A couple of transmission line design questions

[Jroo 10+ year member]

I see a few t line designs that have a "compression chamber" around the sub. Is this done only for really big subs or subs that are very deep? How do you know how large the compression chamber should be and does it affect performance?

If I have a really deep sub, do I have any issues inverting a sub in a T line? Other than possibly hearing motor noise like in a regular box, does that affect performance?

Last question fellas. I have been reading a little on the bandpass T lines and know you have to find out where your sub peaks sealed. The rest of the design or line is based on where the sub peaked at. So where or how is the easiest way to figure out where a sub peaks at in a sealed box?

Thanks guys

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[rebelfromva 10+ year member]

someone else from Richmond....

 

[Jroo 10+ year member]

bump, but certainly a richmonder. Where are my t line gurus?

 

[Joseph7195 10+ year member]

I am not very familiar with the intricacies of T-Line enclosures, but @Moble Enclosurs has some experience designing and implementing them. Not all occasions call for a transmission line, but I know the response is superior in some situations, but really hinder in other situations. You seem to have been doing some research into these types of enclosures, so you probably know more than me on the topic, so when Mobile gets on here, he could help you out more.

I know he has been very busy, and plus storms around the Northeast have knocked his internet out a couple times so it may be a little while before he can respond.

I do know this, if you don't have some basic knowledge (actually a pretty good bit) of knowledge, the explanation he gives may seem a bit overwhelming(it is for me, lol). But there is really no real world way to "dumb" it down. I felt really dumb, lol.

 

[duanebro 10+ year member]

I see a few t line designs that have a "compression chamber" around the sub. Is this done only for really big subs or subs that are very deep? How do you know how large the compression chamber should be and does it affect performance?
If I have a really deep sub, do I have any issues inverting a sub in a T line? Other than possibly hearing motor noise like in a regular box, does that affect performance?

Last question fellas. I have been reading a little on the bandpass T lines and know you have to find out where your sub peaks sealed. The rest of the design or line is based on where the sub peaked at. So where or how is the easiest way to figure out where a sub peaks at in a sealed box?

Thanks guys

Inverting a sub works the same in any enclosure. It won't do anything weird.

A TL with a compression chamber is closer to a ported box than a TL.

The problem with all boxes in car audio is the affect the car has on the box. The higher order enclosures seem to be more affected by this. Just something to keep in mind.

I would think that a double TL will act like a 6th order bandpass, I would try modeling it in hornresp. Using simple math might get you in the ball park, or not.

Not all subs like TL enclosures, I always model a ported box to compare it with. Make sure all your work and larger box are giving you anything.

 

[Moble Enclosurs 10+ year member]

I see a few t line designs that have a "compression chamber" around the sub. Is this done only for really big subs or subs that are very deep? How do you know how large the compression chamber should be and does it affect performance?
If I have a really deep sub, do I have any issues inverting a sub in a T line? Other than possibly hearing motor noise like in a regular box, does that affect performance?

Last question fellas. I have been reading a little on the bandpass T lines and know you have to find out where your sub peaks sealed. The rest of the design or line is based on where the sub peaked at. So where or how is the easiest way to figure out where a sub peaks at in a sealed box?

Thanks guys

Hey Jroo,

The first thing is to note that the compression chamber is designed different than bass reflex designs, though they may look the same. In most cases, for tlines with a CC, you want to keep the CC as small as possible. The implementation of a CC within a Tline has 2 main purposes:

1. To allow for mounting clearance (adequately)

2. To "compress" the output the same as a conventional ported box does to maintain SQL type responses rather than solid SQ, which Tlines are generally made to achieve.

The concept behind a tline revolves around the functionality of organ pipes, but with a scaling difference due to the space we work in. The fact that we can create so much pressure from a tline in such small spaces, allow us to not have to use many of them to get a larger bandwidth in sub frequency usage. This is mainly do to the outside resonances that occur, and not within the design.

