when calculating port length, and you either flare the end with a 45* opening or rounded (kerfed?) opening, do you measure it down the center points or take total port volume into account?
-Drew
Replies (34)
cplkittle on 02/24/2008 19:16:00
If you are talking about the small amount of rounding or 45 degree on the mouth of the port, it will not make that much difference unless you plan to flare it the last 3" or more. If you are off on the length of the port by 1/2" It will probably not even change the tuned frequency by .5Hz.
To answer your question, the length of the port should be measured not counting the flare. If the flare is 3" or more in depth, there is a whole new set of equations to calculate the frequency. I read up on all of that stuff before I wrote all of those enclosure articles in the DIY forum, but I forgot most of it. If you want to find out more, google horn enclosure, folded horn, and PA enclosures. It may take some digging, but it is an interesting trip.
newB on 02/24/2008 19:32:08
http://i228.photobucket.com/albums/ee174/kirbycamry/121907_2121a.jpg
that is a quarter wave Transmission line for an 18, just an example of the port opening i'm talking about. around 3" is what i would end up roughly going with. i'm looking into it because the local shop builder preaches this port opening like its the fountain of youth, keeps saying just the port will boost dbs considerably, so i want to look into designing/building/testing this kind of port. my first thought would be a decrease in port velocity. (opposite from narrowing the port opening to speed up the wave)
-Drew
cplkittle on 02/24/2008 22:44:12
That type of port opening is designed to let the wave expand before it exits the port. I have read (never tried) that by doing so, it pushes the sound foreward instead of letting it escape randomly. Thereby aiming it so to speak.
Narrowing the port opening does not necessarily 'speed up the wave'. If that were the case the frequency would rise and you would get a higher pitch. It will, however, muffle the sound by reflecting some of the sound waves back into the port, and increase port air speed possibly causing port noise.
I have not had good luck with TL enclosures. In my experience they are slow and muddy sounding. Plus you need TONS of wood to make the port. Port length = 1/4 of the length of the sound wave.
If you are building one for an 18" sub and you tune it to 32Hz, the port length will be:
1128 (speed of sound in fps) / 32Hz = 35' 3"
Some people will take a 1/4 of that and call it a transmission line.. in that case the port length should be 8' 10 1/2".
Most of the transmission lines I have seen are home audio applications, and the port gradually increases in size from start to finish. In some cases where a 'true' 1/4 wave length can not be obtained because of the length, polyfill is stuffed loosely into the length of the port to 'slow' the wave down. Alot of time and experimentation is needed.
I don't want to talk you out of it, you may have better luck that I did. I also think everyone should try it at least twice.
Post some pictures and let us know what you think about it.
newB on 02/25/2008 00:52:05
what i really am trying to figure out is how to calculate the flared end as a factor for the total port.
i'll try to re-phrase it, how do i come up with a standard slot vent alignment and add a 3" opening to one side, how do i calculate that into the final vent design
-Drew
Victor on 02/25/2008 01:57:34
new B...
sorry am running very low on time... but we could talk about this on yahoo or any other real time messenger... got a lot of research work on TL's and Horns....
Victor...
By the way, a well designed TL can outperform a ported in terms of loudness and yet be very close to a sealed in terms of transients and crisp clean low frequency reproduction....
newB on 02/25/2008 03:27:57
i dont think i have any of your information.
Email/messanger:
Saxophonewonder2002@yahoo.com
AIM:
Saxwonder05
-Drew
Victor on 02/25/2008 05:10:18
messenger : victorginger@yahoo.com
email : info@sadesigns.in
newB on 02/25/2008 07:43:33
so victor has been working with me and giving me pointers as to which direction to go, and this is my first TL draft for my car. several things i still need to fix and it will be done, also waiting for an email from RD audio to get an exact spec for the cone area of the woofer. these are my drafts:
#s:
http://i40.photobucket.com/albums/e216/saxwonder05/MyTLdraft.png
Projected model:
http://i40.photobucket.com/albums/e216/saxwonder05/MyTLdraft2.png
-Drew
cplkittle on 02/25/2008 22:46:51
Victor, care to share that knowledge?
