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View Full Version : Okay, I need to know if I designed this ported box right...



SomeGuyDude
08-07-2009, 10:37 PM
It's been a while since I've done it, but here we go. My aim for the RE SEX15 was 4.0cu with a port at around 34Hz. Got 'em from the RE site

So here's what I did:

I took optimal dimensions as 16.5" tall and 30" wide. These are INTERNAL dimensions, judging by the numbers in the later steps, hence 16.5" so I can get it 18" tall total. Then a 16.5x3" port, which means a length of 21.15" according to WinISD.

From there it's adding up the displacement (17.25x3x29.19 for the port) 0.633 + 4 + 0.17 for the sub = 4.80cu, yes?

Now it's that fancy-dan formula for my mystery dimension: depth. Take our above numbers and slam them together (4.80*1728)/(16.5*30) = 16.75

So my internal numbers are LxWxH of 16.75x30x16.5 internal, and 18.25x31.5x18 external, correct?

Now, figuring out the dimensions of the WOOD will require a whole lot of sketching, but I think I can do that just fine. I just need to make sure I've got all my digits correct.

My final question: how does one factor in a bending vent? If it has to be 21" long and I've got an 18" deep box, that's an extra three inches. Do I just take the 21" piece of wood that would normally go straight, then just cut it and re-glue/screw it where it would need to be? Seems to me that would affect its effective length, but maybe not.

dappa5
08-08-2009, 12:19 AM
if you need to turn the port you must measure down the center of the port
this will affect you overall volume due to the ports displacement
if you want a net (after all displacements) 4.0 ft^3 you will need to re figure your overall dimentions a 3 " port 21 inches long would make your internal volume 4.02 ft^3
that's before sub so add a little depth and you'll get the volume you want

dappa5
08-08-2009, 12:40 AM
if you increase the overall depth to 19.5 " you'll get 4.45 after port b-4 sub that's with a three inch prt idk if that port length is even valid just going off what you provided

hope this helped next time just post max dims and ask for suggestions plenty of ppl here will add their $0.02

SomeGuyDude
08-08-2009, 10:30 AM
Well I used WinISD for the port length. Punched in a 16.5x3 port in a 4cu box tuned to 34 and it told me 21.15" long. That's really all I know. I'm using the formulae from the EDU sticky.

EDIT: did all that wrong, re-sketching.

GearGuy2001
08-08-2009, 11:06 AM
To bend the port since its longer then the depth of your box run your first wall back until you reach the width of your port as a distance from the back wall

IE 3" wide port then cut Internal Port Wall to 12.25" if 16.75" is your total OD dimensions

16.75" - .75" for back wall and .75" for front wall and 3" for port width= 12.25"

This picture might give you a better idea of how to "stack" the wood...
http://img.photobucket.com/albums/v157/GearGuy2001/caraudio/DSCN2034.jpg

SomeGuyDude
08-08-2009, 11:09 AM
That's what I was thinking. Looks like I'd need a 13" piece front to back and then a 3.5" piece at the back end for 21" total of length. It'd give me an effective front length at 16" and then 5" at the side. The only issue I see is that the less wood means a SLIGHTLY larger box thanks to less displacement. But nothing serious, right?

GearGuy2001
08-08-2009, 11:16 AM
If you were doing a double baffle front thats 1.5 + 13 + .75 (width of wall 1) + 3.5 = 18.75

Youll have to tell me more about the box for me to help (double or single baffle front) Width of Port and Total Length(OD) of the box.

SomeGuyDude
08-08-2009, 10:37 PM
The way it looks now:

Box DepthxWidthxHeight: 16.75x30x16.5 (internal), 18.25x31.5x18 (external)

Port: 16.5x3x21 (obviously internal dimensions)

Single piece of wood for the baffle

The top and bottom would be full size, left side full size, the baffle piece would be on top of the port piece and the right side like the image you gave. The numbers I've got so far with that would be like this, assuming .75" thick MDF (forgive the crudity):

http://i26.tinypic.com/3506p6r.jpg

GearGuy2001
08-08-2009, 10:45 PM
The way it looks now:

Box DepthxWidthxHeight: 16.75x30x16.5 (internal), 18.25x31.5x18 (external)

Port: 16.5x3x21 (obviously internal dimensions)

Single piece of wood for the baffle

The top and bottom would be full size, left side full size, the baffle piece would be on top of the port piece and the right side like the image you gave. The numbers I've got so far with that would be like this, assuming .75" thick MDF (forgive the crudity):

http://i26.tinypic.com/3506p6r.jpg

With that pic you have 18" of Port Length, if you need 21 then you need to make the 2nd port wall 3" longer.

