Question on How to Measure Port length-2 diff. designs

[slikrider20 10+ year member]

because the air in the port ,is not part of the internal volume of the enclosure and seen as a mass by the sub, at all times by the sub.
the sub has two strokes a negative stroke and the positive. port end correction is only good for the negative stroke when air is being pulled in. when the sub its in its positive stroke the air is being pushed out. so end correction would have to be looked at from the out side of the enclosure, if there was a wall at that end. and inside the enclosure that end correction is none existant on the positive stroke. and thats why the end correction is not accounted as port displacement. because its only good for one half of a the subwoofers full stroke and not there for the other half. so it will make zero sence to account for it as a port displacement.

I didn't understand any of that, something about stroking. But i have 4 words for you guys.

WHO GIVES A ****!!!

The difference wouldn't be audible to the human ear. Yall too technical bout ****

 

[PowerNaudio 10+ year member]

lol

 

[Immacomputer 10+ year member]

because the air in the port ,is not part of the internal volume of the enclosure and seen as a mass by the sub, at all times by the sub.

Well that was a grade "A" answer... You basically defined my question with your answer.

And nice random about the sub strokes and end correction only being used by one way of the stroke... where do you get this stuff?

Why don't you do some reading on what a ported enclosure really is.

http://www.audioholics.com/education/acoustics-principles/helmholtz-resonant-absorber

After you read that, take a look here:

http://en.wikibooks.org/wiki/Acoustics/Bass-Reflex_Enclosure_Design

Then, you might want to swing by JL's site as well:

http://mobile.jlaudio.com/support_pages.php?page_id=165

Do you know what all of those sites have in common? They all factor end correction as part of the port. By part of the port, they mean the air mass in the end correction is part of the total air mass in the port. The reason you don't count that as net volume is because that mass of air is NOT being compressed but rather, it resonates. The net volume of air is doing the compression and expansion and that is what drives the port into resonance. How can this mass of air act like net volume and port volume at the same time? It can't and it doesn't.

Subs do not have eyes; they just feel the enclosure volume. We have eyes and when we look at a port, we can see the wood blocking the air. We can't see the end correction of the port but the sub does. The sub can feel the entire column of air that is the port and in that column of air, is the small amount of port that was added due to end correction.

I know it's hard to admit when you're wrong, especially when you have been building and designing enclosures for a long time. But I'm sorry, you're wrong in this case. It won't make much of a difference but it is something to calculate in on future designs.

 

[PowerNaudio 10+ year member]

end correction does not factor in to port displacement. and no of them links say any diffrent.

 

[Immacomputer 10+ year member]

Ok, be stubborn and keep believing that since you think you're better than me. That's perfectly fine by me as I don't plan on buying anything from you.

I guess the concept of what a port is, is way above your head. I guess you're just happy being ignorant and I guess that's cool if that's how you want to live your life. It's too bad your pride will ever keep you from learning.

 

[PowerNaudio 10+ year member]

i guess is too hard for you to get some hard prove of what your talking about.

so sad. this was starting to get fun. muahahaha

 

[Immacomputer 10+ year member]

The port = a column of air mass.

End correction = air mass that is a part of the port.

Net volume = volume of air the sub sees.

Port air volume = volume of air the sub does not see.

Therefore: Net volume does NOT include the end correction because the end correction is part of the port. Also, the end correction does not vary with the strock of the sub. It moves with the column of air in the port.

Read those links and you will see everything I just typed is true. If you cannot understand the logic behind this, you might be borderline retarded.

