Help me build a tube TL?

[SamV]

Hey everyone,

I'm wanting to making an outdoor PA unit and need help. I'm wanting to build a tube TL type enclosure, I had a read through the Acoustic Wave Cannon page and well the maths killed my head as there was a lot of it that was similiar but different.

Basically I have a 11.5 foot length of PVC tube that has an internal diameter of 8.7" and and external diameter of 9.7".

I need a lot of bass, what's the best way to go forward?

The only subs I have at the moment are 4x JBL GT4s and a 900w of RMS power on tap at 2ohm (1000w @1ohm).

JBL Specs are:

12" JBL Subwoofer

Frequency Response: 28Hz - 450Hz
Sensitivity: 93dB
Impedance: 4 Ohms
Voice-Coil Diameter: 50mm
Cut-Out Diameter: 283mm
Mounting Depth: 161mm
Overall Diameter: 311mm
Vas: 100.45 liter
Qts: 0.43
Fs: 24.75Hz
Qes: 0.46
Qms: 6.46
Re = 3.56
Le (at 1kHz) = 2.54
Sd (inches^2) = 82.31
BL = 14.78
Vas (cu ft^3) = 3.22
Cms = 227.58
Mms (g) = 181.74
Mmd (g) = 174.40
Hag (inches) = 1.30
Hvc = 0.31
Xmax = 12mm one way

[GM]

Greets!

Hmm, I did a detailed example for designing a WC near the end IIRC of one of the long threads. Anyway, with only a 138" long pipe you'll only get loading to ~49 Hz.

Anyway, nowadays simple tapped pipe horns are the latest DIY high SPL 'hot ticket', so what gain BW are you interested in?

GM

[SamV]

Only 49? When I did the maths it worked out to around 30hz but then my maths could be flawed.

What is BW? I'm not sure about the gain, I just want something that'll function as a good subwoofer for outdoor events.

[GM]

I really need to turn my computer off late at night rather than try to respond to as many threads as I can before hitting the sack. Anyway, its been awhile since I calc'd one of these and in my haste did a really poor job of explaining that these only work properly AFAIK when the driver's Fs is a half WL of the total pipe length, which is ~49 Hz with a 138" pipe, but you're right in that this equates to a ~24.5 Hz Fp with a usable BW of ~32.7 - 98.2 Hz.

If you still want to use this driver in a WC, then AFAIK you'll need ~274" of pipe for a ~12.3 Hz Fp with a usable BW of ~16.5 - 49.5 Hz. I've never tried loading a too low Fs driver into a WC, so not sure how well it will perform with driver Fs ~ = Fp. Care to build one and let us know? Regardless, one WC won't play all that loud outdoors, though four may be enough.

BW = bandwidth, so what frequency response do you want your subs to reproduce? FWIW, typical peak SPL demand for rock acts is from 60 to 80 Hz, with requirements at 40 Hz down a full 25dB from that at 60 Hz.

GM

[RobWells]

Free (ish) demo of wave cannons..


As you're in London take a trip to Thorpe Park and have a ride on the Nemesis. The last time I went there they were using 1 or 2 wave cannons in the place where you got on the ride. They're bolted to the ceiling. (I last went just before they opened Stealth)

Rob.

[SamV]

I've got a friend who has a B.se Acoustic Wave Cannon.

What kind of parameters do I need to look for in a sub to make the tube work? At 11.5ft it's it's marginally shorter than the AWC. I have £200 to spend on a suitable sub.

[GM]

If the pipe's internal diameter is ~the same as the WC's, just buy a WC replacement driver.

GM