Reconfiguring specs on my BTL enclosure

[bigrank916 72]

Originally I thought my enclosure specs were very close to these, tuning and volume wise:

42W" x 22H" x 22D" - outer dimensions= 9.84961ft3 gross volume

7.3ft3 net volume

tuned to 32Hz

6W" x 20.5H" for 123in2 of port area

port 1-14.5" + port 2- 7" = 21.5" port length

After reading through Chops end correction thread, Ive decided to do the math myself and find out what Ive really got. This is what Ive come up with. Im way off...

The port length is actually 27.5". I had no idea how to measure the port.

The tuning is more like 30.3Hz

port volume calculation:

6W" x 20.5H"=123in2

123in2 x 27.5"=3382.5in2

3382.5in2/1728in2= 1.96ft3 of port volume

9.84961ft3-1.96ft3(port volume)-.26ft3(driver displacement)= 7.89ft3 net volume

Now with end correction, I have come up with these numbers.

The port length is 30.5".

The tuning is actually 29.1Hz

123in2 x 30.5"= 3751.5in2

3551.5in2/1728in2= 2.17ft3 of port volume.

9.84961ft3-2.17ft3-.26ft3= 7.42 ft3 net volume

So now my specs stand corrected. The new numbers are:

42W" x 22H" x 22D"= 9.84961ft3 gross volume

7.42ft3 net volume

tuned to 29.1Hz

123in2 of port area

So in summation of enclosure calcs like RE...they sure arent exact. I knew I was close but thought it was closer than that. Get yourself a calculator, pencil, and paper and do it the right way.

Anything I missed or flubbed up?

[jcarter1885 995]

Glad you posted this because after reading that topic on end correction I was in the dark also, I just started learning how to do these the paper and pencil method (this will help me out a lot).

[bigrank916 72]

Glad you posted this because after reading that topic on end correction I was in the dark also, I just started learning how to do these the paper and pencil method (this will help me out a lot).

It seemed a bit confusing but the images on the JL site helped out a lot. Im a visual learner dude. I need the pics to really understand.

[jcarter1885 995]

You and me both

[NB50 206]

Hate to say it but your still off. You forgot 1.5" in your port length somewhere, if I had to guess it would be .75" for the front baffle and .75" for the port board after the turn(assuming your using .75" wood). Also your volume is not right, your only figuring the internal port volume, in other words you forgot to include the volume of the boards that make up the port. Just a side note also, it bothers me when people figure out the port volume separate from the enclosure and subtract it, that works fine for ports that are straight but as soon as the port turns it will mess up the volume of the enclosure and in the end tuning.

[Kanaworm$ 292]

Are you using any internal bracing?

With what you gave I come up with 8.059ft^3 before end correction.

Bromo could you tell us where were wrong?

[bigrank916 72]

Hate to say it but your still off. You forgot 1.5" in your port length somewhere, if I had to guess it would be .75" for the front baffle and .75" for the port board after the turn(assuming your using .75" wood). Also your volume is not right, your only figuring the internal port volume, in other words you forgot to include the volume of the boards that make up the port. Just a side note also, it bothers me when people figure out the port volume separate from the enclosure and subtract it, that works fine for ports that are straight but as soon as the port turns it will mess up the volume of the enclosure and in the end tuning.

Figures. Not quite sure where you got the extra 1.5" in the port length though. Measuring down the center of both ports, right? 14.5"+3"+3"+7"=27.5" physical length. Yes Im using .75" mdf.

I do understand about the board volume. I did indeed forget to account that. I came up with .13ft3 for the first port board and .06ft3 for the second port board. Sound about right?

How do I figure out the port volume in a way where it doesnt bother you? Seriously, what do you mean? How is it different for the turn?

[bigrank916 72]

Are you using any internal bracing?

With what you gave I come up with 8.059ft^3 before end correction.

Bromo could you tell us where were wrong?

No internal bracing on this enclosure. Only .169ft3 difference. What was your math for that?

