Box Volume Calculations

[shaggerz]

Hey guys,

Although normally I do my research and find out these things for myself, I already have about 2000 hobbies so I thought I'd just ask here.

I want to build a properly tuned ported enclosure (i have always just used sealed but its time for a change) for my sub when I do the boot install properly.

Question 1: as long as the box volume and port size remains constant, will it be OK to change the dimensions of the enclosure as long as I maintain that correct box volume and port size?

Question 2: what are the rules for the position of the port?

Here are the thiele small parameters for the driver I'll be using. It's a Response 12 inch DVC. These are given assuming voice coils connected in parallel for a 2 ohm load.

Dc Resistance: 1.7 ohms
Vas: 79.454L
Qms: 3.238
Qes: 0.446
Qts: 0.392
Sensitivity: 88.192 dB @ 1 watt & 1 metre
BL: 9.992TM
Fo: 28.77Hz
Sd: 514.72 sq cm

Can someone clever please work out the ideal box volume and port size for this driver??

Thanks!

[Phreddy]

Hiya Shagz.

Mate, I've done the calcs for this driver before and this is what I came up with.

Cabinet volume - 50 litres
Port diameter - 2 x 66mm
Port length - 191mm
3dB frequency - ~36Hz

As far as box dimensions go, some folks talk about the "golden figures" but I found they're not absolutely critical. Just don't forget to allow a bit extra for the back-volume of the driver (probably about 3 - 3.5 litres), plus any bracing you'll be using. As far as the port location goes, just make sure they're not within about 100mm of the driver, and that the inside ends of the ports are well away from any of the internal surfaces. Oh, and don't forget to subtract the port volume from the box as well - the air inside the ports can't be considered as part of the box volume itself.

Cheerz Mate, best of luck with it!

[shaggerz]

thanks champ

[StoneX]

Answer 1: Yes, box shape can be whatever as long as volume stays the same.

Answer 2: The port SHOULD be on the same wall as the sub, but it's not essential, just make sure the sub and port are in the same area, so no venting ports through parcel shelves or through the ski port between the seats.

[sganro]

I have seen audio software that you input your speaker info and it generates ideal box volume, port size etc. Not sure how hard it would be to find but it might be helpful if you could find a similar program. Good luck

[Phreddy]

Ummmm - yeah, that's what I used...

There are a few out there, some contenders are Abacus, WinSpk, WinISD, and of course BassBox. (many others, but....)

Shagz' point was that he had enough hobbies without having to learn to drive yet another piece of software. Good suggestion though...

Cheerz!

[shaggerz]

I tried WinISD but when it wasn't painfully obvious to me I gave up

[calais_cruzin]

I got bass box pro 6, havnt accually put it to use yet, but did have a fiddle around with it and seems to be very easy to use.

Does everythink, that i saw anyway, and have box shape chooser and has the measurements of everythink.

I cant wait to make up a box for my boot, should be alot of fun.

[Phreddy]

BB Pro is real good. I used WinISD for the calculations above, it's always done well for me - and the price is right!!

[shaggerz]

OK guys heres my design. These are inside dimensions and the value of x will be calculated so that the volume = 50 litres with bracing, port, and driver displacement subtracted.

The angled side (the back) of the enclosure will be up against the back seats, with the face side facing into the boot void. The "face side" as marked will have a false wall for the boot attached. It will be the side with the driver and ports mounted to it, facing towards the rear of the car.

You guys foresee any problems with that design?

[SoulGrind]

http://www.ajdesigner.com/speaker/ajvented.php you can build your own boxes with these proggies.

[garfa]

BB Pro is real good. I used WinISD for the calculations above, it's always done well for me - and the price is right!!

yeah bloody oath the price is right, why pay for bbpro when winisd is free?

[vt com]

ive run that same sub in a ported enclosure built to the specs by a helpfull member from CAA, I found the sub to sound better in sealed application, I have mine in a sealed enclosure around 40l powering it at 600rms@2ohms and im happy with it

[StoneX]

yeah bloody oath the price is right, why pay for bbpro when winisd is free?

Because they give different results... Only one can be right and I'd rather trust the one the pros pay for and use rather than the freebie from the internet.

[14secvp]

heres a little program to work out box sizes

[Tasmaniak]

yeah bloody oath the price is right, why pay for bbpro when winisd is free?

don't you have a version of BBpro?

[garfa]

stonex: if you are going to get the price you pay for BBPro back in use or improved quality then yes i would go for it. but myself and i am sure many others cannot be bothered effectively wasting the price of BBPro for that small improvment.
ray: yeah just never got around to installing it. winisd did it for me.