vented vs bp..throwing out some ideas

[cxa0897]

im tossing around a couple of ideas in my head to reduce the size of my subwoofer box, yet keep the same output..i know thats improbable, but its worth a shot

i did some modeling in winisd and came up with a 4th order bp for my mag.



im looking at using a 3 inch aeroport to vent it. would there be any audible difference from the current slot ported vented box? Im figuring that the areo should make quite a difference over the slot port, and if i can save nearly a cube without sacrificing much, or possibly even gaining a little bit , it would definitely be worth it to me.

[666WMD]

That looks like you've forgotten a filter on one of them or something. 4th's are usually bigger than ported.

[profundus-sanus]

yep. that bandpass will lose a LOT of output over your slot port box.

when i model what you have there i show around a 5db difference.

[matt.u]

you are way better off just doing a regular ported box using aeros.

[cxa0897]

Originally Posted by 666WMD

4th's are usually bigger than ported.

i thought the same thing too...but the winisd "optimum" bp was even smaller that what i had. it was late last night and i figured id roll with it. wasnt really in the mood to do much thinking

[cxa0897]

Originally Posted by profundus-sanus

yep. that bandpass will lose a LOT of output over your slot port box.

when i model what you have there i show around a 5db difference.

what are you modeling it with prof?

how do you guys think an sa 8 band pass would fair? i figure that shouldnt need more than 1-1.5 cubes total(going by the bigger than vented convention), and im sure it would be pretty impressive

[profundus-sanus]

i'm using a newer version of winisd.

a sa8 would work just fine in a 6th order banpdass of that size. it might be able to keep up with the mag ported, you'll have to nail the box to do it though.

just make sure you get enough delay on the rear wave of the woofer. I'll likely be doing a 6th order for a sa-8v2 when they come out.

[cxa0897]

Thank you prof. I may pick up a v2 for myself after xmas. I love my mag, but I do miss being able to fit my milk crate for fishing in the hatch. Plus an 8 that loud would blow peoples minds

[cxa0897]

so i was messing around in winisd with the t/s posted up for the v2s. this model is for 2 of them. seems incredibly small to me, although the freq resp looks quite good. i always thought that the 6th orders would be bigger than a vented equivalent by a fair bit, and 2 of the vented would be nearly the same volume...

[cxa0897]

remodeled it using the linkwitz and some filters(thanks fallen), and it gives a much more reasonable volume for the 8s.
1.3 cubes at 33 hz,and .5 cubes at 68. gives me an extra 3-4 dbs in the high 20s and low 30s, but i needed the extra volume to fit the ports in. Not exactly what i was hoping for, but a few dbs on the lower stuff is never really a bad thing just waiting on jacob to release some final t/s on the v2s, hopefully they are pretty close so all of this wasnt in vain

[cxa0897]

threw my idea from paper and into sketch up, first time ive made in a box in sketchup, gotta still figure a lot of things out lol. wouldve done this in 10 minutes in autodesk...but theres always a learning curve. anyway, if you guys see any glaring issues with it let me know. its gonna need some fine tuning once the final t/s are released, but im hoping to keep it this general shape and size. box is behind the rear seats in the hatch, 4 3" aeros firing up. theyre flared to 5 inches i believe(parts express variety), so i may need to step up the depth a tad... thatll be in the fine tuning i wish i couldve gotten 4" aeros for the inside, but the lengths just arent feasible. needs to be 20+ inches

[666WMD]

Those ports in the center chamber appear to be too close to the bottom of the chamber.

Also remember with flared ports that although the tube might be 20" long, when you subtract the flange from the length you might only have a 19" throat, which would raise the tuning.
Unfortunately because your subs are facing each other (and I thought that would cause some cancellation), if you put 90 degree elbows in them, then the subs would be firing straight into the ports.

Also with the rear chambers, will you have room for sub mounting depth without hitting the port tubes?

[cxa0897]

those arent the exact lengths of the tubes. ill have at least 1 diameter between the bottom of the tube and the floor. the back of the subs will be in the inner chamber, with the sub firing into the smaller sections. the inner chamber is 24 inches long and i believe the mounting depth on the 8s is around 6-7 inches. should leave plenty of room with the ports at the midpoint

didnt really think about cancellation...im trying to make it so that i can still use my trunk. ill look into making one after finals with the subs on the same plane and see what kind of area itll take up. if it cancels out just a few percent im cool with it, im not chasing numbers at all. just trying something new and outside the box. ive owned nothing but 12 inch woofers in simple boxes. that is a good point though, ill look into it

i just looked up the ports again, turns out the outside diam on them is 6 1/8 inch....probably should have read that one better. i can just stagger them if i wanted, wont look that great though. the description says the port is 11" long, and my box is calling for a ~11.2 inch port. i was just going to make the inside chamber as big as i could to keep that port tuned as low as possible with that length, maybe even add an inch or two if i have the space with a piece of pvc. if i add .12 cubes to the internal chamber the port length drops to 9.9 inches for the same tuning, so i think ill be ok. i have an inch or two of space i can expand it.


