My buddy wants me to build him a box for his JBL GT5-12's. Problem is, JBL only offers specs for a round port, which we are not big fans of.
Somebody help me draw up a 3/4 inch MDF box with 1.75CF per chamber, with slot port airspace equivelent to a 4 inch wide, 10.4 inch round PVC port??
Not too savvy with designing boxes myself, so I figured I would ask somebody who is better at it!
Replies (12)
swez on 06/12/2008 15:44:55
Victor showed me this one a while back. It may help you design a good vent/port with the calculator and knowing the X-max parameters of his sub(s).
http://www.carstereo.com/help/Articles.cfm?id=31
I ran some numbers on the round port mentioned and it appears that JBL is tuning to ~34 Hz, (fB) for this sub in a ported box. (X-max is 14.2 mm)
If you wanted to use a slotted port and tuned to ~35 Hz, it would be 12.0" height, 1.5" wide and 18.4" long per chamber.
FYI: Just remember, this is a low power sub, (275 RMS) with a high efficiency rating. Having a low tuning frequency and moderate power handling could rip the sub apart when pushed beyond recommended power limits. The coil may handle the extra watts, but the spider and joints may not.
Swez
Victor on 06/12/2008 20:36:42
if you simply want to convert a round port into a slot port...
the idea is to maintain the port length and the cross sectional area , meaning maintain the port volume....
(ALL THE DIMENSIONS MENTIONED HERE ARE INTERNAL DIMENSIONS)
let the length of your port be 10.4"
CSarea of the round port will be = pie x radius x radius
CSareaR = 3.14 x 2 x 2 ( radius of a 4" dia port is 2")
CSareaR = 3.14 x 4 = 12.56
hence CSareaSlot = 12.56
hence
Slot width x Slot height = 12.56
a port width of anything below 1.5" will result into audible port noise.
hence a port of 2" x 6.28" will be the conversion of a 4" dia round port.
now if you want the slot height as the internal height of the box, then the slot width decreases to smaller numbers where there is a great chance of audible port noise...
hence it would be more advisable to go with a 1.5" or wider slot.
if you want a square port you can have a 3.55" x 3.55" square pipe.
In all cases the port length remains 10.4"....
Victor...
http://www.mecp.com/downloads/Subwoofer%20Box%20Building%20101.pdf
this should help you build your enclosure pretty well....
SQLThump on 06/15/2008 07:42:03
Ok, so we got the port part taken care of, but I have a 4th grade typical ghetto American math skills, and can't figure for the life of me on what lenght and width I can use with 14.5 inch max height and a 33 inch max width. Both chambers preferably should be completely seperated with different chambers and ports.
Basically, I need to get the depth measurement for a total airspace of 1.75 CF with .15 added for the sub and the displacement for the 2x6.28x10 inch ports. I did try to find some calculators, but mainly found stuff for determining airspace of already built enclosures.....
Victor on 06/15/2008 09:41:52
1 cu.ft = 1728 cu inches...
so H x L x W = volume of the box.
use internal dimensions to find the internal volume of the box..
if a box of external dimension 12" x 12" x 12" = 1728 cu.in = 1 cu.ft
and the thickness of the wood is 3/4"
each internal dimension will be 12"-1.5"( considering the total thickness of 2 opposite sides) = 10.5"
hence 10.5" x 10.5" x 10.5" = 1158cu.in = 1158/1728 cu.ft = 0.67 cu.ft
that will be the internal usable volume the displaced air will occupy inside the enclosure... and the external volume will let you know the space this entire enclosure will occupy inside your cars boot....
if you add once bracing, then you will need to calculate the volume of that brace and deduct it from the internal volume.
you will also need to add that extra thickness added by the brace to the external dimensions too....
also consider the port displacement of 125.6 cu.in or 0.073 cu.ft .....
hope that helps you calculate the dimensions and volume yourself... you can definitely cross check your dimensions here on CK . And if you cant yet figure it out, we can surely spoon feed you... GRIN
SQLThump on 06/16/2008 11:52:51
Ok, I think I am getting somewhere here, the formula's helped the brain function greatly......
