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Klipsch slot port design


CAS

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It appears from the website pics that the slots on the KW-120's are approximately 17" by 2" tall.

With that area it would seem the port probably has to turn a corner or two internally.

Do you think 2" is the minimum height you could use before port noise becomes apparent? What about 1-1/2"? Or is it a function?

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That all depends on the tuning freq., cabinet size, woofer,etc. The port needs to be designed to stay small enough to take up the least space but yet not go over an air velocity of 10% the speed of sound(which equals chuffing) at max spl through all the subs pass band. At least I think its 10%....Not sure if that helps ya...

scp53

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It appears from the website pics that the slots on the KW-120's are approximately 17" by 2" tall.

With that area it would seem the port probably has to turn a corner or two internally.

Do

you think 2" is the minimum height you could use before port noise

becomes apparent? What about 1-1/2"? Or is it a

function?

Yup it has to be bent

Slot loaded tends to reduce port noise a little more than a round one.

Also it is important to have a flared port on either a round or slot

loaded. This reduces the chuffing at higher volumes plus you need less

port length when it is flared.

From WinISD help:

Very important here is to make your ports large enough, so that peak air

velocity won't exceed 5% of sound velocity in air. That is, about 17 m/s

assuming normal environmental conditions.

But most professional subwoofers use the 20 m/s as the chuffling

increase spl a bit more and it is less noticeable on the stage than in

a quiet home. But remember most subwoofers on the market with ports

will experience chuffling at max volume. Even the mightly SVS B4

chuffles but reviewers said it's at such rediculous levels that no sane

person would ever hear it. Safe to say I would go as far as at max

volume 25m/s is fine.... Atleast when you hit max amp power then the

chuffling noise will tell you hey its at max volume you idiot! I am

going to break if you push me harder.

post-13377-1381927920076_thumb.jpg

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My bad.. I thought it was 10%... not 5%... oh well

Thanks for the pic btw. Ive never seen the inside of the thx ultra sub.

Do you really think the flare helps that much on this thx sub in terms

of affecting length? The flare seems very slight from the pic you

posted... imo

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No No Jay, I wasnt doubting that the little round overs dont help with turbulance, Im sure they do! I was just saying I doubt they affect the over all length of the port.

As for the woofer, as many know, looks arnt everything. There are some VERY modest woofers out there capable of much more than "big potent" looking ones. Im talking about both sq and spl. scp53

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oh I doubt the flare does really shorten it. I remember having a 6 inch

port and a flared 6 inch port which is like 9.5 inches wide on the ends

[:o] reduce the port by a measly 2-3 inches. So I doubt it then. but

for turbulence, hell remmeber the first plane to hit the speed of sound

had to be redesigned over and over and the thing that did it was to

curve the back end of the airplane more like an hourglass. Even the

pilot went to the engineers, "Is that really going to help?"

Also JL W7 has the 90 degree ports because they are forced to. The W7

moves soo much air that no round port is capable without the length

being astronomical. The slotted port is bent also to help make it fit

in your car. The thing is though the port tuning and specs do change

when they have a bend or a curve. Hence the kw-120 tries to reduce the

curve to a min. They could have done a 90 degree and gain alot more

internal space, see pics, and lose the handle in the back of the sub.

But there obviously must be a reason. also think water management when

thinking about the 90 degree bend for a port. A 90 degree bend in

plumbing does work but it does lose total flow of water. But its a

compromise then making the walls and floor bigger to accomodate gently

flowing pipes. Heck the rw series subwoofers used the angled port just

so they would not bend the port. So they had the one end of the port on

the corner and the port ended up in the front. If JL could have they

would not have put a 90 degree bend as it sorta changes the tuning

frequency of the port. Think string instrument and when you place your

finger on the fingerboard to make a different sound. Yes same length

overall but you just shortened it a bit by whereever you placed the 90

degree bend. I am sure DrWho can elaborate more on this.

post-13377-1381927920563_thumb.jpg

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No No Jay, I wasnt doubting that the little round

overs dont help with turbulance, Im sure they do! I was just saying I

doubt they affect the over all length of the port.

As for the

woofer, as many know, looks arnt everything. There are some VERY modest

woofers out there capable of much more than "big potent" looking ones.

Im talking about both sq and spl. scp53

true just with life, some dogs are all bark and no bite. I know some

offenders just think having a triple stacked magnet is stronger, Some

people are all about how much xmax instead of Bl, efficency, FS, etc.

Some speakers are more rubber surrounds than actual cone (Think sunfire

junior). Some have a better basket that is more like an automobile rim.

Heck some are square, some are painted red, or silver, etc.

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CAS, what's the specific project you're working on? Curving the port

will change the tuning frequency - I don't remember which way, but

generally a good subwoofer design can be +- a few Hz without causing

too many changes. And don't forget that ports can go at any angle into

the cabinet (diagnals maximize their length).

Also, I believe the KW's are pushing 40m/s at peak output. I know of a

few other commercial "quality" subs with the same issue too. If you're

using winISD it might be a more practical approach to figure out how

loud your usual peaks are and then adjust the port size to be 20m/s at

that SPL. And if you make it a rear-firing port, then you will even

further minmize the audibility.

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I wondering why Klipsch did this? I guess its obviously to save space.... Does anyone know if that chuffing comes into play on the subs published output specs? I know they only publish what is under 10% thd but would they still leave chuffing distortion in it? To me, chuffing at 40m/s would be very bad. Just as bad as thd or any other distortion. hmmm.... scp53

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It was a design choice to make the subwoofer completely front-firing so

it could be flush mounted. And yes, the chuffing comes into play during

loud scenes - but it's usually drowned out by the rest of the sounds

(not to mention it's not very audible when explosions happen either). I

don't think it would be listed as part of the THD spec because it

really isn't harmonic distortion...

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but distortion none the less, I guess my distortion definition is any

sound that is undesirable or not on the original recording.

Well there are different types of distortion and it's important to specify the differences between the different types.

The new RT-12d's are supposed to be the lower distortion versions [;)]

(just less position friendly)

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CAS, what's the specific project you're working on? Curving the port will change the tuning frequency - I don't remember which way, but generally a good subwoofer design can be +- a few Hz without causing too many changes. And don't forget that ports can go at any angle into the cabinet (diagnals maximize their length).

Also, I believe the KW's are pushing 40m/s at peak output. I know of a few other commercial "quality" subs with the same issue too. If you're using winISD it might be a more practical approach to figure out how loud your usual peaks are and then adjust the port size to be 20m/s at that SPL. And if you make it a rear-firing port, then you will even further minmize the audibility.

The problem with winisd in this project is no matter what configuration I try I can't get the velocity to read anything but Qes/Pe!. I'm doing a down-firing slot-vented rear-port enclosure with an old car audio Orion XTR and a spare plate amp.

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