I don't have alot of experimentation time anymore, but I would love to know what information you have. I could not find alot of solid info on the internet, everything was very vague.
cplkittle on 02/26/2008 01:06:22
ok, I found a little more.
A flared or tapered end is equal to 85% of its length relative to overall port length, therefore a 3" flanged opening would equal (3" x .85 = 2.55"
http://www.geocities.com/f4ier/vents.htm
Some people use 50% as a common rule of thumb:
http://www.subwoofer-builder.com/flares-for-sale.htm
Here is a calculator with a flared port correction:
http://www.psp-inc.com/
and a very thorough article about calculating air velocity in the port and the difference the flare makes:
http://www.soundground.ca/forum/showthread.php?t=10
With all of that said, the only difference is that these are round ports with shallow flares. I do not know if it will be the same with a rectangular port or a longer flare. I did read that on a port that gradually increases in size, you subtract 35% every time you double the diameter. If the port area increases 200% over the beginning area, you would subtract 70% of the length for the tuned frequency calculations.
Victor on 02/26/2008 02:12:49
Kittle this is what I shared with him, have asked him to read all the greek and latin and get back with his queries.... Will walk him through the entire process step by step...
http://www.diysubwoofers.org/
http://www.quarter-wave.com/
http://www.t-linespeakers.org/
( Note: Thats a lot of information and reading )
-----------------------------------------------------------------
newB did you receive a reply from the manufacturer ?
Dont really be in a hurry to draft, ure too good at drafting, but dont end up being a drafting machine, keep patience, use pencil and paper to develop a design, you'll notice free flowing imagination and ease of perception. You can then do a final working drawing on the computer.
Try to use the metric system of measurement, you'll find it easier to be accurate with fabrication.
Do not begin any project until you have all the required tools with you.
In case of an enclosure design first collect all the required data, sort the data, keep all the formulaes handy, and see how each parameter is interlinked to each other.
thats it for now, will move ahead once you get the precise Sd from the manufacturer.
Victor...
newB on 02/26/2008 03:15:56
the problem i'm having now is that im not getting a reply from RD (a little disappointing) and i'm coming with weird numbers, me actually measuring the woofer came up with 63in^2 Victor pointed me more towards 77in^2 and i just went to rockford and their P3 is 310cm^2 (48in^2)
no clue where to begin with those numbers-
-Drew
Victor on 02/26/2008 03:34:32
ask the manufacturer.....
newB on 02/26/2008 04:45:42
Victor FTMFW
-Drew
Victor on 02/29/2008 03:31:22
hey... any further developments..???
newB on 02/29/2008 13:44:34
i got an email back telling me the mounting depth was 5" (why? i'm not sure....) so i replied again asking the Sd and have still not gotten a response. i would like to perfect the design before i start building the setup but there is no rush. i still need to get a job, then save, then buy, then boom.
--Drew
newB on 02/29/2008 13:46:48
and the mounting depth he gave me was wrong! lol its 5.75"
ive been occupying my time with this:
http://i40.photobucket.com/albums/e216/saxwonder05/MY10in1.png
http://i40.photobucket.com/albums/e216/saxwonder05/MY10in2.png
http://i40.photobucket.com/albums/e216/saxwonder05/MY10in3.png
-Drew
Victor on 02/29/2008 15:26:33
ok.... dunno why you drafted whatever you did.... just like to tell you something.. ure just toooooooooooo good at it... uve got a very good sense of the 3rd dimension... what prog do you use to make these drawings????
newB on 02/29/2008 17:26:19
its a free download from Google called "Sketchup"
its a really basic and user friendly version of AutoCad
-Drew
Victor on 03/1/2008 03:11:31
its a very user friendly program, can really set your imagination free in the 3rd dimension..... how do u save the drawing in jpeg, bmp, gif or anyother format...??
newB on 03/1/2008 03:50:40
you can screenshot it on PC, or "export as 2D model" and it saves as its own extension that can be read by photobucket, not sure off the top of my head what exactly it is.
