Im pretty new to the Audio world, but I am trying to learn a few of the basics. I was wondering if there is any difference between putting subs in a box, compared to putting them on a wall like behind the back seats. Im trying to think of ways to install a couple 12s and keep alot of hatch space. I figured one would have more bass and the other more clarity, but Im not really all that sure. If I can put them in a vertical wall behind my back seats and still have them hit pretty hard (or atleast not much harder than ther would in a box) Ill just do that. But any help would be appreciated. Thanks

oh boy, where do i start.

first, lets talk about cancellation. when a sub moves in/out of the box, it produces sound waves. the number of waves emmited from the speaker per second is the frequency. most subs will play frequecies of importance of around 160hz and down dependant on the slope and the cut-off point for the low pass on the crossover (this is assuming a 12db/octave at 80hz for those who care). in other words, at 40hz, the sub is transducing one wave function 40 times per second. thats a lot of waves!

now lets take about interference. when a driver is producing 40 (relativly large) waves every second, where do they go? if you are standing in an anechoic (non-echoing) chamber with the speaker elivated 6 feet off the ground, and you are standing a few feet back from the driver (facing it directly), you will hear the waves amplitude peaks/dips all in order, just as you should. your eardrum will be altered by positive pressure at the peak of amplitude (when the speaker moves "outward"), and then a negative pressure when the wave dips to its negative peak (when the speaker moves "inward"). in a car, you arent afforded this...you have surfaces that both muffle and reflect the waves as they leave the speaker. that can send the waves boucing all around the cabin of the vehical. how they interact with each other from that point is called interference. see, these waves can lay on top of each other and align in two different extreems, with an infinate amount of variation between the two.

deconstrictive interference: remember how i said there is a cycle: compression followed by rarefaction (as the sub moves in and out to creat one whole wave)? it is possible that one waves rarefaction cycle can overlap another waves compression cycle. this causes BOTH waves to nullify each other. its like introducing compressed air into a vaccum. no wave=no sound=no pressure (negative OR positive).

constructive interference: it is also possible that two waves can align themselves in a way that both positive peaks line up, as do both negative dips. this form of wave combination results in a stronger wave.

why the hell i just said all this: when youve got a box in the trunk, facing backwards, the waves are reflecting from a relativly close surface, and are all in such close proximity that the overall effect is an increase in constructive interference. this is called "slot loading" or "corner loading" in home audio jargon. when a box is sitting in the backseat, the waves are bouncing/modifying all over the place (off the windshield, off the rear glass, the floor, the seat, the headliner, you, etc..). because it is so random, the likelyhood of deconstructive interference is huge. if you want to put a box in the backseat, it is EXTREMELY important that you block off the front face of the box from the trunk (with a wall, as you suggested). this does 2 things: (a)it eleminates all possible waves from bouncing around the back of the car(b)read my note below. ive already explain why the traditional box-in-the-trunk method works well.

*note (b): by building a wall in the backseat, the main advantage is a smaller area to compress. imagine it liek this: the pressure of blowing up a baloon will be greater than exhaling inside a room. pressure is a whole other devil though, so ill leave it alone for now. ;)

Josh, the answer is NO. That's all you had to type.

man everyone beets me to these forums, you guys suck. like i said to the other guy asking a question .... listen to him, haha :)

What about free air subs? Though limited in quantity they do exist, I'm not sure what they sound like though.

Originally posted by mastrcobb
What about free air subs? Though limited in quantity they do exist, I'm not sure what they sound like though.

Free air subs only work in a sealed trunk like the old 90's cars....they won't do shit in our hatches but blow the hatch cover up and down.

Josh has all the answers.. Whether he is wasted or not he always has the answers. And always gives it to you in depth to educate you. You helped me out alot in getting my shit up and running.

As for the post.. Cerwin Vegas are Free-Air I think I heard. Could always try those

^^^thanks man. ;) aaron is great to, he helps me out a lot.

and on that note, aaron is right. there really is no good way to install a free-air sub in our cars.

Originally posted by SPL_Eclipse
^^^thanks man. ;) aaron is great to, he helps me out a lot. and on that note, aaron is right. there really is no good way to install a free-air sub in our cars.

