Bassboy's 12Hz T-Line HT Sub

[Volenti]

Originally posted by bludbunny
Thanks volenti.
So, my understanding is that sub rolls off to quickly at the lower end to be any good for a HT low Hz TL?

Brett

Yea, it'd probably be ok for music, but the venoms lack the x-max to go really deep and mantain signifigant output, considering you are going to be building a very large, difficult to make enclosure it's worth the effort and cost to source a better quality/more suitable driver.

When time allows I'll look at some of the locally available drivers to see what may be suitable without breaking the bank.

[just a guy]

Volenti, thanks so much for that last graph. It's starting to show me how different the plotted response between MJK's software and dosbox really are. I always said that dosbox was not suitable for design, only for driver selection but it's still not as good as MJK's software.

I fully expected that the larger CSA would make it flat down to tuning, based on dosbox (which shows a 10 db bump at 12 hz) which is obviously not the case. I thought making it the theoretical max (box size 4x driver vas) would flatten it right out down to tuning, but I'm only getting a small bit more extension at the cost of dramatically more excursion and smaller power handling.

At this point, the 15 inch Dayton Quatro mass loaded in the same line is stronger at 12 hz, which does not make too much sense to me. I thought the small vas would make it very strong at tuning in such a large box. I also own a MAW 15 (obviously) which I assume will be stronger than the Quatro (based on dosbox models, although I've never had it plotted with MJK's software).

It looks like I'm going to have hours and days of fun with MJK's software when I get it next week, to try to sort out the facts from the dosbox "facts".

Anyway, I know I'm on the right track, I just need the proper software to put the cherry on top.

Many many graphs to come, and it looks like part 2 of the report is going to get interesting.

[just a guy]

I'm getting a bit ahead of myself here anyway. The first thing I need to do is get all the tweaking done on the big sub and find out what FR curve sounds right to me. Doing some slow sweeps between 13 - 20 hz shows me that the response in that range is pretty close to what I want. Slow sweeps from 20 - 40 hz show this is the part I am unhappy with. My dosbox sims show a 5 db rise between 20 - 40 and this is the reason the LFE's are not quite strong enough for my taste.

Once I get the mass loading done, the 5 db rise between 20 and 40 hz will all but disappear, leaving me very close to flat on the graphs between about 13 - 40 hz. That was the plan from the beginning, and I'm confident that it will sound perfect once tweaked.

I've also got another trick up my sleeve. As Volenti so clearly showed with his graphs here, it is best to place the driver at 1/3 line length, not 1/4 as mine is now, as dictated by the previous incarnation of the box. Although this placement is a popular compromise for full range design, it is quite clear that 1/3 placement will be quite beneficial. I did not have appropriate tools to cut the cross bracing out at the 1/3 location when I did the mods a couple of weeks ago, but I have aquired the proper tools today.

With the mass loading of the driver and 1/3 driver placement, I am expecting a very flat graph FR response (+/- 3db at worst) between 13 and 90 hz, without stuffing. In this alignment, the need for stuffing may disappear completely.

[bjorno]

Brett,

So, my understanding is that sub rolls off to quickly at the lower end to be any good for a HT low Hz TL?

No, My opinion is that all drivers with similar specifications as the Venom could end up as good HT low Hz TL performers.

See the simulation with Venom 15” TL in a 106.7” = 271 cm tapered line, folded or not with CSA =2.4176 x Sd at the closed end and 0.549 x Sd at the terminus.

The Tl is modelled with no driver offset and for this case of applied acoustic Qm dampening, a dense layer = 2 in = 5 cm (modelled density = 38.4 kg/m^3) of mineral wool is placed close to the driver basket.

b

1(2)

[bjorno]

2(2)

[just a guy]

Bjorno is certainly correct, you can most certainly apply that driver in a tl, as I mentioned awhile ago, if you don't mind being 5 or 6 db down at 20 hz and dropping hard.

Personally I can't stand response like that, although most people prefer it. Even in a small room with the sub corner loaded, I would have to set the xo point as low as it would go and I probably still wouldn't be happy with it.

To get my personal preference for strength down to tuning, you need a very aggressive tuning resonance, which requires very large boxes, and severe excursion limited power handling.

I've said it before and I'll say it again, most people would not be happy with the way I design my FR curves, but at the same time, I'm sure a lot of people that have never heard REAL bass down to tuning would like it.

So, yeah, the Venom will work, but for my taste, I'd probably have to build a sub to cover 20 hz and down if I were using that.

[bludbunny]

Bjorno

Thanks for the post. Awesome work.
I currently have a 12" ported sub for the system, and I am happy with that (but too much is never enough) so I think if I was to build something more, I would want to spend the extra money and get something that extends a lot lower, as "just a guy" states.
Thanks very much for the alternative design though - maybe I'll see if my brother in law wants something like that (his wife will shoot me)

Brett

[just a guy]

Don't forget about room gain, it will help a bit, but in my experience it's nowhere near what people would have you believe. It's been my experience that if you want it to sound flat, you have to start with a very nearly flat FR curve.