all in all, its kind of just a mock up for now. the volumes and tuning will most likely change a little bit since i based the design off of the preliminary t/s jacob posted up. if i need to change it and inch here or there i dont really mind, im not building the box until everything is finalized and i get his published specs. just wanted to get it on the computer where i can see it all in scale.

thanks for your help j, you brought up a couple of things i overlooked

[cxa0897]

also, in winisd, the end correction factor actually gives a shorter port length if you use flared ends than if you dont. in my case with flares it is a port length of 11.2 inches and 11.9 without flares from what i recall from physics, the antinodes for port resonance are actually beyond the pipe itself, which may be the culprit here...

[Fallen]

As previously mentioned the centre ports are too close to the bottom. Make sure there's a ports width for clearance.(although I think you mentioned those aren't the real lengths)
For flared ports only count the straight length. Don't include any of the flare.

Anyways great progress! I enjoy reading these threads where enclosure ideas are generated.

I've done the 2 8s in a 6th before, it turned out quite well. Your box looks about right.
If you can't get enough port area with the round ports, slotted works well.

This was for 2 Tangband W8 740Cs



It's got very good output from 35-90Hz. The guy that uses it wanted something that did well with Metal, and this thing delivers.

[cxa0897]

ive been seriously thinking about slot ports due to the limited dimensions i plan on using. came up with this one last night...havent pinned down the exact volumes and tuning yet, but thatll come in time. ill be rounding off the ports a bit, possibly kerfing them. dont really know for sure yet. still got 3 months til the subs come in, plenty of time for me to change my mind



and the model of just about what it is. figured i have bass boost as 60 hz, i can use that at + 1 or 2 to give me something similar to the orange curve i threw in there with paint maybe even reducing the volume of the rear also, get rid of the peak..

ill likely lower the upper tuning freq a bit, itll help out with the dip also. designing these enclosures is a pain in the balls when your trying to conserve space...itd be so easy to just use a square box and use up the whole trunk

[cxa0897]

dumb question time...

if i had the port for the forward chamber come out of the right side so that i can keep it in a straight line, would there be any issues? or should i keep both ports on the same plane?

[666WMD]

Depends on the position of the enclosure in the vehicle and type of vehicle I would think. As long as it wasn't choked by being too close to a wheel arch etc, it may even make it louder.

Have you thought of putting both ports next to each other?

[cxa0897]

i have thought of them being close together, but im concerned about turbulence with that. one would be sucking in while the other is pushing...id prefer to keep em separated just as a precaution, and im a fan of symmetry

it wouldnt be choked off if i put it sideways, its only a 1inch wide port, it would have 3 or 4 inches of space. im gonna keep playing around with it, im sure ill come up with a solution. ive got plenty of time to get this worked out.

[666WMD]

Cool.

[Fallen]

They don't need to be on the same plane, feel free to fire them how you want.
For the most part it's the interactions with the walls in the vehicle that affects the response due to port placement. Realistically the frequencies you're reproducing have such a large wavelength that the 2 ports, even on different planes, sum like a single source. So if there were no walls/obstructions I'd imagine it would make no difference. But since there are, it will affect it. But how much is anyones guess.

[cxa0897]

coolios. i may just try firing it to the side then, or possibly even to the back depending on what works the best for me.

[Fallen]

I didn't try to the side with my buddies 6th, but we did try back vs forward.
Firing back was definitely louder.
I think the best thing to do is experiment!

[cxa0897]

im pretty surre im gonna run the rear chambered ported up, the forward chamber to the rear. works out pretty conveniently for me. itll look a little weird, and assymetrical , but itll work

[cxa0897]

finally got it all worked out. 1.15cubes @ 29 hz(firing up) and .5cubes @ 76 hz(firing back)

leaves a small dip at 45hz, but thats where my bass boost is, so a lil eq should make it nice. other than that its pretty steady from high 20s to the 80s. cant wait for these subs to ship....its ridiculous how bad i want these to come in

im gonna start workin on these the next nice-ish day. that way i can just drop in the subs when they come in