See Josh, keep the answers short and sweet...only rarely is all the technical jargin required :thumbsup

Well thank you very much Josh. I appreciate all the help you gave me in your response. But, I was talking about putting the speakers ON a vertical wall. Like right up against the back seat. Not a wall separating the box in the back seat from the hatch, but like the face of a box with nothing around the subs. If you did answer about that and I missed it I apologize. I really do appreciate all the help. Thank you once again.

Originally posted by Abstract_Zer0
Well thank you very much Josh. I appreciate all the help you gave me in your response. But, I was talking about putting the speakers ON a vertical wall. Like right up against the back seat. Not a wall separating the box in the back seat from the hatch, but like the face of a box with nothing around the subs. If you did answer about that and I missed it I apologize. I really do appreciate all the help. Thank you once again.

You didn't read my response did you? What you're wanting to do is called free air resonance. And in our cars it is impossible to get a good sound. So...like I said before, the answer is NO.

lol, damn my drunken rant was all for naught. :P


"But, I was talking about putting the speakers ON a vertical wall. Like right up against the back seat. Not a wall separating the box in the back seat from the hatch, but like the face of a box with nothing around the subs. If you did answer about that and I missed it I apologize. I really do appreciate all the help. Thank you once again."

just have to ask...are you talking about inverting the subs so that the speaker assemby is out, and they are firing "into" a box? or just no box at all (like they just sit on a a one dimentional plane)?

Originally posted by SPL_Eclipse
lol, damn my drunken rant was all for naught. :P "But, I was talking about putting the speakers ON a vertical wall. Like right up against the back seat. Not a wall separating the box in the back seat from the hatch, but like the face of a box with nothing around the subs. If you did answer about that and I missed it I apologize. I really do appreciate all the help. Thank you once again." just have to ask...are you talking about inverting the subs so that the speaker assemby is out, and they are firing "into" a box? or just no box at all (like they just sit on a a one dimentional plane)?

Dude, stop reading too much into this....he's wanting to jerry rig a piece of fucking particle board in between the rear strut bracing and mount subs to it basically.

Originally posted by SPL_Eclipse
lol, damn my drunken rant was all for naught. :P "But, I was talking about putting the speakers ON a vertical wall. Like right up against the back seat. Not a wall separating the box in the back seat from the hatch, but like the face of a box with nothing around the subs. If you did answer about that and I missed it I apologize. I really do appreciate all the help. Thank you once again." just have to ask...are you talking about inverting the subs so that the speaker assemby is out, and they are firing "into" a box? or just no box at all (like they just sit on a a one dimentional plane)?

exactly! no box at all...just have them on a 1 dimensional plane. with the assembly hanging out. and the sound being fired towards the rear of the car. basically so u would pull down the back seat and see the assembly of the sub.

Originally posted by Abstract_Zer0

Originally posted by SPL_Eclipse lol, damn my drunken rant was all for naught. :P "But, I was talking about putting the speakers ON a vertical wall. Like right up against the back seat. Not a wall separating the box in the back seat from the hatch, but like the face of a box with nothing around the subs. If you did answer about that and I missed it I apologize. I really do appreciate all the help. Thank you once again." just have to ask...are you talking about inverting the subs so that the speaker assemby is out, and they are firing "into" a box? or just no box at all (like they just sit on a a one dimentional plane)?

exactly! no box at all...just have them on a 1 dimensional plane. with the assembly hanging out. and the sound being fired towards the rear of the car. basically so u would pull down the back seat and see the assembly of the sub.

I have said numerous times in this thread that NO IT WON'T WORK SO STOP THINKING ABOUT IT!

Why aren't you listening to me? Do you not want to hear it? Just so you know I am an MECP certified audio installer so I do know what the fuck I'm talking about.

lol, aaron you are angry alot recently. i swear to god you are gonna have a damn heart attack or something, lol.

to the original poster: visit JLaudios tutorial website to read about different encloseure designs. toward the bottom is a section entitled "the myth of the magic box", and right below that is "isobarik loading". those should get you started.

http://www.jlaudio.com/tutorials/index.html

Sorry it jsut pisses me off when people don't want to hear the answers they are given.

To sum it up you can't do it. There are "free air" subs like Elemental Designs O series, but the term is misleading. They just don't have to be in a sealed box with specified dimensions, but the front of the sub needs to be sealed off from the back, which you can't do (without some serious fabriction) because we have a hatch. This will only work in a trunk where the front can be sealed off from the back, so basically the entire trunk would be the enclosure.