Within the design, to answer the second/third question, there can be issues with inverting a sub, BUT, one of the great functions (acoustically) that a tline has, is the ability to mask certain higher frequency resonances, as does any port for that matter, but do to the fact that tlines SHOULD be created "longer" than a standard port, the masking is greater at lower frequencies, which is good for noise reduction if other means of reducing noise is not possible.

Bandpass tlines go into the field of quasi-type Bps or a form of tapped Bp, respectively. As far as the peak is concerned, it depends actually on the output you are trying to achieve that will determine tuning and response. The relationship of this "peak" you have heard of is from the mechanical properties of the sub to make sure that control is kept while operating the driver from a high range of frequencies and not have it unload or distort while maintaining peak voltage for output. SO, it is mainly considered a safe zone, which is ironically implemented by many car audio companies that mass produce enclosures on the side. This also consists normally of a higher tuning than expected for the average listener in regards to sound quality.

Interestingly enough, the sealed concept, without focus on the tuning alone, is something I use to keep the CC small but large enough to allow proper control of the sub. So, wherever you found that info, may have been very reliable! But its not about tuning or peaking more than it is looking at the entire response and limitations of the sub and how it works as a whole.

As far as how I calculate peaks and nulls, I cannot say, but I will tell you that the peaks are not important alone. Other things need to be considered when you deal with CC size for a tline.

Just know that the CC should be smaller than a conventional BR, and that the reversing/inverting of the driver has to be controlled as far as placement within the line, and if you are to use a BPtline, or quasi/tapped, make sure you calculate it the right way, because doing it also "conventionally" will give you very different responses. The physics of a design are just as important as the output. .

Hope that helps!

 

[Jroo 10+ year member]

Moble Enclosurs thanks for the help. You are pointing me in the right direction. There is still a lot of magic beans in T Line design that I dont understand. For instance you said of the CC that you want it small enought to fit the sub, but large enough to still have control. How do you determine that size or that lose of control? Is this something that I would be able to figure out in a program? I know this isnt trial and error.

My bandpass questions came from a design and following a well known guy on another forum. He is know for producing them and the one I have from him sounds incredible. Basically I have a bandpass T line for a single 1508 and want to try another bandpass T line for 4 6.5" subs. I am just trying to figure out how to design it. I am understanding some of the math used to design a quater wave T line, but the bandpass part is what is throwing me off. That where some of my tuning questions came from. He specifically address that the line tuning comes after you find the peak sealed. I just dont know how you determine where it peaks? He also says many subs dont do well with the design, but I dont know what to look for to say a sub is bad or good. Im getting closer but still have some work to do.

 

[Moble Enclosurs 10+ year member]

Moble Enclosurs thanks for the help. You are pointing me in the right direction. There is still a lot of magic beans in T Line design that I dont understand. For instance you said of the CC that you want it small enought to fit the sub, but large enough to still have control. How do you determine that size or that lose of control? Is this something that I would be able to figure out in a program? I know this isnt trial and error.
My bandpass questions came from a design and following a well known guy on another forum. He is know for producing them and the one I have from him sounds incredible. Basically I have a bandpass T line for a single 1508 and want to try another bandpass T line for 4 6.5" subs. I am just trying to figure out how to design it. I am understanding some of the math used to design a quater wave T line, but the bandpass part is what is throwing me off. That where some of my tuning questions came from. He specifically address that the line tuning comes after you find the peak sealed. I just dont know how you determine where it peaks? He also says many subs dont do well with the design, but I dont know what to look for to say a sub is bad or good. Im getting closer but still have some work to do.

Not really that I know of will a program figure for this. Personally, i use my own formula averages and versions to come up with a volume And unfortunately, it is a LOT of trial and error and time and money etc etc.

Yea, they can be quite nice given the right volume //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif. In fact, one of the better ideas to date that I am aware of. Just have to have the right drivers and the right room, etc. A great response from a general tline is easy to obtain, but a more complex one, it takes some work to get it right. Qurater wave and tline generally do not have any direct connection though, any more than any other design that used a port, BUT for those that use them without a CC, it works well enough to sell lol.

