downfiring port help please

[johnmark]

Had a Madisound kit laying around for years and finally put it togeather for my brother in law- the Cygnet kit that uses the Seas P21RF/P woofer and want to try a downfiring vent as the bookshelf speaker will sit back against a wall and on a shelf. So I cant put vent in back and don't want to cut hole in my baffle. I will add some short rubber feet to make speaker sit up an inch or two and put vent thru bottom of cabinet.

Is 1-2" enough clearance ?

Also if someone would help verify my calcs I would really appreciate, as I am only using some freeware to figure vent.
my cabinet volume is .6cf = 17 liters (I know smaller than optimum)
these are the manufacurers specs
Cms 1.0 mm/N
Sd 194 sq cm
Vas 48.3 liters
Qms 1.70
Qes 0.42
Qts 0.34

I come up with a 3" x 10.5" vent to get about 58hz F3

Thanks

John

 

[infinia]

Hi
Mad kit uses flared 2" vents, so your 3" ones will be much longer and eat up valuable box volume.
Bottom port would need at the very minimum the radius of the port for clearance to floor/stand ...wag YMMV. But I would use the dia me thinks.



link http://www.madisound.com/catalog/product_info.php?products_id=379

Recommended cabinet dimensions are 19" H x 12" W x 10.5" D. See attached PDF for a detailed drawing.

Alternate box alignments:
0.75 cubic feet with Flared 2" vent by 7" long for an F3 of 48Hz
or
1.0 cubic feet with Flared 2" vent by 6" long for an F3 of 43Hz
or
1.2 cubic feet with Flared 2" vent by 5.5" long (or non-flared 2.5" vent by 8.5") for an F3 of 40Hz.

(Subtract 1" from length if using non-flared ports on any of the above)

Sealed box of 0.25 cubic feet will result in an F3 of 90Hz

 

[johnmark]

Right I know what the page at Madisound says,
But I already have a smaller box made and have some 3" port on hand.

 

[Ron E]

Is 1-2" enough clearance ?

1-2" clearance is fine and closer to 1" might be beneficial in this application, lowering tuning slightly and suppressing the ~80Hz bump in response you otherwise would have.

Your calcs are fine.

 

[crazyhub]

Re: Re: downfiring port help please

1-2" clearance is fine and closer to 1" might be beneficial in this application, lowering tuning slightly and suppressing the ~80Hz bump in response you otherwise would have.

Your calcs are fine.

with a 58hz F3, 17 liters VB, 3" port diameter, external components R 0.4 ohm, walls covered, Unibox gives me 4.55" port lenght, not 10.5"!...and a nice 4db bump around 80hz yes!
Flat response with a 52hz F3 with a dia port of 3" and 16.5" lenght / or if dia port 2" length=6.9"