Enclosure Design Fundamental Q:s

TimberJon
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I dont know anything about subwoofers.

I can only guess that the bigger the volume, larger the drivers, and more power they can handle (RMS) the larger the ports, or more ports will be needed.

Id like a box that can utilize my two JL 12W7-3s, and through slot-style ports, fire both into the trunk, and into my cabin from between the rear seats. Attatched is some rough sketches of my ideas.

What i dont know, is the math required, (the formulas wont even help me) and the fundamentals. Ive seen 4 round ports, but slot ports arent the same.

To get an idea of where im going, i need to know if: when you add more ports, does the volume in the box have to increase or decrease? does it matter how far the bass has to travel out of the slot-style port? Im curious, because of my intended design. If it can work, Do i cut the volume? or add some.

If its just stupid, then can i just stick the usual Two ports and fire them into the cabin? The box design would be odd if thats the case. I'll have to think of how ill do that. im thinking (top view again, drivers at the bottom) start the channel at the front of the box, run along the sides to the back, angle 90 degrees to the center of the back panel, and exit, dual slot-style.

Possible?

 
larger the volume, the less power it needs, as the subs will be more efficient. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

as for your designs, I really haven't thought about having dual pot exits like your first design. your second design resembles a bandpass, and it usually doesn't sound good.

if you add more ports, the port legths will have to increase dramatically.

search for the net for winISD pro and play around witht the program a bit to know what is possible and what is not.

 
Thank you..

you mentioned that you really havnt thought about dual port designs. If i dado and rabbitbit the necessary places for structural support, liquid nail, drywall screw every 4 inches, and vulkem (sealant used in petroleum industry) the joints, do you think it would work ok? i can always start over. But id like to know if there are any negative effects of having the port structure like that. should i shorten it? you said lengthen. do you mean make the channels run longer?

 
after staring at the 1st CAD drawing for a min or two, i see it this way.

If the W7s are mounted facing the rear of the trunk, then its a dual ported enclosure. Its firing open air into the trunk, through the ports into the trunk, and through the ports, into the cabin. Since its not sealed by the subwoofer itself, the cabin and trunk are almost sharing the air space. Im wondering about bass boosting properties, or cancellation issues. I look at it as the ripples of bass the subwoofer it sending out, and how the waves are coming out of the port in the trunk. do the waves hit each other and mess up? or does it all sound the same.

The front of the sub is pushing say 50% of the air. but the rear of the sub (inside) is pushing air out the rear - 25% - and back into the trunk - 25%.

SO, i see two points pushing air into the trunk while there is only one point pushing air into the cabin. it may not be air.. but its how i visualize it.

Q: will the bass bounce off the trunk, and get ****** into the cabin? like the pressure of 2 against 1? will it equal out? or would it be better to fire the 2 points into the cabin, where the greater volume is?

As you can see i really want to know what will work, but id rather experiment with the ideas until i get some facts down, than experimenting with the time and materials.

Ive got to be raising valid questions here..

Would it hurt to narrow the channel width going to the trunk by half, and keep the channel to the cabin twice as wide as the trunk channels??

That might help.

Does someone have some prefab pieces they can try this concept out on?

 
yes 2nd design was a quickthought, scratch second idea.
Well, looking at it again, it's really a 2 ports per chamber design. It could work, but unnecessary.. i'd also be concerned about cancellation...

Again, to get dual ports, the length will dramatically increase.

 
Ive seen some dual 12" boxes that house 2 ports per chamber. but only round ports. plastic.. and spun aluminum. Never seen it done with slot styles either. Im gunna get WinISD pro, i had it once, and lost it somewhere. i might have it on backup. But i dont remember seeing this kind of factoring in there. If it says yea i can use 1 slot port per chamber, and the length needed is this much, can i cut that in half and add the 2nd port for that chamber?

anywho. If the channels need to be longer, can only one be longer?

Is the second drawing feasable? looks awkward..

 
I always thought if you run multiple ports, it should be of the same length, else it would be an awkward push pull port.

There are no problems if you were to extend the ports outside of the enclosure...better for increasing box volume. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

And if you try winISD, it'll show you that if you want one port, it'll show you "Z" number of inches. If you select 2 ports, then winISD will give you "Z" x 2. I would still keep to using a single port per chamber, or beter yet, use a common chamber and a single large port that'll vent into your cabin.

 
ok i redid the strange box. where originally i had two channels ending up in 4 ports, i instead... created two channels exterior to the original box, thus keeping the target volume, but increasing the box's overall length and width.

look better?

As it is, i reinforced the wall between the chambers to match the thickness of the front walls. Something about it being thin gave me the ticks and i started to twitch. anyways, IDEA! ding. With this box setup, matching Factory specs for the subs.. Could i... share the chambers, make them common, with say.. two 4" Holes stacked?

Also, when i calculate the internal volume, do i add the channels volume? or do i stop where the channel starts. or do i add half the channels volume? Say each chamber had to be 2 cubes, does the channel count? or do i double the volume of the channel and subtract it from the 2 cubes? *spins around and falls, dizzy*

 
Ok, the second attachment looks more familiar to me.//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif I'd prolly go with that, so much easier to calculate.

Some people choose to go with that divider in the middle,but I'd prefer a single large box instead, to increase volume (generally, larger volume = louder).

Yes, you need to take the channel volume as part of the port. So therefore, when you calculate the net volume of the box, it's

net volume = gross volume - (sub displacement + port displacement + any other extra wood)

 
GOODY GOODY!!

So, better box design.. should i use any sound dampening materials to line the walls of the box or chambers? in the walls maybe? i can use compression fittings to allow the thinner walls to retain their rigidity.

I put a hole in the center wall of the box. Id like to keep that piece there for structural support. Rounded edges and a simple router job would finish that piece up. Look good?

 
GOODY GOODY!!
So, better box design.. should i use any sound dampening materials to line the walls of the box or chambers? in the walls maybe? i can use compression fittings to allow the thinner walls to retain their rigidity.

I put a hole in the center wall of the box. Id like to keep that piece there for structural support. Rounded edges and a simple router job would finish that piece up. Look good?
Yes, that's what I refer to as a brace, for structural rigidity. Try to smoothen out the edges, especially on the ports (using the 45 degree angle blocks like on your previous drawings.)

 
oh, and I wouldn't waste tiem with the damping material in or around the box.

what you could do is to use resin and make sure all panels get a single coat. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 
will do. braces will take time to cut on the back panels. but at least i have an idea. Should i use an inch MDF for the front and center walls, and 3/4 for the rest? or 1/2?

resin is a wilco. no prob there. and a good idea..

 
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