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View Full Version : guide vanes in a port?



xluben
12-03-2006, 12:47 AM
has anyone thought of/tried this idea?

looking over some charts for my fluid dynamics class, and it seems that well implemented guide vanes would be much more effective than the often-recommended rounding of port bends (mainly in L-shaped slot ports, but could also apply to labyrinths).

here's what i mean:

http://img142.imageshack.us/img142/8971/flow1customma1.th.jpg (http://img142.imageshack.us/my.php?image=flow1customma1.jpg)

as you can see there is a change in loss coefficient by a factor of 5!

i also have some other numbers that show that rounded corner (with a small radius, ie. router-ed corner) would have much less affect (of course doing both would be best).

i'm not sure of the best way to implement this, but maybe some thin-walled pvc cut into 1/3's would work :confused:

not too much info on a 180 degree turn (as done in car audio boxes) it's just so bad for flow (and in most cases, not practical), so it's not included in my texts, but i'm sure the info's out there somewhere.

and obviously, a flared, straight port is going provide the best airflow possible :)

some more interesting charts:

http://img142.imageshack.us/img142/5889/flow3customby7.th.jpg (http://img142.imageshack.us/my.php?image=flow3customby7.jpg)

seems that flared, external port(s) with a large baffle on the outer end would further increase airflow (because air flows into, and out of, a port).

any one with free time and a TL want to test any of these 'theories'? (ie. guide vanes if you have an L-port or a port baffle if you are running flared, external ports)

jmanpc
12-03-2006, 12:50 AM
interesting. but too much of a PITA

heyman421
12-03-2006, 12:54 AM
if the vanes drifted from PERFECT linearity, it could change the tuning of the port

and if the vanes weren't perfectly parallel to each other, god only knows what kind of issues you'd have, probably noise

xluben
12-03-2006, 01:07 AM
if the vanes drifted from PERFECT linearity, it could change the tuning of the port

and if the vanes weren't perfectly parallel to each other, god only knows what kind of issues you'd have, probably noise

anyone have a link to the derivation of the tuning equation?

that'd be a pretty good read. i'm sure they had to make a lot of assumptions.

looks like (from all the equations i've seen online) they accounted for flared ends by having to add an inch to the overall length, to achieve the same tuning.

BUT no where have i seen anything to account for bends (rounded, L-shaped, or 180 degree)

SO, if you assume the port equations are derived for straight ports, bending them is going to affect tuning in various ways.

judging by the fact that a flared opening adds one inch (and looking at the various friction factors in my text):

each 90 bend is going to need about 1/2" shorter port (for the same tuning)
each 180 bend is going to need about 1" shorter port (for the same tuning)

so all those people with five 180 degree bends could be tuned (up to) a few hz lower than they think :)

(obviously all the numbers i just gave are pretty rough, and based on quick proportions done in my head, so ymmv) :)

Eugenics
12-03-2006, 01:20 AM
i always wondered this myself. but after putting that much work into something i'd probably just say **** it and get aero's

Pyro_By_Nature
12-03-2006, 03:30 AM
I'd be willing to try it, maybe around late december? Maybe once things calm down a little.

helotaxi
12-03-2006, 11:01 AM
The degree of precision that I've got a feeling you'll need to realize a gain rather than a loss from a guide vane setup is most likely going to be beyond the capability of 99% of the people diong this type of work. The only real gain I could see from this anyway is allowing you to run a smaller port wihout noise. If the port is large enough, the velocity inside is would be low enough to make the influence of the guide vanes negligible.

The second part is only discussing a flare vs. no flare. The reentrant setup isn't flared at all and what you have shown doesn't indicate the need for a port end baffle in combination with a large flare. It only shows that in the absense of a flare of any kind a baffle is better than no baffle but a rounded entrance is better still with a large flare better than a small one. The mouth of the flare creates a bafle of sorts as well. The definition of what is "slightly" vs. "well" rounded would be nice to know as well. Defined in percentage of port diameter would be most meaningful I think.

PV Audio
12-03-2006, 11:07 AM
I know that Porsche utilizes that sort of system on the 997 turbo, but I cannot imagine that it would be anywhere near being worth it for a subwoofer enclosure.

iamamp3pimp
12-03-2006, 11:51 AM
I'd be willing to try it, maybe around late december? Maybe once things calm down a little.

would that be after, or before the box that DBB designed for you

PV Audio
12-03-2006, 11:53 AM
would that be after, or before the box that DBB designed for you
Half zing :crap:

xluben
12-03-2006, 11:56 AM
The degree of precision that I've got a feeling you'll need to realize a gain rather than a loss from a guide vane setup is most likely going to be beyond the capability of 99% of the people diong this type of work. The only real gain I could see from this anyway is allowing you to run a smaller port wihout noise. If the port is large enough, the velocity inside is would be low enough to make the influence of the guide vanes negligible.

i think i'd have to agree with you (and everyone else) on that one. probably not worth the effort, and it still won't perform as well as a straight port.


The second part is only discussing a flare vs. no flare. The reentrant setup isn't flared at all and what you have shown doesn't indicate the need for a port end baffle in combination with a large flare.

i was looking at Fig 8.22 (a) and i assumed that even with a flare, the friction coefficient could be lowered even more with a large baffle. but i guess from those diagrams i don't really have the data to back up that statement.


