Determining Volume

[Saydee]

Hello,

Any one want to help a newbie?

This is my first time posting on this forum. This is also the first enclosure I have built and I am looking forward to the quiet time spent in my workshop.

After having done some research I have decided to build my own enclosure based on the Adire 54 Liter Enclosure. I will mate that enclosure with a 12" Shiva MKIII and a 250W Plate Amp from Parts Express (300-795).

From the advise I've read from other accounts I will be using 1" MDF instead of the 3/4" as outlined in the 54L. enclosure plans. This is where I run into a problem. I do not know how to properly increase the size to retain a 54L. internal volume.

Unsuccessfully, I decided to figure out how 54L. was calculated. Here is my work:

I used .75" for height in my L*W*H volume calculations

I then converted cubic inches to liters (1 cubic inch = .01639 liter)

Materials per Shiva Sealed Cabinet Application.pdf from Adire Audio
QTY Size Total Volume of each panel cut
2 15.5"x19.5" = 7.43 liters ; My work: (15.5*19.5*.75)= 226.688 cu in. * 2 pieces = 453.375 cu. in. * .01639 = 7.43 l.
2 15.5"x14" = 5.33 liters
3 18"x14" = 9.29 liters
2 18"x6.625" = 2.93 liters
1 Shiva Driver = 3.00 liters

This is a total of 27.98 liters

Hole/Baffle Cut Outs

pi*r^2*h, where h=.75 converted to liters after calculation used where cylinders where cut

QTY Size Total Volume of cuts
1 11" = 1.68 liters
8 4" = 1.24 liters
1 12"x6.25" = .92 liters
2 6.25"x5.625" = .43 liters

This is a total of 4.70 liters

Enclosure
The volume of the enclosure is 18"*14"*15.5" = 3906cu . in. or 64.0 liters

Therefore the volume is the enclosure volume minus the material, plus the hole/baffle cuts:
64l. - 27.98l. + 4.70l. = 40.72 liters

Why don't I get 54 liters?

My big question...Assuming I did get 54 liters how do I work back once I increase the MDF thickness to 1"?

I'd like to use think strips of wood (1"x1") on each joint of the exterior walls of inside the cabinet (I'm sure these have a name) to use as additional support. So I would need to include the volume of those in my calculations.

Is using wood glue enough?

If anyone is familiar with this enclosure where to you make the cup for the plate amp? It seems with the mid brace in the middle of the back panel there is no good place to make the cutout for the plate amp. What is recommended for the cutout for installing the amp?

[sreten]

hi Saydee,

the simple answer is to increase all exterior dimensions
by half an inch and the internals will stay the same.

So, 18" x 14" x 15.5" becomes 18.5" x 14.5" x 16.0".

But if its easier 18 x 15 x 16 will be very near.

If you use 1"x1" battens in the corners there will be twelve of
them - simply add another half inch to ONE of the dimensions
will be well near enough.
I'd suggest with 1" MDF the battens are totally unnecessary.

Note that for a sealed cabinet such attention to volume is fairly
pointless, a +/- 10% difference will hardly make any difference.

Also note if the cabinet is stuffed with BAF / Dacron its effective
volume will be ~ 15% higher than its actual volume.

/sreten.

[Saydee]

So I increase the outside dimensions by 1/2" and not 1/4" even though I'm increasing the MDF from 3/4" to 1"?

Do you feel the enclosure is strong enough without the "battens" (thanks for the vocab help)?

If I did use the battens you say increase one of the dimensions by 1/2". Wouldn't I have to increase the total box size and not just one side?

Thanks for helping me out. I'm sure this type of post has been beaten to death, but I wasn't able to find my answers while searching around.

[sreten]

Each side of the cube moves out 1/4" so the corners
move 1/4 + 1/4 = 1/2 an inch.

The volume of the battens will be 12 x 1 x ~ 16.

Increasing one side by 3/4 is the nearest, but if you
want to be really picky, increase each dimension by 1/4".

I think it would be fine without the battens.

Wood glue will be fine.

/sreten.

[sreten]

I've finally found the application plans your using from Adire Audio.

With the bracing used I can't see the point of using 1" MDF over 3/4".

To install you plate amplifier you need to extend the top, bottom
and sides and add another panel with the cutout for the amp.

/sreten.

[Saydee]

Yes, the plans can be found at http://www.adireaudio.com/Files/Seal...plications.PDF on Page 16.

Sorry for needing to be spoon fed on this, but when installing the plate amp you said that I will need to "extend the top, bottom, and sides and add another panel.

I don't follow what you mean by this. Extending the sides will still require the internal bracing to move as well. The problem is the sides of the enclosure are 15.5" around and the bracing bisects all these walls. By moving the sides out the bracing must be lengthened as well. The cutout for the amp is 9"x9.5" and the amp is 4.5" deep.

[sreten]

Hi,

one way of doing it :

Assuming you are using 3/4" MDF.

In the back panel you put a cutout for the amplifier.
Around this cutout you build a rectangular raised section to
clear the back of of the amplifier.

If the amplifier needs 4.5" clearance the section will be 3 3/4".
Make this from 3/4" MDF - like the sides of a shallow box.

On top of this section you fit a 3/4 MDF LID to completely
seal the amplifier from the pressure in the subwoofer.

You need to add a rectangular cutout in the vertical brace
for the box you've added to the back panel. If there are
any circular cutouts in the rear brace where the new cutout
is needed simply omit them.

All the parts remain the same size.

The box will be smaller by 8.5 litres by my calculations.

If you want to correct for this extend the sides, top /
bottom and the length of the rear brace by 2".

/sreten.

[sreten]

P.S.

I've done some basic checking and a plain box made out
of 3/4" stock 18" x 14" x 15.5" has internal dimensions of
16.5" x 12.5" x 14" = 47 litres.

So checking the plans :
exterior dimensions are 19.5"x15.5"x15.5", internally
with 3/4" stock a plain box = 18 x 14 x 14 = 58 litres.

The notes also state a filling of 16 ounces of Polyfill is used
and this accounts for internal volume being lower than the
design volume for the alignment.

So I don't think there's anything wrong with the plans.

/sreten.

[Saydee]

In the back panel you put a cutout for the amplifier. Around this cutout you build a rectangular raised section to clear the back of of the amplifier. If the amplifier needs 4.5" clearance the section will be 3 3/4". Make this from 3/4" MDF - like the sides of a shallow box. On top of this section you fit a 3/4 MDF LID to completely seal the amplifier from the pressure in the subwoofer. You need to add a rectangular cutout in the vertical brace for the box you've added to the back panel. If there are any circular cutouts in the rear brace where the new cutout is needed simply omit them.

I am having a hard time visualizing what you mean here. My problem is that I tried to picture what you are saying before I fully read you post and now I am forcing your plan into what I "think" your describing.

Could you explain it differently or provide a drawing of some type?

Will the amp be protruding into the enclosure at all, or is it flush mounted in this new small box I would need to build?

Why would the internal circular cutouts be removed on that side? Would that disrupt airflow?

[sreten]

You cut the cutout in the back panel - which is smaller than
the amplifier plate so the amplifier can be attached by the
screwholes around the edge of the amplifier plate.
You screw the amplifier to the back panel.
The amplifier now sticks into the sub -
well it would except the rear brace is in the way.

You enclose the amplifier with a box built onto the back / inside
of the back panel. But the rear brace is still in the way so you
cut out a rectangular section in the rear brace so you can fit
your modified back panel.

Omitting the two central circular cutouts in the rear brace
will have no effect at all on airflow.

/sreten.