Thoughts on this QWTL design

[Triticum Agricolam]

So the purpose of putting the driver 1/5 or 1/3 of the way down to the line is to smooth out that big spike you get around 85 Hz. You gotta play with the lengths a bit, but here is what I got:

That fixes the funkyness at 85 Hz, but we still have the big spike at tuning.

Here is the desired frequency response, IMHO:

And here is how I got that:

I have the driver 1/3 of the way down the line, the line is tapered and it has much smaller cross sectional area, the problem with these parameters is you would have to reverse mount the sub. There is another solution though.

One nice thing about TLs is you can stuff the line to reduce spikes in output around tuning. Here is the result:

And here are the specs:

The only thing I changed from your model was to move the driver to the 1/3 point, and added 10 oz of polyfil evenly spread through out the line. The nice thing about using polyfill is you can change the amount of stuffing to get the sound you want without having to rebuild anything.

[_paralyzed_]

I'm continually amazed at your knowledge Triticum.

[DLHgn]

So the purpose of putting the driver 1/5 or 1/3 of the way down to the line is to smooth out that big spike you get around 85 Hz. You gotta play with the lengths a bit, but here is what I got:

That fixes the funkyness at 85 Hz, but we still have the big spike at tuning.

Here is the desired frequency response, IMHO:

And here is how I got that:

I have the driver 1/3 of the way down the line, the line is tapered and it has much smaller cross sectional area, the problem with these parameters is you would have to reverse mount the sub. There is another solution though.

One nice thing about TLs is you can stuff the line to reduce spikes in output around tuning. Here is the result:

And here are the specs:

The only thing I changed from your model was to move the driver to the 1/3 point, and added 10 oz of polyfil evenly spread through out the line. The nice thing about using polyfill is you can change the amount of stuffing to get the sound you want without having to rebuild anything.

I always knew the polyfill helped but dang, I didn't know that much. What would be the cons of using the polyfill and what would be the cons of using the hard tapper? Also, using this same concept, could I tune lower and not have any negative repercussions or, is so, what would they be? Because this is meant for HT use I would like the lowest possible usable output but I would also like it to be able to be used for music and games as well. What will I have to sacrifice and compromise?

[Triticum Agricolam]

There aren't lot of cons to use polyfill, the purpose of it is to decrease the efficiency of the system. The spike in output around tuning is because the box is too efficient and you are getting too much output over a limited frequency range. Reducing the box size accomplishes the same thing, but you can't do that if you want to avoid reverse mounting the sub. So the con of using polyfill is the box ends up bigger than it would otherwise have to be, but that doesn't sound like its a problem for you.

The cons of using a tapered line design is its harder to design and build. Laying out a taped line can be REALLY tough to do sometimes. If you want to go down that route, I have a design that someone else came up with that will work well for you sub. Its tuned to about 23 Hz, so you should have lots of low end output. It will still need some stuffing, but not very much. Here it is:

Here is a little bit different design that would also work well. This is a mass-loaded transmission line, similar in performance, just a little different layout:

Both of those designs came from a big thread on DiyAudio.com, you can see it here:

http://www.diyaudio.com/forums/subwoofers/216201-lab-12-based-offset-driver-mass-loaded-transmission-line-od-ml-tl-design-bj.html

[DLHgn]

So would tuning the line lower have any negative side affects (besides being larger)? Also, would a very low tuned t-line like this still sound good playing music and video games?

[Triticum Agricolam]

Other than the larger size there really is no disadvantage to tuning lower for your application. It will sound just fine for music and video games.

[DLHgn]

Other than the larger size there really is no disadvantage to tuning lower for your application. It will sound just fine for music and video games.

Sweet. I'll have to play with some designs when I get a bit of free time and post them on here

[DLHgn]

How much would adding polyfill affect the overall output of the system?

[Triticum Agricolam]

How much would adding polyfill affect the overall output of the system?

Not much other than around tuning. The polyfill mostly affects the output of the transmission line itself, any output coming directly off the cone isn't going to be affected much.

Here is a graph showing what comes from the line and what comes from the cone:

The black line is output from the TL and the lighter grey line is output from the cone. The purpose of the polyfil is just to tone down the output from the line a bit.

[DLHgn]

In hornsrep, how do you know how much stuffing you're using in the line when viewing the loudspeaker wizard? Also, earlier when you said 10 oz of polyfill, did you mean a total of 10 oz over the whole line or a 10 oz mat over the whole line?