Quick question though, the way I plan to design the ports is stacked one on top another in the center. Problem is, with 3 rows of 3/4 MDF, and 2 ports that are 6.28 tall, our total external height exceeds the max of 14.5 by .41, which believe it or not, will affect severly how well the box will fit in the car as 14.5 barely stuffs in, and is totally lodged in my trunk. Can we make each port a 1/4 inch wider and of course, 1/4 inch less tall?
I am assuming yes, since the more heavily stressed dimension of the port is the width, and we are increasing that.
Here is my design based on that assumption.
http://s152.photobucket.com/albums/s191/GhettoHooptyBucket/?action=view¤t=ghettobox3.jpg
Thank you very much for making me learn it myself. It was difficult, but I learned a lot already.........
Victor on 06/16/2008 20:07:53
before we go ahead...
look at this...
CS area of 10" x 3" = 30 sq.in
now if this cant fit and i decide to decrease the length by 1" and increase the width by 1 inch instead...
CS area of 9" x 4" = 36 sq.in .....
so altering the port dimensions the way you said cannot be done...
now..your design shows one sub, but i believe ur friend has got 2...
please measure all 3 workable dimensions of the car's trunk and get back for enclosure help.......
SQLThump on 06/18/2008 17:04:32
The goal was to shorten the port's height by 1/4 inch and increase the width by the same. Meaning the port's dimensions would be 6H x2.25W X10 inch length. I do see the error here, but I have attempted to correct it.
The goal here is to make 2 boxes that fit my Buick and his Blazer perfectly. I am restricted to 14.5 inches height in my trunk area, but have ample depth and width. His Blazer is restricted by 33 inches of width but has height and depth to work with. We both have identical JBL GT5-12 subwoofers, so we want to design one box that will fit well with both vehicles, but will be built to JBL's specs.
The design I showed is dual chambered, so there is two of the chamber described within the whole thing. I didn't measure out both sides of the visual aid to save time.
The port you originally called for, 6.28x2x10 has a total volume of 125.6 cubic inches, with 12.56 square inches of port exit. How about a port with 6"H, 2.25"W, giving it a larger port exit of 13.5 square inches, and taking the length down to 9.3 inches, giving it a pretty similar internal volume of 125.55, slightly smaller by .01 cubic inches. Is this workable?
jrose2002 on 06/18/2008 17:44:50
Here are some web pages on boxes mabe this will help you a bit in you decisions they give calculations.
http://www.carstereo.com/help2/Articles.cfm?id=31
http://www.the12volt.com/caraudio/boxcalcs.asp#por
also here are 2 pages for this site that has some good info
http://www.clubknowledge.com/Car_Audio_FAQ/?t16
http://www.clubknowledge.com/Car_Audio_FAQ/?t29
Victor on 06/18/2008 18:05:22
here are the internal sizes of each chamber for a sub.
12" height x 15" width x 17" depth = 1.77 cu.ft
considering the sub displacement + port volume will net a total internal volume of 1.75 cu.ft.
i have noticed you write 10" port length instead of 10.4".... do not ignore even the smallest bit...
with every minute change in enclosure specs or port dimensions there will be a directly affected change in tuning frequency, SPL, transients and over all performance of your Bass engine...
------------------------------------------------------------------------------
Do not change the port dimensions .. keep them 6.28"x2"x10.4"
Fb = 38.1 Hz ( Tuning frequency )
------------------------------------------------------------------------------
Now, this is what JBL suggests, if you want a 35Hz Fb then just increase port length to 13" ( that is all that is allowed, i hope you do not change any other dimensions, cause that will change the entire scenario... if you wanna experiment then its a different case )
many people do deviate from factory suggested enclosures, but those are experts who know what they are doing and have a specific goal in mind...
i would suggest you stick to these dimensions i noted and you'll be a happy boomer....
