8" sub box question

In a "free air" design, you MUST isolate (seal) the front of the speaker from the rear. If you don't, you have nothing. The front and rear waves cannot combine as they just cancel each other out.
Back in the early 90s we were using the rear seat back areas as the mounting board and then sealing it off from the cabin area. Basically using the entire trunk for a pseudo enclosure. Worked ok with speakers designed for that application and pouring a ton of power to it.

You will see a dramatic improvement in performance by putting that lil sub in a proper enclosure.

At least you didn't just nail it in to the board (yes, I've seen that).

 

here it is, never mind the wires to the left, this pic was taken before i finished it. you would have to remove all the panels to see any wires, i took this as a test fit before i installed everything since i had to take it all out to install dynomat behind the back panel against the back wall.

 

Well the speaker said it was free air capable
so I assumed this meant it performed decently in that application.
Which is does. It fills nicely.
And I had never even heard a sub in an IB application.

But my prior system to this hit 151.1 db at 47hz (usaci) (with 1 - 15" and 1200w I designed the ABC box it was in)
and I am desiring just a hair more output so possibly sealed... or possibly switch to a 12 and do some changes in that route... Ive got alot to think about but please don't insult my install abilities people. Ive been around the block a time or two and this was my first attempt at building something with such little space so I was shooting blind and I actually did ok

The issue lies in that I love the response the sub delivers... Its just not loud enough.

 

You do not have it in a "free air" configuration. There is no isolation of the front to back.
Not knocking your install ability...just pointing out the way you have it installed is totally wrong and will never work. Nothing personal, please don't take it that way.

Put it in a proper enclosure and you'll have MUCH better performance. A single 8" will never be a bass monster, but a proper box will help a lot.

 

don't want a bass monster... just a little more... i mean a LITTLE no thundering roof shaking ear needle poking feeling

but why isn't it free air?
so it has to be a gynormous sealed box to be free air?
ie your trunk

 

I am gonna go build a .5 cubic foot box real quick and invert mount the sub...
(do you have to reverse the + - when you do that? I forgot) and see what it sounds like then

 

You just have to be able to isolate the front wave from the rear wave is all. Technically, a trunk would be a sort of enclosure, but not in the sense of a normally constructed "box". Considering the size of a trunk, the speakers are basically in "free air". The surrounds and spider of a free air speaker are much more robust/stiff compared to a normal driver that is designed to go in a small sealed box. You also need some good power to throw at a free air driver, they are not a very efficient design.

In your case from what I can see from the single picture is, that if you had a solid board sealed to the wall of the truck and the speaker mounted to it...it would be much better. But as it is the wave can simply escape from that huge opening cut for all your other electrics. That is the way it appears from the picture. Correct me if I am wrong. Hard to tell from one picture.

A test box is a great idea. When you start talking about switching +/- around, you are talking about phasing issues. I don't know how you have yours wired, but if it does not have any bass response, reverse them and see if it changes it. If it does for the better, it was out of phase with the rest of the system. If no change occurs, then you got what you got.

 

ya i thought about it today while i was at work
and the reversing is only necessary if you have 2 subs
one inverted and one not
so that they do not counteract eachother!

you are right about the open side.
but their is also a small hole in the rear of the sub. but this shouldnt cause counteracting problems as it send sound waves in 2 different directions, even though they aren't 180 degrees but 90 degrees so im sure their is some interference but not as much as you were suggesting... I will begin building the box in about 30 minutes and it shouldnt take more than 30 minutes
im a little rusty but its coming back
also I am considering a complete revamp from original ideas...
this would require a tool box on the back of the truck so I have somewhere to store stuff as this would remove all of my storage area

 

that small hole in the back of the sub (middle of the magnet) is for the voice coil cooling. As the speaker moves up and down it basically creates a fan effect over the voice coil and it's former. The speaker cone actually does the separating from the front to the back.
Sound waves will bend where ever necessary to unfold if you will...direction with larger freqs does not matter.

If that big ol open space for your components is open to the rear of the speaker...it's going to make a huge difference in performance...and all bad.

 

no no no the small hole is something i made in the box (don't ask)
kool didn't know that about the sound waves canceling like that
(shoulda went to more physics classes)

 

ok...so what's the hole for?



How'd the box turn out? Test it?

 

ok so i made the test box and i like the difference
It does give some nice increase
Ive also decided to add another sub
Im also designing another box/amp rack
that would hold 2 of the 8" subs in about .3 cubes each after displacement
and double as a amp rack

I went and bought more screws and a sheet of 1/2" MDF

this should be slightly different...
Im trying to take cues from Mr. Marvs boxes

here are pics of my test box lol took about 15 minutes start to finish

 

Glad ya got the performance you were hoping for. Can't wait to see the end result. A solid seal on your boxes is crucial. You gotta squeeze every ounce of performance outta them 8s.

You could port the boxes, but you usually have an increase in internal volume needed and the port size and length are very specific in tuning the box. That's a whole nother chapter....

 

I built an ABC box
only thing i can't handle is a horn box design

 

Round 2 of box

here is one side



I designed the box so that it is 3 main pieces

the 2 sub boxes(first two pieces) mount to the amp rack(third piece)

 

nice. Looking good so far. Fun ain't it? yer making me want to go out and build a single 10" box for my regular cab.

 

i tried to get by without liquid nailing the face on but it made a rattle noise so i liquid nailed it hoping that solves the problem
(i hope its not blown, it doesnt sound blown though...)

When im done itll be mounted on the inside of the box i inverted backwards mounted it cause its easier that way this is just temp till i finish the box and order the other sub. its drying in the sun right now ill update once its done and i hook it up again

 

ok so i still have a rattle
its coming from the sub itself
but its not a popping like i previously experienced in subs
any idea what it is?

is the sub garbage or what?

 

Can you move the cone carefully by hand? If so, does it move smoothly or does it feel like it's rubbing on something?

If it's not smooth...you might have a trashed sub. Running a sub that is designed for a box in a free air application, it's not too hard to physically damage a speaker. The air inside a box acts as an air spring to help support the speaker cone. That's why free air drivers are made differently.

 

pioneer says it can run free air