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Old 5th November 2006, 08:54 PM   #1
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Question subwoofer, box calculation

Hello im new to this site ,just found it and already love it.

In the past i have built a few speakers in form of pre calculated kits (just building the box and putting everything togteher).
Now however im going to build an active sub from scratch, just bought the amp (hypex hs 200) and driver (dynabel dy9610).
I did put all the data for the driver in on winisd pro and i plan to go for a wented box with 40l volume -3db on 25hz and a nice flat response curve.
The question however is wether i got this right or messed it up somehow(what did i not think about ?).
So im hoping someone with more knowhow will take the time and check it for me and give me some advise, i have put the driver data on the bottom of this post.
Then about the shape of the box:
Im in the lucky situation of having access to a cnc machine(and i know how to program and run it) so i can fool around a bit with the shape of the box,im thinking curved sides 5 cm thick made out of 30 mm mdf witch i cut to shape and stack to get the needed height.
In the sides i will cut slots that will later be filled with lead or sand to give it som more dead weight.
My thinking is that curving the sides vill make them stiffer, but does it have any negative effect on sound?

Ok thats it for now all input is welcome

Driver data:mms 212g, cms0,12mm/N, sd320cm2, bl15,6 N/A, re 3,7ohm,qms2,71, qes 0,65, qts 0,53, vas 16,7l, xmax 28mm, pe 600w
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Old 5th November 2006, 09:38 PM   #2
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Couldn't see where fs (Resonant frequency) was...I needed that to crunch some numbers.
Perhaps if you keep the curvature at less than 100mm Radius you should be OK....think of the waves traveling thruout the box & if you note some possible focusing of waves building up....symetrical dimensions should be avoided....think random dimensions so as not to "pile up" waves. The driver should be offset so as to keep with the randomness theory.
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Old 5th November 2006, 10:22 PM   #3
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Default fs

Hello Rick thanks for that fast reply , the fs is 32hz for the driver.
As for the shape it would be something like rifle bullet (flat front and the sides curving at first out, and then back in until they meet in a point ) hope you understand what i mean by that

jan
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Old 6th November 2006, 04:44 AM   #4
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
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My calculations for a sealed box were way too big..16.9 cubic feet for a Qtc of 1.0 (Underdamped) bigger for a Qtc approaching Ideal at .707.
I was thinking an oblong box with 4 inch radia at the corners with layered up seven ply plywood some 15 inches high...varnished outside with a dark smoked glass top.
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Old 7th November 2006, 12:49 AM   #5
Ron E is offline Ron E  United States
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Your box calcs look fine, but you really need 2-100mm dia ports or 1-150mm dia port. Look at how long your port will be. You might wish to consider PR's.

Shape doesn't matter much at low frequencies, so do what you want within reason.

In a sealed box, that woofer is more suited to cars, but you may be able to EQ it a bit with your plate amp. BTW, Ricks calcs appear incorrect.

Good luck
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Old 7th November 2006, 09:35 PM   #6
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Thanks , but (might be a stupid question but anyway) whats a PR ?
Was thinking about using a square port 5cmx10cm witch would give me something like 50 cm lenght, sound about right ?
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Old 7th November 2006, 10:17 PM   #7
lndm is offline lndm  Australia
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A long port can support resonance near the bass range. FWIW, 50cm is a quarter of a wavelength at around 170 Hz. Making your ports shorter, and correspondingly narrower would work but then you'd find they couldn't keep up with the airflow at high volumes. It's up to you.

Or you could look at the Passive Radiator(PR), as Ron E said.
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Old 8th November 2006, 02:20 AM   #8
Ron E is offline Ron E  United States
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You will want to keep port velocity down. - 2x 100mm diameter ports is what it takes to stay under 5% of the speed of sound in the vent. Whether you can use shorter, smaller area ports is up to your listening style - if you like loud, you should go with the larger ports, preferably flared, or a PR. If this is just for average home use, I would probably still use at least 1x 100mm diameter port - which could work fine even at relatively high SPL as long as it has a large radius flare at each end.
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Old 9th November 2006, 04:04 PM   #9
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Can i bend the vent, like for instance make it like a spiral or will this obstrukt the airflow to much?
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Old 9th November 2006, 09:28 PM   #10
lndm is offline lndm  Australia
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You could. You could try to run the port along the edges to save clutter. That would also give you something to anchor it to. Ending the port away from the edge is good. Sorting through the PVC fittings in the hardware shop may take you back to your childhood meccano set days A cardboard port can be a good choice.
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