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entropie
01-25-2008, 12:28 PM
i was wondering if this concept was even viable. imagine a small (1.0 ft) sealed fiberglass enclosure tucked in the rear corner of a trunk. the majority of bass waves are trapped in the trunk and only find passage to the cabin through small openings in the rear deck.

question: is there a way to design ports for those openings to facilitate the passage of bass waves through them? basically, i think it's like designing a single reflex bandpass enclosure.


http://www.the12volt.com/12voltimages/bandpass.gif


thoughts or comments?

dman4486
01-25-2008, 12:29 PM
sounds like a PITA!

Hecta G
01-25-2008, 01:03 PM
sounds exactly what i was trying to do in mine but turned out to be a royal pain. My guess, from your description the port would lead into your trunk?

I can tell you what I was going to before I figured out that my trunk would not be as usable as I wanted.

My intension was (now this is where the pros and the season veterans are going to think I am off my rocker), after figuring out port length, i was going to use those straight cylinder type of balloons and other materials to mock up a path or a "tunnel" in which the air mass would travel from somewhere inside the trunk to the cabin of the car. Once a had a good path i was going to start fiberglassing.

I was prepared for the worst but I thought it would just take me too long and with wife and kids......aaaagh the drama....

Hecta G
01-25-2008, 01:30 PM
after reading your thread again it hit me, you are wanting to use the trunk as the ported enclosure???

If so, that's not what I was thinking about. In that case you'd have to be sure that your trunk was truly air-tight minus the port of course since you want all the air to exit the port not some crack in the trunk.

entropie
01-26-2008, 10:29 AM
after reading your thread again it hit me, you are wanting to use the trunk as the ported enclosure???

If so, that's not what I was thinking about. In that case you'd have to be sure that your trunk was truly air-tight minus the port of course since you want all the air to exit the port not some crack in the trunk.


yep. basically the way i figure it is the trunk is essentially the second chamber of the enclosure. based on reading this pdf file (http://www.ozaudio.com/docs/Bandpass_Enclosures.pdf), "as the ported chamber increases in internal volume the system becomes more efficient." however, as that happens "the bandwidth becomes thinner."

with my car, a '95 bmw m3, the trunk is very tight and i believe my alumapro bp-10 suffers from the "one note" bass mentioned in the pdf file. now, i understand to gain the exact appropriate port length would be impossible due to the fact the trunk is not sealed blah, blah... but my question is: does anyone believe the use of ports hanging from the rear deck (possibly tappered ones) would improve the range of bass.

fyi, with the seats down, the bass notes take on a new persona. with the seats up the bass gets greatly silenced.

bass maniak
01-26-2008, 10:42 AM
Be a ***** to figure out the volume of the trunk to port it correctly at the freq you want......

mile098
01-26-2008, 11:40 AM
^^x2 and ud have to find a sub that is suitable for the space in your trunk minus the sealed enclosure...and sealing off the trunk is sort of a mission impossible...probably doable, but IMHO not worth the effort put into it

theothermike
01-27-2008, 12:10 AM
here what i think you could do.it sounds like a form of IB to me.

1 board hold sub. the baffle board in an ib setup. the front board then directs the waves through rear deck. and the port is on the rear deck.

seems like ib to me.

Punk In Drublic
01-27-2008, 02:19 PM
Plus if you put anything large in the trunk, the volume of the ported part would change, as well as the tuning.

entropie
01-31-2008, 12:33 PM
thanks for you input guys.
i'm gonna keep thinking about it.

Immacomputer
01-31-2008, 12:50 PM
You should experiment with various lengths of PVC pipes. Even though it will be difficult to impossible to calculate the tuning frequency, you could always experiment by ear to see what you think sounds best. I doubt it will work well but there is a pressure build up in the trunk which will excite the air mass in the port.

I would start with like 2 or 3 4" PVC pipes and start them with a length that is close to the max height you have available while keeping the ports about 6" from the bottom of the trunk. Then, you can trim them down and see how the sound changes.

Be careful though, as making small changes may make the differences harder to tell. You may want to have two sets and make one set your max length and make the other only about 4" deep each or so. Replace them back to back and see if you can tell a difference. It will only cost you around $10 at Lowes for the PCV pipping.

entropie
02-08-2008, 10:57 AM
thanks, when i get around to trying i'll post my findings. (might take a while to find time)