AutoCad for broke College students who need to design woofer boxes GRIN
-Drew
admin on 03/1/2008 07:21:59
Very cool program! Thanks for sharing!
http://sketchup.google.com
newB on 03/1/2008 15:15:56
let me know if anyone downloads the program and needs help grasping the basics on how it works, if enough people take interest i'll write a tutorial on the program and how it can be used in box design
-Drew
cplkittle on 03/1/2008 17:41:38
That is a good idea. I haven't downloaded it yet, but tips and tactics are priceless.
newB on 03/2/2008 15:48:43
now that i'm really thinking about it, a tutorial would be very lengthy with lots and lots of pix. i wish i could take a screenshot but make it a video!
-Drew
cplkittle on 03/2/2008 22:38:04
You could do a powerpoint and post it on a free site like
http://www.datafilehost.com/
It is free as long as it is downloaded once per week.
newB on 03/3/2008 01:46:13
ppt seems like a good idea, assuming people take interest in using it for enclosure designs
-Drew
swez on 03/3/2008 05:06:42
Have used .ppt for several things in the past. It does have its limits, but is still a very good visual aid tool to share ideas, give pictorials and wiring guides.
A while back, had a few ideas for customers that wanted pictorial drawings of how to assemble/configure a given system. Using .ppt as the tool on hand, it worked out pretty well for all. Yes, it's time consuming and cumbersome to do things like this in .ppt, but a picture or diagram is often superior to text instructions only.
Victor and I worked on a DIY piece that was formatted with .ppt. It is now available in link form from this:
http://www.clubknowledge.com/Car_Audio_FAQ/?t33
Swez
PS Pretty basic pictures here, but they have helped a lot of people learn how to wire subs correctly. (21,513 page views proved that huh?)
newB on 03/7/2008 01:12:32
Sd of the 10" RD is 85.2in^2
the TLine is looking less and less appealing with that size of a line
-Drew
Victor on 03/7/2008 01:37:01
what has Sd got to do with the line length....???
Sd is only used to reference the cross sectional area of line at different places...for ex, woofer loading and port opening.
the line length depends on the Fs of your driver. for a QWTL the line length will be 1/4th of the wavelength at Fs.
http://www.t-linespeakers.org/design/classic.html
http://www.t-linespeakers.org/design/rules.html
http://www.t-linespeakers.org/design/taper.html
http://www.t-linespeakers.org/design/foldings/index.html
read these again...
Victor...
newB on 03/7/2008 03:47:43
right, and the overall volume of the line increases, just a tad more than i can go for my little car.
1130/33=34.24 full wavelength
34.24/4= 8.6'
8.6x12= 102" long line length
85x102= 8731.8in^2 of Line
8731.8/1728 = 5cuft+wood displacement
i was hoping i could keep it around 4cuft gross for the single 10, i'm really not excited about 6cuft for a single 10
my options now are two 10s on 1500watts in 1.5cuft per chamber @35hz or a single 10 on 300w in a TL
as much as i want to persue it i just dont have the space for 6+cuft of box especially in my tiny lil car
-Drew
cplkittle on 03/7/2008 11:37:09
JL makes a 6" sub (6W0). This would be perfect to experiment with. If you can build a box with a single 6" sub that thumps, that is a really strong selling point.
I built a 1.25 cuft ported box for a pair of 4" coax speakers that really turned heads. I tuned it to 36Hz and ran the amp without any filters. The speakers were our cheapest model ($12/pair Qpower speakers). That was my example of how much difference a properly designed enclosure made.
newB on 03/10/2008 08:01:18
so the RD classic is out of operation and i have yet to determine why. i do not presently have access to a volt meter to check the coils but that will happen shortly. Everything appears to be in working order cosmetically, tinsel leads appear normal, view through voice coil vents shows a linear and tightly wound voice coil with no apparent damage.
will keep everybody posted- i just dropped the 1.5@40hz single 10 box with the assassin instead of the RD and have concluded that life boomless is cold and emplty.
-Drew
MrBrownstone on 03/10/2008 16:26:21
the easy answer to your 'what is the port length' question is where the apex of the flared end begins.
The flared end has some wave guide capabilities, but more or less creates an acoustic effect whereas the summation (and cancellation) of waves begins in a more controlled manner. You can more effectively locate nodes, then move the box to point them at the microphone placement.
Since it's all frequency specific, there's no benefit to a full range audio system as you'll get 1 or 2 notes (and harmonics) that are stronger, but at the same time, the same goes for cancellation.
