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Infinity kappa 120.9w in ported box.

post #1 of 7
Thread Starter 
I am working with a infinity 120.9w car subwoofer in unibox. It is intended for HT/music. I want to build a vented box approx 20" by 20" by 20". That gives me approx 91 liter internal volume after 1" wall is subtracted. I have simmed the driver with 72 liter internal volume, giving me approx 19 liters for the driver itself, bracing, port and stuffing.


http://winauto.ua/manuals/en/Manual-Car-subwoofer-Infinity-KAPPA-120-9W.pdf


I am inspired by SVS and hope to achieve similar performance. If I don’t quite get there it is OK. I just want a good sub for a reasonable amount.


http://www.data-bass.com/data?page=system&id=66


I have sim-data in PDF format here:


kappa120.9w.refleksbox.72l.pdf 114k .pdf file

kappa120.9w.refleksbox.72l.grafer.pdf 90k .pdf file


I have also simmed the box in winisd since unibox can’t calculate group delay. I get a max delay 31ms at 21Hz and a smooth phase-plot showing 305 deg. at 10Hz, 222 deg. at 20Hz and a steep slope towards higher frequencies.

Let me hear what you think. Suggestions are welcome :-)

Dan
Edited by splotten - 10/5/12 at 8:43am
post #2 of 7
everything looks good except that ricci mentioned the native tuning frequency of the svs is 20hz. looks like your model is a little higher than that. with a 500w amp, i suspect that you will be within a db or so of the svs.

it is kind of a coincidence, but there is another guy who is doing the exact same thing and i can't remember the last time that someone around here built a clone.
post #3 of 7
Thread Starter 
Thank you for looking it over.

I completely new to this, but for now I have chosen 24Hz box tune in an effort to juggle port size, port length and cabinet size. Any deeper and the port becomes unmanageable in length if I want a decent port size. The SVS has a shorter 4” port, but if I try that dimension port velocity increases somewhat and comes outside the recommended values in Unibox. Also, as the port length increases the port resonance creeps down. I want to X-over at 80Hz and chose to keep the port resonance at roughly 3 x 80Hz. I am not sure if the port resonance is very important but 240Hz or so feels safe as it would a long way down when x over Is applied.

I have done some more calculations and with the proposed 20” cube I’m close to the anticipated internal volume with 2 internal bracing frames, the driver and the port. I have increased the port size a bit to keep port velocity down and it stays at 24m/s with 250 watts applied. I don’t understand how SVS can get away with a 4” port. In my box that would give me 34m/s at 250 watts applied. Am I missing something?

Going forward building the actual box I’d like to ask if there I any restrictions in placing the internal port? I’m building a square/slotted port (16 x 7cm) and the natural way to do it would put the internal port right up against the back of the cabinet. Is that OK or would it somehow impair the airflow not having the port “in midair”? I could build an internal "chimney" if that is better?

As for internal dampening I think I’ll go with lining the cabinet walls. I’m thinking 1” soft insulation is a good place to start. It’s not a lot but it certainly is a lot more than my old XTZ 12" sub. Maybe 2” insulation is better?

I’d like to round over the port ends, hoping to minimize port noise. Unibox predicts a 1” increase in port length with “2 flared ends”, however I does not say anything about the size of the flares. I’m building the whole box, including the internal port with 1” MDF so I have sufficient material to make a decent round over. I guesstimate that the predicted 1” increase in port length can be applied if I round both ends with a ½" bit. Is that in the ballpark?



Thank you for your time :-)
Dan
post #4 of 7
you have really done your homework.

"for now I have chosen 24Hz box tune in an effort to juggle port size, port length and cabinet size."

that's cool. i just wanted to mention everything possible. the amp probably has a second order high pass filter built in around 20hz or so, so your driver will have good protection and you'll still get down to about 20hz or so.

"I don’t understand how SVS can get away with a 4” port."

a lot of chuffing can be masked by spl at higher frequencies and the roundovers really help too. that is something that won't show up in a sim.

"As for internal dampening I think I’ll go with lining the cabinet walls."

that isn't necessary. lining cab walls is needed on mids because of reflections.

"I’m building a square/slotted port (16 x 7cm) and the natural way to do it would put the internal port right up against the back of the cabinet."

as you start to go under about one diameter, the port can start to get a little jammed up. that can actually be used to reduce tuning by a hair, but you don't want to go too close.
post #5 of 7
Thread Starter 
Ok thanks.

I’m on the right track I guess. Good to know :-)

I will skip the lining, focus on good round overs and keep the bigger port area and the 24 Hz tune.

I am not completely sure that we are on the same page regarding the internal port. Are you saying that i shuld keep the mouth of the internal port away from the cabinet walls and the internal bracing, at a distance no less than the diameter of the port itself?

Many subwoofers with slotted ports have the cabinet floor and backwall as an integral part of the vent, and because of that, the port right next to the back cabinet wall. Is that not a good practice or is the other approach just a little better?



Dan
post #6 of 7
"Are you saying that i should keep the mouth of the internal port away from the cabinet walls and the internal bracing, at a distance no less than the diameter of the port itself?"

roughly, yes. the short diameter, not the long one. 7cm in your case or a little less will be okay and will give you a little bit of lower tuning. i wouldn't jam it up more than that.
post #7 of 7
Thread Starter 
Ok. That gives me a good guideline designing the internals of the cabinet. I might go with 21mm MDF instead of 1”. Calculated weight with 1” MDF and good bracing is close to 80 pounds. That’s a little much. 21mm might also give me an overall smaller box.

I find I have a hard time learning google sketchup, so it might take me a while to get it done, but I’ll post my result here when I’m done.

Thanks again.


Dan
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