SomeGuyDude
08-08-2009, 11:01 PM
Okay, I'm not doubting you, I just need to get an understanding of why that is.

I was under the impression that a bent port length is calculated by going down the center of the vent. So that means you'd start at the front and go down 16" (the center of that corner being 1.5" from each side) and then another 5" to the right from there, meaning a 1.5" gap before you hit the wood, then .75" for the wood thickness, then 2.75" for the remaining five. Like this:

http://i28.tinypic.com/vfi7io.jpg

What's the right way to calculate vent length when it has to turn a corner? The 18" is just the length of the inner wall of wood. And if it's as simple as that, life just got a LOT easier.

csu87
08-08-2009, 11:04 PM
Okay, I'm not doubting you, I just need to get an understanding of why that is.

I was under the impression that a bent port length is calculated by going down the center of the vent. So that means you'd start at the front and go down 16" (the center of that corner being 1.5" from each side) and then another 5" to the right from there, meaning a 1.5" gap before you hit the wood, then .75" for the wood thickness, then 2.75" for the remaining five. Like this:

http://i28.tinypic.com/vfi7io.jpg

What's the right way to calculate vent length when it has to turn a corner? The 18" is just the length of the inner wall of wood. And if it's as simple as that, life just got a LOT easier.
thats how i do it. hope its right:crap:

GearGuy2001
08-08-2009, 11:05 PM
Okay, I'm not doubting you, I just need to get an understanding of why that is.

I was under the impression that a bent port length is calculated by going down the center of the vent. So that means you'd start at the front and go down 16" (the center of that corner being 1.5" from each side) and then another 5" to the right from there, meaning a 1.5" gap before you hit the wood, then .75" for the wood thickness, then 2.75" for the remaining five. Like this:

http://i28.tinypic.com/vfi7io.jpg

What's the right way to calculate vent length when it has to turn a corner? The 18" is just the length of the inner wall of wood. And if it's as simple as that, life just got a LOT easier.
Hrm I always thought it was measured on the inside wall, but I guess I could be wrong lol

I guess it does make more sense to measure down the center.

SomeGuyDude
08-08-2009, 11:14 PM
Yeah I was kinda grappling with that myself, and it's about all I can figure. After all if you take a length of bendable tubing that's 20" long and you kink it, the outer side gets longer and the inner side gets shorter, but the center distance remains the same. Or here's another way of looking at it, with an inner wall (the red line) that stays two units long:

http://i32.tinypic.com/ae8p74.jpg

But since we added a curve, now the area of the path is 5sq instead of 4sq. But again, I'm just a guy with a calculator, if anyone with more experience wants to correct me, please do.

SomeGuyDude
08-08-2009, 11:19 PM
thats how i do it. hope its right:crap:

LOL yeah it's kind of an important thing since it can create a massive alteration in the tuning of the sub. I mean three inches off the port length can be the difference between a 34Hz box and about 36Hz, which could potentially be enough to throw the whole project off.

atlninja82
08-09-2009, 10:08 AM
im pretty sure your port length would be 13.75 + .75 + 2.75 + .75 + 3. which would make it 21

SomeGuyDude
08-09-2009, 11:18 AM
Okay, so I didn't screw that up? That's what I needed to know.

atlninja82
08-09-2009, 12:23 PM
nope its right.

SomeGuyDude
08-09-2009, 02:28 PM
Sexcellent. Thanks a lot, man. And I can use RE's calculator to quickly get all my wood dimensions, get Lowe's to chop 'em up for free, borrow my uncle's Sawzall and I'm ready to start building.

