building a sub box

8659 Views 23 Replies 6 Participants Last post by vaBooM, May 14, 2004

titanium3

Discussion Starter · Apr 21, 2004

2

i'm thinking of building a sub box for my 3 hatch... i did a little research and found a lot of info... and have some questions for the experts... my first questions relates to the shape of the box, what is the optimal shape for a box... most boxes i see are rectangular in general, if this is the optimal shape what would i lose by going with a different shape like a three sided pyramid to fit in a corner... here is a picture of various shapes of boxes, any comments on any of the designs is much appreciated..

my next question is about ported boxes... can odd shaped boxes be ported? and in general are there any rules for the size, location and number of the ports? i've also noticed different types of porting, here's a picture of some diffent designs, again any comments on any design is much appreciated...

basically i want to build a box for my 3 but don't want to loose all the space and don't really want a big rectangular thing in my car... i know that there is a stealth box someone made that goes were the jack is but its small volume restricts the size of sub selections and i want something bigger...

any links to websites that may anwer any of these questions or related topic would also be helpful... i don't mind doing a little digging to find my answers... thanks in advanced for your help... :wink:

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vaBooM

· #2 · Apr 21, 2004

Shape dont matter one bit. Its all airspace...

Same with ported boxes. As long as the vent/port is perfectly (or near) linear. So no weird shapes.

I would suggest you doing a false floor with say, single 12" ported or 2 12". Getting the port right on odd shapped boxes can be tricky. A few places to start to get to know box building:

www.bcae1.com - Scroll down to like the low 100s on the right hand side.

http://www.jlaudio.com/tutorials/ports/index.html - A very good tutorial of slot porting.

Slot porting with WINisd = Here

Good luck!

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crzyone01

· #3 · Apr 21, 2004

I would tend to disagree, the shape of the box is quite important in how the sound will travel after "hitting" the different sides/angles inside fo the box. But in general unless you are really trying for competition this point is not to be worried about. As for the size of the box that is also important if you know what sub you are going to get build a box around it so you cane "tune" the sound(read: in Hz) coming from the box. As for ports they are extremely important and the size/type of a port all varies on the type of sub you end up with. Making larger/smaller & longer/shorter ports is how a vented box is "tuned" which is again all dependant on which sub you go with. Also if you are trying the corners a suggestion may be to go with 2 free air subs and mount them each on a baffle in thecorners where te seats meet the hatch. That's relaly about it, well that and the type of material going to be used for the boxes. If you havce a sub/s in mind go ahead and post them and I'll try to narrow down some of these ideas.

- Phil Rogers

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nab33

· #4 · Apr 21, 2004

I was thinkin of gettin TWO 12" Kicker Comp VR... what do you think the dimensions for a ported box would be? :lol: anyone

vaBooM

· #5 · Apr 21, 2004

CrzyOne01 said:
I would tend to disagree, the shape of the box is quite important in how the sound will travel after "hitting" the different sides/angles inside fo the box. But in general unless you are really trying for competition this point is not to be worried about. As for the size of the box that is also important if you know what sub you are going to get build a box around it so you cane "tune" the sound(read: in Hz) coming from the box. As for ports they are extremely important and the size/type of a port all varies on the type of sub you end up with. Making larger/smaller & longer/shorter ports is how a vented box is "tuned" which is again all dependant on which sub you go with. Also if you are trying the corners a suggestion may be to go with 2 free air subs and mount them each on a baffle in thecorners where te seats meet the hatch. That's relaly about it, well that and the type of material going to be used for the boxes. If you havce a sub/s in mind go ahead and post them and I'll try to narrow down some of these ideas.

- Phil Rogers

There are plenty of ways to manipulate wavelengths.. ie: PolyFil, rounded wood trim etc etc. I once heard an SQ vehicle as USAC with a totally round sphere as the enclosure, a false floor was built to add additional airspace and the port. Sounded phenominal.

I do agree different port lengths and surface area effectively directly affect tuning of the box. Building the box to recommended ported specs is a must.. but WINisd helps if your wanting to see the frequency response curve. Port length is a direct relation to box size, and WINisd will help you get it right.

vB

titanium3

Discussion Starter · #6 · Apr 22, 2004

what's a false floor? and what's its purpose

vaBooM

· #7 · Apr 22, 2004

Meaning you build up the floor to gain extra airspace or for amp racks/flushing in amps etc etc.

titanium3

Discussion Starter · #8 · Apr 24, 2004

ok... i've come up with the following design...

it will fit between the back seats and the cargo tray when its flipped up...

i have a few questions...

am i sacrifising anything by having the woofer fire of to the side instead of towards the back of the car? and if so how much...

the box is designed for a rockford fosgate punch stage 3 10" and i was able to get the requirements for box volume and port diameter & length but i really didn't find anything on where the port should be located... my question is does it matter where the port is... could i put it on the opposite side of the box from where it is now?

another question i have is about materials... i know to use 3/4" MDF for the box but what about the inside... should i line it with something or is the bare wood enough... i've seen some boxes with some stuff inside and was wondering what it was for...

any other comments or questiions on this design are very welcome... thanks in advance for any advice

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vaBooM

· #9 · Apr 24, 2004

You can put the port anywhere you wish... it hasnt necessarily been proven its any louder firing in the opposite direction as the sub.

Firing backwards will be the loudest. Reason being the wavelength of low end frequencies take a good 6~8 feet of travel before they are the loudest. Firing back would reflect off the back then travel forward. Hence why subs sound the cleanest firing foward and loudest by firing backwards.