Yea, the bandpass part depends on where you have the sub located in the design to figure for the output and I am not sure of an easy way to do it or really explain it. If you treat each section of the enclosure the way its meant to be treated, it will work. Putting the right placement on everything and making sure the area changes, if any that occur are correct, and length is correct, etc, you will get the right response from a program. Mine, I use numbers lol. Then I use those numbers to make/create the response and I found it to be very similar to some programs in most cases. I only did it this way because i could and it was more personally rewarding, so I can't really give any insight on my personal process, but Im sure something like hornresp or akabak or some pro program will be able to get you a good start on it. I actually used HR to verify a lot of my work in the past because of the formulas that are used in HR are direct.

Yea, many subs that are designed for SPL only may not be suitable, but from my experience, given enough volume, any sub will work. Its that limitation that makes it much more difficult in car audio //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif. As far as one working, I just model it. I don't rely on ts parameters to tell me personally whether it works or not, I let the design parameters tell me that. You'd be surprised of what you can achieve by calculating for nearly all design layouts out there and picking one on how tough it can be sometimes and how similar some of the other designs are in response that look nothing alike lol. But yea, best best is to layout the idea, then break it down to the point where you get confused, then figure on how the acoustics will work in that space and go from there.

Tlel you the truth, its no different than modeling a box, then putting it in a car and seeing what it can do after.....as the car is really a box too. A car can put any box and turn it into a BP lol. And quasi designs are popular "underground" designs because of the physics that occur that are similar to "inside a car" output before even being placed into the proper environment. In other words, they have great output before any gain is even considered because of their size, and layout and the way the sound travels inside the box alone.

Take a design that you have in mind, then draw out a top view of the layout without any top to it, like its see-through, then break it down, map the changes and calculate the acoustics for each part of the design and if you know how to do that properly (given a large amount of equations lol-serisouly no joke lol) then you can get one very accurate final response based on a combined calculation of the responses within a certain average and that is where your final response curve will be. Sounds very very confusing because it is, and that is somewhat how I come up with mine but you have to have the right tools to do it. And to tell you the truth, not a single person I know of has the same formulas that I use, and averages that I use or methods. Some of the formulas are deviations, but they are mad dot be manipulated for accuracy and quite frankly, they needed to be. Too many generalizations out there to make it all work given the changes that can occur with each design.

I account for that, but its very tough to explain how in words. Just takes time. Tell you the truth, even with all of the formulas you can get online, or in a book or from others, you still need the most important factor of all-trial and error.

Without this, the understanding of the constants of each design will be minimal and confusion will clutter your success in the field.

Not one design operates exactly like another. And for this, general rules, for me, go out the window.....BUT similarities are still present, such as that with a tline+CC and a standard BR. The response curves can be similar, but the way the subs move, and the efficiency may differ quite a bit, along with phase changes. SO, in theory, they may look the same, but sound quite different. And if those changes are not considered, you'll chase your tail wondering why and may never know unless you experiment.

I have a model that I did to help understand pressure relations in a vehicle with proper tuning and such as without it, the concept is very confusing. But with it, it all made much more sense on how certain things work. So, I built a small scale model to test my theories, my calculations, etc and had errors, but then figured how to correct them by making changes and monitoring the changes and figuring if there were any linear audible or notable differences that can be used for all designs, rooms, gain plots, etc to make it much easier in the end.

10+ years later, Im still improving. Takes time and don't expect to understand it form a book, because personally, most of the acoustical pdf files you can find on the net right now are based on trial and error and posted results, rather than exact occurrences that are repetitive. Most of audio is still explorable by most of us involved and that is what makes it so exciting.

So, that all being said, if you are trying to figure on how a design "works", build it, test it, change it, test it, change it, test it, etc etc etc. Then you will have a good idea, but the changes even have to be relevant to design. They cannot be symmetrical, they cannot be scalable, etc. They have to be inconsistent in physical form to show computable consistencies in calculation.

Of course there are easy ways to design. There are easy ways to make a box just plain sound great. But to get really involved, you have to spend the hours and do it productively and the way to do that is to test and build, repeat, repeat, etc.

