# Improved Port Area Calculator



## Triticum Agricolam (Nov 3, 2015)

I'm sure most people here have come across the "12-16 sq in of port area per cube" guideline for slot ports and the "9-12 sq in per cube" for aeros. The problem with both of these is they only consider box volume. Both input power and tuning frequency, along with box volume, have a great effect on how much port area you need. This is why I've been recommending to people to NOT use those rules of thumb. Online you can find several websites (such as carstereo.com) that have port area calculators using the formulas developed by Dickason or Small. These have a similar problem of ignoring input power and these formulas aren't really relevant for our modern, high Xmax subs. The best solution is to use box simulation software (WinISD, BassBoxPro, etc) to determine how much port area you need based on the specifics of your system. However this is time consuming and not everyone has access to that software or has the desire to learn how to use it well. I wanted to come up with something is quick and easy to use, and should hopefully give a lot better results than the rules of thumb or the obsolete formulas. Here it is, to make this easy I'm using Google Docs:

https://docs.google.com/spreadsheets/d/1VREceNxz9YOcFlI8O_TG62-4O-l3Q2IjD5qsEkVVh28/edit?usp=sharing

This is what it looks like:



This will probably always be a work in progress, but so far I think it should work pretty well. I encourage everyone to use it and give me your feedback! Please note that due to the fact its a Google docs document multiple people can edit it at the same time. So if the number are changing on you while you use it, its someone else, just have patience.


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## Triticum Agricolam (Nov 3, 2015)

Here is how I developed the formulas that go into this. 

Most people tune their ported boxes to between 30-35 Hz, as long as you stay in that range you can ignore tuning frequency for the most part. So that leaves us with box volume and input power. I've noticed that if you view input power in terms of how many watts you have divided by box volume (which I'm calling "power density") there is a lot of similarities between different systems. For example, if you have a 4 cubic foot net volume box and you are going to be putting 2,000 watts of power into it, your power density is 500 watts per cube. Different size systems with the same power density are going to require very similar amounts of port area per cube to have similar port velocities. So a 4 cu ft, 2,000 watt system needs just about the same port area per cube as a 2 cu ft 1,000 watt system does.

When looking at systems with different power densities, a system with double the power density of a different system does not need twice the port are per cube to keep port velocities similar, it only needs about 50% more. Using that info if you calculate the power density of an enclosure (say 500 watts per cube) and then take the square root of that number (22.36) this gives us a value that can be used to calculate port area that will scale properly with different power densities. 

The absolute max port velocity I like to see through a slot port is 30 meters per second. To keep port velocities right around 30 m/sec you can multiply the square root of the power density by .605 and that will give you how many sq in per cubic foot of box volume you need. So in my example of a 500 watts per cube enclosure that means you need 13.5 sq in per cube.

Round or aero ports are tolerant of slightly higher port velocities and slot ports are, so with those ports your multiply the square root of the power density by .5445. This will give you a slightly lower required amount of port area. 12.2 sq inches in my example. 

Like I said, 30 m/sec is the max I like to see. At that point you will still be loosing some output to port compression and port noise is fairly likely. If possible using more port are than that is a good idea. I like to keep port velocities under 22 m/sec if I can. This applies to both slot and round/aero ports. To do this the number you multiply by is .82, so for my example we end up with 18.3 sq in per cube. 

Previously I said as long as you are tuning between 30-35 Hz, you can ignore what the tuning frequency is, but what if this is a bandpass box with its much higher tuning? Or what if you want to tune to the low 20s? Fortunately differences in tuning frequency affect how much port area you need similar to changes in input power. To compensate for different tuning frequencies I take the square root of the tuning and multiply it by .17677 and then multiply that by the results of my formulas above. This results in very similar peak port velocities regardless of tuning frequency.


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## DeLander (Feb 23, 2006)

Interesting. 
I'm assuming that these figures are arrived at by using RMS power and are only calculated at tuning frequency. 
Sorry. I'm kind of a noob with ported enclosures.


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## Triticum Agricolam (Nov 3, 2015)

DeLander said:


> Interesting.
> I'm assuming that these figures are arrived at by using RMS power and are only calculated at tuning frequency.
> Sorry. I'm kind of a noob with ported enclosures.


The figures are based on the maximum input power you expect to be putting into the system. 

Peak port velocity is USUALLY right around the tuning frequency of the enclosure. I included tuning frequency in the calculation because port velocity will increase at higher tunings assuming all other parameters remain the same.


