I want to run 2* Alpine Type R Subs with an Alpine D500 Mono 1000Watt Amp. I would like to do something like crazy eclipse did with her setup where it is all flush on some MDF board. Now my question is, Do Subs need to be in a box to work properly? Or Can I mount them rite onto the board and have them hang from the MDF board and just have the whole inside of the trunk be the enclosure... I really cant illustrate this so I hope that you guys have some sort of idea what I mean.

Thanks In Advance

Mike

"Do Subs need to be in a box to work properly? Or Can I mount them rite onto the board and have them hang from the MDF board and just have the whole inside of the trunk be the enclosure"

well, yes and no.

a quick synopsis of why you use a box: the signal being delivered to a sub is in an a/c format, meaning that theres a baseline at wich there is no electricity being passed on to the sub, but a wave is overlayed on top of that. as the wave moves above the null line the sub cone moves outward (assiming correct mechanical polarity). the wave the decends to the null line and the sub moves back to its resting point. after that, the wave makes an identical form, only below the line, causeing the sub cone to move inward towards itself. this wave is a 180 degree oppposite of the "front" wave. this applies to a sub that is hanging by a string in open air. as the sub moves, there are two physical wave fronts produced...one from the front of the subs cone and one from the back. assuming the open air setup, these waves will collide and produce what is called cancellation. because the two waves are equil in amplitude (volume and structure), but slightly off in timing, the "up" wave (made by the front of the cone) will negate the "down" wave (produced by the back of the cone). by putting a sub in a box, you change the reflexive qualities of the subs movement, as well as getting rid of cancellation caused by "down" (or more properly "rear") wave interference.

SEALED BOX: when it moves forward, it creates a partial vacuum inside the box that adds resistance to the subs movement. this is called rarification. when the sub goes on its opposite stroke (inward), it compresses the air inside the box, also creating the exact same amount of resistance. this is called compression (not to be confused w/ audio or electrical compression). this does two things: it competly isolates the front and rear waves so they dont cancell each other out. the resistance from the sealed design changes the physical properties of the subs mechanical reaction to an input signal. by putting the sub in a larger and larger box, you present the sub with less mechanical resistance, and by putting it in a smaller enclosure you increase resistance. i wont get into how that effects the sub so much, but just know that a smaller box tends to have a responce curve that is "peakier", meaning it will play at a middle-bass note louder and fall off in the low and (to a lesser extent) upper bass notes. this sounds pretty good for kick-drums and slap bass, but can sound weak w/ rap and electronically produced low bass notes. a larger box will shift the peak range down so that lower notes sound better, but it also looses some of the "punch" asociated with a smaller box. it also decreases the amount of power the sub can handle (due to the lower mechanical resistance i mentioned earlier).

VENTED (or) PORTED: by adding a tuned port (basically a tube or a cubical shaped opening that encompasses 3 dimensions) to a box, you are (in effect), re-alighning the rear wave of the sub to the front. with this setup, you are adding the energy coming from the back of the sub to the energy coming from the front of the sub in a way that doesnt cause cancellation (over a majority of the frequencies) by changing the velocity of the rear-exiting wave front. port tuning is a very complicated matter, so i wont explain much about it. just know that the the port is tuned to a certain set frequency, and the lower tuned box responds much like a large sealed box. a higher tuned box sounds much like a small sealed box. the difference is that porting adds quite a bit of volume, since you are combining (or "coupling") the rear wave to the front. the problem is that below the tuning frequency, the sub acts just like as if it was hanging from a string in open air, and this lack of mechanical resistance will cause damage to the sub quickly, plus you will get next-to no sound out of it at those frequencies.

