Help with box for beginner

[paulh]

Hi, bit of a total novice here, but all the same i've decided to make my own MDF stealth shelf which will have some 6 x 9s on the underside, and cover with acoustic cloth. Making a good job will be the easy bit, I know how to use MDF etc, and I already have all the materials from a company that makes aftermarket stealth shelves, but doesn't do my model of car.

I also want to mount a sub onto to the underside of this shelf, and enclose it. Reason for this is so that the trunk space still has maxmium usage, and when covered with carpet to match the trunk it will be hard to find should someone break in the trunk.

I need help in two areas.

First, maybe an easy one. If I make a box from 3/4" MDF, is there any point adding any sound damping material to this? (I have installed dynamat type stuff throughout the car)?

Second, not so simple I would guess: What about the shape of this box, and how is it going to affect sound?

To clarify my plans: The rear parcel shelf is about 4" x 3", quite a huge thing. It will be re-made from 3/4" MDF and have three holes cut for a pair of 6 x9s, and 12" sub. That will be covered in acoustic cloth so that the holes can't be seen. The 6 x 9s will be mounted underneath, and then a sealed box will be made for the sub which is then mounted also underneath. I have a special shallow sub which means I want to keep the box shallow, so it will be more like a 'tray'. So, it could be 3 x 3 ft, but only 6-9" high.

Is this going to work? Should it be ported? Should I throw wadding in?

Does it matter what shape it is? Is space just space?

How much space should I be aiming for? As much space as possible? (Sub = High power handling capacity of 600 watts, RMS power 200 watts, High sound pressure level of 90 dB (2.83 V/m).

Should I get the box to incorporate the 6 x 9s on either side?

I'm not after best solution ever, I'm after best solution with the box mounted as I have explained, on the shelf, because the way I use my trunk dictates this, so sorry if it will be a bit of a crap question to answer, but....

Any suggestions really appreciated.

-p

[Trixter]

First, maybe an easy one. If I make a box from 3/4" MDF, is there any point adding any sound damping material to this? (I have installed dynamat type stuff throughout the car)?

NO. You should have to.


Second, not so simple I would guess: What about the shape of this box, and how is it going to affect sound?

Shape does not matter as long as the box is well built and air tight.


Is this going to work? Should it be ported? Should I throw wadding in?

In should work. Porting it is up to you. It depends on how you want it to sound and if you box is large enough to accomidate a port. You have to figure that the port will take up space inside you box. As far as wadding goes, I assume you talking about poly-fil, it wouldn't hurt to add some, espicially if it's a sealed box.


Does it matter what shape it is? Is space just space?

Answered above.


How much space should I be aiming for? As much space as possible? (Sub = High power handling capacity of 600 watts, RMS power 200 watts, High sound pressure level of 90 dB (2.83 V/m).

You should try and give the sub it's RMS rated power. If you match it up build the box to the recommended size. If you underpower it, go a little larger, like .5cu', and if you over power it you can go a little smaller.


Should I get the box to incorporate the 6 x 9s on either side?

No. over time you will damage the 6x9's due to the air movement of the sub.

[paulh]

GREAT!!! Thanks, that was easy.

Only two things are not clear;

1) On my question about sound damping on the box; your reply seems to say both No, and then Yes I should. Please clarify.

2) Second, how do work out or find the recommended size (in cubic cm I presume) for my box?

And another quicky; what sound difference does a port give?

;-P

[Trixter]

GREAT!!! Thanks, that was easy.

Only two things are not clear;

1) On my question about sound damping on the box; your reply seems to say both No, and then Yes I should. Please clarify.

I should have said "shouldn't" and not "should"...sorry about that.




The manufatcure should have a recommended box size.

[quote=paulh]And another quicky; what sound difference does a port give?

;-P

A port allows you to get the lower notes, and in some cases get louder, more easily than a sealed box. Especially if your working with a small box.