Port Calc Sites (inconsistencies)

[robert J]

Here is the closest I can come to 1.43 Vb, 34Hz and the highest port volume I can seem to get for a 400Wrms NVX 12"

 

[Jeffdachef 5,000+ posts]

Thanks for your reply.
tricky balancing the port area which needs to go up and Vb that needs increasing while the tuning freq needs to go down. I can manage to get acceptable net Vb 1.43 and tune 34Hz but can't seem to get the port volume number above 9 and keep those numbers. I see that port length drops Hz while hardly changing port volume and net Vb, while port diameter greatly increases port volume but kills my net Vb and Hz tune. I will figure it out, just need to play with it for a while.

Also,

the 'DESIRED NET VOLUME" is confusing in the help section. What exactly does entering a number there accomplish? The two pics below are the same except for the second one has "desired net volume" plugged in? I don't get it.

I notice the port Hz, net volume, port volume numbers change but not the dimensions.

Cheers.

EDIT:

 

DUH!!! add another port. Seems like a lot of port though for the box.

 

Leave the desired volume stuff alone, useless, look at your gross volume, how can your net be more than your gross volume? If you are shooting for

1.43 cubes, your gross volume needs to be around 1.8 cubes because after subtracting the space the port, sub and bracing takes up, you arent left with anything. Your issue right now is your dimensions are WAAAAY too small.

 

go with a single 4 inch round port. You need to go a lot bigger with your box, you dont have enough airspace to tune low as you want it.

 

[robert J]

This is starting to look pretty good. I think the way to go may be with a slotted port on one side incorperating the outer panel, top, bottom and one baffle. How do these numbers look?

 

[robert J]

Leave the desired volume stuff alone, useless Your issue right now is your dimensions are WAAAAY too small.
go with a single 4 inch round port. You need to go a lot bigger with your box, you dont have enough airspace to tune low as you want it.

Thanks for your time and attention M8. I am trying to stuff this box into my spare tire area of the trunk which is 24"x 8" x 24", but even then, the above box won't quite fit, need some more tweaking. I hear what your saying about physical dimensions and not being able to tune that low.

My Alpine Spec sheet says "Filling an enclosure can allow for approximately a 20% smaller box due to its thermodynamic capabilities... Vented Enclosures: It is

recommended that the interior walls of a vented enclosure be lined with 1/2" to 1" fiberglass sheeting or polyester batting. This

will greatly reduce sound reflections in the enclosure. Loose filling in a vented enclosure is not recommended as it can impede air

flow through the vent."

according to this theory, I could get my 1.43Vb down to Vb1.14

Cheers. and thanks for all your input.

 

[Jeffdachef 5,000+ posts]

Thanks for your time and attention M8. I am trying to stuff this box into my spare tire area of the trunk which is 24"x 8" x 24", but even then, the above box won't quite fit, need some more tweaking. I hear what your saying about physical dimensions and not being able to tune that low.
My Alpine Spec sheet says "Filling an enclosure can allow for approximately a 20% smaller box due to its thermodynamic capabilities." according to this theory, I could get my 1.43Vb down to Vb1.14

Cheers. and thanks for all your input.

only works for sealed, completely useless for ported. Also builds heat faster and does not get dissapted as well, stuffing will fly out of the port over time or the fill will get caught in your voice coil ruining your subwoofer. You never plan any ported subwoofer builds with polyfill in mind, thats a disaster waiting to happen.

Forgot to tell you, your port length cant be longer than any of the dimensions.

you can do 8x23x23 with a 17 inch long 4 inch port for 34hz 1.45 cubic feet. You can safely do up to half the port diameter to the rear wall for the port to breathe.

 

[robert J]

Forgot to tell you, your port length cant be longer than any of the dimensions.

you can do 8x23x23 with a 17 inch long 4 inch port for 34hz 1.45 cubic feet. You can safely do up to half the port diameter to the rear wall for the port to breathe.

I thought you could bend the port around the rear of the box in an "L" shape to get the length needed?

 

[subzero 5,000+ posts]

I thought you could bend the port around the rear of the box in an "L" shape to get the length needed?

You can.

I don't know about the other guys, but I use a combination of port calculators to cross check the specifications.

Here is a list of sites I use:

Products Menu

RE AUDIO - Box Calculator

Speaker Enclosure Volume Calculator

https://www.the12volt.com/caraudio/boxcalcs.asp

Car Audio - Subwoofer Box Dimension Calculator

Port Length Calculator

 

[robert J]

Cheers Sub!

what do you think of this one? http://www.hometheatershack.com/forums/enclosure-volume-calculator/

 

[Jeffdachef 5,000+ posts]

You can.
I don't know about the other guys, but I use a combination of port calculators to cross check the specifications.

Here is a list of sites I use:

Products Menu

RE AUDIO - Box Calculator

Speaker Enclosure Volume Calculator

https://www.the12volt.com/caraudio/boxcalcs.asp

Car Audio - Subwoofer Box Dimension Calculator

Port Length Calculator

Calculations should be all the same its basic math, same sh*t as winisd calculations, its all the same formulas, nothing different except RE box calculator thats proven and well known to be beyond garbage and completely innacurate. However newbies dont understand the concept of port, sub and bracing displacement and that you need to figure that out first get a proper cubic feet number(accounting in thickness of the wood and overall bracing used) then add on the net airspace afterwards to get a total gross cubic feet airspace to try and achieve with your dimensions. Thats how We used to design boxes by hand.

However all of the noobs completely mess it up and get it wrong and use the port dimensions into a box without subtracting displacements. Leaving them with a much smaller box and a much higher tuning and they dont understand why their box sounds like garbage.

Torres and xplicit audio's ultimate car app literally cleans up all that for you and includes everything in the calculations. The most accurate way is google sketchup where you can 3d model the enclosure and get everything down to the millimeter accurately.

Cheers Sub!
what do you think of this one? http://www.hometheatershack.com/forums/enclosure-volume-calculator/

They are only valid if you understand the concept of what i just said. I'd stick with torres or ultimate car app on the phone. Especially since you look like you have no understanding of the proper math to design sub enclosures and you'll most likely end up with a cr@ppy port that'll cause compression (aka loss of output aka strangling your sub) and port noise judging from your original design with the 3 inch aero. The port area per foot keeps you relatively in check especially since you are new to this.

The proper way is to model it up on winsid and see rear air velocities according to your input power.

 

[buckeyes#1 10+ year member]

I've used torres a few times how accurate is this program ? So some swear by it

 

[robert J]

Sketchup is cool. I did not know about it. Yes, the port is the same width front to back, 2 inches. The box isn't matched to a sub or tuned, just tried to through one together. Now I will try one with the correct Vb and port sizing/tuning.

 

[Papermaker85 5,000+ posts]

Just do the formula. Lol