2 of these chambers will give you a 12" x 30" x 17" of internal volume
the external dimensions will be
12" ( + 1.5") x 30" (+2.25 of both sides and internal board that seperates both chambers ) x 17"( +1.5")
= 13.5" x 32.25" x 18.5" ( this considering the board size to be 3/4")
now these dimensions i guess are pretty workable for both yours as well as your friends car..... keep in mind the port size does not change...
and one port goes for each chamber...it is always better to keep both the subs in separate chambers....
hope that helps..
Victor...
PS: I hope you and your friend are good at wood working skills, if its a leaking enclosure, god help your ears....
SQLThump on 06/18/2008 19:16:55
forgot to mention, the 10.4 was an error on my part. the actual port length is 10 inches.
I am kind of wanting to expeirment a little, if the first box isn't perfect, it's going in his vehicle anyway.
let me run one more design by you before I submit...........
Victor on 06/18/2008 19:22:50
cant upload at photobucket due to site maintenance...
gimme your mail id.. have sketched up a quick diagram to give u an idea...of how the box would look, you already have the dimensions...
it'll be easier for you to visualize and build...
Victor on 06/18/2008 19:30:12
note: with a 10" port your Tuning Freq will be 38.69 Hz... with a 10.4" it will be 38.1Hz ......... and a 13" port will be 35Hz....
length of port and tuning freq are inversely proportional when the given CS area of the port remains constant. ie. 6.28" x 2"..
it is not recommended to go below 35Hz, as these are low power rated subs in a big ported enclosure and you will not want to stress them with over excursion...
having a single port with both the subs in the same chamber, or even with 2 ports aligned vertically like in your design you need to keep both the subs in the same chamber, this is not recommended in a ported enclosure...
you better decide to have both the subs in different chambers, this is as good as having two different enclosures itself, with a common wall in between....
PS: Let your friend have a good enclosure too...
Somebody help me draw up a 3/4 inch MDF box with 1.75CF per chamber, with slot port airspace equivelent to a 4 inch wide, 10.4 inch round PVC port??
Not too savvy with designing boxes myself, so I figured I would ask somebody who is better at it!
Replies (12)
swez on 06/12/2008 15:44:55
Victor showed me this one a while back. It may help you design a good vent/port with the calculator and knowing the X-max parameters of his sub(s).
http://www.carstereo.com/help/Articles.cfm?id=31
I ran some numbers on the round port mentioned and it appears that JBL is tuning to ~34 Hz, (fB) for this sub in a ported box. (X-max is 14.2 mm)
If you wanted to use a slotted port and tuned to ~35 Hz, it would be 12.0" height, 1.5" wide and 18.4" long per chamber.
FYI: Just remember, this is a low power sub, (275 RMS) with a high efficiency rating. Having a low tuning frequency and moderate power handling could rip the sub apart when pushed beyond recommended power limits. The coil may handle the extra watts, but the spider and joints may not.
Swez
Victor on 06/12/2008 20:36:42
if you simply want to convert a round port into a slot port...
the idea is to maintain the port length and the cross sectional area , meaning maintain the port volume....
(ALL THE DIMENSIONS MENTIONED HERE ARE INTERNAL DIMENSIONS)
let the length of your port be 10.4"
CSarea of the round port will be = pie x radius x radius
CSareaR = 3.14 x 2 x 2 ( radius of a 4" dia port is 2")
CSareaR = 3.14 x 4 = 12.56
hence CSareaSlot = 12.56
hence
Slot width x Slot height = 12.56
a port width of anything below 1.5" will result into audible port noise.
hence a port of 2" x 6.28" will be the conversion of a 4" dia round port.
now if you want the slot height as the internal height of the box, then the slot width decreases to smaller numbers where there is a great chance of audible port noise...
hence it would be more advisable to go with a 1.5" or wider slot.
if you want a square port you can have a 3.55" x 3.55" square pipe.