It only shows that in the absense of a flare of any kind a baffle is better than no baffle but a rounded entrance is better still with a large flare better than a small one. The mouth of the flare creates a bafle of sorts as well. The definition of what is "slightly" vs. "well" rounded would be nice to know as well. Defined in percentage of port diameter would be most meaningful I think.

Fig 8.24 does explain loss coefficient vs. flare radius.

the 4" precision ports have a 7.5" out flare radius, including the mounting flange.

i'm not sure how wide the mounting flange is, but if you assume the OD of the actual flared portion to be 6" that would give you a r/D ratio of about 0.25, which puts it in the 'well-rounded' category (with a very low loss coefficient).

also looking at that graph/diagram it appears that a port baffle wouldn't affect the loss coefficient (therefore wouldn't help airflow).

PV Audio
12-03-2006, 11:59 AM
I don't like your sig, it makes me jealous :(

Immacomputer
12-03-2006, 12:00 PM
If you have enough port area, I doubt the velocity of the air would be high enough to worry about guide vanes.

PV Audio
12-03-2006, 12:02 PM
If you have enough port area, I doubt the velocity of the air would be high enough to worry about guide vanes.
Agreed, as I said previously. If you have a large enough cross section, then the air will just flow out of the port, instead of being pushed out of the port. The pushing is caused by the compression of air by the small width, thus, you get port noise when the air exits.

xluben
12-03-2006, 12:02 PM
I don't like your sig, it makes me jealous :(

don't worry i've only gotten listen to them for a week or two.

then my amp broke. then the replacement came doa.

i think it's been close to two months without bass :crap:

helotaxi
12-03-2006, 12:50 PM
Another thing I got to thinking about in the shower (**** you for getting me thinking) is aerodynamic flutter. I'm afraid that the rapidly reversing airflow would induce flutter in the vanes. Make them rigid enough to resist it and they would probably end up so thick that they displace enough air in the port to negate their benefit. The design work that would have to go into the cross-sectional profile would be prohibitive as well I would surmise. Might make a good final project for a aero eng or some such major.

Pyro_By_Nature
12-03-2006, 02:14 PM
would that be after, or before the box that DBB designed for you

Right after you finish licking my *** crack.

iamamp3pimp
12-03-2006, 03:36 PM
Right after you finish licking my *** crack.

hey, im just saying bro......I dont have any issues with you. im just saying......it took you quite a while (still waiting) to work on the plans that would have solidified Death By Bass on the boards as someone that knew what he was talkng about.

Eugenics
12-03-2006, 03:37 PM
Another thing I got to thinking about in the shower (**** you for getting me thinking) is aerodynamic flutter. I'm afraid that the rapidly reversing airflow would induce flutter in the vanes. Make them rigid enough to resist it and they would probably end up so thick that they displace enough air in the port to negate their benefit. The design work that would have to go into the cross-sectional profile would be prohibitive as well I would surmise. Might make a good final project for a aero eng or some such major.

some sheet metal would probably do the job just fine.

iamamp3pimp
12-03-2006, 03:39 PM
hes bitter.


What's up Preston

Immacomputer
12-03-2006, 04:34 PM
hey, im just saying bro......I dont have any issues with you. im just saying......it took you quite a while (still waiting) to work on the plans that would have solidified Death By Bass on the boards as someone that knew what he was talkng about.

Do you want me to bring the horn he designed to the meet in December? I could possibly arrange that if you wanted to hear it for yourself.

iamamp3pimp
12-03-2006, 04:37 PM
no not necessarily.

i wansnt trying to start a flame war...

:/

Eugenics
12-03-2006, 05:25 PM
hes bitter.


What's up Preston

Just trolling the forums. You?

iamamp3pimp
12-03-2006, 06:45 PM
getting told to perform various homosexual acts is all. Thats not a very heterosexual thing to say btw, but thats my opinion on the situation. In my opinion, i think that he might not be as hetero as he wants us all to believe. Then again, with comments like that, maybe he doesnt know what to believe himself...

helotaxi
12-05-2006, 12:17 PM
some sheet metal would probably do the job just fine.

For a continuous linear flow, it probably would. The flow in a port is neither. Ever seen the vertical stabs on the early versions of an F-15. Fluttered like an SOB. They were a bit more significant than sheetmetal. Tacoma Narrows bridge ring any bells?

Flipx99
12-05-2006, 12:37 PM
What if you contoured them like the wing of a plane, to push the air away from the corner.

Pyro_By_Nature
12-05-2006, 11:06 PM
hey, im just saying bro......I dont have any issues with you. im just saying......it took you quite a while (still waiting) to work on the plans that would have solidified Death By Bass on the boards as someone that knew what he was talkng about.

Well, at the current point in time, I have too much stuff going on to build a box just to "solidify" someone's rep. on a forum.I've said it once and I'll say it again, when I get time.

Hey, you're the one licking, not me. :p:

helotaxi
12-06-2006, 12:26 PM
What if you contoured them like the wing of a plane, to push the air away from the corner.

Any type of airfoil (you would have to have some type of contour to keep turbulence to a minimum) would have to be symmetrical along both its axes. Any flaws in the symmetry of pressure would induce flutter.