[Kanaworm$ 292]

Are you using any internal bracing?

With what you gave I come up with 8.059ft^3 before end correction.

Bromo could you tell us where were wrong?

No internal bracing on this enclosure. Only .169ft3 difference. What was your math for that?

I used this except for the port ... Enclosure Volume Calculator (EVC)

I did the port math real quick at work by hand. But am distracted so more than likely way off.

[j-roadtatts 1,129]

Yeah aren't ports fun to design. I just designed my own enclosure with kerfed port and did ALL the math myself. I double checked my numbers on two port calculators and was only a 1/4 of a hertz off on tuning so I'm pretty happy.

Don't forget to cut the port wall shorter 1/2 the width/height (depending on box type) of the port.

I sent a PM to that guy on here that claims to design boxes for people but he never PMed me back after two weeks so I figured it out myself.

[bigrank916 72]

Are you using any internal bracing?

With what you gave I come up with 8.059ft^3 before end correction.

Bromo could you tell us where were wrong?

No internal bracing on this enclosure. Only .169ft3 difference. What was your math for that?

I used this except for the port ... Enclosure Volume Calculator (EVC)

I did the port math real quick at work by hand. But am distracted so more than likely way off.

What number did you use for the port volume in in3? That one threw me off. My port volume is in in2.

Edit: brain fart, got it.

[NB50 206]

Port length = .75" for the front baffle + 14.5" length to the bend + 6" of port in the bend + .75" board that makes port wall + 7" port length after bend = 29" physical port length + 3" half port width for end correction = 32" of effective port length.

Then way I calculate volume is after the port is already in the box. You cut up the spaces in to squares and add them together.

Like this, don't pay attention to the numbers in the picture it is just an example.

Where your green area is 33.75" internal width * 13.75" internal depth * 20.5" internal height = 9513.28 in^3 + (the orange area 26.75"internal width * 6.75" internal depth * 20.5" internal height = 3701.53 in^3) = 13214.81 / 1728 = 7.65 ft^3 - .26 sub displacement = 7.39 ft^3

End result looking like this.

[bigrank916 72]

Yeah aren't ports fun to design. I just designed my own enclosure with kerfed port and did ALL the math myself. I double checked my numbers on two port calculators and was only a 1/4 of a hertz off on tuning so I'm pretty happy.

Don't forget to cut the port wall shorter 1/2 the width/height (depending on box type) of the port.

I sent a PM to that guy on here that claims to design boxes for people but he never PMed me back after two weeks so I figured it out myself.

That enclosure had some math going into it, I bet. Thats pretty good to get that close too.

Actually this enclosure is already built. Just trying to figure out the real specs so I know where to go from here when I build a new one.

Those guys that make enclosures on here are super busy. At least thats what Ive always heard.

[bigrank916 72]

Port length = .75" for the front baffle + 14.5" length to the bend + 6" of port in the bend + .75" board that makes port wall + 7" port length after bend = 29" physical port length + 3" half port width for end correction = 32" of effective port length.

Then way I calculate volume is after the port is already in the box. You cut up the spaces in to squares and add them together.

Like this, don't pay attention to the numbers in the picture it is just an example.

Where your green area is 33.75" internal width * 13.75" internal depth * 20.5" internal height = 9513.28 in^3 + (the orange area 26.75"internal width * 6.75" internal depth * 20.5" internal height = 3701.53 in^3) = 13214.81 / 1728 = 7.65 ft^3 - .26 sub displacement = 7.39 ft^3

End result looking like this.

Now I see where the 1.5" extra comes from. Thanks for clearing that up. These visual aids are awesome.

Are you sure you dont want me to paypal you funds for a copy of this program?

[Kanaworm$ 292]

^^ x2 ^^

[j-roadtatts 1,129]

^^ x2 ^^

[jcarter1885 995]

x3, I tried it already. C'mon bromo help us with the box designing software.