In all cases the port length remains 10.4"....
Victor...
http://www.mecp.com/downloads/Subwoofer%20Box%20Building%20101.pdf
this should help you build your enclosure pretty well....
SQLThump on 06/15/2008 07:42:03
Ok, so we got the port part taken care of, but I have a 4th grade typical ghetto American math skills, and can't figure for the life of me on what lenght and width I can use with 14.5 inch max height and a 33 inch max width. Both chambers preferably should be completely seperated with different chambers and ports.
Basically, I need to get the depth measurement for a total airspace of 1.75 CF with .15 added for the sub and the displacement for the 2x6.28x10 inch ports. I did try to find some calculators, but mainly found stuff for determining airspace of already built enclosures.....
Victor on 06/15/2008 09:41:52
1 cu.ft = 1728 cu inches...
so H x L x W = volume of the box.
use internal dimensions to find the internal volume of the box..
if a box of external dimension 12" x 12" x 12" = 1728 cu.in = 1 cu.ft
and the thickness of the wood is 3/4"
each internal dimension will be 12"-1.5"( considering the total thickness of 2 opposite sides) = 10.5"
hence 10.5" x 10.5" x 10.5" = 1158cu.in = 1158/1728 cu.ft = 0.67 cu.ft
that will be the internal usable volume the displaced air will occupy inside the enclosure... and the external volume will let you know the space this entire enclosure will occupy inside your cars boot....
if you add once bracing, then you will need to calculate the volume of that brace and deduct it from the internal volume.
you will also need to add that extra thickness added by the brace to the external dimensions too....
also consider the port displacement of 125.6 cu.in or 0.073 cu.ft .....
hope that helps you calculate the dimensions and volume yourself... you can definitely cross check your dimensions here on CK . And if you cant yet figure it out, we can surely spoon feed you... GRIN
SQLThump on 06/16/2008 11:52:51
Ok, I think I am getting somewhere here, the formula's helped the brain function greatly......
Quick question though, the way I plan to design the ports is stacked one on top another in the center. Problem is, with 3 rows of 3/4 MDF, and 2 ports that are 6.28 tall, our total external height exceeds the max of 14.5 by .41, which believe it or not, will affect severly how well the box will fit in the car as 14.5 barely stuffs in, and is totally lodged in my trunk. Can we make each port a 1/4 inch wider and of course, 1/4 inch less tall?
I am assuming yes, since the more heavily stressed dimension of the port is the width, and we are increasing that.
Here is my design based on that assumption.
http://s152.photobucket.com/albums/s191/GhettoHooptyBucket/?action=view¤t=ghettobox3.jpg
Thank you very much for making me learn it myself. It was difficult, but I learned a lot already.........
Victor on 06/16/2008 20:07:53
before we go ahead...
look at this...
CS area of 10" x 3" = 30 sq.in
now if this cant fit and i decide to decrease the length by 1" and increase the width by 1 inch instead...
CS area of 9" x 4" = 36 sq.in .....
so altering the port dimensions the way you said cannot be done...
now..your design shows one sub, but i believe ur friend has got 2...
please measure all 3 workable dimensions of the car's trunk and get back for enclosure help.......
SQLThump on 06/18/2008 17:04:32
The goal was to shorten the port's height by 1/4 inch and increase the width by the same. Meaning the port's dimensions would be 6H x2.25W X10 inch length. I do see the error here, but I have attempted to correct it.
The goal here is to make 2 boxes that fit my Buick and his Blazer perfectly. I am restricted to 14.5 inches height in my trunk area, but have ample depth and width. His Blazer is restricted by 33 inches of width but has height and depth to work with. We both have identical JBL GT5-12 subwoofers, so we want to design one box that will fit well with both vehicles, but will be built to JBL's specs.
