T18 Turbocharger

[jbell]

If any of you have followed the SVS wars, you'll recognize the term 'turbocharger' or 'variable port tuning' that the HSU, SVS, and other ported cabinet subs have embraced.

The idea is by either lengthening a port, or blocking one of many ports, you can change the tuning of the sub, so that when you want loud, you can have it, and when you want low, you can reconfigure for that as well. You don't have to 'settle' on what the manufacturer wants to give you.

Well, I've been playing around with a T18, and it only has a 7' long 40hz path. So, what can be accomplished if you lengthen that path? Can you do what the ported cabinet guys are doing, and get HT low when you want, and loud(er) music when you want?

The answer is kinda, yes. By adding this, I got +8db @30hz, and +6db @ 40hz, BUT... still nothing really usable below 28hz -- that is true with or without it. Now, it's not exactly the same as a ported cabinet, because it was overall louder, and I had to turn down my amp to get it to integrate with my mains with this added. It gave some more 'authority' to the sound of the T18, so I'd say it's worthwhile, when you just want 'a little more.'

So... If a T18 is all the wife will let you in the house with. (A table tuba is out.) Build it with dual drivers, 24" wide... and when the guys come over, set it on top of the turbocharger and crank up the movie!!

[bgavin]

Build your platform so the sides extend up to the top of the T18. That is the part that will lengthen the horn significantly.

Calculate the flare using the T18 mouth flare.

[jbell]

I followed the flare on the bottom, and since it rocked the cabinet back, it allowed the face to continue the flare as well.. Wall corner kinda extends the horn on up, but you are right, there's nothing on the other side. my goal was to see if that was enough...


edit: stood plywood up on both sides to make sure that the horn path was being followed up the wall, and it made almost no difference. Maybe a 1/10th of a db here or there.

I was really amazed that I could get 6db just by doing this.. Which is the same as a double in cabinet/power.

[Sydney]

Keep it up jbell!,
The small size of the T18 makes it ideal for experiments.
BTW: Along similar lines, I had sketched out several possible "horn extenders" for the T18 that would cradle 2 cabs and extend out the 12.09 degree final flare, adding 4' to 8' + of horn length.
In my case, it was considered for integration to the underside of wooden seating risers.

[jbell]

yea, I'm more efficient with the cradle, and it goes lower, but it seems like I'm still maxed at 126.... Once I get there, more power does nothing...

So... for those wanting above 126 in room, you'll need more than one T18.

[Sydney]

And ear protection!

[bgavin]

This is a variation of the V-Coupler, but for corner use. The idea is completely sound (there's a pun), so no reason why it won't work.

It doesn't take much imagination to come up with a modest two-sided plate to extend the horn another 4' up the wall. This can work just as well in a bar, as it will at home.

Accurate dB measurements are a must.

[jbell]

This is a variation of the V-Coupler, but for corner use.

That hadn't occurred to me, but yea, I guess you're right... I don't completely get why I hit a wall at 28hz and 126db... Am I hitting xmax?

Also, is 126 past what most people are getting out of T24's? I'd have to think this is close, and to do it with only a pair of $25 dollar drivers, is cool.

I'm tempted to build a 4pack... seems like a nice small modular way to get a TON of sound. (a 4 pack should exactly equal the volume of a single T36, and if my math is right, should actually outperform it...)

[RubiconProSound]

I'm currently building two T18's with an extended mouth so that they look like a mini T30. My goal is to see if there is any benefit to V plating them similar to the larger Tubas. Once they're done I'll do a comparison between these and my AT's. I just got True RTA and my Behringer RTA mic is on the way....It's just too cold in the garage right now to finish them.

On a side note... I thought I read somewhere that when you extend the path length you should also increase the driver chamber airspace in proportion...

[Sydney]

I thought I read somewhere that when you extend the path length you should also increase the driver chamber airspace in proportion...

Reasonable assumption...
T18 and TT use the same driver. The TT has enough load from the front 13' horn length that the the rear chamber has minimal loading.
Ref. AudioXpress articles on the T18 & TT.
( I've played enough with the rear chamber volume of my T18 to see "where it was goin'" )

[Bill Fitzmaurice]

I thought I read somewhere that when you extend the path length you should also increase the driver chamber airspace in proportion...

Not necessarily. A simple answer doesn't exist.