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As recall, Vb is to be tuned to speaker free air resonance 25hz.....At the time I made the
PVC duct, I made it long to be trimmed if needed....It sounded so good I left it....... later
I added A coupling / splice to extend the duct to facilitate testing / tweeking. I should
test the Z and check the two resonance peaks...I will take photos..You will enjoy you
cabinets what is the Vb ??? ........GC
FWIW, it calcs to ~14-15 Hz as a simple BR depending on the amount of internal bracing which is a bit too low for a duplex in theory, but real world performance trumps it of course.
GM
This is really only true when driven with a high system impedance (Qt). When the driver's Qts dominates system Qt, it also dominates cab alignment.Quote:
Originally Posted by 604man
GM
this is really great info ,although have used the 604 in max 9 cft boxes and 6 cft boxes, was always afraid of heavy TT rumble , but now with big digital bandwith every one should try it once.
how inert should the cabs be to avoid internal mumbo jumbo
thanks and a happy new year
It's not about how inert it is, but how stiff it is since it's a lot easier to push the cab's Fs above the intended BW than below it to ensure it can't be excited. I mean if you want to make it inert enough to push its Fs below the intended BW, that's fine, just understand it needs to be built out of many inches thick concrete or similarly massive material and damping TT rumble will probably require walls built like concrete suspension bridges to get such a low Fs damping.
Others have gotten close enough with stone slabs (slate, marble, etc.) over a plywood construction, but they were small speakers with a fairly high Fs, not the low tuned, relative behemoths we ideally need; so using at least 19 mm no-void Baltic or Apple Birch combined with some bracing to tie all six sides together to keep it from 'breathing' will work fine, and while not exactly light, at least it's movable by most folks with a cheap hand truck if there's not a lot of stairs.
Making it some form of TL allows less bracing to boot since its high aspect ratio places most of the resonant pressures along its length, so not as much cross bracing required. Factor in that the bigger the cab, the lower the pressure nodes and very little bracing is required, mostly in the form of ridge boards glued in to break up the large panel areas into a lot of very high aspect ratio strips with a cross brace to do double duty as a motor support.
All that's left then is reflections off the back of the driver, which is easily handled by the standard top, one side and back being covered with insulation to 'taste'.
GM
I just tried posting 5 pictures with text and several replies to posts and *EVERYTHING*
went off to never never land....If you would like photos comments e-mail me @
george_craig@att DOT com
George don't use the attachments, Do you have a Photobucket,Flicker,Picassa, account.If so, just upload the pics to those hosts copy the direct link and then click the insert image link above in the toolbar when replying. You can insert up to 6 images.Just like this,heres the button on the toolbar. :2thumbsup:
http://www.hostboard.com/forums/hbmc.../2011/01/3.jpg
BTW: You don't need that Http:// in the insert image link,paste over or delete that.
I posted 17 photos ; Image hosting, free photo sharing & video sharing at Photobucket
..............GC
Those are very nice boxes, but I think you might need a few front to rear braces. Both of those panels have a lot of big surfaces that aren't tied to anything. OTOH, if they aren't adding colorations, leave them be.
Great job, and I like the adjustable ports.