When I finish a design, I ask people what it sounds like or if it sounds good to them and they generally give me great input that I can use to improve if at all. Im at the point now where I am pretty settled on what I can do for design now. but it took a 1/3rd of my life to get there. Don't stop and now you know that most of audio truth lies in realistic performance rather than numbers and generalizations (such as peaks that were mentioned), you know what to do from there. If you want to figure it out, build a small scale, with higher tuning and go from there. Have a receiver capable of a full response without crossovers and use that to test, such as a music receiver for Home use (generally nothing car audio related).

The concepts of power, efficiency, phase, timing, placement, size, and all acoustical factors are all proven and tested over time. BUT, they can still be improved. Just have to know how. Explaining that is improbable for real world applications for most of us as technicality will exist. No real easy way around it if you want it correct.

 

[CAT MAN 5,000+ posts]

Not really that I know of will a program figure for this. Personally, i use my own formula averages and versions to come up with a volume And unfortunately, it is a LOT of trial and error and time and money etc etc.
Yea, they can be quite nice given the right volume //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif. In fact, one of the better ideas to date that I am aware of. Just have to have the right drivers and the right room, etc. A great response from a general tline is easy to obtain, but a more complex one, it takes some work to get it right. Qurater wave and tline generally do not have any direct connection though, any more than any other design that used a port, BUT for those that use them without a CC, it works well enough to sell lol.

Yea, the bandpass part depends on where you have the sub located in the design to figure for the output and I am not sure of an easy way to do it or really explain it. If you treat each section of the enclosure the way its meant to be treated, it will work. Putting the right placement on everything and making sure the area changes, if any that occur are correct, and length is correct, etc, you will get the right response from a program. Mine, I use numbers lol. Then I use those numbers to make/create the response and I found it to be very similar to some programs in most cases. I only did it this way because i could and it was more personally rewarding, so I can't really give any insight on my personal process, but Im sure something like hornresp or akabak or some pro program will be able to get you a good start on it. I actually used HR to verify a lot of my work in the past because of the formulas that are used in HR are direct.

Yea, many subs that are designed for SPL only may not be suitable, but from my experience, given enough volume, any sub will work. Its that limitation that makes it much more difficult in car audio //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif. As far as one working, I just model it. I don't rely on ts parameters to tell me personally whether it works or not, I let the design parameters tell me that. You'd be surprised of what you can achieve by calculating for nearly all design layouts out there and picking one on how tough it can be sometimes and how similar some of the other designs are in response that look nothing alike lol. But yea, best best is to layout the idea, then break it down to the point where you get confused, then figure on how the acoustics will work in that space and go from there.

Tlel you the truth, its no different than modeling a box, then putting it in a car and seeing what it can do after.....as the car is really a box too. A car can put any box and turn it into a BP lol. And quasi designs are popular "underground" designs because of the physics that occur that are similar to "inside a car" output before even being placed into the proper environment. In other words, they have great output before any gain is even considered because of their size, and layout and the way the sound travels inside the box alone.

Take a design that you have in mind, then draw out a top view of the layout without any top to it, like its see-through, then break it down, map the changes and calculate the acoustics for each part of the design and if you know how to do that properly (given a large amount of equations lol-serisouly no joke lol) then you can get one very accurate final response based on a combined calculation of the responses within a certain average and that is where your final response curve will be. Sounds very very confusing because it is, and that is somewhat how I come up with mine but you have to have the right tools to do it. And to tell you the truth, not a single person I know of has the same formulas that I use, and averages that I use or methods. Some of the formulas are deviations, but they are mad dot be manipulated for accuracy and quite frankly, they needed to be. Too many generalizations out there to make it all work given the changes that can occur with each design.

I account for that, but its very tough to explain how in words. Just takes time. Tell you the truth, even with all of the formulas you can get online, or in a book or from others, you still need the most important factor of all-trial and error.

Without this, the understanding of the constants of each design will be minimal and confusion will clutter your success in the field.

