/4 wave effect (both waves would be inverted 1/4 so they'd still be out of phase). Running different lengths could, however help as long as they're at different frequencies/lengths. Unfortunately designing this in a folded T-Line would be extremely difficult.

[Chris Hammer]

What about a tline on each side? Haha just wondering what that would do

Running the same length on each side would not work as you'd be effectively cancelling out the 1/4 wave effect (both waves would be inverted 1/4 so they'd still be out of phase). Running different lengths could, however help as long as they're at different frequencies/lengths. Unfortunately designing this in a folded T-Line would be extremely difficult.

Would that in essence make it peak at different frequencies? Like making one side at say 35hz and the other side longer or shorter like 25 or 45....I just throw my boxes on top of my back seatsso room isn't a big deal....I think the hardest part would be designing a removeable section so you can remove the sub unless you just leave it in.

[the_garynator]

What about a tline on each side? Haha just wondering what that would do

Running the same length on each side would not work as you'd be effectively cancelling out the 1/4 wave effect (both waves would be inverted 1/4 so they'd still be out of phase). Running different lengths could, however help as long as they're at different frequencies/lengths. Unfortunately designing this in a folded T-Line would be extremely difficult.

Would that in essence make it peak at different frequencies? Like making one side at say 35hz and the other side longer or shorter like 25 or 45....I just throw my boxes on top of my back seatsso room isn't a big deal....I think the hardest part would be designing a removeable section so you can remove the sub unless you just leave it in.

You would have to tune one side to a pretty different frequency. Think about it this way, say you've got a T-Line tuned to 35hz, it's 8ft long. Now you add one tuned to 40hz to the other side, and it's 7.5ft long. This would in turn make the 8ft section act like it's only .5ft long, hence pretty much messing up the T-Line.

the only way you could make this work is if you were tuning on a broader range where you could keep one side vastly shorter than the other in some way shape or form...for example, if you wanted to have it tuned to 35hz (say a standard one needs to be 8ft long for 35hz) and then a higher frequency (standard) 1ft long (not sure what this would tune to off the top of my head). You'd need the low tuned side 9ft long and the front side would be 1ft. The issue in design you'd run into is that you'd be limited to only certain ratios since the sound wave coming out of the longer side would need to exit the line at a complete 360 degree of where it originated. I.E. the long side line lenth would need to be 8 times as long as the standard TLine length for a the tuning frequency of the short side's line. It may be possible to only need to be 4x as long but i'm not sure how that would work.

It may be possible to bring the tuning frequencies closer together but I'm not sure how well that would work. Theoretically it would provide the same benefits of running a standard t-line except at two different pass-bands/frequencies. Basically I would say, without knowing the ins and outs of single T-Line theory, it'd be very difficult to even begin to design a functional dual T-Line bandpass enclosure. I've never done the math, and I could be completely off base on the dual T-Line theory, but I beleive it is possible as i've seen people move woofers into the t-line before. And honestly it's really not techically dual T-Lines, it's still a single but the driver is just moved to a position within it.

I think this is generally done in T-line to cut down resonant frequencies at higher frequencies (there are port resonances that come up at certain multiples (higher frequencies) of the main tuning frequency...when the length coresponds with 1/2 wave of a higher frequency, 3/4wave, etc.

Also, here's a link to Martin King's site that I was referencing earlier in the thread: http://www.quarter-wave.com/