FREE AIR (or)INFINITE BAFFLE (or) ISOBARIC: this is the situation you are asking about. In this case, you adding a very minimal of mechanical resistance to the sub because of the fact that there is no box. the sub must sit in an airtight baffle that seperates the front and back waves though, otherwise there would be tons of cancellation. the idea is that certain subs are built for this application, and thier natural mechanical characteristics lend themselves to this type of setup. most subs are designed to be put into sealed or vented type enclosure, so this isnt really a viable option for most of the product out there. thats not to say it cant sound good though, i actually prefere the natural sound of an infinite baffle setup w/ most subs, although you loose a LOT of output and the sub wont handle much power (again, because of the lack of mechanical resistance). the upside is that the install can be much easier, and (as i mentioned earlier) the responce can be a lot more natural, especially on music like jazz, where you dont want a lot of big peaks and dips in the frequency response. it sounds nearly unlistenable with more electronic stuff like rap though, because you loose a lot of impact.



so in conclusion: i would recommend you go with the manufacturers specs for a sealed box w/ those subs (ive heard them in a lot of installs in the past, and i liked that the best). as a side note, ive always had the best luck w/ building a box on the larger side if possible. ive only scratched the surface on this long ass near-diatribe about boxes, so i recommend you go to a site like www.sounddomain.com and do some research there. im sure youll find info that will takes days to sort over, lol. if you have any more questions, please feel free to ask, i love talking about this obsession of mine, lol.:cheers

Thanks SPL, I'll tell yea.. You always got an answer to my questions and its a big help.. Thanks :)

Sweet explanation!

So I have a couple questions for ya, I would like to tune my phase inverter AKA "port" with my Box. Can you give another little break down of what happens in a Bandpass with the tuned port. I have a 1000W 10" sitting in my trunk with 1000W Amp going to it. It hits deep bass HARD (which is good for Three 6 Mafia and most underground rap).

Anyway let me know, your explanation was great

^^^LOL, i stayed away from bandpass, aperiodic, aperiodic bi-chambers, transmission line, passive radiator, etc. enclosures for a reason.....theres a lot more physics going on there thats hard for most people to understand. im going to refer you to this awesome link from JL audios website:

http://www.jlaudio.com/tutorials/bandpass/

they break it down pretty well there. the MOST important thing to remember about a bandpass is that all the values are critical and can suffer from NO variation. you cant fudge on the construction of one in any way. acousticly, when designing a bandwass enclose you must choose what you want...a low amplitude design that covers a large portion of the bass frequencies, or a "peaky" box that is insanely loud at a center frequency, but with amplitude that falls off quickly both above and below the tuning frequency of the port.

BTW, thanks for the compliments. :D please ask more questions if youve got them.

Originally posted by EclipseTenzoR
I would like to do something like crazy eclipse did with her setup where it is all flush on some MDF board.

OMG I think I'm blushing... especailly since you said HER.
:*

Undergoing MAJOR modifications, inside and out
member# 2498 / girl member# unknown

Yes... I know ... I am aware that you are a girl

OMG I didn't know crazy eclipse was a girl.



About your type R's. They are an extremely sensitive sub to airspace. If you want an open basket (so you can see the magnet) you have to measure the displacement of the cone, then build a box to the type R specs but subtrace the cone displacement from the total cubic inches of your box dimensions.


A lot of people forget that the sub itself displaces air. So if they build a box for 1 cu foot of air they build it 1 cu foot exactly and forget that the sub itself displaces .65 cu ft or whatever the case may be. This is the same but opposite if you want to face the subs into the box. In that situation you have to build the box smaller compensating for the extra air space your cone makes.


Air in a box is there for a reason. It's a suspension for the sub. Basically think of it this way. If you took the shocks out of your car and drove on straight springs you'd be bouncing all over the place, right? Same with a sub. If they don't have the air to support them they distort like a mother. Now if you get "freeair" subs then you dont' have to worry about that. But Alpine Type R's are NOT FREEAIR SUBS! Hell, you're not even supposed to bandpass them. They are sealed box subs designed for Quality in reproduction, not extreme bass.


If you want a sub that will put out a shit load of bass and is really forgiving on the whole sealed, freeair, bandpass debate then buy Cerwin Vegas.

crazyeclipse, are you hot? lol

I have been wondering the very same thing..

