New Box Design + calculations=aren't adding up.. PICS

[snb778 1]

Hey guys,

I have been talking to a member on here about some calculations I used from BCAE1.com, and something just isnt adding up right.. here is a pic of the box I HAD DESIGNED by a member, so I trust this will work, but I just wanted to enter in the info on BCAE1 to see if they would give me about the same specs.. NOPE....>>>>>>>>

This is the box I want to build... but when I put the specs into the BCAE1 site... it tells me to build a 1.3" port... what am I doing wrong here with this program?????????

Height? =15 Inches

Width? = 39.5 Inches

Depth1? =26.5 Inches

Depth2? = 26.5 Inches

If the above dimensions are OUTSIDE dimensions, enter the thickness of the wood below.

Wood Thickness? =.75 Inches

Speaker Displacement? = .246 Ft

[snb778 1]

someone please?? This is frusterating... I want to be able to start to build my own boxes, but I dont get how to calculate port size, and something isn't goin right with what I'm doin here

I payed 20 bucks for the design, just because I don't know how to do port's....the rest I can do.

Thx

[Mike P. 0]

You have net volume of 7.2 cubic feet. To tune it to 38hz with a 5 inch round port, the port length needs to be 1.4 inches. Port area is 19.63 square inches.

Edited May 5, 2008 by Mike P.

[snb778 1]

You have net volume of 7.2 cubic feet. To tune it to 38hz with a 5 inch round port, the port length needs to be 1.4 inches. Port area is 19.63 square inches.

See I dont like that part of that site because I don't want a round port, yet it asks for port diameter... But where you enter, "Sq. Port Ratio H:W? = 1: .5 " that means you want a rectangle port as far as the calculation is concerned..

But you're saying even if i wanted a 5" round port for 2 15"s in a 7.2cu. ft. box the port would only be 1.4" long???? I'm so lost

[Mike P. 0]

What size port do you want to use?

[snb778 1]

What size port do you want to use?

I want to use the port designed in the picture above... a slot port that is 15" tall, and 5.5" wide that is 13.25" in length

But that program isn't giving me anywhere near that

[Mike P. 0]

Your pic isn't showing up for me. Anyways, a slot port that is 15" tall, and 5.5" wide that is 13.25" in length will tune your box to 38hz. It's all good!

[snb778 1]

Right, BUT... my problem is I had to pay someone 20 bucks to design that, and I want to be able to do it on my own...

Entering all the same info on that site gives me a 1.2" port length, not 13.25... see my problem. I don't understand why its giving me a 1.2" port

Edit: that pic in my first post isnt showing up??... I see it... hmmmmh

Edited May 5, 2008 by snb778

[tezin87 0]

go to reaudio.com and use their box builder

and your port would only be 13.5'' tall if your box was 15'' tall (subtract 3/4'' for top and bottom of box)

Edited May 5, 2008 by KHARPS

[Mike P. 0]

It appears that program is only for round ports. Since your slot port is 15" tall, and 5.5" wide, it has a surface area of 82.5 square inches. A round port would need to be 10.25 inches diameter to have the same surface area as your slot port. Enter 10.25 port diameter into the program and see what length you get.

I agree with the above poster. It looks like a much better program.

http://reaudio.com/speaker_box/LPort_Box_Calc.html

Edited May 5, 2008 by Mike P.

[snb778 1]

It appears that program is only for round ports. Since your slot port is 15" tall, and 5.5" wide, it has a surface area of 82.5 square inches. A round port would need to be 10.25 inches diameter to have the same surface area as your slot port. Enter 10.25 port diameter into the program and see what length you get.

10.25 gives me this....

Box Front Angle =90 Degrees

Gross box volume =7.176 Ft3

Net box volume = 6.393 Ft3

Port Length = 16.4 Inches

Port Area = 82.5 Inches2

Port Volume =.73 Ft3

little closer, but still a few" off.. im gonna try RE site and see what it gives me real quick.

thanks for the help

[snb778 1]

It appears that program is only for round ports. Since your slot port is 15" tall, and 5.5" wide, it has a surface area of 82.5 square inches. A round port would need to be 10.25 inches diameter to have the same surface area as your slot port. Enter 10.25 port diameter into the program and see what length you get.

I agree with the above poster. It looks like a much better program.

http://reaudio.com/speaker_box/LPort_Box_Calc.html

I just went there, and that program asks for the "Square Port Length 1, and Square port length 2" which is what I don't know how to do...assuming I didnt already have a box designed for me... but what would I put in there anyways?

but yes that seems like a MUCH better program

[tezin87 0]

i just realized reaudio's program is for L-shaped ported enclosures. so the length of the first port wall will automatically be one port width away from the back wall because they are expecting you to add another port wall to the right. so if you don't want to use an L-shape port, you might not want to use this program. the shortest they're going to let you make the port is 20.25'' (26.5-.75 for the back of the box-5.5 for the width of the port) and that gave you a tuning of 29hz i believe.

[snb778 1]

i just realized reaudio's program is for L-shaped ported enclosures. so the length of the first port wall will automatically be one port width away from the back wall because they are expecting you to add another port wall to the right. so if you don't want to use an L-shape port, you might not want to use this program. the shortest they're going to let you make the port is 20.25'' (26.5-.75 for the back of the box-5.5 for the width of the port) and that gave you a tuning of 29hz i believe.

ahhhh thats to bad!!! ahhh, i wanna verify this design in right!

