High Efficiency Speaker Asylum

Ping GM! the Vb of the combined sphere and plinth is now about 47-48 litres

203.129.43.154

I used a big&wide block-board thick door 35mm thick, and two more layers of 18/19mm MDF that I scrounged! About 17 litres added to the original 5 to 6 litres.

I can make each about 5.7cm's higher still, giving me about 12.5 more litres! IE 60 litres! (The circular holes are about 53 cm's across R being 26.5cm, 2206 cm2, times 5.7. I'd definitely be tuning this to ~20hz or 2/3 the average Fs of 30hz.) Approximately an EBS alignment!

The ports in the spheres are glued in, and would be very hard to remove, so I'm going to stuff the ones in the sphere that will face down into the plinth (becoming part of the bass-only enclosure). I'll put plastic mesh on each end, too.

I can buy 6.6cm i.d. extend-able ports to ~27cm's - the extension's i.d. is probably 7cms. This would fit with room to spare, in the existing 47l encl, plinth plus sphere.

So, ... roughly how long would I need - to start out my testing - for 25hz Fb in 47litres and 20 hz in 60 litres, with one of these. With the sphere sitting on on top - all I have to do - is lift IT up, and off the plinth part, and adjust the port length, and measure, and listen, again!
IT weighs 70 pounds or so!

And, is 6.6 cms enough to avoid air speed problems inside the port in a box this size!?

The next size up in extend-able ports is 8.5 (and 9cm) i.d, to 32cms long - or even more 9cm plumbing pipe!

I estimate there is about 40 cm's port length (interior height less a bit) available now, plus 4 or so more if I do go bigger/higher with the plinth.

TIA

Warmest
Timbo in Oz
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm

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