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## Grinder (Dec 18, 2016)

You mention "round or aero ports," and I'm wondering if you're referring to flared ports, or ordinary tubes.

In short, I'm wondering how all of this might translate to flared ports, such as those produced by Precision Sound Products.


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## Triticum Agricolam (Nov 3, 2015)

Grinder said:


> You mention "round or aero ports," and I'm wondering if you're referring to flared ports, or ordinary tubes.
> 
> In short, I'm wondering how all of this might translate to flared ports, such as those produced by Precision Sound Products.


When I say aero ports I'm referring to a flared circular port. The ones PSP makes are a good example, but people can make their own as well. 

I think all ports should be flared, but I wanted to make sure I had all my bases covered when it comes to terminology.


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## Grinder (Dec 18, 2016)

Triticum Agricolam said:


> When I say aero ports I'm referring to a flared circular port. The ones PSP makes are a good example, but people can make their own as well.
> 
> I think all ports should be flared, but I wanted to make sure I had all my bases covered when it comes to terminology.


Thank you for the clarification; and most of all, for all of the interesting thoughts and information you've shared in this thread!!!


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## Hillbilly SQ (Jan 26, 2007)

I feel like this is the proper thread for me to bring up this question that has bugged me for a while. When a flared port has a pretty severe flare on the inside of the box how much compensation is needed to prevent chuffing when you're trying to shove 6" of funneled air into a 4" port? I just think of all the times I've been in a line where we were moving pretty good and then a bottleneck (like a guy not getting his Suburban out of the way of an exit before 55,000 people left a stadium at one time) caused the massive inflow to trickle out in pairs. An aeroport seems like it would cause this same problem if you don't go bigger than you would normally use for a standard pvc port. That said, I'm using an aeroport in my current build without the inside flare. Not because I was afraid of what I described above because the sub is low xmax but because I didn't feel like cutting the center piece that was about right for length without the inside flare:blush:


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## Grinder (Dec 18, 2016)

Hillbilly SQ said:


> I feel like this is the proper thread for me to bring up this question that has bugged me for a while. When a flared port has a pretty severe flare on the inside of the box how much compensation is needed to prevent chuffing when you're trying to shove 6" of funneled air into a 4" port? I just think of all the times I've been in a line where we were moving pretty good and then a bottleneck (like a guy not getting his Suburban out of the way of an exit before 55,000 people left a stadium at one time) caused the massive inflow to trickle out in pairs. An aeroport seems like it would cause this same problem if you don't go bigger than you would normally use for a standard pvc port. That said, I'm using an aeroport in my current build without the inside flare. Not because I was afraid of what I described above because the sub is low xmax but because I didn't feel like cutting the center piece that was about right for length without the inside flare:blush:


Good question.

I'm talking way out of school here, but I think chuffing is caused by the sharp corners of a non-flared port, and compression would tend to reduce velocity, but not necessarily (or directly?) result in chuffing.

In any case, I'm eager to hear what the experts have to say.


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## Grinder (Dec 18, 2016)

...and I'm dealing with an issue right now, where I'm getting chuffing from an 8.5" long 3" PVC port (8" sub in 1 cube, approximately 42 Hz tune). I've just pulled out it and thrown in a Precision Sound 3" flared port kit, at it's full 17" length, just to see what would happen.

Chuffing is almost entirely gone, and air movement (velocity?) is waaaaaay down (not at all sure why). Now I'm going to cut it down to about 9.5 inches and see what happens.


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## Grinder (Dec 18, 2016)

At 17" I was seeing a 27Hz tune (point of least excursion with tone generator, no x-overs, no EQ).

Now, at 9.5" long, I'm up to 37Hz, with almost no chuffing, and still waaaaaay less apparent air movement (with the 3" x 8.5" PVC I was getting blasts of air at times from a far as 7 feet away, and now I can feel very light air movement with my hand 6 or 7 inches in front of the port), but output seems to be, if I'm not mistaken, noticeably higher than with the 3" x 8.5" PVC port (which, I just remembered, I was supposed to have been trimmed down from 8.5" to achieve the 42 Hz target, whereas at 8.5" I think it was actually doing something more like 39Hz). I need to trim it a bit more and see what happens.

I've heard that higher port velocity = higher output (to a point anyway), and I must have wrongly interpreted that strong blast of air I was getting, as high velocity, when maybe it's more akin to laminar flow, or resulting from higher pressure. IRDK. But it really does seem that output has increased, despite the seemingly reduced airflow. Interesting...