Seal all the seams with a bead of caulk or liquid nails. The white stuff usually in boxes is PolyFil. Its pillow material that is like cotton.. it slows waves down making the sub think its playing in a much larger box. It also smoothen out ripples and standing waves.

vB

titanium3

Discussion Starter · #10 · Apr 24, 2004

thanks vB... your definately a wealth of information...

so let me ask another some more questions...

if the box is already the size recomended for the woofer is there any advantages to the polyfil?

and if i do make it so that the sub fires backwards does it matter if the cargo divider in the hatch is up and the box is between it and the back seats?

also when you say the port can be placed anywere do you mean that it doesn't have to me in line with the firing direction of the woofer? can it be perpendicular (the sup firing backwards and the port out to the side is what i mean)

thanks again for the resposnse

vaBooM

· #11 · Apr 25, 2004

titanium3 said:
thanks vB... your definately a wealth of information...

so let me ask another some more questions... if the box is already the size recomended for the woofer is there any advantages to the polyfil?

and if i do make it so that the sub fires backwards does it matter if the cargo divider in the hatch is up and the box is between it and the back seats?

also when you say the port can be placed anywere do you mean that it doesn't have to me in line with the firing direction of the woofer? can it be perpendicular (the sup firing backwards and the port out to the side is what i mean)

thanks again for the resposnse

Adding a little bit of PolyFil will kill standing waves. Adding alot will make the sub think its playing in a bigger box.

As long as the subs excursion wont whack it, it shouldnt be a problem. It may rattle though.

Ive seen some installs where the response curves on meters were actually cleaner when the subs were firing backwards and the ports were firing to the side. Its definately not any louder, but it seemed to clean up the frequencies. Anyways, it dont matter one bit where the ports are firing. As long as they are covered or trapted in any way.

vB

titanium3

Discussion Starter · #12 · Apr 25, 2004

Thanks vB

do you think the rear firing design would sound better than the side firing design even if the cargo divider is always up? i checked it out and it probably won't rattle... even if it does it will be easy to fix...

titanium3

Discussion Starter · #13 · Apr 25, 2004

As long as they are covered or trapted in any way.

do you mean as long as they are NOT covered or traped?

vaBooM

· #14 · Apr 26, 2004

titanium3 said:
Thanks vB

do you think the rear firing design would sound better than the side firing design even if the cargo divider is always up? i checked it out and it probably won't rattle... even if it does it will be easy to fix...

I dunno. Never faced such a dilemma before. It shouldnt make a big difference whether its up or down. If it were I, I'd fire the subs on the sides with the ports facing the rear. Dunno why, just never done it before. Experiment.... may lead to a louder setup.

As long as nothing is stopping the air from leaving the port, then you should be fine.

vB

StratoBlue

· #15 · Apr 29, 2004

Porting Location

Most manufacturers recommend that ports should radiate unobstructed from same plane as the speaker. They say it gives you more linear response. What do they mean by "more linear"?
I have a 1.25 cubic foot sealed box that I'd like to put a port in.
The box was designed to be a selaed box and doesn't have enough room to put a 3" port on the same plane. I was thinking about putting the port on the top of the box. Would this set up sound OK? They also recommend that where the port end up inside of a box to be at least the length of the port diameter away from any walls. Can anyone tell me what the reason is?
It'll be really hard to meet all these recommendations without getting a brand new custom enclosure. Thanks.

crzyone01

· #16 · Apr 29, 2004

Just one quick questions, why is everyone wanting to port their boxes ? Typically a sealed enclosure will yield tighter bass as well as the option for handling more power depeing on the woffer chosen

.

- Phil Rogers

bknauss

· #17 · Apr 29, 2004

Sealed is much more inefficient at the lower frequencies. If you want the real low stuff to play well, then you need ported (this statement was made with lots of assumptions and generalizations)

titanium3

Discussion Starter · #18 · Apr 29, 2004

i'm pretty sure u can put the port on top because i've seen some boxes made by q-logic that have ports on top... when they say a more linear responce i think they mean that all fequencies are reproduced more of an equal level (i'm not an expect this is just what i've gathered from reading posts so someone correct me if i'm wrong...

when they say the port should be atleast the lenght its diameter away from any walls i think they mean that the end of the port inside the box should be away from the wall... most of the boxes i see have ports pretty close to the corners...

about having the port on the same plane as the speaker, i don't think thats important becase most home theathre subs have the speaker and port fireing in a perpenducal planes... i have the logitech thx speaker set for my computer with that setup and it POUNDS...

one thing you should watch out for is box volume... for the same sub, the ported box volume requirement is always larger than the sealed volume requirement... and don't forget to substract the volume displaced by the port and the sub from the overall box volume... that the actual volume of air in the box which the specs call for...

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titanium3

Discussion Starter · #19 · Apr 29, 2004

one more question for the experts... what's better a round tube port or a slot port

vaBooM

· #20 · Apr 30, 2004

Sealed and ported is much like Class AB and Class D amps. Sealed and AB amps arent one bit effiecient. They take more power to make sound. Ported and D amps are highly effiecient and need less power for the same output.

It used to be said that sealed enclosures will take much more power than ported. True, to a certain extent. So happens my sub takes well over RMS rated power in a ported box. Odd, cause in a sealed it only took about half (hmm...).

With rounded edges, slot and round dont make a difference. If done correctly, they should be 99% alike. Always always always make sure the width of the port (say 3") should be 3" away from the back, 3" away from the side and 3" away from the sub.. with the exception of slot porting, which only needs to be 3" away from the sub and the back.

vB

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