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Discussion Starter · #1 ·
Hi Guys,

I'm kind of new to the DIY speaker scene, I've built "The Golden Boys" from PE, and 5 Bargain aluminum MTM's 3 of whish are currently the front speakers for my soon to be 5.1 HT, they produce decent bass already, but I'm ready to build a sub for my 10' by 12' room. I already have a Dayton SD215-88 8" Shielded DVC Subwoofer part number 295-480 and a Dayton SA70 70W Subwoofer Amplifier part number 300-784. After looking around the internet I got interested in the transmission line idea. Will this work well with these products? I wouldn't have to use the sub for music if that makes a difference, I'm mainly interested in gaining dramatic LFE for dvd's. please help! Any comments or suggestions are appriciated!!
 

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I tried making a transmission line sub with that same amp and driver. It worked but my results were less than spectacular. I don't know what went wrong - the driver had the right parameters and it modeled well. It is possible I didn't have enough patience to work with the design.

You can have the enclosure to play with if you want.
 
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Discussion Starter · #3 ·
Did you try closing the termus up some by adding MDF to each side? From what I've read this "loading" might help the response, also did you stuff this pipe or not? Thanks for the reply I'm interested to hear what you tried
 
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Discussion Starter · #4 ·
Would anyone be able to give me the best dimensions for this transmission line? What adjustments should I make to Boom's design? Thanks for the help
 

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No I did not add MDF to the sides. I'm not really sure what you mean by that anyway. Yes I did stuff the inside. I probably could have experimented more with the stuffing but I lost heart and didn't. I still don't know why the extension was 10 Hz less then modeled. So I took the sub apart and moved on to other things.

It is a shame. I love how transmission lines sound. My omni-speakers I made and my old HTD level 3's are tranmission lines and my TABAQs I made (but not designed) are mass loaded transmission lines. I just couldn't get a TL sub to work. Someday (in another house) I may make a big straight pipe one - we'll see.
 

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Maybe I'm being too picky. Here is the modeled graph (red) vs. my measurements (purple). There is a chance I was just taking bad measurments (my room is far from optimal for sub frequencies). To tell the truth I had a lot of projects going on then which could also be why I got distracted. You know, why focus on a 70 watt 8" sub when I was making a 2000 watt 15" one for a friend? Maybe I'll put this back together and play with it a bit.
 

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Discussion Starter · #7 ·
No I did not add MDF to the sides. I'm not really sure what you mean by that anyway.

I simply meant to make the opening smaller because from what I've read if you make the opening smaller it will make the TL seem longer. I don't know if that makes a big difference. Again, I'm a newby to subs and TL's, so I've been trying to learn as much as possible about both at once.
 

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No I did not add MDF to the sides. I'm not really sure what you mean by that anyway.

I simply meant to make the opening smaller because from what I've read if you make the opening smaller it will make the TL seem longer. I don't know if that makes a big difference. Again, I'm a newby to subs and TL's, so I've been trying to learn as much as possible about both at once.
Ah. I could give that a try. As you can see from the pics I took of it, the TL itself is tapered which does reduce the length needed.

My original plan was to make the whole thing from 8" PVC pipe. That lasted until I found out how expensive 8" pipe is.

I guess one thing I noticed is that since TL subs need to be so long, you might as well use large drivers as they won't make the final design that much bigger. If I were to do it again I'd probably use something bigger than an 8". Also, because it is hard to get a really low tune in a small package, I'd take a look at some pro-sound woofers.
 
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Discussion Starter · #9 ·
Yeah It looks preety good and from that thread it sounds like it worked preety well, what would you suggest I do different if I make a similar setup? I think I'm gonna try to start working on it sometime after new years so anything you think I should try to improve it is appreciated, I could make a simple sealed box, but that seems so boring, I'm ready to branch out and try something different.
 

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Also, check this out. There is a chance I should have made my T-line wider.
Guys...A couple of points which might help to improve your TL systems..

Firstly, If you're using a high resonance speaker (which you should be) you need more volume..
Increasing the width of the cabinet by 50% (from your current width) will lower the cabinet/speaker resonance dramatically..
This of course would mean starting from scratch again, which you probably won't want to do.:bigsmile:

The other alternative is to use a lower resonance speaker in your existing cabinet..but not the best alternative..
I'm not sure what the Fs. is of your current speaker, but it shouldn't be any lower than about 35Hz.

As far as the loading of the line..The only part of the line that needs to be correctly loaded is the first chamber..The rest of the line need only have the sides covered with Dacron or the like..

Also, the original TL systems where never designed to powered by a plate amp or external amplifier..as in a sub system..They are purely an acoustic speaker system, similar to a BR system and were connected directly to the receivers L&R channels...
Basically they are the bass part of a 2 or 3 way system..not a sub..and obviously you can not connect it to the LFE output of a receiver..
 

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I guess one thing I noticed is that since TL subs need to be so long, you might as well use large drivers as they won't make the final design that much bigger. If I were to do it again I'd probably use something bigger than an 8". Also, because it is hard to get a really low tune in a small package, I'd take a look at some pro-sound woofers.
Boomie, one of the most effective TL systems is the straight line system..
All it requires is to build a long (the length of the quarter wave) square, tapering tube, with the speaker in one end tapering to the port in the other end.
The whole tube is then lightly packed with the acoustic loading material..
You don't even need the driver facing you, providing that it's not too close to a side wall..