In any case, I sincerely apologize if any/all of this is out of place or otherwise unwanted in this thread, as I'm not so clear on protocol...


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## Triticum Agricolam (Nov 3, 2015)

Grinder said:


> At 17" I was seeing a 27Hz tune (point of least excursion with tone generator, no x-overs, no EQ).
> 
> Now, at 9.5" long, I'm up to 37Hz, with almost no chuffing, and still waaaaaay less apparent air movement (with the 3" x 8.5" PVC I was getting blasts of air at times from a far as 7 feet away, and now I can feel very light air movement with my hand 6 or 7 inches in front of the port), but output seems to be, if I'm not mistaken, noticeably higher than with the 3" x 8.5" PVC port (which, I just remembered, I was supposed to have been trimmed down from 8.5" to achieve the 42 Hz target, whereas at 8.5" I think it was actually doing something more like 39Hz). I need to trim it a bit more and see what happens.
> 
> ...


So a higher amount of air through the port = higher output, this is not the same as higher port velocity though. High port velocity is actually bad for output because air resistance increases exponentially with velocity (a 2x increase in velocity causes a 4x increase in air resistance). This air resistance is what causes port compression and robs you of output. 

Flared ports help the air make a smooth transition from the port to the surrounding area. This reduces air resistance and port noise. For this reason you can usually use a slightly smaller port if it has flares on the ends.


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## Triticum Agricolam (Nov 3, 2015)

Hillbilly SQ said:


> I feel like this is the proper thread for me to bring up this question that has bugged me for a while. When a flared port has a pretty severe flare on the inside of the box how much compensation is needed to prevent chuffing when you're trying to shove 6" of funneled air into a 4" port? I just think of all the times I've been in a line where we were moving pretty good and then a bottleneck (like a guy not getting his Suburban out of the way of an exit before 55,000 people left a stadium at one time) caused the massive inflow to trickle out in pairs. An aeroport seems like it would cause this same problem if you don't go bigger than you would normally use for a standard pvc port. That said, I'm using an aeroport in my current build without the inside flare. Not because I was afraid of what I described above because the sub is low xmax but because I didn't feel like cutting the center piece that was about right for length without the inside flare:blush:


An aeroport (well flared round port) allow you to use a slightly smaller port under most conditions due to smoother airflow. The best solution is to just use a large enough port to begin with though. 

When it comes to adding flares, the recommendation I see most is to make the flare radius 1/4 of the diameter of the port. So a 2" port would want a 1/2" flare radius, a 3" port gets a 3/4" flare radius, etc.


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## Grinder (Dec 18, 2016)

Triticum Agricolam said:


> So a higher amount of air through the port = higher output, this is not the same as higher port velocity though. High port velocity is actually bad for output because air resistance increases exponentially with velocity (a 2x increase in velocity causes a 4x increase in air resistance). This air resistance is what causes port compression and robs you of output.
> 
> Flared ports help the air make a smooth transition from the port to the surrounding area. This reduces air resistance and port noise. For this reason you can usually use a slightly smaller port if it has flares on the ends.


Thank you. That makes sense.

Can a given sized flared port _seem_ to move less air than the same size non-flared port tube (while _actually_ moving _more_ air, of course), due to differences in how air enters and/or exits a flared port, versus a non-flared port (I'm trying to understand the blast of air I was getting from the 3" PVC tube, versus the seemingly much lighter air movement of the 3" flared port)?


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## Justin Zazzi (May 28, 2012)

I'm curious how your method of power density in watts per cubic foot compares to using something like maximum displacement combined with frequency, which is what I think most simulation programs use for this kind of thing. If you know maximum displacement (from cone area and Xmax) and you know amplitude vs frequency (from box tuning), then you can chart velocity vs frequency.

It seems like it would not be too hard to build a spreadsheet similar to what you have done but with the displacement/frequency method. I'm really curious how that would compare in terms of numbers.


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## Triticum Agricolam (Nov 3, 2015)

Jazzi said:


> I'm curious how your method of power density in watts per cubic foot compares to using something like maximum displacement combined with frequency, which is what I think most simulation programs use for this kind of thing. If you know maximum displacement (from cone area and Xmax) and you know amplitude vs frequency (from box tuning), then you can chart velocity vs frequency.
> 
> It seems like it would not be too hard to build a spreadsheet similar to what you have done but with the displacement/frequency method. I'm really curious how that would compare in terms of numbers.