Originally posted by a_miller_76
A lot of people forget that the sub itself displaces air. So if they build a box for 1 cu foot of air they build it 1 cu foot exactly and forget that the sub itself displaces .65 cu ft or whatever the case may be. This is the same but opposite if you want to face the subs into the box. In that situation you have to build the box smaller compensating for the extra air space your cone makes.

So question. Let's say the sub itself displaces 0.5ft^3 and the sub spec says I need 2ft^3 for air displacement. How big of a box do I need to build? So do I need to build a box that has 1.5ft^3 without the sub in? or 2.5ft^3? I'm confused how to adjust/calculate to the sub's displacement.

ok, if the cone of the sub is going into the box that you will be building, you must ADD the volume the sub takes up. If you invert the sub (face of the sub facing inside the box), then just design the box for the subs specs.

Originally posted by mitsuman297
ok, if the cone of the sub is going into the box that you will be building, you must ADD the volume the sub takes up. If you invert the sub (face of the sub facing inside the box), then just design the box for the subs specs.

Not exactly.


If your sub displaces .5^3 ft and needs a 2.0^3 ft box then you build your box 2.5^3 feet to compensate for the sub displacement. You basically ad the sub diplacement to the over all footage of the box.

If you're going to face the subs INTO the box you have to remember that there is going to be air in the cone of the sub. Take a ruler and lay it across the sub and think about it. There is a sizeable depression in the cone. So what you do is fill it with water until the water is level with the top (don't do this to paper cones or untreated wood pulp cones). Then you measure the displacement of the water, say it's .25^ft and you SUBTRACT that from the total box footage. So if you're going to face them into the box and it needs to be 2.0^ft and you have .25^ft of cone displacement you make the boxt 1.75^ft.

Originally posted by mitsuman297
ok, if the cone of the sub is going into the box that you will be building, you must ADD the volume the sub takes up. If you invert the sub (face of the sub facing inside the box), then just design the box for the subs specs.

Originally posted by a_miller_76
Not exactly. If your sub displaces .5^3 ft and needs a 2.0^3 ft box then you build your box 2.5^3 feet to compensate for the sub displacement. You basically ad the sub diplacement to the over all footage of the box.

Sorry, I'm kind of confused. Are you guys talking about the same thing? mitsuman297, when you say "must ADD the volume the sub takes up" is it the same thing as a_miller_76 is saying? I'm going to have the cone inside the box, so I'm not going to face the sub to the box thing. So, like a_miller_76 said, if 0.5ft^3 for the sub and need 2.0ft^3 for air displacement, I need to build 2.5ft^3 correct?

and more thing, does the shape of the "air" matter? Like have combination of 1ft^3 of cylinder shape and 1ft^3 square box together type of thing. As long as I have the right air displacement, i'm ok right?

If you're going to put your sub magnet first into the box then yes, what I said about adding it (making it 2.5^3ft) is correct.


Now, wtf do you mean about 1pt cylindrical and 1pt square? Make a mspaint drawing. And yes, the shape of your box is critical

Originally posted by a_miller_76
Now, wtf do you mean about 1pt cylindrical and 1pt square? Make a mspaint drawing. And yes, the shape of your box is critical

Well, I'm about to start making a fiber glass enclosure in the spare tire well. Since it isn't a perfect square or anything, I was wondering if that makes a big sound difference. From what the SPL_Eclipse's post, I think he was talking about mechanical resistance (air) that make the sound different. So, I though as long as I keep the air displacement (mechanical resistance) I would be ok. or am I wrong?

If you're gonna do it in your spare tire well make sure you wall out specific enclosures per sub and make the walls very very thick. MDF doesn't flex much making it great for subs so that the air stays rigid.

Oh, and you want your subs to be seperate so they don't reflect off each other causing distortion. I know you see a million boxes with no dividers and audio shop guys will say "eh, you don't need it." but that's because they're lazy.

alright aaron, i know what you're saying now with the inverted sub enclosure volume. Sorry about the confusion to everyone else.