 

[PowerNaudio 10+ year member]

it amuses me to see you fight over such an small none importand fact.

you know that even if you account for end correction, your tuning and enclosure volume are going to be off. if you design and build your best enclosure then measure your response, is not going to give you the same results you calculated.

specially in a vehicle. thats where experiance comes in buddy. i don't need to "account for end correction volume", never had and doubt that ill start, because like i stated before, its a constantly changing value its not accurate. and its too small to make a difference. yes i account for end correction for the tuning. but thats it. i also account for cabin gain and research on how the particular sub that i design the enclosure performs in different environment, enclosures done by others and my personal build and tests, yes i read, i have been reading and continue to read every thing i can get my hands on, that is audio related. oh im by no means an expert, since im still studying and will keep studying this field. since its my hobby of preference and also kind of a part time job. you can see my builds and designs. there are very few. people that are not happy with either. and by few i mean 1. till this date all the enclosure i have made bring a smile to the customers face. when they hear exactly what they wanted from the sub they purchased. or when they bought the $30 bucks sub that in my enclosure sounds like a $200 dollars sub. i keep designing and building because i do it well. im not the best. but i do it well. and to this date not accounting for the end correction volume hasn't affected any of the enclosures so far. im sure many builders and designer don't account for it either. im also sure that your enclosures or designs aint any better.

ps: to the op sorry for the thread jack.

 

[Immacomputer 10+ year member]

..."constantly changing value"...

Wow... you seriously don't get it, do you?

It's not going to make a huge difference but it could. It's also something called "attention to detail," something that any respectable designer/builder should have.

The reason why I keep going on is because I do want people to learn and have a better understanding of what's going on. I also HATE false information being spread around by people who are supposed to know a thing or two. I thought you were one of those people who actually cared about people learning as well. I guess you're not and really only care about your e-status.

I'm happy that your customers are satisfied, I truly am. I'm not doubting your designs or your building skills. What I am doubting is your actual understanding about what is going on. When you try to pass on information, you **** sure better know that it is correct. In this case, you're not correct and you are spreading around lies, just like some other people on that CAJ website. That's how rumors like "bigger subs means worse sound quality". You don't want to see that anymore than I do and that is why I'm trying to explain this to you.

Well, go ahead and believe what you want but please just stick to designing and building and don't try to teach. It's also NOT a thread jack because the OP was asking how to find the length of the port. I gave him the answer and also provided links that can help in the future. Hopefully he will follow logic and truth and not this "the length changes because the sub moves" ******** you're trying to spread.

 

[PowerNaudio 10+ year member]

guy, just because you think its right doesn't make it right. just because you feel its a lie or wrong info. doesn't make it so.

i have never mislead any one on this or any forum. and i alway try to give this new guys the proper information.

accuracy in the math doesn't always mean its accurate on the final result. i don't account for it because it doesn't need to. if i needed to account for it belive me i would. its not like a will take more the a second to do it. but its not necessary. none what so ever.

you think you're helping some one, when all you're doing is creating confusion. if it made a difference in the accuracy of the final product. it would be take in to consideration big time and would of been talked about since ever. it sounds to me like you just discovered this and feel like you have to tell the world about your new discovery.

you know what i have never meet anyone accounting for port end correction volume like you are, i have allot of conversation daily on the enclosure design subject, i do lots of research on a daily basis on the enclosure design subject as well. its not that i don't understand the philosophy behind it. its just that its not necessary. if you want to account for the .05cuft taken up by your port end correction displacement, be my guest. but don't make a new guy think that he has to and that it will make a difference, because it doesn't. if you want to teach them how to design the enclosure properly, then put more effort in the what it takes to optimally design a ported enclosure. taking in to consideration cabin gain, which actually make for more then 10dbs of boost. finding the optimal volume of the enclosure for a given sub. will actually gain you over 3dbs in comparison to a poorly enclosure designed, how to proper design your port to eliminate port noise and, getting the most audio frequencies from the given sub. thats help. not some dumb .05cuft or less of port end correction displacement. you dumb ****.

and what ever beef you have with caj.com keep it between you and who ever it was. its not my fault you **** at life.

 

[PsychoTheRapist 5,000+ posts]

I hate to rain on anyones parade but after doing a little research it seems the end correction is a very vital in the performance of an enclosure...

taken from audioholics.com

One area often overlooked is that of port end-correction, without which a design may be rendered ineffective. Basically speaking, the air immediately outside either end of the port acts in sympathy with the design air mass in the port. This has the effect of increasing the apparent length of the port (fig1), and hence affects the tuning frequency of the resonator.

Fig1.

