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View Full Version : Kurfed/Flared porting



netzero
09-04-2008, 11:20 AM
Ok, so I've got a box design I'm gonna build myself, but I really wanna try a flared port. I was just wondering for those who have does it themselves, how much does the average kurfed/flared L shaped port effect tuning, versus a standard 90* edge? And any tips on how to go about that? Thanks

blackbonnie
09-04-2008, 11:24 AM
from what i understand it isnt that much...but im not an amazing box designer either

benchambers80
09-04-2008, 11:28 AM
soak it in the pool, works better.

Propimp
09-04-2008, 11:31 AM
iirc, you take the lenghth of the flared part and divide it by 2. and add that to the lenght of the port and that is the total lenght of the port. I hope this made sence.

Pl8er
09-04-2008, 11:34 AM
I think that a kurfed (i always spell it kerfed LOL) looks ****. Much better looking than a standard port.

Now does anyone have an explanation of how the soaking works? Do you soak, then bend then let dry? That seems like it would take a very long time.

mikey7182
09-04-2008, 11:35 AM
I am kerfing the ports on my upcoming enclosure as well. I don't think you are required to calculate port area any different than with a standard slot vent. I've always been told the main reason to do it is because the kerf helps reduce "chuffing" at higher output. Not to mention bent MDF looks cool as hell! :D

Pioneer~Saturn
09-04-2008, 12:05 PM
Yea, x2 on what propimp said...id add about half the length of the flared section to the total length...shouldnt change the tuning drastically. And yes, they look like the secks :)

Immacomputer
09-04-2008, 12:21 PM
I think that a kurfed (i always spell it kerfed LOL) looks ****. Much better looking than a standard port.

Now does anyone have an explanation of how the soaking works? Do you soak, then bend then let dry? That seems like it would take a very long time.

It is spelled "kerf" and not "kurf". Also, the soaking comments are from people making fun of somebody here who soaked the MDF in his pool to make it bend. This is NOT what you do with MDF. A treated plywood can handle the moisture and not bloat like MDF does.

A problem with bending is either from too shallow kerf cuts, uneven depth kerf cuts (ie, the board doesn't stay completely flat when the saw is cutting the lines), too little cuts for your intended radius, or too short of spacing between cuts (goes hand in hand with the previous).

As far as calculating the distance of the effective air mass for the port, I have found that with a circular flare, it's safe to use up to about twice the width of the port for effective port length.

You can see what I mean in this picture of an enclosure that I built:
http://i35.tinypic.com/eskmcx.png

The port was 2" wide and the effective port length extended to around the 4" wide portion. The blue line segments represent the actual port length.That wasn't measured very scientifically but I think it is a pretty safe bet for judging actual line length.

Pioneer~Saturn
09-04-2008, 12:48 PM
It is spelled "kerf" and not "kurf". Also, the soaking comments are from people making fun of somebody here who soaked the MDF in his pool to make it bend. This is NOT what you do with MDF. A treated plywood can handle the moisture and not bloat like MDF does.

A problem with bending is either from too shallow kerf cuts, uneven depth kerf cuts (ie, the board doesn't stay completely flat when the saw is cutting the lines), too little cuts for your intended radius, or too short of spacing between cuts (goes hand in hand with the previous).

As far as calculating the distance of the effective air mass for the port, I have found that with a circular flare, it's safe to use up to about twice the width of the port for effective port length.

You can see what I mean in this picture of an enclosure that I built:
http://i35.tinypic.com/eskmcx.png

The port was 2" wide and the effective port length extended to around the 4" wide portion. The blue line segments represent the actual port length.That wasn't measured very scientifically but I think it is a pretty safe bet for judging actual line length.

Good post right there...great description!

netzero
09-04-2008, 06:32 PM
Thanks everyone for the info, its all starting to come to me how im going to go about it. Immacomputer especially, thanks man. Few questions to your diagram, So If you don't calculate the port 'inset' from the box front and compensate by extending the entrance of the port, i'm assuming you might tune your box 1~2 Hz higher than you wanted?

Also, do you have any methods or number to help. Like: blade depth/blade width, amount of cuts, frequency of cuts, and when to start and stop cutting? Thanks

Immacomputer
09-04-2008, 10:36 PM
If you count the end of the flare as effective length, then yes, your port length would be shorter than you designed and you might be off by a couple Hz.

I can't speak for anybody else as I don't know how other people do it but this is the methodology that I have used in the past and it's always worked out.

Blade depth: 5/8" for 3/4" MDF works but I usually go a little deeper to help it bend. Going deeper will usually make it easier to see the kerf cuts but the number of cuts also affects that.

Blade width: I use a 10" table saw blade that is 1/8" wide.