The design I showed is dual chambered, so there is two of the chamber described within the whole thing. I didn't measure out both sides of the visual aid to save time.
The port you originally called for, 6.28x2x10 has a total volume of 125.6 cubic inches, with 12.56 square inches of port exit. How about a port with 6"H, 2.25"W, giving it a larger port exit of 13.5 square inches, and taking the length down to 9.3 inches, giving it a pretty similar internal volume of 125.55, slightly smaller by .01 cubic inches. Is this workable?
jrose2002 on 06/18/2008 17:44:50
Here are some web pages on boxes mabe this will help you a bit in you decisions they give calculations.
http://www.carstereo.com/help2/Articles.cfm?id=31
http://www.the12volt.com/caraudio/boxcalcs.asp#por
also here are 2 pages for this site that has some good info
http://www.clubknowledge.com/Car_Audio_FAQ/?t16
http://www.clubknowledge.com/Car_Audio_FAQ/?t29
Victor on 06/18/2008 18:05:22
here are the internal sizes of each chamber for a sub.
12" height x 15" width x 17" depth = 1.77 cu.ft
considering the sub displacement + port volume will net a total internal volume of 1.75 cu.ft.
i have noticed you write 10" port length instead of 10.4".... do not ignore even the smallest bit...
with every minute change in enclosure specs or port dimensions there will be a directly affected change in tuning frequency, SPL, transients and over all performance of your Bass engine...
------------------------------------------------------------------------------
Do not change the port dimensions .. keep them 6.28"x2"x10.4"
Fb = 38.1 Hz ( Tuning frequency )
------------------------------------------------------------------------------
Now, this is what JBL suggests, if you want a 35Hz Fb then just increase port length to 13" ( that is all that is allowed, i hope you do not change any other dimensions, cause that will change the entire scenario... if you wanna experiment then its a different case )
many people do deviate from factory suggested enclosures, but those are experts who know what they are doing and have a specific goal in mind...
i would suggest you stick to these dimensions i noted and you'll be a happy boomer....
2 of these chambers will give you a 12" x 30" x 17" of internal volume
the external dimensions will be
12" ( + 1.5") x 30" (+2.25 of both sides and internal board that seperates both chambers ) x 17"( +1.5")
= 13.5" x 32.25" x 18.5" ( this considering the board size to be 3/4")
now these dimensions i guess are pretty workable for both yours as well as your friends car..... keep in mind the port size does not change...
and one port goes for each chamber...it is always better to keep both the subs in separate chambers....
hope that helps..
Victor...
PS: I hope you and your friend are good at wood working skills, if its a leaking enclosure, god help your ears....
SQLThump on 06/18/2008 19:16:55
forgot to mention, the 10.4 was an error on my part. the actual port length is 10 inches.
I am kind of wanting to expeirment a little, if the first box isn't perfect, it's going in his vehicle anyway.
let me run one more design by you before I submit...........
Victor on 06/18/2008 19:22:50
cant upload at photobucket due to site maintenance...
gimme your mail id.. have sketched up a quick diagram to give u an idea...of how the box would look, you already have the dimensions...
it'll be easier for you to visualize and build...
Victor on 06/18/2008 19:30:12
note: with a 10" port your Tuning Freq will be 38.69 Hz... with a 10.4" it will be 38.1Hz ......... and a 13" port will be 35Hz....
length of port and tuning freq are inversely proportional when the given CS area of the port remains constant. ie. 6.28" x 2"..
it is not recommended to go below 35Hz, as these are low power rated subs in a big ported enclosure and you will not want to stress them with over excursion...
having a single port with both the subs in the same chamber, or even with 2 ports aligned vertically like in your design you need to keep both the subs in the same chamber, this is not recommended in a ported enclosure...
you better decide to have both the subs in different chambers, this is as good as having two different enclosures itself, with a common wall in between....
PS: Let your friend have a good enclosure too...
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