-Drew
Replies (34)
cplkittle on 02/24/2008 19:16:00
If you are talking about the small amount of rounding or 45 degree on the mouth of the port, it will not make that much difference unless you plan to flare it the last 3" or more. If you are off on the length of the port by 1/2" It will probably not even change the tuned frequency by .5Hz.
To answer your question, the length of the port should be measured not counting the flare. If the flare is 3" or more in depth, there is a whole new set of equations to calculate the frequency. I read up on all of that stuff before I wrote all of those enclosure articles in the DIY forum, but I forgot most of it. If you want to find out more, google horn enclosure, folded horn, and PA enclosures. It may take some digging, but it is an interesting trip.
newB on 02/24/2008 19:32:08
http://i228.photobucket.com/albums/ee174/kirbycamry/121907_2121a.jpg
that is a quarter wave Transmission line for an 18, just an example of the port opening i'm talking about. around 3" is what i would end up roughly going with. i'm looking into it because the local shop builder preaches this port opening like its the fountain of youth, keeps saying just the port will boost dbs considerably, so i want to look into designing/building/testing this kind of port. my first thought would be a decrease in port velocity. (opposite from narrowing the port opening to speed up the wave)
-Drew
cplkittle on 02/24/2008 22:44:12
That type of port opening is designed to let the wave expand before it exits the port. I have read (never tried) that by doing so, it pushes the sound foreward instead of letting it escape randomly. Thereby aiming it so to speak.
Narrowing the port opening does not necessarily 'speed up the wave'. If that were the case the frequency would rise and you would get a higher pitch. It will, however, muffle the sound by reflecting some of the sound waves back into the port, and increase port air speed possibly causing port noise.
I have not had good luck with TL enclosures. In my experience they are slow and muddy sounding. Plus you need TONS of wood to make the port. Port length = 1/4 of the length of the sound wave.
If you are building one for an 18" sub and you tune it to 32Hz, the port length will be:
1128 (speed of sound in fps) / 32Hz = 35' 3"
Some people will take a 1/4 of that and call it a transmission line.. in that case the port length should be 8' 10 1/2".
Most of the transmission lines I have seen are home audio applications, and the port gradually increases in size from start to finish. In some cases where a 'true' 1/4 wave length can not be obtained because of the length, polyfill is stuffed loosely into the length of the port to 'slow' the wave down. Alot of time and experimentation is needed.
I don't want to talk you out of it, you may have better luck that I did. I also think everyone should try it at least twice.
Post some pictures and let us know what you think about it.
newB on 02/25/2008 00:52:05
what i really am trying to figure out is how to calculate the flared end as a factor for the total port.
i'll try to re-phrase it, how do i come up with a standard slot vent alignment and add a 3" opening to one side, how do i calculate that into the final vent design
-Drew
Victor on 02/25/2008 01:57:34
new B...
sorry am running very low on time... but we could talk about this on yahoo or any other real time messenger... got a lot of research work on TL's and Horns....
Victor...
By the way, a well designed TL can outperform a ported in terms of loudness and yet be very close to a sealed in terms of transients and crisp clean low frequency reproduction....
newB on 02/25/2008 03:27:57
i dont think i have any of your information.
Email/messanger:
Saxophonewonder2002@yahoo.com
AIM:
Saxwonder05
-Drew
Victor on 02/25/2008 05:10:18
messenger : victorginger@yahoo.com
email : info@sadesigns.in
newB on 02/25/2008 07:43:33
so victor has been working with me and giving me pointers as to which direction to go, and this is my first TL draft for my car. several things i still need to fix and it will be done, also waiting for an email from RD audio to get an exact spec for the cone area of the woofer. these are my drafts:
#s:
http://i40.photobucket.com/albums/e216/saxwonder05/MyTLdraft.png
Projected model:
http://i40.photobucket.com/albums/e216/saxwonder05/MyTLdraft2.png
-Drew
cplkittle on 02/25/2008 22:46:51
Victor, care to share that knowledge?
I don't have alot of experimentation time anymore, but I would love to know what information you have. I could not find alot of solid info on the internet, everything was very vague.
cplkittle on 02/26/2008 01:06:22
ok, I found a little more.