Amount of cuts: Well, this one can be simple or tricky. You can really choose your own destiny here as far as how many cuts you want to do but there is minimum. The minimum amount of cuts you can do to make a 90* bend is 11 cuts. Any less than that, and you will not get 90*. If you go with 11 cuts though, your angle will actually be greater than 90*. This can be good and bad and it will vary with different blade widths (I use 1/8" but some blades may be larger or smaller). If you're going to fill the gap then it is fine and the more cuts you make the easier it will bend. It will also have a smoother flow with more cuts. But, you do lose strength so unless you fiberglass or epoxy from the inside, you shouldn't make too many cuts over 11 for a 90* bend. I usually do 10 cuts and then I don't get a perfect 90* angle but I prefer the look and the wood all aligns on the inside. You can see what I mean about getting slightly less than 90* in this picture:

http://i18.tinypic.com/6ufjnle.jpg

Cut spacing: This will depend on the radius you want. What you have to first decide on is the inner flare radius (Rf) and angle (θ). The angle will give you the number of cuts (Nc) you need. I use these equations to get line spacing (Ls):

Ls = [(2*Rf*pi) / (θ/360) - (Nc*Bw)] / Nc

Where Bw is your blade width. Also note that the angle (θ) needs to be in degrees in order to get the actual arc length for the piece of wood. It seems confusing but it's really simple. The numbers work well enough that you can incorporate it with any flare angle, radius, and number of cuts.

Starting point will be based on when you want the flare to begin and the ending point will just happen as you make the cuts with the constant spacing. Let me know if any of that was unclear.

Ali1
09-04-2008, 10:39 PM
If you count the end of the flare as effective length, then yes, your port length would be shorter than you designed and you might be off by a couple Hz.

I can't speak for anybody else as I don't know how other people do it but this is the methodology that I have used in the past and it's always worked out.

Blade depth: 5/8" for 3/4" MDF works but I usually go a little deeper to help it bend. Going deeper will usually make it easier to see the kerf cuts but the number of cuts also affects that.

Blade width: I use a 10" table saw blade that is 1/8" wide.

Amount of cuts: Well, this one can be simple or tricky. You can really choose your own destiny here as far as how many cuts you want to do but there is minimum. The minimum amount of cuts you can do to make a 90* bend is 11 cuts. Any less than that, and you will not get 90*. If you go with 11 cuts though, your angle will actually be greater than 90*. This can be good and bad and it will vary with different blade widths (I use 1/8" but some blades may be larger or smaller). If you're going to fill the gap then it is fine and the more cuts you make the easier it will bend. It will also have a smoother flow with more cuts. But, you do lose strength so unless you fiberglass or epoxy from the inside, you shouldn't make too many cuts over 11 for a 90* bend. I usually do 10 cuts and then I don't get a perfect 90* angle but I prefer the look and the wood all aligns on the inside. You can see what I mean about getting slightly less than 90* in this picture:

http://i18.tinypic.com/6ufjnle.jpg

Cut spacing: This will depend on the radius you want. What you have to first decide on is the inner flare radius (Rf) and angle (θ). The angle will give you the number of cuts (Nc) you need. I use these equations to get line spacing (Ls):

Ls = [(2*Rf*pi) / (θ/360) - (Nc*Bw)] / Nc

Where Bw is your blade width. Also note that the angle (θ) needs to be in degrees in order to get the actual arc length for the piece of wood. It seems confusing but it's really simple. The numbers work well enough that you can incorporate it with any flare angle, radius, and number of cuts.

Starting point will be based on when you want the flare to begin and the ending point will just happen as you make the cuts with the constant spacing. Let me know if any of that was unclear.


what's thr pros and cons of having flared vs. slot? or is it all just cosmetic?

SPY
09-04-2008, 10:59 PM
It can help reduce port noise, but mostly it's just cosmetic.

I use a circular say which has a thinner blade than a table saw.

I do 16 kerf cuts for a 90* bend and it comes out very smooth. Again spacing depends on diameter of the kerf.

http://i347.photobucket.com/albums/p466/titanium03g/DSCN9239.jpg

tommyk90
09-04-2008, 11:07 PM
It's also a slim chance that you will even notice a slight change in the tuning frequency with a kerfed port the same length as a normal slot port anyways, especially once the enclosure is placed into a vehicle.

At that point the resonant frequency of the vehicle and the car acoustics can change the tuning/frequency response.

Immacomputer gave a very clear and simple explanation though.