I guess I could just make the port wider, and make an L.... I've just never seen a port with 1 piece, and no L shape.... is that ok?

Edited May 5, 2008 by snb778

[KU40 173]

get winISD. www.linearteam.dk. I use the pro version. so very simple. It just doesn't give you cutout dimensions, but with 2 minutes and a little brain power you can figure those out. To change between rectangle and round port just click on the port shape.

[shizzzon 461]

I got THE THING that you need.

Bookmark this site-

http://www.carstereo.com/help/Articles.cfm?id=31

go down a little and there you have it, make sure you choose slot port because slot port changes the physical length required compared to a square\round port because acoustical length is increased by sharing part of the enclosure.

Oh, and the REAL length required is about 11", 11.14" to be exact. (this is for 7.2 cubes net)

Remember, slot ports require less physical length as mentioned above.

It is rare to find a slot port calculator, that's why i made a thread about it the other day until i found this calculator.

Because slot ports use less physical length, they displace less... meaning that you will gain a little volume back inside the enclosure as well.

[snb778 1]

I got THE THING that you need.

Bookmark this site-

http://www.carstereo.com/help/Articles.cfm?id=31

go down a little and there you have it, make sure you choose slot port because slot port changes the physical length required compared to a square\round port because acoustical length is increased by sharing part of the enclosure.

Oh, and the REAL length required is about 11", 11.14" to be exact. (this is for 7.2 cubes net)

Remember, slot ports require less physical length as mentioned above.

It is rare to find a slot port calculator, that's why i made a thread about it the other day until i found this calculator.

Because slot ports use less physical length, they displace less... meaning that you will gain a little volume back inside the enclosure as well.

very cool, I will try it in a sec. I just downloaded WinISD pro... doesnt have alpine in there for some reason, but I'm gonna see if I cant download the technical data myself.

THanks for all the help again guys! I just want to figure out how to calculate port instead of payin someone else to do it for me...if its this easy.

Edit: just tried that website... told me 10" for:

Enclosure volume: 7.4

Disired tuning frequ.: 38

Vent Height: 13.5

Vent Width: 6"

Edited May 5, 2008 by snb778

[shizzzon 461]

T/S parameters have NOTHING to do with tuning a box so pick any sub in there and calculate your port length.

WinISD does NOT calculate slot port designs so your design will not be accurate with WinISD.

[Mike P. 0]

A slot port is a rectangular port and WinISD will model it. All you so is subtract the volume of the port from the volume of the cabinet to get the net volume. It works fine for me.

[shizzzon 461]

No, a slot is NOT a square port.

A slot port is a square port that uses 3 of it's 4 walls from the enclosure wall.

Looking into the port from outside, when you reach the end of the port, the acoustical length is LONGER than a square ports because it is still using the enclosure's walls as part of the port.

IF you did not know this then the designs that you have done for yourself are actually tuned lower than you think.

[Mike P. 0]

In theory yes, but does it matter in the real world? Model the same size sub and port in WinISD and the one at reaudio.com. The difference in port length for the same tuning frequency with the same port area is less then half an inch. Build 2 subs with one having a port length of half an inch longer. Can you tell the difference?

[snb778 1]

ok, I officially quit..... I tried to get that WinISD to work according to all the parameters and specs that alpine gave me on the subs, and I try to save it, and it says there is an "inconsistency" with the QTS, QMS, and VAS or something... tried to click help...entered in data like 5 times according...didnt let me save...problem with the same 3 specs.

I just want to find a SIMPLE program, where I can enter in

A. Box dimensions

B. Driver size

C. Preferred tuning Frequ.

D. Speaker Displacement

and BAM, give me the port dimension

best one so far is the REaudio calculator.... But it wouldn't allow me to verify my current design that I had made for me

Edit: Pretty much everyone of these online sites asks for a port diameter.... What are you supposed to put if its a slot port????

Edited May 5, 2008 by snb778

[shizzzon 461]

the best one is the link i showed you above.

The RE calculator... i am suppose to go over that calculator to see if it has any discrepancies in it's calculations but i have yet had time to check it out.

Mike P. difference is small but difference is there.

IF someone were in desperate need for perfect accuracy in tuning, this is a must know.

Competition is one.

If you are pressed for space in your box, this is another good time to know this.

I might check that RE calc out now, ..i'll attempt it, heh

[snb778 1]

the best one is the link i showed you above.

The RE calculator... i am suppose to go over that calculator to see if it has any discrepancies in it's calculations but i have yet had time to check it out.

Mike P. difference is small but difference is there.

IF someone were in desperate need for perfect accuracy in tuning, this is a must know.

Competition is one.

If you are pressed for space in your box, this is another good time to know this.

I might check that RE calc out now, ..i'll attempt it, heh

ya that RE one is really nice, especially because it gives you the dimensions for all your cuts... I would almost use their design, but I payed dude to design that one for me...I just really wish I could see the design on paper, telling me it is correct. I'm sure it is, but I want to know how he got the 13.25" length for the port

FOUND SOMETHING FOR ALL OF YOU!! You guys will be able to utilize this a lot better than I can i'm sure, but its almost like that other program I downloaded only it uses an easier to use program... gives you tons of info.. check it out.. Quick install.

http://www.pvconsultants.com/audio/eq/boxcircuit.htm

Edited May 5, 2008 by snb778

[sick6ness 1]

You should ask him, how he calculates all this or what he uses and share it with us