How Off Is RE Calculator??

[mcsoul 10+ year member]

I'll have to play with the re website and look at what you guys

are talking about.

Edit:

It looks to me that using the OP's design, the port legnth the tool

exhibits is 24.75", the actual legnth is 23.75" and if you build the box

with 23.75 with 2.9cft of volume your tune would be deeper than

30.844; by my calculations anyway. It appears re is adding the displacement

of the wood used to make the port to the figure of 2.9 (ft3). When you calculate

2.77, which is the actual ft3 displacement, the port measurments are

correct (or very close). The 24.75 measurement they use for port length

is one I cannot explain, they are just adding an inch that I cannot account for.

Basically, I'm saying the ft3 they are using is off by the displacement of the

port wood. Whatever, I'll use winISD to design the box and that RE tool looks

great to determine the cutouts for the MDF.

Just my opinion, there is a lot more brainiacs on here way better than me.

I could be way wrong.

 

[miker 5,000+ posts]

They dont add up because you guys are just using the lengths which is the inside (shortest) side of the port...if you add up the length from the middle of the port and then add half of the port's width on top of that because its a slot port (because a little bit outside of the port inside the enclosure still acts like part of the port because the wall of the port keeps going because it's the side of the enclosure..) like you should..it should add up //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
...you nubs //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

lol at you being the first to say that. //content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif

 

[brmcm15 10+ year member]

i used this calculator and it said one of my pieces of wood needed to be 52" long!

i ended up wasting $30 of mdf cause i was retarded....

 

[mcsoul 10+ year member]

Also, if anyone were to use that tool and not adjust the

default 1.5" port witdth to match the "vent mach" for

thier application (required port area); they could easily

end up with a box that sounds like ***. RE's tool does not

even mention port area, you have to know what your doing.

 

[Moe Lester 10+ year member]

RE's tool works fine. If you manipulate the numbers to fit your application there should be no issue. The program does not factor in T/S params so if the box sounded bad it is because the airspace and tuning or something else in the install is wrong.

 

[miker 5,000+ posts]

So if you figure out your displacement, and required port area before hand..

You'll be ok! ?

Now I'm leaning towards using RE instead of paying someone...

 

[mcsoul 10+ year member]

So if you figure out your displacement, and required port area before hand..
You'll be ok! ?

Now I'm leaning towards using RE instead of paying someone...

I agree with this statement, and so am I!

I'm going to use the displacement calc here:

http://www.bcae1.com/spboxnew2.htm

I'll use winISD for port calculations. Subtract out my port, port wood, bracing and speaker displacements, then use the RE tool to tell me what cuts to make.

I would not use the RE tool to make a wedge shaped ported box, I'm not sure how to calculate vent length that way, unless the interior end piece is slanted at the same angle kind of like an oval track and field finish line? Not worth it, I'll stick to a 90degree box unless someone explains how to do an agled port.

 

[Symon_say 10+ year member]

I agree with this statement, and so am I!
I'm going to use the displacement calc here:

http://www.bcae1.com/spboxnew2.htm

I'll use winISD for port calculations. Subtract out my port, port wood, bracing and speaker displacements, then use the RE tool to tell me what cuts to make.

I would not use the RE tool to make a wedge shaped ported box, I'm not sure how to calculate vent length that way, unless the interior end piece is slanted at the same angle kind of like an oval track and field finish line? Not worth it, I'll stick to a 90degree box unless someone explains how to do an agled port.

The ported calculator on BCAE1.com works just like winISD, i do a little try with all the box calculator i can get, and BCAE1.com, winISD and re tool (total lenght) and some formulas i found here and in ROE forum give pretty close numbers no more than 1" between then, but bassbox pro give a little bit off port lenght to the same tuning.

Now i'm using BCAE1.com to calculate port lenght winISD to confirm that and bassbox to see vent velocity and some other graph and data than helps me to design a better box.

PS: Re tool dont give correct numbers, the total lenght of a port should be measure in the center of the port, no matter how i calculate i couldnt make the L1 and L2 to make TL (total lenght) i draw the box in autocad and measure all the posible situacion and coulndt find it, so they might be bringing something to the equiation that i'm mising.

 

[crazyassazian 10+ year member]

It's not that off, pretty on point IMO, when I compare it to other calculators. It's just that the RE calculator measures port length on the outside wall, like someone stated before. Don't be hesitant to use it.

 

[blazinb2000 10+ year member]

I used the calculator for my last box build and it turned out fine and sounded great.

 

[IDSkoT 5,000+ posts]

I have a question, on RF's website, they say 1.79 cu. ft., is that with port displacement or with out?

 

[Farva 10+ year member]

Wow yet another thread on yet another board discussing the accuracy of the RE Calculator. First and foremost its off, but not so drastically that will render it useless! For example, say you wanted to build slot port enclosure for an FI Q12 subwoofer. After some thought your initial plan is for 2.3 cuft tuned to 32 hertz.

After playing around with it you get 2.459 cuft tuned to 32.026 hertz with 31.25 inches of port before displacements, which you believe should work. Now if you break that down and use WinISD Pro or even any accepted formula (say the one from JL Audio on Ports) you will get the results below. In this case I just used WinISD Pro for the ease of automation of the port length. I also included the equation below if you prefer using good ole mathematics. Even taking the 28.75 total port length into account (end correction adjustment) you will still be off after displacements.

Here is design straight from the calculator. (old version 1st new version 2nd)





Modeled in SketchUp.



Actual port length.



The calculator shows 28.75 inches, to account for the end correction, and yes you can see that the actual port length (taking end correction into account) adds up to 28.75 inches.

Volume of the enclosure before sub displacement (as you can see all other displacements accounted for i.e. port including end correction).



Now take into account the subwoofer displacement (Fi Q has 0.16 cuft). So now your net volume, all displacements taken into account, is 2.2 cuft. Just plug the new variables into WinISD Pro, so now your enclosure is actually 2.2 cuft tuned to 34 hertz.

Or if you prefer good ole mathematics. (the formula below differs slightly from the one on JL Audio site, but thats due to the conversion of cubic inches to cubic feet)

• Fb = 0.159*SQRT[(Av*(1.84*10^8)]/(Vb*1728*[Lv+(0.823*SQRT(Av))])
  
• Fb = 0.159*SQRT[(31.25*(1.84*10^8)]/(2.2*1728*[28.75+(0.823*SQRT(31.25))])
  
• Fb = 0.159*SQRT(5750000000/126783.36)
  
• Fb = 0.159*SQRT(45352.95)
  
• Fb = 0.159*212.96
  
• Fb = 33.86
  

So you are off a tenth or so of a cubic foot of airspace and around twoish hertz in resonance, in this case. What does this all mean? Its simple, the calculator is far from accurate but will produce a bassheads daily trunk beater. Which I believe was the intent in the first place. Now get me a d@mn liter of cola, and liter is French for give me some fawking cola!

 

[DePratt 10+ year member]

Farva the enclosure calculator is a little different now, idk if that would affect your results

 

[Farva 10+ year member]

Farva the enclosure calculator is a little different now, idk if that would affect your results

No it doesnt... I edited my post, thanks!

 

[WhoSayWho? 5,000+ posts]

Im sure they designed it too be way off and not very accurate at all.

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