The apparent increase in port length is calculated as 0.732 x the port diameter (for a flush-fitted port, with little or no flare). Naturally, then, any shift in design frequency is connected to the diameter of port used, as well as to the cavity volume, in consequent calculations. At the volumes likely, and with a 3" - 4" port, the uncorrected resonant frequency will be off (high) by around 10Hz - 15Hz. Which in real terms is sufficient for the device to lack proper excitation by the target room mode, and hence prove ineffective.

Where f is the resonant frequency (Hz), c is the speed of sound (1120ft/s), p =3.14, S is the area of the port (ft 2 ), L is the length of the port (ft), D is the diameter of the port (ft), and V is the cavity volume (ft 3 ).

Modified to include port end-correction the formula elicits a marked change in resonant frequency. For so function (frequency) specific a device, it is vital that port end-correction be taken into account.

 

[Immacomputer 10+ year member]

The comment about CAJ had to do with another thread here where somebody said this: "I was told on CAJ that you needed to add [end correction length] to the port length..." I don't know who it was and I don't care but somebody tried to make a thread explaining how to make ported enclosures and said to just add it to the total length of the port. This would cause people to make the port walls much longer than needed and they could be adding 6 or more inches to the port length. You try to tell me that it won't make a difference.

I also don't "think" I'm right; I know I am right and the facts are here. You seem to have trouble putting them together and you still think I have no clue what I'm talking about. I bet you think this because I don't compete or sell enclosures.

The problem I have here is NOT the small amount of air but your understanding of how the port works and how end correction works. End correction CAN be a huge factor, especially if the port is pretty wide.

I'm not trying to teach anybody to build enclosures right now, I'm trying help clear up the obvious end correction confusion people have.

I guess I **** at life now? You can back this up how? Kind of like your idea of the sub's stroke changing end correction... awesome.

Please though, keep up your research. Maybe one day you will understand. Maybe you won't though and you will keep on going thinking you're better than me and know more than me. I really hate it when people are proven wrong and yet they continue thinking they are right; It blows me away.

You sir, are a moron.

 

[PowerNaudio 10+ year member]

dude, too simple, do the math your self, maybe then you'll finally learn that the difference is not a negligible one. and you'll see that you wont give a **** about the difference.

go ahead change the port length by 4" and see for your self how much of a difference it makes.

 

[Texas Tech 10+ year member]

Hey you said on MY second picture the length would be calculated by adding 15+3+.75=18.75 Where did you get the 3" and .75" from. I know why you calculated 15 inches, because it is the actual length of the port, but i dont see why you added in 3 and .75 inches. Could you further explain that please

And on this one

http://www.putfile.com/pic.php?img=3305668

You would basically just have to calculate one side of the "T" port" so on that diagram you would just do 10.25+5.75+1 (cuz that is half of the width [2"]) or would you do 10.25+5.75+2 because the width of the "T" port is really 4 inches?

So to recall, so i feal assured on this, on MY first diagram, the T port with a wood board down teh middle to seperate the two ports, to calculate the length you would add 12+7+1.5(because that is half of 3,the width)

And also on your second diagram, the "L" port

http://www.putfile.com/pic.php?img=3305715

To calculate that length you would add 21.25+18.75+2 (half of the width)

I am trying to get all the basic port ideas down so i can put them all together for really good information on how to calculate different kinds of ports.

Sorry to cause all the comotion....i didnt know this would become dramatic...I should have just watched an episode of Real World...lol jk please no body throw anything at me i am just playing

 

[Texas Tech 10+ year member]

o and by the way, taking the time to make those diagrams on the putfile.com site is really good, i am impressed seriously. What did you use to create those

But seriously you guys rock, i have been asking these questions for i dont know how long now and no one has really given me any kind of response that can answer my questions, cool forum

And i understand that a 1 inch difference may not make an audible difference, but i am very interested in this stuff, and i like to know how to do it and do it right. I am a person that doesnt want to be told the answer, but how to actually find the answer, that goes for everything i do. I like to be able to explain it after i learn it. I dont mean to be rude or anything, i dont want to make anyone mad.