Not one design operates exactly like another. And for this, general rules, for me, go out the window.....BUT similarities are still present, such as that with a tline+CC and a standard BR. The response curves can be similar, but the way the subs move, and the efficiency may differ quite a bit, along with phase changes. SO, in theory, they may look the same, but sound quite different. And if those changes are not considered, you'll chase your tail wondering why and may never know unless you experiment.

I have a model that I did to help understand pressure relations in a vehicle with proper tuning and such as without it, the concept is very confusing. But with it, it all made much more sense on how certain things work. So, I built a small scale model to test my theories, my calculations, etc and had errors, but then figured how to correct them by making changes and monitoring the changes and figuring if there were any linear audible or notable differences that can be used for all designs, rooms, gain plots, etc to make it much easier in the end.

10+ years later, Im still improving. Takes time and don't expect to understand it form a book, because personally, most of the acoustical pdf files you can find on the net right now are based on trial and error and posted results, rather than exact occurrences that are repetitive. Most of audio is still explorable by most of us involved and that is what makes it so exciting.

So, that all being said, if you are trying to figure on how a design "works", build it, test it, change it, test it, change it, test it, etc etc etc. Then you will have a good idea, but the changes even have to be relevant to design. They cannot be symmetrical, they cannot be scalable, etc. They have to be inconsistent in physical form to show computable consistencies in calculation.

Of course there are easy ways to design. There are easy ways to make a box just plain sound great. But to get really involved, you have to spend the hours and do it productively and the way to do that is to test and build, repeat, repeat, etc.

When I finish a design, I ask people what it sounds like or if it sounds good to them and they generally give me great input that I can use to improve if at all. Im at the point now where I am pretty settled on what I can do for design now. but it took a 1/3rd of my life to get there. Don't stop and now you know that most of audio truth lies in realistic performance rather than numbers and generalizations (such as peaks that were mentioned), you know what to do from there. If you want to figure it out, build a small scale, with higher tuning and go from there. Have a receiver capable of a full response without crossovers and use that to test, such as a music receiver for Home use (generally nothing car audio related).

The concepts of power, efficiency, phase, timing, placement, size, and all acoustical factors are all proven and tested over time. BUT, they can still be improved. Just have to know how. Explaining that is improbable for real world applications for most of us as technicality will exist. No real easy way around it if you want it correct.

you do it again!

 

[Durango03 10+ year member]

wtf just happened in here? //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

 

[wenn_du_weinst 10+ year member]

I wonder how many times Moble pisses box designers off. I only do my own so I could care less, but I know a ton don't like secrets getting out.

 

[Moble Enclosurs 10+ year member]

I wonder how many times Moble pisses box designers off. I only do my own so I could care less, but I know a ton don't like secrets getting out.

Well, likely a lot lol. But the difference is, mine are not designed like any others. So, its not their secrets lol. Plus, audio and acoustics can only be manipulated so many ways. For instance, there are limited amount of propagation paths that sound takes, no more, no less. Things like that can't be changed. So, the knowledge of it can be in fact universal. Its how you use it with other calculations that make it accurate or inaccurate. Like one big equation with little parts. So, if you have the equation right, the solution is always correct. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif.

In audio, errors are present beyond the calculations we use, but luckily they are minor and can be reduced. Such as that with damping and losses. Each material has its own acoustical loss to it. But, we tend to average it for car audio due to the consistent types of materials used. So, there is an error, but we minimize it by having SOME sort of loss. So, none of that is really secret, just needs to be implemented is all. lol

 

[Moble Enclosurs 10+ year member]

wtf just happened in here? //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

I logged on

 

[duanebro 10+ year member]

I wonder how many times Moble pisses box designers off. I only do my own so I could care less, but I know a ton don't like secrets getting out.

None, most people just look at his posts and think "I don't understand any of this. I had better just buy a design." He is just making more buy designs.

ME did say what doesn't work, but I will guess that most people will still do the same things over and over because they heard it was the right way and now have it in their head that it must be so.

 

[Durango03 10+ year member]

suppose all of this would have made more sense if I knew the slightest bit about T-lines but honestly I first heard about them yesterday while reading through Moble's website. Seems to be worth researching..