Plus most people probably don't factor in for end correction anyways, which will drop the tuning. I usually don't bother either because the change is fairly miniscule; 1 hz is the most i've seen.

netzero
09-05-2008, 01:05 AM
Well, thank you everyone, this has definitely helped me figure out what im gonna do, and i think with some practice the kerfed port is gonna be sweet! Immacomputer, I really like the less than 90* bend there, it adds even more artistic flavor to the already **** flare. And the perfect explanation on the distance formula, thanks man. Hope this helps anyone else with questions on kerfed porting!

lvjeffro
09-05-2008, 01:18 AM
this thread answered allot of questions i had re: kerfeded ports...

twisztdauthorit
09-05-2008, 01:34 AM
make sure you make your cuts real even and very deep. If there not deep enough they wont bend. I always start out on a test piece of wood to setup the table saw

Immacomputer
09-05-2008, 08:07 AM
Yea, even cuts will make all the difference in the world. When running the wood through (or circular saw if you don't have a table saw) the table saw, make sure that both ends are supported well and that the piece of wood is not bowing up. On my first kerfed panel, the wood was very long and it would cause the panel to bow up in the center where I was cutting and while I was cutting. I didn't have the end hanging off of the table saw supported and it did not bend well at all. If you're using a circular saw, make sure the center and sides are all supported so the same doesn't happen.

netzero
09-05-2008, 01:08 PM
I usually make big cuts with a circular saw, but I've got an old radial arm saw i inherited, and i think that would do very nicely. How would you make the cuts straight on a table saw?

PSturmer
09-05-2008, 01:13 PM
Ok, so I've got a box design I'm gonna build myself, but I really wanna try a flared port. I was just wondering for those who have does it themselves, how much does the average kurfed/flared L shaped port effect tuning, versus a standard 90* edge? And any tips on how to go about that? Thanks

if its a port 17'' long with a 3'' radius flare then you take 17 - 3/2. it is half the effective length. i tried making a flare once out of wood. just be careful because the wood is very fragile when it has 10 cuts in it.

Pioneer~Saturn
09-05-2008, 01:36 PM
I usually make big cuts with a circular saw, but I've got an old radial arm saw i inherited, and i think that would do very nicely. How would you make the cuts straight on a table saw?

With a fence :crap:...lawl

fbi90909
09-05-2008, 01:55 PM
lol, when i did my box with the kerf i used a circular saw. first i took a straight edge of a board then clamped it into position, then took the saw and sit it next to the clamped board as a guide, made a cut, then took it off and measured how far from the clamped board the cut was. that gave me a general measurement to know where to clamp and where my cut was going to be. worked out pretty good for me and gave me the straight cuts i needed.

IMO, make lots of cuts. don't just go for bare minimum. the closer the cuts the more flexibility you have along with a smoother curve on the frontside. if you make few cuts, when you bend the wood you will most likely end up with a lot of straight bends and to me isn't as appealing. you can sand it down to be smoother at the bends but it will then begin to loose it's strenght as your taking away the little amount of wood it has left..

i don't know if mentioned or not but i would also recommend you to fiberglass the cut side to give additional strenght and so the kerfed area can settle and not want to bend back.

Pioneer~Saturn
09-05-2008, 02:58 PM
lol, when i did my box with the kerf i used a circular saw. first i took a straight edge of a board then clamped it into position, then took the saw and sit it next to the clamped board as a guide, made a cut, then took it off and measured how far from the clamped board the cut was. that gave me a general measurement to know where to clamp and where my cut was going to be. worked out pretty good for me and gave me the straight cuts i needed.

IMO, make lots of cuts. don't just go for bare minimum. the closer the cuts the more flexibility you have along with a smoother curve on the frontside. if you make few cuts, when you bend the wood you will most likely end up with a lot of straight bends and to me isn't as appealing. you can sand it down to be smoother at the bends but it will then begin to loose it's strenght as your taking away the little amount of wood it has left..

i don't know if mentioned or not but i would also recommend you to fiberglass the cut side to give additional strenght and so the kerfed area can settle and not want to bend back.

Yea, definitely pour resin on the back and let harden (atleast)...if not add mat to it for some strength as well

Immacomputer
09-05-2008, 04:40 PM
If the inside wall touches, you really don't need to fiberglass or resin the inside.

thorshammer1
09-06-2008, 04:20 PM
This thread was very informative. Was also looking into a flared port. Might even try going to a 12inch port. lol

on1wheel01
02-06-2009, 02:25 AM
old thread i kno but man that box is sick

DDSC
02-06-2009, 06:25 AM
sticky???

thorshammer1
02-06-2009, 09:05 AM
sticky???

x2

Dj Arr
02-06-2009, 09:23 AM
Don't do more than 10 cuts, the port will become weak unless you have a port wider than 5" as the bend will be best much larger.

The thickness of the blade doesn't matter. If you have a wider blade do less cuts.
soak=no
Pack wood glue and mdf dust in the kurf and then shape it.
If your worried about being able to see lines along the kurf because you did minimal cuts don't worry. It's stronger, AND you can use bedliner to cover that up. Looks great.

Port noise reduction and you will probably notice a difference in the sound it's self. I don't know how to explain it, less puff puff and more mmmmmmmmmmmm. :]


sorry, seen a lot of crap in there.

x3 sticky