Once I figure out if I'm buying a T5 or an RE ***...

atlninja82
08-09-2009, 04:04 PM
just be careful with lowes cutting for you. i have made the mistake of letting them do it for me a few times and i dont let them do it unless i have "my guy". theres only one guy that makes sure its right on or very close to it. so make sure you tell them you want as little error as possible or the cuts might be way off. good luck.

SomeGuyDude
08-09-2009, 04:06 PM
Yeah. That's the problem. I don't have access to the necessary tools so I gotta hope for the best. Back when I was cutting the stuff myself I had a tendency to get the angles wrong. I'll have measuring tape with me when I go haha.

atlninja82
08-09-2009, 04:44 PM
haha well go buy them. they will last you forever.

ryls
08-09-2009, 04:52 PM
im pretty sure your port length would be 13.75 + .75 + 2.75 + .75 + 3. which would make it 21

actually isnt there another 1.5 inches of port length(half the width of the port) due to port end correction seeing as the port is on one of the enclosure walls

atlninja82
08-09-2009, 07:15 PM
actually isnt there another 1.5 inches of port length(half the width of the port) due to port end correction seeing as the port is on one of the enclosure walls

im not sure i understand what you are saying. no i dont think there is another 1.5 inches

SomeGuyDude
08-09-2009, 07:49 PM
im not sure i understand what you are saying. no i dont think there is another 1.5 inches

I know what he means. Eons ago guys would talk about something that I -believe- was dubbed "port correction" where basically you'd consider another few inches (half the width of the vent) inside the box as part of the port in all calculations. I think it came about because someone did some really rudimentary physics and didn't understand exactly what he was doing, but it caught on. Don't think it's legitimate though.

Actually I got lazy and started using this thing: http://www.reaudio.com/speaker_box/LPort_Box_Calc.html

Since I'm looking to make a box for a T4, this actually made things easier because the Soundstream manual says don't even take sub displacement into account, so I can do things straight as it says.

ryls
08-09-2009, 08:02 PM
I know what he means. Eons ago guys would talk about something that I -believe- was dubbed "port correction" where basically you'd consider another few inches (half the width of the vent) inside the box as part of the port in all calculations. I think it came about because someone did some really rudimentary physics and didn't understand exactly what he was doing, but it caught on. Don't think it's legitimate though.

Actually I got lazy and started using this thing: http://www.reaudio.com/speaker_box/LPort_Box_Calc.html

Since I'm looking to make a box for a T4, this actually made things easier because the Soundstream manual says don't even take sub displacement into account, so I can do things straight as it says.


Here is a link that explain more what i was talking about
http://www.caraudio.com/forum/showthread.php?t=357091 there are alot more posts here and there about it in alot of other threads aswell. Also im pretty sure if your using the re calculator it is already adding in the port correction, but dosnt take into account sub displacement.

dappa5
08-09-2009, 08:09 PM
if you increase the overall depth to 19.5 " you'll get 4.45 after port b-4 sub that's with a three inch prt idk if that port length is even valid just going off what you provided

hope this helped next time just post max dims and ask for suggestions plenty of ppl here will add their $0.02


ok so what are you looking for ??


It's been a while since I've done it, but here we go. My aim for the RE SEX15 was 4.0cu with a port at around 34Hz. Got 'em from the RE site

So here's what I did:

Then a 16.5x3" port, which means a length of 21.15" according to WinISD.
My final question: how does one factor in a bending vent? If it has to be 21"

i was under the impression that was what i provided ??
why are you arguing every answer you get??
w/e G/L with build

SomeGuyDude
08-09-2009, 08:09 PM
Here is a link that explain more what i was talking about
http://www.caraudio.com/forum/showthread.php?t=357091 there are alot more posts here and there about it in alot of other threads aswell. Also im pretty sure if your using the re calculator it is already adding in the port correction, but dosnt take into account sub displacement.

So I was right about the term? And yeah, I figured if it's a factor, RE would have it already as part of its equations, and as for displacement Soundstream's instructions even say "4.0ft^3 (w/o sub displacement)" so apparently that's not even a factor to them.