Both Small and Dickason developed port area formulas decades ago based on cone displacement. Here is a good example of a port area calculator using those formulas: Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Those calculators have a big flaw though, they assume you are going to be pushing a sub to its Xmax. With today's high Xmax subs in many cases it isn't even possible to push a sub to its Xmax in a ported box without burning it up. So with those formulas what you get is ridiculously oversized port area recommendations.

Also those calculators completely ignore input power, which has as big of an effect as anything on how much port area you need. If you have sub with 30 mm of Xmax and you are only going to feed it 500 watts you don't need the same amount of port area if you were going to give it 2500 watts.

While it may seem very counter-intuitive, when it comes to how much port area you need, cone displacement (or cone area in general) just don't matter much.


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## Justin Zazzi (May 28, 2012)

Triticum Agricolam said:


> Those calculators have a big flaw though, they assume you are going to be pushing a sub to its Xmax.
> 
> .....
> 
> Also those calculators completely ignore input power, which has as big of an effect as anything on how much port area you need. If you have sub with 30 mm of Xmax and you are only going to feed it 500 watts you don't need the same amount of port area if you were going to give it 2500 watts.


Okay, think I see your approach now. You're saying that since the cone excursion in a ported box in generally lower overall, and since people tend to put woofers into them that are capable of tremendous excursion (which ends up not being used to the fullest), that using the woofer's value of Xmax is not the best value when determining displacement capability of the woofer, and in turn determining the minimum port diameter you should use.

It seems like your calculator uses power density as an input because you're making the assumption (likely a fair one to make too) that most subwoofers used in ported boxes in cars have a similar sensitivity rating, or at least similar enough that you can make a "rule of thumb" assumption when building your calculator.

Did I understand you right?

If that is the case, you might want to emphasize the importance of a sub-sonic high-pass filter. The excursion of a woofer might be less than Xmax in most cases, but it can certainly exceed it below port resonance, and very quickly at that. Since your tool is allowing us the flexibility to use a slightly smaller port diameter, then the turbulence caused by excessive excursion below resonance will be worse, and the importance of a sub-sonic filter will be greater.

I like what you've done here, and I look forward to reading more of what you come up with !


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## nineball76 (Mar 13, 2010)

Smaller? Using this calculator my port went from being 15" long to 41" long while keeping a 35hz tune. Optimal port area being 24" per cube! 

Sent from my LG-V20 using Tapatalk


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## Triticum Agricolam (Nov 3, 2015)

Jazzi said:


> Okay, think I see your approach now. You're saying that since the cone excursion in a ported box in generally lower overall, and since people tend to put woofers into them that are capable of tremendous excursion (which ends up not being used to the fullest), that using the woofer's value of Xmax is not the best value when determining displacement capability of the woofer, and in turn determining the minimum port diameter you should use.


Yup, pretty much. I will just add that displacement capability really isn't related to port area needed.



Jazzi said:


> It seems like your calculator uses power density as an input because you're making the assumption (likely a fair one to make too) that most subwoofers used in ported boxes in cars have a similar sensitivity rating, or at least similar enough that you can make a "rule of thumb" assumption when building your calculator.
> 
> Did I understand you right?


For port area calculations, the sensitivity of the sub isn't really important, for the same reason that cone displacement isn't really important. At the frequency where port velocity is the highest its really the enclosure that is playing, not the sub. There is virtually no output from the cone and very little excursion. For this reason I don't need to make any assumptions about driver sensitivity.




Jazzi said:


> If that is the case, you might want to emphasize the importance of a sub-sonic high-pass filter. The excursion of a woofer might be less than Xmax in most cases, but it can certainly exceed it below port resonance, and very quickly at that. Since your tool is allowing us the flexibility to use a slightly smaller port diameter, then the turbulence caused by excessive excursion below resonance will be worse, and the importance of a sub-sonic filter will be greater.
> 
> I like what you've done here, and I look forward to reading more of what you come up with !


Sub-sonic filters really are a completely different issue. If someone is expecting to play much below the tuning frequency, they should be using a high pass filter regardless of port area, IMHO. Really they should use a high pass filter whether they are expecting to need it or not. 

While in some cases my tool may make people aware that they can use less port area, I think in a lot more cases it will indicate to people that they need to use MORE port area. Especially when it comes to the SPL folks and round (aero) ports. Those are quite often undersized.


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## Triticum Agricolam (Nov 3, 2015)

What motivated me to make this calculator was a discussion I was involved in on Facebook a couple days ago. Someone had two FI SP4-15 subs in a 8 cu ft box, they wanted tuned to 35 Hz, on 9k watts of power and wanted to know if three 6" aero ports was enough. 

You had people who blindly adhere to the guideline "9-12 sq in of port per cube for aero ports". Three 6" ports is about 90 sq in, so they thought he was good to go. 

Then you had someone else who posted a link to a port area calculator that used Dickason's formula (Xmax based), it said you need 337 sq in of port.....per sub. 

The answers from both groups of people were equally unreasonable. I wanted to make something that would be as easy to use as possible and provide a much more accurate result.


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## Grinder (Dec 18, 2016)

Bump.

Sticky?


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## Holmz (Jul 12, 2017)

Triticum Agricolam said:


> Here is how I developed the formulas that go into this.
> 
> ...
> 
> ...


I am trying to follow along...
Do all ^those factors^ and ^numbers^ map to some physics in a direct way?
Or are the numbers based upon some empirical observations?




Grinder said:


> Good question.
> 
> I'm talking way out of school here, but I think chuffing is caused by the sharp corners of a non-flared port, and compression would tend to reduce velocity, but not necessarily (or directly?) result in chuffing.
> 
> In any case, I'm eager to hear what the experts have to say.


I am no expert either, but ^that^ is my understanding too.

And engine intake trumpets operate at much higher velocities, but the trumpet guide the air into the runner, which is perhaps a comibination or retaining a non turbulent flow, and something analogous to matching impedance between the tube and the outside world like a compression driver??


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## Grinder (Dec 18, 2016)

Holmz said:


> .... I am no expert either, but ^that^ is my understanding too.
> 
> And engine intake trumpets operate at much higher velocities, but the trumpet guide the air into the runner, which is perhaps a comibination or retaining a non turbulent flow, and something analogous to matching impedance between the tube and the outside world like a compression driver??


I now see (I think) that, given sufficient power, vent compression would tend to increase (rather than reduce) vent velocity; and that, with increased vent resistance/compression/velocity, we will reduce output potential long before we induce chuffing (especially when using flared vents).

While I don't know much about intake trumpets (aka "velocity stacks" - https://en.wikipedia.org/wiki/Velocity_stack), air velocity and turbulence, it seems that for engines and bass reflex systems alike, more airflow (vent resonance) = more power (output).


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## Grinder (Dec 18, 2016)

Holmz said:


> .... I am no expert either, but ^that^ is my understanding too.
> 
> And engine intake trumpets operate at much higher velocities, but the trumpet guide the air into the runner, which is perhaps a comibination or retaining a non turbulent flow, and something analogous to matching impedance between the tube and the outside world like a compression driver??


From https://www.diymobileaudio.com/foru...-discussion/169290-port-size-vs-box-size.html :

I highlighted the portion that might (?) address your interesting intake trumpet analogy.



Andy Wehmeyer said:


> Ive been designing boxes for nearly 30 years using lots of different programs. My go-to is LEAP.
> 
> I don't understand the port area vs. box volume rule of thumb either. What really determines the necessary port area is the velocity of air in the port and that depends on the size of the cone and the strength of the motor. At Fb, the radiation impedance inside the box is VERY high, and the motor and the cone drive the resonance. For any given port area, the velocity in the port increases as more power is applied to the woofer. The woofer doesn't move much.
> 
> ...


You might find this thread interesting as well:
https://www.diymobileaudio.com/foru...generate-more-spl-without-spending-penny.html



...and with the final paragraph of the above A.W. quote, and with just a glance (so far) at the above linked DIYMA thread, suddenly this interesting non-parallel vent tube shape comes to mind:


Oscar said:


> .... Going back to ports, this is the one I was talking about, ad Parts Express still has them @ $4 each.
> 
> 
> 
> ...


...though, unfortunately, they're no longer available ...and I never got around to ordering some.  https://www.parts-express.com/flared-port-tube-3-id-x-11-l-with-5-flared-ends--269-165


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## N2ne (Mar 29, 2020)

If I may does or does nitot the mech mass play a part in the given velocity of movement as a lighter softer suspension need less area than one with a stiffer heavier moving I.e. 500 watts on a 2 inch cool will have a more coefficent output compared to the heavier stiffer design there for creating a more sustainable fluent velocity in a given port area on less power because the mass of the air particles will be separated much much easier than that of hotter stiffer more friction based suspension causing the seperation needing longer not necessarily more area so they have time separated and form a uniformed patter.in this case chuffing smoother slicker surface.we use release wax will increase out put more efficiently.so would you say that mechanical mass may need to be accounted for also the actual surface of which the air is to travel across.so we could say a smoother less grippy surface will produce less blow and more veo.given the proper length and right suspension to output efficiency of said power source? Or would one care the surface as hot air caused from friction of larger mass air particles. Doesnt have an effect on port area as mechanical mass doesn't matter as the particles of air have the same mass none heavier than the other there for not having an effect on port noise or active compression in the given area of release hmmmmmmmm? We test use mold release wax flare and unflare the same port material and then base each test of individual theory to single out the most notable variable to cause a anomaly in the test and then test it as a whole.or maybe i need to get a girlfriend.😀😀.I say we try and see what happens from pvc hep avm pp plu fg wood and so on.


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## jasonrodgers07 (6 mo ago)

Triticum Agricolam said:


> I'm sure most people here have come across the "12-16 sq in of port area per cube" guideline for slot ports and the "9-12 sq in per cube" for aeros. The problem with both of these is they only consider box volume. Both input power and tuning frequency, along with box volume, have a great effect on how much port area you need. This is why I've been recommending to people to NOT use those rules of thumb. Online you can find several websites (such as carstereo.com) that have port area calculators using the formulas developed by Dickason or Small. These have a similar problem of ignoring input power and these formulas aren't really relevant for our modern, high Xmax subs. The best solution is to use box simulation software (WinISD, BassBoxPro, etc) to determine how much port area you need based on the specifics of your system. However this is time consuming and not everyone has access to that software or has the desire to learn how to use it well. I wanted to come up with something is quick and easy to use, and should hopefully give a lot better results than the rules of thumb or the obsolete formulas. Here it is, to make this easy I'm using Google Docs:
> 
> Triticum's Improved Port Area Calculator
> 
> ...


Triticum,

I stumbled upon your calculator and really liked the concept. It made a lot of sense. You are definitely on to something! I enjoyed combining and adding to your calculator.

*1.) With the Tuning Frequency adjustment 'factor':*

The tuning adjustment factor of 0.176776695296637 is simply a fixed parameter, and was found to be the inverse of the square root of the tuning frequency = 1/32^0.5 (32Hz) only. So, 32Hz was the only frequency that would be accurate; any frequency above or below 32Hz the frequency adjustment factor will be incorrect.

*2.) With the Power Density 'factors': at 59 deg/F*
0.605 (for 30m/sec) was found to be constrained for a Volume (Vb) = 2.521ft^3.
0.5445 (for 32m/sec) was found to be constrained for a Volume (Vb) = 2.8ft^3.
0.82 (for 22m/sec) was found to be constrained for a Volume (Vb) = 1.86ft^3.

However, all three were factors for the 'Power to Volume' ratios (Power Density) as fixed correction factors. All 'factors' for tuning and power density, under each desired 'port air velocity' were off and giving incorrect values against any combination of: enclosure volume, power, tuning.

So, I set-out to identify and solve for these 'factors'. This will allow us to design/build more accurately! Win-Win!

*Additions to the base-line calculator: 

Additions:*
For inputs, I included 'Air Temperature' (deg/F), '# of Ports' (quantity), and a 'Desired Slot Port Height' (inches).
For outputs, I added 'Port Length' (inches), Port Diameter (if a circle is desired), Port Width (if a slotted port is desired), Slotted Port 'ratio', and a few other things.

*'In-Work':*
I'm currently implementing the '# of Ports' as a functioning input variable for the spreadsheet, but I at least wanted to get this info and spreadsheet out to you, or anyone else that finds this of interest. I will include this feature, plus a few other ideas I'm kicking around, and will include them on a future version update, stay tuned!

_*UPDATE* _ Today, I implemented the '# of Ports' into the formulas. NOTE: Be aware that when you have more than one port, the cells will display the port specifications for EACH port (Labeled 'per Port'). I also added scroll-bar sliders for each port air velocity, which makes it easy to manipulate values to meet you goal(s).

*Thought Process:*

Initially, I knew I had to separate ALL variables. I then created two separate tables. One table for the tuning 'frequency adjustment', and one table for the 'volume adjustment'. These were centered around each port air speed (30m/sec^2, 32m/sec^2, and 22m/sec^2), for the time being. At this point, I had six tables in total (one for each port velocity times two functions); three for the 'frequency adjustment' versus frequency and three for 'volume adjustment' versus volume. I found that all of their 'slopes' to be descending logarithmic curves. From these curves, I was able to arrive at a solution, and combine them into a condensed and complete formula. I then combined the datasets from both charts into one chart. For each port air velocity, where the lines crossed, this was the corollary factor, based on the given inputs: Volume, Frequency, Power, and Velocity.

I found that the power to volume (Power Density) ratio isn't a stand-alone factor by itself, but was strictly related to the enclosures volume (Vb net) only, at this point. The 'tuning' and 'power' input parameters are both stand-alone variables, irrespective of the Volume (Vb net). Both the Tuning Frequency parameter (Fb) and the Power (Watts), has a direct-relationship/tied to and imbedded within the 'Equivalent Diameter' formula (See: Step 3), and again, Power (Watts) has a direct-relationship/tied to the 'Combined Constant' (K) (See: Step 6).

*Solution Process:*

To solve for the individual 'volume correction factors' (k'), I used the tables I made, mentioned previously, and I found the logarithmic slope solution as the 'raw' k'-value(s) (constants) factor(s), for each 'desired preset' port air speed, but we cannot simply use these yet! To solve for the 'Combined Constants' (K), I had to work the problem in reverse.

*Preliminary solution for the individual 'volume correction factor' constants (k'): *

For slotted ports at: 30meters/sec^2: k' = 1.35611297481307 * Vb net^-0.999999999999998
For round/aero ports at: 32meters/sec^2: k' = 1.27135591388727 * Vb net^-1
For slotted/round/aero ports at: 22meters/sec^2: k' = 1.8492449656542 * Vb net^-1

*Solution for the 'combined correction factor' (K), in reverse: 

Step 1.)* Speed of Sound (c) = 6.43855 * ((Temp-32)*(5/9)+273.15)/273.15)^0.5
*Step 2.)* Mach % = (Velocity meters/sec^2 / 0.3048) / c
*Step 3.)* Equivalent Diameter = (((((13.7*Power^0.5)/Frequency)/10)/Mach %)^0.5)*2
*Step 4.)* Port Area required = Pi * (Equivalent Diameter / 2)^2
*Step 5.)* Port Area per ft^3 = Port Area required / Port Air Velocity
*Step 6.)* K = Port Area per ft^3 / Power^0.5

*Here are a few examples:

Example Enclosures #1 and #2 are for 30meters/sec^2 peak port air velocity: *

Example Enclosure #1: 2ft^3, 800W, 31Hz, at 59deg/F: The combined correction factor is: K = 0.7872139103521520, not 0.605.

Example Enclosure #2: 2ft^3 800W, 34Hz, at 59deg/F: The combined correction factor is: K = 0.7717783434825020, not 0.605.

*Example Enclosures #3 and #4 are for 32meters/sec^2 peak port air velocity: *

Example Enclosure #3: 5.625ft^3, 4500W, 26Hz, at 95deg/F: The combined correction factor is: K = 0.3235427144827520, not 0.5445.

Example Enclosure #4: 5.625ft^3, 4500W, 36Hz, 95deg/F: The combined correction factor is: K = 0.2336697382375430, not 0.5445.

*Example Enclosures #5 and #6 are for 22meters/sec^2 peak port air velocity: *

Example Enclosure #5: 4ft^3, 2000W, 32Hz, at 72deg/F: The combined correction factor is: K = 0.5264396195869420, not 0.82.

Example Enclosure #6: 4ft^3, 2000W, 35Hz, 22m/sec, 72deg/F: The combined correction factor is: K = 0.4813162236223470, not 0.82.

*Here is the final solution:

Temperature = T (deg/F)
Volume = Vb (ft^3)
Power = P (Watts)
Frequency = *_*fb (Hz)*_
*Velocity = Vp (meters/sec^2)

Area per Cubic Foot (in^2/ft^3) =* *((PI() * ((SQRT((((13.7 * SQRT(P))/fb)/10)/((Vp^2/0.3048)/(643.855(((T-32) * (5/9)+273.15)/273.15)^0.5*1.687809858)))*2)/2)^2)/Vb)

Screenshot:*









*Google Sheets Link: Improved Port Calculator (Ver 1.1)

Excel version of spreadsheet: Available by request 

Note: I made 'scrollbar-sliders' for the Input Variables. These will not be displayed in the Google Sheets version.

Please feel free to correspond or contact to discuss. 

Thank you,

Jason *


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## Justin Zazzi (May 28, 2012)

jasonrodgers07 said:


> Triticum,
> 
> I stumbled upon your calculator and really liked the concept. It made a lot of sense. You are definitely on to something! I enjoyed combining and adding to your calculator.
> 
> ...


Hi Jason! What an amazing first post you made there.

I would love to explore a copy of the excel version (and also see how those slider bars work).

This is fascinating!


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## jasonrodgers07 (6 mo ago)

Justin Zazzi said:


> Hi Jason! What an amazing first post you made there.
> 
> I would love to explore a copy of the excel version (and also see how those slider bars work).
> 
> This is fascinating!


Hey Justin. 

Thank you very much. Happy to be here. 

I would be more than happy to share a copy of the Excel file when I finish, but the website will not allow *.xls file types as attachments. The sliders definitely make quick-work of manipulating the input parameters.

I found a few minor bugs in my calculator and I'm still working on incorporating '# of Ports' (quantity) into the formulas.

I will post a link to the revised version when I'm finished.

Jason


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## jasonrodgers07 (6 mo ago)

I've made a lot of additions and reorganized the sheet. I applied quite a bit of 'conditional formatting' to the cells. This makes it super-quick work to iterate out a solution for a given design; In addition to the sliders, the conditional formatting makes it fool-proof to design ANY port (for a 3rd Order Enclosure) SUPER EASY. Too, I made three 'GYR' color scale pictures to further aid for the 'Port Air Velocity' slider.

Due to the complexity and involvement of the spreadsheet, this version (Ver 1.3) will be available only by request, and not on google sheets.

*Screenshot:*









Thank you,

Jason


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## Justin Zazzi (May 28, 2012)

Thank you for sharing your work.
I forgot how much fun this topic is.


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## PRP98svt (Oct 29, 2009)

Hi, unfortunately I cannot send a PM, but would it be possible to receive a copy of this?
Thanks!
Patrick





jasonrodgers07 said:


> I've made a lot of additions and reorganized the sheet. I applied quite a bit of 'conditional formatting' to the cells. This makes it super-quick work to iterate out a solution for a given design; In addition to the sliders, the conditional formatting makes it fool-proof to design ANY port (for a 3rd Order Enclosure) SUPER EASY. Too, I made three 'GYR' color scale pictures to further aid for the 'Port Air Velocity' slider.
> 
> Due to the complexity and involvement of the spreadsheet, this version (Ver 1.3) will be available only by request, and not on google sheets.
> 
> ...


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## pwnt by pat (Mar 13, 2006)

Holmz said:


> I am trying to follow along...
> Do all ^those factors^ and ^numbers^ map to some physics in a direct way?
> Or are the numbers based upon some empirical observations?
> 
> ...


Guide is a bit of a misnomer, but essentially yes.

What happens with flow in a tube is similar to baffle step for a speaker. You end up with a pressurized reflection off the edge. On a tube, since it's round, this reflection comes from every direction at once. The result of this is the reflection actually creates a stall, a dead air space in the area, and reduces the effective throat area of the tube. The radius entry pushes the edge of the tube farther away from the throat and diffuses the pressurized zone.

I think I have a research paper about it on my laptop with pressure gradient graphs I'll see if I can find tonight

essentially this


https://www.highpowermedia.com/retimages/induction-system_profiles.jpg


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## jasonrodgers07 (6 mo ago)

PRP98svt said:


> Hi, unfortunately I cannot send a PM, but would it be possible to receive a copy of this?
> Thanks!
> Patrick


Sure man. When I'm done with it. I'm adding lots of things to it. I'm slow getting finished because Thanksgiving and all.


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## jasonrodgers07 (6 mo ago)

Ok guys, I finally had some time to sit down and finish this calculator up. Here it is! Message me if you would like a copy. Lemme know if you find any discrepancies/errors, thx!

-Jason

PS: I also made a 2nd Order Calc for sealed enclosure design.

Here is the 3rd Order Enclosure Calc for Slotted Ports:


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## jasonrodgers07 (6 mo ago)

Here is a screen shot of my Sealed Enclosure Calc. 

-Jason


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