Bassboy's 12Hz T-Line HT Sub

[hooha]

Bassboy sent me a PDF describing his T-Line he built for HT. Despite the fact he used a Mach 5 MAW-15 driver, his write up about achiving serious lows is quite interesting, and worth reading.

He references a number of different sub drivers one can use in this design as well.

Click here for article

Way to go Bassboy!

Mark

[just a guy]

Yup, I'm bassboy, in heart if not in name (someone had my name in this forum already). Glad you like my little story, stay tuned for part 2.

I wasn't really expecting this driver to work in this application, just imagine my surprise. Now I'm thinking about getting a couple more of the same drivers for OB bass from 30 to 60 hz to eliminate the majority of my room issues. One coil open should provide just about a perfect qts for OB use and it's got lots of xmax too, and the perfect fs to get down to 30 hz strong.

I'd like to make another big tl for the other corner too, not because I need the extra output, but just to make the room look more symetrical. I can make it for just over $200 for the driver and box, power not included. ~$100 for the driver delivered, 2 sheets mdf, assorted shop supplies (glue, liquid nails, screws, etc).

[bludbunny]

Bassboy
This is a fantastic read - especially for someone like myself who is keen to have a play with a transmission line setup for the same type of output.
I just need to try and find a similar driver in Australia, and then I'll give your design a go.
Have to wait until our new house is completed, then I'll have the room (not to mention a 6m x 9m workshop) to try it all out!

cheers,
Brett

[just a guy]

Since a couple of people have asked me about this sub so far, I'd like to point out a couple of things.

First off, I started with the challenge of working with a box that was already made. There were not many options to make the optimum line, and if I had it to do over, it may or may not end up like the first one.

Second, this write up is all about trying to get the average diy'er to look into tl's as an alternative to boring old ported boxes. I'm trying to get people to research and understand tl's. For that reason, I intentionally did not include detailed measurements of my project, although there's plenty of info there to figure it all out.

This write up was never meant to be a set of working plans that everyone should copy (although it works great), it's meant as an inspiration to stir up interest in tl design.

[bludbunny]

Bassboy - i understand what you mean there.
I suppose the easiest option for someone is to select the same driver and "copy" your design to get similar results.
I cannot do that - as I am in Australia and there is limited drivers to choose from. There are so many bargains in the states!!!

What I would like to put forward to add to this discussion is would the following driver be usable in a TL with similar dimensions?
Venom 15"
I have read some theory (cannot remember where - maybe by Bassboy?) that a TL works the same way as a normal enclosure - so it I used two of these, I would need to double the volume of the line? So the best way to get more output, would be to use four drivers, two pairs of isobarics?

Just thinking out loud.....

[just a guy]

I'm still not recommending that anyone should copy my box exactly, everything can be adjusted to suite personal tastes. I still don't even have mine tweaked yet, I just got some insulation today, so I won't have final results and impressions for some time yet.

The driver you linked to does not seem appropriate, off the top of my head, unless you like your bass rolled off a bit towards tuning. The qts is quite high and the vas is not too low, which means a largish box.

I have been considering a much smaller design lately using the MAW-12 in a box about 5 cubic feet and very similar response to my big box but with a bit less max SPL potential.

I believe it is true that if you double the drivers you need to double the line thickness, but I am not 100% sure if that is exactly correct. Following this assumption, I believe 2 iso loaded pairs (4 drivers) will equal the original 1 driver CSA, but again, don't trust me on that.

Anyway, the point is that if you select your drivers right, you don't need dual drivers in the line for massive output, you can just add a second cab or more if desired. This is a much more modular and manageable solution.

Before very recently I never expected to get 12 hz at over 100 db out of a 5 cubic foot box with only a couple hundred watts, so this is a pretty big revelation for me.

I will post an example of this new design, which I also do not recommend as working plans, at least til the experts get a look at it and give it a passing grade. It still sounds a bit too good to be true, so time will tell. And sims of the driver you mentioned too (in my original box so you can compare directly with the drivers in the article). Tomorrow. Too late now.

[just a guy]

So I can't sleep. Here's the Jaycar you linked to in the same line as the one in the article. Just as predicted, the low end is quite rolled off. Usually you could fix that by adding weight to the driver, but in this case the qts is so high already that if you add weight, this speaker won't be good for much except OB.

[just a guy]

And here is a MAW-12 in a 5 cubic foot tl. The line length is 171 inches. The taper rate is 4:1. The closed end is 500 cm square. The open end is 125 cm sqaure. The only spot in the line that you could mount the driver would be right at the closed end because the CSA gets so thin. So thin, in fact, that the size of the terminus is starting to get problematically small. No mass loading of the line is needed, as the mouth is already so small.

The driver, however is heavily mass loaded. The fs is reduced from 23 hz down to 15 hz and the qts is raised from .29 (I think) to about .47.

Any of the resident experts care to comment? I'm thinking this is on the edge of being too small, and a shallower taper and longer line length might be in order.

You might notice that the harmonics in this one look suspiciously like the one above. That is because in the one above (and in the articles) I used a 4:1 taper rate to simulate my physical 2:1 taper rate with mass loading because this dosbox program can't account for mass loading. In this graph, it is also a 4:1 taper rate, but this represents a real taper, as I might build, as opposed to the steeper virtual taper above to simulate mass loading of the line. Hope you understand that, if not, just disregard this, it's not that important.

By the way, these shots are taken at max excursion which happens at 400 watts for the Jaycar and 200 watts for the MAW-12.

[Volenti]

This is what MJK's software makes of your MAW-12 line;



Not too far off considering, the resonances match up well.

[just a guy]

Can you clarify about a couple of parameters you used? Is your sim with a mass loaded driver, as mine was? How much stuffing?