Hey all I'm starting on a new project where I want to meld a sealed box with a T-line'esque enclosure.
I'm using a 15'' Dayton PA380 driver.
Imagine the driver loaded into a sealed box (1.75' for this driver's specs). Instead of having the cone fire into open space as sealed cabinets do, I want to enclose the forward sound pressure in a 5 x 16" labrynth tuned to 47Hz (about 48" long). I'm not sure if this is a 4th order system or not... It's like taking a sealed box and sticking a giant port in front of the cone.
Is this a feasible design since the only direct sound would radiate from the 5"x16" port mouth?
Thanks!
What are you trying to do? That is a PA/instrument speaker.
You will need to model it first as a coupled cavity enclosure sealed one side and ported the other.
That will tell you the correct volume of the sealed cavity, it will also tell you your tuning frequency.
Then you need to model the line. Your tuning frequency Fp will be the same as the ported model. That will then tell what the pipe length Lp needs to be.
You need to run a TL model as the volume of the pipe Vp is also critical and related to driver Vas.
A two to one taper on the pipe away from the driver would be optimal I suspect The driver should be placed 1/4 to 1/3 of the distance of the length of the pipe from the closed end, to suppress third and fifth harmonics.
The you need to decide if the pipe should be aperiodically damped or not. If the pipe is not damped, then I don't think you will have any advantage over a port tuned coupled cavity box.
If damped you probably won't have a lot of output.
This driver is very low Qts, and I think the Qt of your system will be very low with this approach and not very satisfactory.
Coupled cavity designs, of which this would be an unusual variant have had their day in all honesty and are not very satisfactory except as an extender to a system without crossover. Remember they are band pass top and bottom. If you use a full crossover they cut off too soon on the top end to be any use from an LFE output, when the mains are rolled off.
Now this is where the significance of total system Q is important. One of the big problems with coupled cavity systems, is that as bass is tightened, with low Q, then the bandwidth is progressively restricted as Q decreases. As you increase Q, the bandwidth increases, but the quality of the bass decreases. Bose bass modules, with their awful gooey bass exemplify the problems of high Q band pass designs.
Your speaker I think will be the poster child for one note bass. This has long been a justified criticism of band pass designs.
As to order, my guess is that the undamped line would be fourth order and the damped one second order. However you are in uncharted waters here.
If you don't mind the high likely hood of wasting time money and effort go ahead. If you don't want that risk, then don't build it.
One thing for sure, if you pull the sealed box volume, pipe lengths, cross sectional area and pipe volume out of the back of your neck, you will waste your time for certian.
If you do the above calculations and measurements after your build, it would be publishable. This is really to be regarded as a research project and not likely a useable practical project.
