Port style info needed please.

I am in the process of trying to design a rather "thin" sub enclosure of a bout 3 cuft. for use in my garage. Max depth can be only about 12"; width can go to 36" and height to about 20". My calculations indicate that this will probably need a port that is at least 12" long if not longer (4" tube). Can I just use two 2" X6" rather than one 4"X12" with the same result ??? Pro and cons ?? Thanks..
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
Can I just use two 2" X6" rather than one 4"X12" with the same result ??? Pro and cons ?? Thanks..

A 2" port has 1/4 the area so it would be ~1/4 as long as a 4" diameter port, 2 of them will be half as long, as you indicated. How small you can go with the port depends on the driver size, the tuning frequency and how loud you want it to play without making nasty turbulent noises from air rushing in and out of the port. Making a slot port or putting a single elbow in the port can help fit it into the box.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
OK , in a 3 cu ft box would it be better to use a 4"x14" or a 3"x7" port tube ??? (TFreq is 26 Hz.) and why?

Bigger diameter (area) is always better in ports. If you are worried about fitting the 14" port in it would probably be better to make a "diffuser port" as this is a bit better than making an elbow. Port downwards into a space walled on three sides. Start with the 14" tube but you will likely end up cutting a fair chunk off after testing....

[edit] You could also put a nice flare on the 3" port and it would probably work OK.
check out a paper called maximizing port performance mentioned in this thread:
http://www.diyaudio.com/forums/subwoofers/233516-port-area-vs-efficiency-2.html#post3442795
 
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A 3" port is inadequate for a good 12" woofer. 4" port minimum, bigger if it's a long-excursion subwoofer.

Elbows...blecch. Think about it-how can air flow smoothly through that? Maybe a big radiused elbow, but you'd have to smooth the joints somehow.

It would be much better to run the port out the side or the top or the bottom-maybe a shelf port.
 
go to your local hardware store and put a piece of pvc pipe in an elbow and see if it lines up smooth on the inside.
you might be surprised at how smooth it can be, because those pieces are modeled to work together afterall .. and any turbulence from a lack of smooth is going to help cause a clog.

it is easiest if you simply think about the air inside the tube as solid from one end to the other, no different than a solid speaker cone moving in and out.

if you really had a little bit of rough edges where the two pieces meet, and you really wanted to smooth them..
maybe this would work:
get a hot glue gun.. get a tube that wont burn or melt when touching the hot tip.. bend the tube at a 90 degree angle (or 45 if you want) and get yourself a tool that will smear the glue smooth like a putty knife.

as long as you can reach in there all the way and move, and as long as you can see what you are doing .. you should be able to smooth the joint.

but i think if you've got a smooth cut on the pipe and the pipe is shoved up all the way into the elbow, it should be smooth enough and i don't see why you are looking for such astonishing perfection .. but then again, computer modeling would be a whole lot more easier if the stupid tube was perfectly smooth right?..
 
As this box is kind of a thin rectangle would it be OK to offset the speaker to the left on the front baffle and run the 4" tube in from the right side of the box (looking at the rectangle front on) ??? Plenty of room to use a 4'x14" straight flared tube if I bring it in from the side. Does it make any difference which side the port comes in from??(will probably use a flared tube kit from PE for this)
 

OscarS

Member
2011-01-02 10:44 pm
Okay. Then explain how the statement was valid.

I've always believed this too.

like RonE said, the bigger the port area the better. this was the part about "minimizing vent mach speed". The part about minimizing internal surface area was to remind the OP about the losses that occur when two Ports of equal cross sectional area but unequal internal surface area are compared---there are more port losses in a high aspect ratio rectangular port than a square port, and similarly more losses in a square port than in a circular port (for a given cross sectional area). the circular port minimizes internal surface area for a given cross sectional profile.
 
go to your local hardware store and put a piece of pvc pipe in an elbow and see if it lines up smooth on the inside.
you might be surprised at how smooth it can be

Yes, that is a good point. I guess the word "elbow" sets me off because I often see it in a context where someone is gonna make a 90 degree sharp elbow out of wood.

I think a shelf port on another side is still preferable, but if the radiused elbow enables a larger port area then it could be a good solution.
 
oh i think most people growing up heard ports tuned at high frequencies and they don't ever get to see the value of a belching extension.

instead, all of the ports are setup for the low bass extension where the box doesn't have any compression & it requires a smaller amount of power to get the speaker to move .. yet most people aren't using the equalizer to boost the frequency any , thus the possibility is there & nobody hears it or knows it.

go to a place like best buy and fire up the demo speakers in the ported box and they might as well go no lower than 40hz
the same thing stupid 2-way speakers can provide, except much louder.

then to make matters worse, they leave the low pass filter up high.. so the subwoofer doesn't sound like a sub woofer , it sounds like a woofer playing really loud.

then, with that inertia, their mentality makes the claim 'well they are advertising we can & should listen to it louder .. why not upgrade the door speakers and put in some amplifiers for them to make the whole thing louder?'

and i'm jst banging my head :headbash: thinking 'whole thing?!! you haven't heard bass extension or a flat frequency response yet'

then i could go on about phase mismatch and time delay adjustments needed too.

it's like the industry tries to get everybody to sleep with the most ugly mate with healthy reproductive organs as mentally and|or emotionally possible.
and for what? because it saves beauty?
there won't be any beauty left if it stops being born..!
duh
:rolleyes: