Port: How long is too long?

[Triticum Agricolam]

12 minutes ago, Joshdashef said:

Not to divert from ops topic, but what’s the impact of going between the port width and double the port width or more of clearance from a exterior panel and the port wall? 
 

I always figured a bare minimum of the port width would be needed, and anymore wouldn’t effect anything. 

Anything less than two port widths away has a good chance of affecting the tuning frequency.  Generally this isn't a huge deal, but just something to keep in mind.   Anything less than one port width away will likely impede airflow and at that point it will negatively affect output.  

[Triticum Agricolam]

42 minutes ago, akuma4u said:

Hey,.. so basically i have a box right now which i used your calculator for and i got minimum port area required.. its 2 cubes and 34hz and has a 3.25 inch wide port.. im using a sundown sub a u series 12 and giving it 2000rms. it sounds ok.. but i was wondering if i could get MORE output from it. so i called sundown. Their tech suggested since im overpowering the sub (its a 1500rms sub) they said i should go smaller on the box 1.75net and tune a lil higher and use 24 to 28sq inches of port area,, this way i can put MORE power to the box and get more output using a smaller box. so i had a test box built and im picking that up tomorrow. it actually has 21 sq inches of port area.. i had a discussion with the EMF audio guy about this and he told me to go smaller on the port area as it will give me a wider bandwidth and better roll off above and below port tuning frequency.. i actually told him about your calculator and he said some stuff about how the big port would be good for SPL but not for music heres what he actually said:

"Appropriate port area depends on the tuning, volume, usable bandwidth, and motor force. A bigger port area will narrow your usable bandwidth as you can't stray too far above or below tuning without reaching mechanical limits. For SPL applications that doesn't matter, for musical applications it does. While you might gain 0.5 dB at a peak you may lose the ability to keep a linear response and you may not be able to play below tuning at all where a smaller port area you could play 8-10 hz below tuning and be fine. Motor force is a factor because of the Qes. A higher Qes will control movement on it's own without relying on the enclosure as much. A bigger port reduces mechanical control from the enclosure."

 

"compression does happen before being audible, but that just means the port becomes less efficient. The concept is right for maximizing SPL, it's bad for music"

 

"I would do 24 sq in of port area. I'll give general specs, I will not do designs. I did look at that link you provided and I find there to be some issues with calculation, like not figuring in displacement in any form. Power alone will yield very different results of pressure in the enclosure which ultimately makes the port resonate to have compression to start with."

 

anyhow... i build a box based on what he said, 12 sq inches a cube,. and i wanted to build another box with as close to optimal of a port as possible as per your calculator which btw doesnt even work for me right now i dunno what happened... maybe take a peek it seems like its broken? , so ya when i tried to build a 1.75net with my MAX dimensions which are 13.5 tall x 32 wide x 17 deep, the port was coming in like at 40 inches or so and it was leaving like half an inch of space between the end of port and side wall. so i couldnt get it to work out.

 

so NOW, i guess i have to go for a smaller port..or as big or one i can fit in my max dimensions and keep a 36hz tuning while keeping 1.75net..

 

sorry no drawn diagrams ive just been using Torres to design at the moment..

 

 

 

 

OK, so I've seen some of the videos the guy from EMF audio has put out on youtube.  I commend that guy for trying to educate people, and for the most part he does a good job of that, but there is a percentage of info he puts out that is incorrect.  He should know better.

Like I said before, port area isn't a good way to flatten an output peak, the guy from EMF may disagree, but I can prove my claims with actual measurements.  Here is the results of an experiment where I used the same enclosure, just with different external ports and measured the frequency response.  The port with very little port area had exactly the same frequency response as the port with much more port area:

 

The most egregious comment the EMF guy made was that you should undersize the port so you can play farther below tuning.  That's just stupid.  Below tuning the output from the port becomes out of phase with the output from the cone, so they actively cancel each other out.  This is a giant reason why you shouldn't try to play much below tuning, if you need to have output lower, tune lower.  Also the whole logic behind reducing port area for cone control is completely flawed.  If you are going to depend on air resistance to reduce cone movement, that's only going to be effective when port velocity is high (like right at the tuning frequency).  Port velocity drops dramatically below tuning, so reducing port area isn't going to do shit for cone control. 

As far as why my calculator doesn't include any displacement inputs, its because cone displacement doesn't matter much for port area.  I address that in this post here: 

 

[shredder2]

What kills me with all these calculators is the way "rules and givens" are used. For example... a box tuned 32hz at the drivers limit will likely need a subsonic. That  Subsonic will lower port velocities drastically... making a smaller port feasable.

Volume/tuning power and filters affect velocities and to properly size the port area modeling can't be beat imo. 

Now I've "undersized" my port for a given volume/power and seen 140fps+  but after setting up my filters correctly when modeling it lowers it a good bit under100fps. What's hard to figure accurately is actual power without testing... Imo once your power is figured port sizing is a snap

[1point21gigawatts]

2 hours ago, Triticum Agricolam said:

I'm always looking to make my calculator better.  Please, what flaws have you found?  Maybe I can find a way to fix them.  

I use to follow your work and insight and then I decided to use your calculator on one of my builds. It yielded so much port area when using around 8000 rms that it makes it impossible to tune unless probably if I made the enclosure’s volume crazy big. The size of the enclosure was around 4.5 cubic feet after displacements, I don’t remember the exact size. And the desired tuning typed in the calculator was 35hz. Then I took the calculated port area from your calculator and put it into programs with the same specs that were used to calculate in your calculator and no matter how long I made the port, the tuning stayed around 50hz. The only way to remedy that was to decrease the port volume. And then this dude who started the thread was told so much port area by your calculator, using 2000 rms (since it’s lower rms it makes tuning possible, but length has to be too long) that he would have to bend the port twice. The only way to remedy that problem is the same remedy, decrease the port area. So that brings me to think said port area formula has to be the culprit, not the calculator. Because no matter what, it yields crazy amounts of port area that makes tuning and sizing almost impossible. I was really disappointed when I used your calculator because after reading your insight for so long and gaining so much respect to see flaw was devastating because shortly after I seen the formula you use to find end correction factors and it has me questioning how you came up with it and why not use the standard formula, add radius of port width? This I was wanting to ask you because I very intrigued on it and how it’s calculated. This I don’t doubt you on because I have to understand it first before I can say anything on that matter. I would like to hear from you on that matter. But that port area matter is messed up somewhere. I still think your an awesome enclosure designer and forum famous, for sure. But that port area thing is off and I tried to make it work but I couldn’t. Many people have and they run into the same or similar problems. Don’t let this make you think wrong or wrong of me or whatever, I’m just keeping it real. I can’t do it any other way. If I did it any other way then that would be fake. Let me know what’s up with that end correction factor formula you use. And don’t hate me or dislike me for this. I have to keep it real no matter what and would want the same it return. 

[Triticum Agricolam]

43 minutes ago, 1point21gigawatts said:

I use to follow your work and insight and then I decided to use your calculator on one of my builds. It yielded so much port area when using around 8000 rms that it makes it impossible to tune unless probably if I made the enclosure’s volume crazy big. The size of the enclosure was around 4.5 cubic feet after displacements, I don’t remember the exact size. And the desired tuning typed in the calculator was 35hz. Then I took the calculated port area from your calculator and put it into programs with the same specs that were used to calculate in your calculator and no matter how long I made the port, the tuning stayed around 50hz. The only way to remedy that was to decrease the port volume. And then this dude who started the thread was told so much port area by your calculator, using 2000 rms (since it’s lower rms it makes tuning possible, but length has to be too long) that he would have to bend the port twice. The only way to remedy that problem is the same remedy, decrease the port area. So that brings me to think said port area formula has to be the culprit, not the calculator. Because no matter what, it yields crazy amounts of port area that makes tuning and sizing almost impossible. I was really disappointed when I used your calculator because after reading your insight for so long and gaining so much respect to see flaw was devastating because shortly after I seen the formula you use to find end correction factors and it has me questioning how you came up with it and why not use the standard formula, add radius of port width? This I was wanting to ask you because I very intrigued on it and how it’s calculated. This I don’t doubt you on because I have to understand it first before I can say anything on that matter. I would like to hear from you on that matter. But that port area matter is messed up somewhere.

Thanks for responding to my request.  

If you were going to put 8000 watts into a 4.5 cu ft enclosure, I can certainly understand why my calculator didn't give you very usable numbers.  I never intended it to work under that kind of extremely high power situation.  My experience has been been once you get to around a 1000 watts of power per cubic foot of box volume, it becomes almost impossible to get enough port area keep port compression at a reasonable level.  Your enclosure was WAY past that point.  At those power levels you just have to do the best you can and deal with the consequences.  For this reason I put a big warning message in my calculator if you get over 1000 watts per cube.  Maybe you didn't see it when you were using my calc, but this is what it looks like. 


 

[shredder2]

3 minutes ago, 1point21gigawatts said:

I use to follow your work and insight and then I decided to use your calculator on one of my builds. It yielded so much port area when using around 8000 rms that it makes it impossible to tune unless probably if I made the enclosure’s volume crazy big. The size of the enclosure was around 4.5 cubic feet after displacements, I don’t remember the exact size. And the desired tuning typed in the calculator was 35hz. Then I took the calculated port area from your calculator and put it into programs with the same specs that were used to calculate in your calculator and no matter how long I made the port, the tuning stayed around 50hz. The only way to remedy that was to decrease the port volume. And then this dude who started the thread was told so much port area by your calculator, using 2000 rms (since it’s lower rms it makes tuning possible, but length has to be too long) that he would have to bend the port twice. The only way to remedy that problem is the same remedy, decrease the port area. So that brings me to think said port area formula has to be the culprit, not the calculator. Because no matter what, it yields crazy amounts of port area that makes tuning and sizing almost impossible. I was really disappointed when I used your calculator because after reading your insight for so long and gaining so much respect to see flaw was devastating because shortly after I seen the formula you use to find end correction factors and it has me questioning how you came up with it and why not use the standard formula, add radius of port width? This I was wanting to ask you because I very intrigued on it and how it’s calculated. This I don’t doubt you on because I have to understand it first before I can say anything on that matter. I would like to hear from you on that matter. But that port area matter is messed up somewhere. I still think your an awesome enclosure designer and forum famous, for sure. But that port area thing is off and I tried to make it work but I couldn’t. Many people have and they run into the same or similar problems. Don’t let this make you think wrong or wrong of me or whatever, I’m just keeping it real. I can’t do it any other way. If I did it any other way then that would be fake. Let me know what’s up with that end correction factor formula you use. And don’t hate me or dislike me for this. I have to keep it real no matter what and would want the same it return. 

Meh.... modeling lets you determine a ton. Instead of dinging the calc... realize its limitations and either model or find a knowledable designer.

There's a reason I lurk around here... lately a ton of disinformation seems to be normal. I size MY ports properly and have designed a couple... lol

[Triticum Agricolam]

49 minutes ago, shredder2 said:

What kills me with all these calculators is the way "rules and givens" are used. For example... a box tuned 32hz at the drivers limit will likely need a subsonic. That  Subsonic will lower port velocities drastically... making a smaller port feasable.

Volume/tuning power and filters affect velocities and to properly size the port area modeling can't be beat imo. 

Now I've "undersized" my port for a given volume/power and seen 140fps+  but after setting up my filters correctly when modeling it lowers it a good bit under100fps. What's hard to figure accurately is actual power without testing... Imo once your power is figured port sizing is a snap

You are correct, a properly set subsonic filter will lower port velocity, but I wouldn't say it lowers it drastically.  The other problem is not everyone uses a subsonic filter and of those that do, not all of them are set correctly.  If you size the port for no filters, at least you have the worst case scenario covered.  

For example,  here is a comparison in port velocities between using a filter (yellow) and no filter (green)
 

[1point21gigawatts]

6 minutes ago, Triticum Agricolam said:

Thanks for responding to my request.  

If you were going to put 8000 watts into a 4.5 cu ft enclosure, I can certainly understand why my calculator didn't give you very usable numbers.  I never intended it to work under that kind of extremely high power situation.  My experience has been been once you get to around a 1000 watts of power per cubic foot of box volume, it becomes almost impossible to get enough port area keep port compression at a reasonable level.  Your enclosure was WAY past that point.  At those power levels you just have to do the best you can and deal with the consequences.  For this reason I put a big warning message in my calculator if you get over 1000 watts per cube.  Maybe you didn't see it when you were using my calc, but this is what it looks like. 


 

Then the enclosure was a little bigger and tuned to 34hz because I didn’t see that and I didn’t calculate 8000 watts because of rise. I think it might of been close 4.75 and 34hz. I know I said around 4.5 but honestly the main thing I remember is it telling me a port area of about 89-92sq” or something like that. Which is like 40% bigger than recommended. All I know is we keep running into problems with that calculator and the formula might be to blame. I understand the whole concept of having to increase the port because of more rms to yield better output and not have port noise (really that only involves the width), but it doesn’t have to be crazy big like your calculator tells us. Idk dude. A bunch of people are running into similar problems. 

[shredder2]

18 minutes ago, Triticum Agricolam said:

You are correct, a properly set subsonic filter will lower port velocity, but I wouldn't say it lowers it drastically.  The other problem is not everyone uses a subsonic filter and of those that do, not all of them are set correctly.  If you size the port for no filters, at least you have the worst case scenario covered.  

For example,  here is a comparison in port velocities between using a filter (yellow) and no filter (green)
 

I always setup winisd with Q factors/specific losses and temps before modeling... once the enclosure type to be used is determined. I look at loading and impedances within a desired volume tune and compromise as all enclosures have to be... no unicorns in the enclosure world but best is what you end up with. And ya.... subsonics can and will drastically affect port velocities in my exp.

And that affects port sizing... what you think will need 68in2 of port can drop to 55in2 and that affects length drastically.

[1point21gigawatts]

26 minutes ago, Triticum Agricolam said:

Thanks for responding to my request.  

If you were going to put 8000 watts into a 4.5 cu ft enclosure, I can certainly understand why my calculator didn't give you very usable numbers.  I never intended it to work under that kind of extremely high power situation.  My experience has been been once you get to around a 1000 watts of power per cubic foot of box volume, it becomes almost impossible to get enough port area keep port compression at a reasonable level.  Your enclosure was WAY past that point.  At those power levels you just have to do the best you can and deal with the consequences.  For this reason I put a big warning message in my calculator if you get over 1000 watts per cube.  Maybe you didn't see it when you were using my calc, but this is what it looks like. 


 

Well then that shows that the formula has flaw then. Because most of the people that look up to you at enclosure building run big systems and want to use your calculator. Can’t you just tweak the formula or the calculator and fix it? Tell me your theory on end correction factors. I want to clear this up because I need to understand how you come up with the numbers you were telling one guy on an old thread I came by the other day. Because the regular way to come up with the end correction is different. I want to know if you have found another variable to add in to calculate the end correction factor. I still don’t doubt you on builds and designs by any means. I’m just bummed about that port area calculator.