One thing I forgot to ask you in the other post was..What did you use for filling in the line?
 

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Thanks for the tips! I got some questions though.

The other alternative is to use a lower resonance speaker in your existing cabinet..but not the best alternative..
I'm not sure what the Fs. is of your current speaker, but it shouldn't be any lower than about 35Hz.
Are you talking about Fs here? Are you saying Fs should be greater than 35 Hz or less than? The driver I used and that spresser was talking about using, is the Dayton 8" shielded subwoofer. It has an Fs of 28Hz. In my design I was trying to tune the cabinet (the quarter wavelengh) to 35Hz or so. Someone on DIYaudio used the Martin King TL sheet to suggest a cabinet design which is what I went off. That being said I understand TLs aren't as predictable as traditional sealed or ported enclosures.

One thing I forgot to ask you in the other post was..What did you use for filling in the line?
I used Polyfill. I have a big bag in my basement - I use it for everything. Is this not a good fill?
 

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Are you talking about Fs here? Are you saying Fs should be greater than 35 Hz or less than? The driver I used and that spresser was talking about using, is the Dayton 8" shielded subwoofer. It has an Fs of 28Hz. In my design I was trying to tune the cabinet (the quarter wavelengh) to 35Hz or so. Someone on DIYaudio used the Martin King TL sheet to suggest a cabinet design which is what I went off. That being said I understand TLs aren't as predictable as traditional sealed or ported enclosures.



I used Polyfill. I have a big bag in my basement - I use it for everything. Is this not a good fill?
I hadn't realized that you're using an 8" speaker..
Personally, I don't believe that you can get that real deep down clean bass that TL's are known for with an 8" driver..
It's like If you compared an 8" BR system against a 12" BR system from the same maker, I think you would notice a difference in the lower register..

A Fs.of 28Hz is probably a bit low, as I'm suggesting that 35Hz. is the lower limit, but with your smaller volume TL, it should be ok..

If you have the total line filled with polyfill, then this may be your problem..
The only place that you should have any polyfill is in the lining of the chambers, not the filling..
The first chamber only should be filled...

When I was building TL systems, I used to use a very open material for the first chamber filling..
It was a stranded springy woollen material, very similar to the old "horse hair" batts (if you can remember them)..They used to be used for carton filling, prior to polystyrene..
Unfortunately I can't remember what the material was called, but I used to get it from craft shops and should be still available..

The first chamber is filled with this woollen material and lightly packed in..It gives enough dampening but still allows air to flow...
Incidentally, when your filling is the correct amount, you should still be able to detect a small amount of air flow from the front port.
 
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Discussion Starter · #16 ·
Thanks for the help Prof.

but does all this info mean I should just make a sealed sub and give up on the TL idea? It sounds like there is alot working against me here. I really just want to get the most out of my amp and driver what is the best option?
 

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I think Prof isn't saying not to do it, he's just trying to give you reasonable expectations i.e. you aren't going to get room shaking bass with an 8" driver in a T-line. Honestly, you won't get room shaking bass with an 8" anyway - no matter what enclosure. That being said a ported or PR enclosure will give a bit more low end output but it will sound different.

IMHO T-lines sound better even if they are a bit harder to get just right. The only thing that comes close to being as natural sounding would be a dipole sub and you definately need bigger drivers and more power for that!
 
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Discussion Starter · #18 ·
ok, so boom do you think the project you made justifies me making a TL over a sealed or ported sub, or should I wait until I get my hands on more power and bigger woofers to try a TL? I would love to do it but maybe what I have now doesn't make it worthwhile at this point in time
 

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ok, so boom do you think the project you made justifies me making a TL over a sealed or ported sub, or should I wait until I get my hands on more power and bigger woofers to try a TL? I would love to do it but maybe what I have now doesn't make it worthwhile at this point in time
Like so much in this hobby that depends on what sound you really want and how much you are willing to experiment. For completely selfish reasons I'd love for you to take my design and improve it. Then I could copy your work and everyone goes home happy. :bigsmile: That being said I don't know how much you like to experiment and how tolerant you are of not getting something right on the first try.

So if you want the TL sound and don't mind experimenting I'd go that route. If you want a proven design go with something else. A sealed box would be easy and foolproof. PE has designs for a PR sub using the same amp and driver. I have also made that one - it has almost 10 Hz more extension then what I was getting with my flawed TL, but only about 2Hz more extension that what the TL should have been getting. Or you could do a straight pipe TL which, although larger, is easier to design and more likely to get right on the first try.
 

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To put the whole thing into perspective...
If I had the time and money again, and of course the space, I would be building a pair of TL's, using 12" or 15" speakers in approx.8 cuft. cabinets..
These would be my Left and Right channel BASS speakers ONLY..
I would then have a pair of seperate cabinets..holding mid range and tweeters, sitting on top of the TL's..

Then I would have a seperate powered sub, and a centre channel speaker of course, to make up the front line up..

If either of you listen to a lot of music with your respective setups, then a TL is well worth having..
They are a very musical sounding bass speaker, ideally suited for music reproduction..but in a home theatre setup, they just don't have the impact that a good powered sub can give..
 
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