Would anyone be so kind as to give me TL spec suggestions?

[GuyPanico]

I'm have a difficult time deciding what dimensions to make my TL. Mainly where to compromise between length, and fill density to achieve the best sound quality. What i'd really appreciate is if somebody could run my T/S specs through MJK's sheets and give opinions. What i'm looking for is the best musical sub I can make. I do plan on experimenting some, but would like to build it optimally first, then tweak to my liking from there.

FS 25.5
Vas 133.1L
Re 4.16
Qes .28
Qms 4.57
Bl 13.2
Sd 510cm

The largest tube I can get a hold of is 12.5" ID. Which comes out to 1.55sd. 120" is my absolute maximum hieght, although less would be preferred. I'm going to start construction this weekend, as soon as I figure out (with much help from all of you) my starting point. Thanks so much guys!

 

[bwbass]

This is going to be a straight sonotube, right?

Tuning to the driver's Fs will take 130+ inches of line, and of course if it's straight you need to have room to mount the driver and not block the terminus at the other end.

Hardware stores seldom have diameters larger than 12", you can get the bigger ones from concrete form suppliers - I found mine in the phone book. If you nest two tubes you could fold it and make it much shorter.

 

[Tweeker]

Some stuffing would probably bring it down to Fs.

 

[GuyPanico]

By nesting, do you mean like in picture I drew up below? That's a really good idea. Wish I had thought of it.

What size, and how much did you pay for your tube if you dont mind me asking?

Also, is there a general rule of thumb as to stuffing density vs. it's effect on the drivers percieved volume (for example .5cuft ~+10%)?

 

[bwbass]

Yes, similar to your drawing.

This is the one I did with a 12" tube inside a 16" one:

An externally hosted image should be here but it was not working when we last tested it.

I joined the two tubes along one side for simplicity's sake, like this:

An externally hosted image should be here but it was not working when we last tested it.

I modeled your driver in a similar "concentric" design with the same tubes in MJK's TL Sections sheet and wound up with a line length of 121". I shortened the line a bit to smooth the impedance curve a bit more and broaden the first gain peak as MJK suggests for a low Qts driver like yours.

Of course this is only one possible alignment, but it may give you a good place to start.

1st section: 57" x 1.43Sd - .5 lbs/ft^3 stuffing
2nd section: 7" x 1.43Sd to 1.05Sd - .5 lbs/ft^3 stuffing ("bend" section)
3rd section: 57" x 1.05Sd unstuffed

I got this response in the model:

An externally hosted image should be here but it was not working when we last tested it.

edit: Oh, and I think both tubes, cut to 6 1/2", set me back about $55 combined with tax.

 

[GuyPanico]

I guess that's the way to go then. Pretty ingenious. Found some places in the phone book, i'll have to call them Monday and hope they sell by the foot and not in 12ft sections or something. How happy are you with your TL? Anything you would do differently?

Thanks a ton.

 

[bwbass]

I think my TL worked out great... in my narrow experience it's the cleanest, most extended and precise bass I've heard.

I probably should add a brace connecting the inner and outer tubes to make the sub more rigid. Tweeker here on the forums suggested this, and I think it's a great idea.

By the way, the gap between the end of the 12" tube and the MDF "floor" in this design comes out to about 4.25".