vented enclosure

[so n so chicago 10+ year member]

I got a premanufactured enclosure... WAIT!!! don't shoot

I am still a newbie

Anyhow it is 0.75" MDF, really small though, but it was real cheap...

Anyhow, I am trying to figure out what the internal volume is and the frequency of the box is.

It is one chamber for two 12"s and has a slot port in the middle. I have done TONS of reading and my confusion is still: when making calculations using the box dimensions do I include the width of the slot or completley ignore that part. Also, the slot is made with a particular length (10.5") of 0.75" MDF wood. Is there a formula for how much volume that would take up, i.e. the slots is made of two pieces of wood that are .75" thick, 12.5" tall and the length is 10.5".

i wish I could draw a picture, but like I said it has one slot in the middle.

PRIMARY QUESTION IS:

To measure the internal volume do I exclude the section that makes the slot port, i.e. subtract 0.75" X2 (thickness of both pieces of wood that make the slot port) and subtract the 2.5" that acutally makes the hole from the total width?

FYI, the dimensions are as follows...

outside dimesions of box...

H 14"

W 32"

D 15.5"

Square port (not including the thickness of the wood):

W 2.5

H 12.5

the length is 10.5"

I know the box is really small and probably tuned really high (and therefore will likely sound like crap), but it was cheap and I want to see how it sounds and would still like to be able to figure out the frequency it is at.

all stabs at answering this post are appreciated

Thank you

ps

FYI: I understand generally how to get volume, i.e. in the case of a sealed enclosure.

I know it won't "fix" the lack of size, but I am hoping that polyfill will help if needed once I figure out the numbers. Additionally, I have 2 JL12w6v2s that the manufacturer recommends only 1.5cf for each in a vented enclosure anyhow...

addendum:

will using polyfil increase the tuning (by decreasing volume) or will it actually decrease tuning by its "slowing down of the air effect"?

Click to read more...

 

[so n so chicago 10+ year member]

thanks

i did and re-did the math and am certain that the effective volume is 2.68cf and 2.5 including driver displacement.

using WinISD, the box is actually tuned to about 46 or 47Hz.

Still small, still tuned high...yep

actually it meets JL's recs for a vented box, but is tuned too high

i hope polyfil will help but we'll see

you got about the same numbers i did

thanks again

i hope polyfil helps

the box actually meets JL's recs for volume but is just tuned too high

 

[so n so chicago 10+ year member]

Well, I installed it and it actually didn't sound as bad as I thought it would (keep in mind all I listen to in my car is rap), but it didn't compare to my sealed enclosure in SQ, just a hell of a lot louder as one would expect.

Now, I by no means claim to have a real "vented enclosure” experience as the box was very small (although within JL's recs) and tuned too high. So, I will make no judgments on vented vs. sealed boxes.

One thing I noticed though is that my car wasn't made to hit hard. Although it does hit somewhat and on long bass notes you can literally feel your insides vibrating (accompanied by a slight nauseous feeling [i love it] it just doesn’t punch you like I have felt in other cars. This is actually a sealed enclosure I am talking about. With my pre-manufactured vented box (yes, I am sorry I have put you through the torment of even contemplating this) it got a lot louder and the floor of my car vibrated. Really weird but I could feel the bass in my feet and that is something I have never experienced even in other really loud cars I’ve been in. Still, it wouldn’t punch me in the back like I have felt in other people’s cars. I have a 95 Mercedes so my guess is that the car is just really well insulated between the car and the trunk.

Also, someone suggested that I stuff a t-shirt or towel in the vent and I did, that made the box sound noticeably better. Actually now that I think about it, some songs did sound better with this setup than in the sealed setup, but overall I am probably going to go back to sealed unless I can figure out how to decrease the tuning of a square slot vented box without too much difficulty. I am just not willing to give up my entire trunk yet (that much space that is) for a suitable slot box setup.

Thank you for all of your input, I really appreciate it.