JTR Noesis 3TX Port Geometry

Max Warasila

Graduate
Feb 20, 2013
1,217
72
48
Richmond, VA
Does anyone know how the 3TX port is formed? It doesn't seem like it has enough space for the path length required, and I also don't understand how the length works given the angled cabinet past about 10cm deep into the cabinet from the front.

Thanks in advance.
 
Max,

Shelf (or any shape) ports can be angled on the sides, the length works out to be roughly what it would be with a straight-sided shelf port with the same area as the mid-point of the trapezoid. The 3TX Fb is likely near 80 Hz, so does not require a very long port.
The port could have a continued section going up at the back behind the lower woofer, can't tell from the photos seen.
 
  • Like
Reactions: David Morison
Plus one to everything Art said of course.
Remember also that a shelf vent can behave as if it's larger than the physical shelf, due to 3 out of the 4 walls continuing on beyond that.
So if you were comparing the predicted vent length from a modelling program like WinISD etc, you'd need to adjust that expected length downwards.
Using the alternate End Correction factors in the first post here, a rough estimate of something like the 3TX (30l net internal tuned to 73Hz) the actual shelf length required might be as low as 3cm; ie only a double thickness of the timber. Even if the net internal volume of the cab is smaller, or the tuning lower, the required length is still short - 25l to 70Hz would need 15cm of shelf, compared to the 39.2 predicted by WinISD.

HTH,
David.
 
Hi Max,
Art and David have forgotten more about speaker building than I've learned yet, and the only reason I'm chiming in is because i have a pair of 3TX. I'd happily share picts and dimensions of the box, but since it is a current commercial product, I don't feel that information belongs to me to give away.

What I do think is fair to say, is that the guys' information on how shelf ports work is reflected by measurements I've taken.
(I tried setting up a 3TX with active x-overs for a learning exercise..... http://forums.prosoundweb.com/index.php/topic,164582.0.html )

I can also say I'm not so sure when you call a design a ported box, or when you call it a transmission line.....I think it gets hazy based on the actual port geometry....
 
Last edited: