Acoustic enclosure for a DC

I have done enough of my 'must do now that i'm retired' domestic jobs to enable me to start thinking of my list of 'ME' jobs, of which the first is moving my JET (= generic) 2HP DC outside of the shed. I am doing a major rearrangement of the shed which will put me out of woodwork action for a while, so I might as well upgrade my dust collecting at the same time. The key elements are

• move the DC outside
• upgrade all internal rigid PVC pipe to 125mm
• minimise lengths of flexible droppers and increase all to 125mm
• fit (or at least allow for) a 125/150mm cyclone
• increase dust outlets on (at least) the drum sander and disc sander to 125mm (from 100mm and 50mm respectively)
• fit 125mm flexible to all other machines regardless of size of outlet
• continue to develop a range of 125mm PVC DC fittings including new couplers, rigid to flexible adaptors, replacement lids for a number of drum sander brands and 125mm (and 150mm) bell mouths that fit to sheet metal flat plates to upgrade table saws, thicknesses and planers

Other than this ....my time is my own?
The current plan to move the DC outside involves a new concrete slab outside the current pedestrian access door and, as I have fabulous neighbours, an acoustic cubicle manufactured from acousticell concrete blocks.
Now, some design logic (notice the small font on "logic"?);

1. the air input to the DC includes the dusty air rushing in through a 125mm diameter pipe and through the impeller and out through the pleated filter which has a huge surface area AND the air drawn in through the cowl of the TEFC motor that drives the whole calamity.
2. SO, my acoustic cubicle will require an outlet of AT LEAST the same area as a 125mm pipe AND a further inlet and outlet of AT LEAST the inlet area of the motor cowl.....?
3. as the cubicle will have an entry and exit maze to stop direct line transmission of noise, there will be at least a 4 fold decrease in flow efficiency and increase in surface friction SO....
4. I will design it with an entry and exit baffled maze of at least 6 times the cross section of the inlet pipe (125mm DIAM) and TEFC motor cowl (200mm DIAM)
5. rather than have filtered air continuously recycle within the cubicle and potentially increase the temperature, I will endeavour to get the motor cooled by its own supply of outside ambient air.

Has anyone built an enclosure, internal or external, that was TOO well sealed and hence they suspected that the DC efficiency has decreased due to back pressure?

(an unusually serious....) fletty

Acoustic enclosure for a DC