Quarter Wave / T-Line tutorial-UPDATED

[FISHKILLER]

Hello all,

Call me crazy but I have been wanting to try a larger SG sub in a T line in my truck. After some research and not quite enough measuring, I purchased a TC LMS ULTRA. Super nice sub it seems, very excited about this beast!

Here is my problem, I am only able to get a line length of 24HZ. THis sub has an Fs of 20.5 Is this going to mess my SQ or output up? I have read this WHOLE thread, checked the links, WOW, lots of great info. I reduced my line area size by 15% to save a little space.

So what do the pros say? Is 24HZ tuning going to be ok? My box design is nice I think, sub back, port back, All corners radiused to keep exact line area for entire length. Double baffle of course to keep sub in place proper like. Any and all help much appreciated!

[bbeljefe]

I don't think you'll have any problems with that sub tuned a little higher than Fs. TC subs tend not to follow convention so if it were me, I'd try it. But what I wouldn't do is spend a lot of time making the box really nice before knowing how the sub will perform above tuning.

[FISHKILLER]

I follow you there. WIll hold off on the outside finish or carpet of box but I still feel the need to radius all my inside corners and give it my best shot. I am trying for a flatter response and better SQ than the normal slot port box most have. You feel I am headed in correct direction?

[bbeljefe]

I follow you there. WIll hold off on the outside finish or carpet of box but I still feel the need to radius all my inside corners and give it my best shot. I am trying for a flatter response and better SQ than the normal slot port box most have. You feel I am headed in correct direction?

You would have to have side by side data to know without question but from what I can reason, perfectly round radiuses won't provide enough of a difference to make them worth the effort. That reasoning might be invalid if we were talking about an anechoic chamber but we are talking about a vehicle cabin, which is a much more hostile environment for sound. Also, this thread contains some interesting data that, to me at least, demonstrates that perfectly smooth surfaces and turns do not benefit a loudspeaker as much as one might think. In fact, perfectly smooth surfaces can reduce air flow. Granted, the thread I linked involves port surfaces and not bends but I don't think there's much difference in the two for the purposes of this topic.

Another thing to consider is that when we're discussing loudspeaker vents (which is basically all a t-line is), we're not actually discussing air flow so much as air oscillation. And like water flowing from a faucet, the bends and turns inside the pipe that feed the faucet have a negligible effect on how well the water flows relative to the shape of the terminus from which it flows.

Anecdotally, I have listened to lines with and without wave guides and I've not been able to discern any difference in tonal quality or output. Of course, a meter may tell another story but frankly, I'm not interested in slight differences on the screen of an RTA or dB meter. I'm only interested in what my ears tell me.

[FISHKILLER]

Awesome read and great info. Why has that thread ended I wonder? I have Several bends in my box, one 90 back of sub to back of box, two 180s, then a 90 out. What I gathered from that read is I should leave my corners as they are constructed, which will cause some turbulence, or, I could radius all my corners then dimple them for a buffer. THAT would be labor intensive for sure of course.

Thinking more on it I may just construct box, then paint the entire port with a flex seal or bedliner type of product for a touch of texture the entire length.

Of course we will never know the correct way......all situational dependent. How do you feel about entire port length textured?

[bbeljefe]

Awesome read and great info. Why has that thread ended I wonder? I have Several bends in my box, one 90 back of sub to back of box, two 180s, then a 90 out. What I gathered from that read is I should leave my corners as they are constructed, which will cause some turbulence, or, I could radius all my corners then dimple them for a buffer. THAT would be labor intensive for sure of course.

Thinking more on it I may just construct box, then paint the entire port with a flex seal or bedliner type of product for a touch of texture the entire length.

Of course we will never know the correct way......all situational dependent. How do you feel about entire port length textured?

I have no idea how texturing the entire port length would work. My first guess is that it would be insignificant, save the first foot or so at the terminus but I could be entirely wrong.

Again, we aren't really dealing with air flow in a loudspeaker, we're dealing with air oscillation... so only the air at the end of the terminus is flowing in and out of the box.

[FISHKILLER]

Couple more questions for ya, thanks for the input by the way!

Any thoughts on port and sub facing same direction? Also what about clearance in front of my port opening? Gonna have about six inches in front of sub but only about four in front of port....Gonna start measuring and cutting tomorrow. Sorry for all the questions!

[bbeljefe]

All but one of the t-lines I've built have the subs and port on the same face so yeah, sounds good. As for loading space is concerned, you should be fine there.

[FISHKILLER]

The reason I have my heart set on doing this T line enclosure is hoping for the most accurate sounding sub while keeping my output. In other words I want it PERFECT! Not asking to much! HA.

In your experience do you feel I am on the right track? Or standard ported box tuned flat give me the same results?

[bbeljefe]

No question about it... build it.