A flared or tapered end is equal to 85% of its length relative to overall port length, therefore a 3" flanged opening would equal (3" x .85 = 2.55"
http://www.geocities.com/f4ier/vents.htm
Some people use 50% as a common rule of thumb:
http://www.subwoofer-builder.com/flares-for-sale.htm
Here is a calculator with a flared port correction:
http://www.psp-inc.com/
and a very thorough article about calculating air velocity in the port and the difference the flare makes:
http://www.soundground.ca/forum/showthread.php?t=10
With all of that said, the only difference is that these are round ports with shallow flares. I do not know if it will be the same with a rectangular port or a longer flare. I did read that on a port that gradually increases in size, you subtract 35% every time you double the diameter. If the port area increases 200% over the beginning area, you would subtract 70% of the length for the tuned frequency calculations.
Victor on 02/26/2008 02:12:49
Kittle this is what I shared with him, have asked him to read all the greek and latin and get back with his queries.... Will walk him through the entire process step by step...
http://www.diysubwoofers.org/
http://www.quarter-wave.com/
http://www.t-linespeakers.org/
( Note: Thats a lot of information and reading )
-----------------------------------------------------------------
newB did you receive a reply from the manufacturer ?
Dont really be in a hurry to draft, ure too good at drafting, but dont end up being a drafting machine, keep patience, use pencil and paper to develop a design, you'll notice free flowing imagination and ease of perception. You can then do a final working drawing on the computer.
Try to use the metric system of measurement, you'll find it easier to be accurate with fabrication.
Do not begin any project until you have all the required tools with you.
In case of an enclosure design first collect all the required data, sort the data, keep all the formulaes handy, and see how each parameter is interlinked to each other.
thats it for now, will move ahead once you get the precise Sd from the manufacturer.
Victor...
newB on 02/26/2008 03:15:56
the problem i'm having now is that im not getting a reply from RD (a little disappointing) and i'm coming with weird numbers, me actually measuring the woofer came up with 63in^2 Victor pointed me more towards 77in^2 and i just went to rockford and their P3 is 310cm^2 (48in^2)
no clue where to begin with those numbers-
-Drew
Victor on 02/26/2008 03:34:32
ask the manufacturer.....
newB on 02/26/2008 04:45:42
Victor FTMFW
-Drew
Victor on 02/29/2008 03:31:22
hey... any further developments..???
newB on 02/29/2008 13:44:34
i got an email back telling me the mounting depth was 5" (why? i'm not sure....) so i replied again asking the Sd and have still not gotten a response. i would like to perfect the design before i start building the setup but there is no rush. i still need to get a job, then save, then buy, then boom.
--Drew
newB on 02/29/2008 13:46:48
and the mounting depth he gave me was wrong! lol its 5.75"
ive been occupying my time with this:
http://i40.photobucket.com/albums/e216/saxwonder05/MY10in1.png
http://i40.photobucket.com/albums/e216/saxwonder05/MY10in2.png
http://i40.photobucket.com/albums/e216/saxwonder05/MY10in3.png
-Drew
Victor on 02/29/2008 15:26:33
ok.... dunno why you drafted whatever you did.... just like to tell you something.. ure just toooooooooooo good at it... uve got a very good sense of the 3rd dimension... what prog do you use to make these drawings????
newB on 02/29/2008 17:26:19
its a free download from Google called "Sketchup"
its a really basic and user friendly version of AutoCad
-Drew
Victor on 03/1/2008 03:11:31
its a very user friendly program, can really set your imagination free in the 3rd dimension..... how do u save the drawing in jpeg, bmp, gif or anyother format...??
newB on 03/1/2008 03:50:40
you can screenshot it on PC, or "export as 2D model" and it saves as its own extension that can be read by photobucket, not sure off the top of my head what exactly it is.