They also mention fiberglass insulation, so I'll have to snag some of that.

atlninja82
08-09-2009, 10:57 PM
So I was right about the term? And yeah, I figured if it's a factor, RE would have it already as part of its equations, and as for displacement Soundstream's instructions even say "4.0ft^3 (w/o sub displacement)" so apparently that's not even a factor to them.

They also mention fiberglass insulation, so I'll have to snag some of that.

sub displacement is always a factor. they must have figured the volume needed was 3. somethin net and with the added sub displacement came out for 4 cubes even or close to it to make it easy.

SomeGuyDude
08-09-2009, 11:04 PM
sub displacement is always a factor. they must have figured the volume needed was 3. somethin net and with the added sub displacement came out for 4 cubes even or close to it to make it easy.

Well yeah, that's what I mean. They have the numbers set so I don't have to worry about it on MY end. Which is convenient. I can just use round numbers.

So as it stands I'm looking at 16x16x38. Takes up the entire hatch from side to side but not too deep or tall. Question though: Is it possible to tune a box too low? If the manufacturer says 34Hz and I'm aiming at 33 or under, can that screw with the sub's potential somehow?

http://i26.tinypic.com/5r3o5.png

Second question: is 16" too short for a 15? I mean, the hole is 14.25" or something but am I cutting too close for actually mounting it? 17" wouldn't be a problem at all.

atlninja82
08-09-2009, 11:35 PM
Well yeah, that's what I mean. They have the numbers set so I don't have to worry about it on MY end. Which is convenient. I can just use round numbers.

So as it stands I'm looking at 16x16x38. Takes up the entire hatch from side to side but not too deep or tall. Question though: Is it possible to tune a box too low? If the manufacturer says 34Hz and I'm aiming at 33 or under, can that screw with the sub's potential somehow?

Second question: is 16" too short for a 15? I mean, the hole is 14.25" or something but am I cutting too close for actually mounting it? 17" wouldn't be a problem at all.

1st question
i donno about that one. why would you want it that low dude? 34 is plenty low.

2nd
ive heard its recommended to leave atleast 3 inches on either side but you will be fine. i would just make sure wherever youre mounting it, make it a double baffle if possible.

SomeGuyDude
08-10-2009, 08:06 AM
On the tuning, 34's low enough that it won't bottom out playing some of the ultra-low music? That's what worries me here. One problem I always have with box-building is that it'll be crazy loud for most freq's but then drop off like mad. Lil Jon's Get Low was a good example of a low tone that just never hit right.

Yeah three inches on either side just can't happen. That'd be a 21" tall box at least. Double baffle sounds like a good idea though. Just gotta re-tool the box a little.

atlninja82
08-10-2009, 09:19 AM
yea just double baffle it and you will be fine. if you are that scared of it not being strong enough around the edges just make sure you use a **** ton of wood glue. glob it on there and resin the inside, do some bracing and resin the inside and the box wont come apart.

and yea 34 should be plenty low. my dd's are tuned to 39 and it hits the lows real well and doesnt bottom out..... well not yet... haha i dont think they are broken in yet but yea 34 will be plenty low imo.

SomeGuyDude
08-10-2009, 09:28 AM
All right cool. That always worries me. I don't know exactly how the roll-off works below the tuning freq but if I end up building this box and the sub starts flapping I'll be annoyed, y'know? But if you're rolling at 39Hz obviously 34'll be fine.

I just measured my L7 for reference and the outer diameter is like 15.75", which means I'd practically be drilling the sub into the top and bottom pieces. That's just cutting it too close for comfort. So 17" tall it is, to get a little extra space. That means 36x17x16 with the four main boards (top/bottom/left/right) cut .75" extra thick to make space for the double baffle.

SomeGuyDude
08-10-2009, 07:49 PM
Okay so I'm looking into designing the box, and in the T4 manual it says it recommends stapling 1" thick fiberglass insulation to the inside of the box.

Two questions:

1) Does it matter what kind this is? I've never used this crap in a box before and I'm a little lost on this one. Seriously, just the pink stuff? Does it come in 1" thick sheets?

