Finding Displacement/Area of subs and port

[vnsmanual]

Hey just wondering whats the best way to determine the displacement or area taken up by your subs and ports?

just designing a new box and wondering how people work out there numbers.

Thanks

[acarmody]

What sub? Most decent sub manufacturers will state it in the specs or on their website.

As for port, its a simple area calculation.

[vnsmanual]

The subs a Mach 5 IXL 12, it didnt come with anything stating the size, i contacted them and had no luck, they basically said to google methods on testing for the area, as they do not have that information available.

[acarmody]

Having had a look at the sub, I would simply work out the area of the magnets and then add 2-3 litres, it will be close enough that it will make basically no difference to the box.

You know the formula for working out the area of a cylinder right? Its Pi time the radius squared, then times that by the length.

[vnsmanual]

ok so the box has a reccomended size of: Ported: 51ltrs (1.8 cu. ft.) 33hz tuning

so the box should be 51 ltrs, plus the area of the magnets, plus 2 or 3 litres, plus the area of the port?

Im going to make up a couple of ports, this shouldnt matter greatly?

Aldo just just so i understand the area of the port does not belong to the box, like the air in the port is not part of the 51 ltr volume of the box?

[acarmody]

I think you got it. Its 51L plus the sub displacement, plus the port displacement, to make something like 60-70L in total.

What do you mean 'make up a couple of ports'?

1.8cu.ft box is pretty small for a ported enclosure. I know that is whats recommended but I pretty sure you can go bigger if you want too.

EDIT: Generally 0.02cu.ft is pretty safe for working out sub displacement. Very bastardized rule, but will be close enough for a 12" sub.

[acarmody]

I got a bit bored. If you make the box out of 25mm MDF, and make it 500mm Wide, 400mm Deep, and 395mm Tall. Use a round PVC pipe port, and make it 360mm long (or 375mm with 15mm flare on each end). Then you will have a box with 1.8cu.ft. of volume.

[vnsmanual]

I've actually got a box built already that is considerbly larger than the one you just designed and it works really well HVCP helped design it with me. It works really well but it's huge And I know that I need to sacrifice looks and space for bass but currently I can't get my spare tyre out! So a smaller box is in order. The one I have now is a tad over 4 cubic ft. So will I notice a huge difference from the one I have now to your one? Because your box is like 2.1 cubic ft isn't it? So it would be like half the size!

[vnsmanual]

Oh and I've got a sheet of 18mm so I'll use that and double up the baffle.

[acarmody]

Ah yeah I remember a thread where that huge box was mentioned.

Well a smaller box won't hit as low as the bigger one, but it may gain some more up higher.

[vnsmanual]

would my best bet be to build the box to the biggest area i want to take up, which i think i worked out to be around 3 cubic ft, that way im not going down as much in size? so im not loosing as much of the low stuff? is there anything i can do to the smaller box to regain that lower stuff?

[acarmody]

Apparently stuffing it to 50% capacity with that polyfill helps it down low a bit. Can't personally vouch for it.

Yeah work out the max you can built it to be and use that.

[vnsmanual]

oh ok i have heard a little about poly fill before, where can you get it from and how much is it? if i build it to say 3ft cubed for example will the port size you mentioned above still be right? is 33 hz fine, and i use 6 inch pvc for my ports is that what the above one is desinged for.

Thanks heaps for your help!

[acarmody]

I got a big bag of polyfill from Spotlight of all places, I think it was for pillow stuffing or something.

This will help you, PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Remember enclosure volume does not include port or sub displacement.