AutoCad for broke College students who need to design woofer boxes GRIN
-Drew
admin on 03/1/2008 07:21:59
Very cool program! Thanks for sharing!
http://sketchup.google.com
newB on 03/1/2008 15:15:56
let me know if anyone downloads the program and needs help grasping the basics on how it works, if enough people take interest i'll write a tutorial on the program and how it can be used in box design
-Drew
cplkittle on 03/1/2008 17:41:38
That is a good idea. I haven't downloaded it yet, but tips and tactics are priceless.
newB on 03/2/2008 15:48:43
now that i'm really thinking about it, a tutorial would be very lengthy with lots and lots of pix. i wish i could take a screenshot but make it a video!
-Drew
cplkittle on 03/2/2008 22:38:04
You could do a powerpoint and post it on a free site like
http://www.datafilehost.com/
It is free as long as it is downloaded once per week.
newB on 03/3/2008 01:46:13
ppt seems like a good idea, assuming people take interest in using it for enclosure designs
-Drew
swez on 03/3/2008 05:06:42
Have used .ppt for several things in the past. It does have its limits, but is still a very good visual aid tool to share ideas, give pictorials and wiring guides.
A while back, had a few ideas for customers that wanted pictorial drawings of how to assemble/configure a given system. Using .ppt as the tool on hand, it worked out pretty well for all. Yes, it's time consuming and cumbersome to do things like this in .ppt, but a picture or diagram is often superior to text instructions only.
Victor and I worked on a DIY piece that was formatted with .ppt. It is now available in link form from this:
http://www.clubknowledge.com/Car_Audio_FAQ/?t33
Swez
PS Pretty basic pictures here, but they have helped a lot of people learn how to wire subs correctly. (21,513 page views proved that huh?)
newB on 03/7/2008 01:12:32
Sd of the 10" RD is 85.2in^2
the TLine is looking less and less appealing with that size of a line
-Drew
Victor on 03/7/2008 01:37:01
what has Sd got to do with the line length....???
Sd is only used to reference the cross sectional area of line at different places...for ex, woofer loading and port opening.
the line length depends on the Fs of your driver. for a QWTL the line length will be 1/4th of the wavelength at Fs.
http://www.t-linespeakers.org/design/classic.html
http://www.t-linespeakers.org/design/rules.html
http://www.t-linespeakers.org/design/taper.html
http://www.t-linespeakers.org/design/foldings/index.html
read these again...
Victor...
newB on 03/7/2008 03:47:43
right, and the overall volume of the line increases, just a tad more than i can go for my little car.
1130/33=34.24 full wavelength
34.24/4= 8.6'
8.6x12= 102" long line length
85x102= 8731.8in^2 of Line
8731.8/1728 = 5cuft+wood displacement
i was hoping i could keep it around 4cuft gross for the single 10, i'm really not excited about 6cuft for a single 10
my options now are two 10s on 1500watts in 1.5cuft per chamber @35hz or a single 10 on 300w in a TL
as much as i want to persue it i just dont have the space for 6+cuft of box especially in my tiny lil car
-Drew
cplkittle on 03/7/2008 11:37:09
JL makes a 6" sub (6W0). This would be perfect to experiment with. If you can build a box with a single 6" sub that thumps, that is a really strong selling point.
I built a 1.25 cuft ported box for a pair of 4" coax speakers that really turned heads. I tuned it to 36Hz and ran the amp without any filters. The speakers were our cheapest model ($12/pair Qpower speakers). That was my example of how much difference a properly designed enclosure made.
newB on 03/10/2008 08:01:18
so the RD classic is out of operation and i have yet to determine why. i do not presently have access to a volt meter to check the coils but that will happen shortly. Everything appears to be in working order cosmetically, tinsel leads appear normal, view through voice coil vents shows a linear and tightly wound voice coil with no apparent damage.
will keep everybody posted- i just dropped the 1.5@40hz single 10 box with the assassin instead of the RD and have concluded that life boomless is cold and emplty.
-Drew
MrBrownstone on 03/10/2008 16:26:21
the easy answer to your 'what is the port length' question is where the apex of the flared end begins.
The flared end has some wave guide capabilities, but more or less creates an acoustic effect whereas the summation (and cancellation) of waves begins in a more controlled manner. You can more effectively locate nodes, then move the box to point them at the microphone placement.
Since it's all frequency specific, there's no benefit to a full range audio system as you'll get 1 or 2 notes (and harmonics) that are stronger, but at the same time, the same goes for cancellation.
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