2) How many staples per square inch is a good idea here? If it's too many I'm pretty sure it'll get smushed down too far to be useful, too few and I'm gonna open up my trunk and find shreds of fiberglass everywhere.

atlninja82
08-10-2009, 10:58 PM
Okay so I'm looking into designing the box, and in the T4 manual it says it recommends stapling 1" thick fiberglass insulation to the inside of the box.

Two questions:

1) Does it matter what kind this is? I've never used this crap in a box before and I'm a little lost on this one. Seriously, just the pink stuff? Does it come in 1" thick sheets?

2) How many staples per square inch is a good idea here? If it's too many I'm pretty sure it'll get smushed down too far to be useful, too few and I'm gonna open up my trunk and find shreds of fiberglass everywhere.

alright building boxes is like the way people make anything. everyone has their own way of doing it. you dont need to fiberglass the inside or use staples . thats just one way of doing it . the biggest thing is making sure your cuts are right on and brace accordingly. and use a **** ton of wood glue. screws are up to you.

atlninja82
08-10-2009, 11:04 PM
http://www.youtube.com/watch?v=k3hIsQTQCVo

tuned to 39 hz and kills the lows imo.

SomeGuyDude
08-10-2009, 11:04 PM
Dude I should be like, paying you for the amount of consultation you're giving me. :laugh:

So the fiberglass isn't necessary? Seemed like a weird thing to point out in the manual, but if it's not needed then it's not needed so whatever. I'll call it an outside possibility and decide later if I want to bother.

Yeah, my normal way of building is wood glue and c-clamp the hell out of everything, then screw it shut and use silicon sealant on all the inside edges once all that's in place. It's a little surprising that you'd say screws are optional though. I didn't think wood glue was that strong. :laugh:

All right, looks like I'm pretty much done with the design phase. At least in terms of getting my methodology down. Now it's just a matter of making sure which sub I'm getting and then pick up the materials.

Also that video is ****ing outrageous. WOW. Awesome work mang.

dappa5
08-10-2009, 11:16 PM
yeah great design it looks like it wangs lol

dappa5
08-10-2009, 11:22 PM
IS THERE ANY ONE ON HERE THAT CAN GIVE ME A DESIGN THAT WILL DO THAT??
or that could help me and walk me through every thing i need to kno??
if so that guy would awesome

atlninja82
08-11-2009, 08:08 AM
IS THERE ANY ONE ON HERE THAT CAN GIVE ME A DESIGN THAT WILL DO THAT??
or that could help me and walk me through every thing i need to kno??
if so that guy would awesome

HAHAHAHAHAHAHAHA :laugh::laugh::laugh::laugh::laugh::laugh:

atlninja82
08-11-2009, 08:12 AM
Dude I should be like, paying you for the amount of consultation you're giving me. :laugh:

So the fiberglass isn't necessary? Seemed like a weird thing to point out in the manual, but if it's not needed then it's not needed so whatever. I'll call it an outside possibility and decide later if I want to bother.

Yeah, my normal way of building is wood glue and c-clamp the hell out of everything, then screw it shut and use silicon sealant on all the inside edges once all that's in place. It's a little surprising that you'd say screws are optional though. I didn't think wood glue was that strong. :laugh:

All right, looks like I'm pretty much done with the design phase. At least in terms of getting my methodology down. Now it's just a matter of making sure which sub I'm getting and then pick up the materials.

Also that video is ****ing outrageous. WOW. Awesome work mang.

haha na dude trust me i was in your spot not too long ago. haha im just passing on the knowledge.

but no fiberglass is not necessary. and neither is silicon. if your cuts are close enough and you wood glue and clamp it down you will be leak free. and the reason i say screws are necessary is because the wood glue is actually stronger than the mdf. but if you dont have time to F around with the clamps all day just screw it down and it will work. i normally clamp it down and then screw it down while the box is clamped.then un clamp and do then next piece. clamp, screw, move on.

alright man good luck. any more questions feel free to pm me or ask me here. haha thanks a lot man. that was all thanks to dappa5