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Hi Kevin> The disadvantages of going that route are that you have to concentrate on building the riser the same way you would any other subwoofer, well braced. Yes, harder than a sonsosub> You also don't have the advantage of moving the sub to optimize location. True, though with the driver and ports on 3 other sides I hope will partly mitigate this> If you get any kind of port chuffing or out of bandwidth noise, you will hear it much easier than you would with the subwoofer at a more traditional locationThat’s mitigated by sizing ports so that port speed at high volume is less than 25 m/sec (and at moderate volumes, less)?
I appreciate most of your points, eg that 18-60 Hz is most important. Though as I see it, an EBS compared to sealed, moves the f3 down a little more than am octave. So for sealed KISS, even if of a lesser importance, the trade-off is quite some extension is lost.I hadn’t checked group delay, but thought that below 50 Hz, it wasn’t really audible(?)The long ports can be at the far end from the listening position, about 10 feet away, facing the opposite direction.If I’m using Unibox correctly, the Tempest in 25 cu feet tuned to 13.5 Hz: with 4 * 3.6 inch (stormwater pipe) ports need ports lengths of 21 inches, and has its 1st resonance at 294 hz, well outside the passband. So it appears that done this way, chuffing and resonance would not be a problem. . ?
Post the dimensions of your room and I'll predict your room mode frequencies for ya.As you know, we cannot "hear" below 20Hz, although we can detect and "feel" frequencies as low as 2Hz. If your port noise is below 20Hz, it can be neglected. Also, designing a system for a predicted relatively small SPL increase in subsonic bands (like pushing f3 down from 20Hz to 12Hz) may or may not be detectable and may or may not be worth the efforts, especially once the system is installed in a space where those effects can be masked or completely cancelled by room modes.Now don't get me wrong, I think if sub-sonics interest you then you should go for it and build the system that models best to you and see what happens. Only the meters can tell you for sure what you are getting, and that requires building something to take the measurements. My only interest is making sure you understand the trade-offs, especially when attempting such a large scale construction.As an aside, I once built a theater system where we consumed over 100 cuft under the stage in an EBS alignment using eight 18" Harbinger woofers in push-pull alignments. It modeled out to 8Hz at over 120db. However, after all the careful planning, the custom ports made from machined sewer pipe, and many hours of hard work building the thing, it measured and sounded better with the ports sealed and the woofers operating IB. Who knew?
Thanks again dyohn, That on-line calculator is good and does highlight a problem. When I input the room dimensions more accurately, I have a big problem at 51 – 56 Hz: one axial and two tangential modes in that small range. Maybe I should diy (is it?) a Helmholtz resonator tuned to 55 Hz?> still am not sure why you feel you need 12Hz subsonicsI do enjoy the odd bit of organ music What Hz might a T Rex’s foot stomp and similar effects be at?Btw, the word from an EBS evangelist http://www.hometheatershack.com/forums/diy-subwoofers/print-1820-llt-explained.html?pp=50
That was one of the best posts I have ever read on any forum or paper about audio Kevin. You should cut and paste it everywhere. I especially like "Inaudible is inaudible and you don't get extra brownie points for making it twice as inaudible as another solution." Brilliant.The "true believers" out there will argue with you, of course, but they will anyway no matter what you post unless you are simply reinforcing their preconceived notions. But anyone with any engineering background - and especially acoustics engineers - will applaud you, as I do. Thanks for writing that!