4th order sp4

[ncc74656 2]

I have only recently built my first vented box and ive built a few sealed but anyone can do that. I want to try a 4th order to see how it works.

 

my goals are to flatten my response curve and hit 30-90 hz. a large part of this is just the experience so its not all about the sound but i do want to get a more musical setup with high output volume.

 

I played with things all night and read up with what i could to see how this thing is ment to work.

 

thoughts?

 

the .33 cubic that is directly off the sub cone in the vented box is not taken into consideration on the torres sheet. by my math the tuning will lower itself a bit with that.

 

 

 

 

[shizzzon 461]

I'd throw that program in the garbage.

 

Tell me how it's getting 2.97cuft port displacement based on the following-

 

32x7" port opening using 0.75" wood

Physical length= 11"

 

That's not even 2.0cuft displacement.

 

It can't calculate simple math so how's it going to calculate tuning?

[ncc74656 2]

i had always heard good things about this program. what program should i use?

 

by the math i see a 7" tall port plus a 1.5" piece of wood to 8.5" X 32" wide with a common port wall and then total length of port which is 19.5".   the port is 11" long plus 3.5" end correction and 3.5" port width to the rear plus wood thickness of 1.5".

 

so 8.5X32X19.5 is 5304 cubic inches divided by 3.06944 displacement of port.

 

i list this to demonstrate my understanding of this and if i am wrong to allow others to correct me. 

 

in the program i did not select 3 common port walls wich does throw it off, i just noticed that. 

 

 

thoughts? 

[shizzzon 461]

Actually, since your last pic finally loaded for me, your physical length INCLUDES the baffle thickness = 11"
 

 

So, it's taking an extra 3.5" to addon internally for acoustical length.  

So the ACTUAL internal physical length is 9.5", not 11" and an extra 3.5" for acoustical length= 13"

 

So.. by your drawing, the port displacement including acoustical displacement Internal is 2.05cuft

 

I dont know if your drawing or if the Torres calculator information put in is conflicting with each other but as of right now, 

Either the input information is wrong or Torres is calculating the wrong outcome.

[ncc74656 2]

so the torres port length should be 9.5" and its factoring in a half port width extension past the port as a "physical" port. right?  so the physical wood length should be 3.5" shorter to obtain the same frequency?

 

i used this program to build my last box as well so if its wrong here id assume it was wrong there too?

[shizzzon 461]

Like i'm sayin, make sure your drawing is 100% what Torres' information is using and calculating or else you will have a wack result.

 

Also, very recently someone else on this forum also told me he heard Torres was good to use and he also kept getting erratic answers with Torres when i was reviewing it's math so we put in VERY BASIC information and it still displayed a box of 0.8cuft off on port displacement which threw other results off as well.  Tuning in the end was calculated to be 9hz different than other calculations.

 

 

What, in my opinion, i do not like about Torres is it wants the GROSS information.

that means it is calculating things that may change or not account for to get to your NET volume.

 

If you only deal with Net volume, there shouldn't be anyway possible to screw the calculations up.

[ncc74656 2]

hmmm, ok let me get my head around this and i will post up on here in a bit what i think the math should be to make sure i understand it all. 

[ncc74656 2]

ok so i used some other calculators online like this one: http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm

 

and im not sure if i should enter net or total volume into these things or if i should enter the net volume before or after the port displacement is taken into account...  

 

id like to do the math manually as it seems there are countless programs/opinions out there on how to calculate tuning and they are all different. 

 

 

the sketchup is built directly off of the specs in torres so id expect the tores to be more correct.

Edited August 18, 2013 by ncc74656

[ssh 924]

You can manually calculate port length with:

 

Note that enclosure volume is net, and in cubic inches, so multiply your volume in cubic feet by 1728 to get cubic inches for Vb.

Port area has to be converted to radius of circle in inches. Since area of circle is pi*r^2, you can translate your port area in squared inches to radius of circle by dividing by pi, and square rooting.

 

IE: 2.92ft^3 volume and 24in^2 port area, 30hz tuning

2.92ft^3 x 1728 = 5045.76 in^2

24in^2 / 3.14 = 7.64, square root of 7.64 = 7.64^0.5 = 2.76in radius

 

Lv = [ (1.463 x 10^7 x (2.76)^2 ) / (30^2 x 5045.76) ] - 1.463(2.76) = 20.5 inches.

 

So with the net volume of the enclosure being 2.92ft^3, 24in^2 port area, and 30hz tuning, the port length would need to be 20.5 inches. The displacement of the port is portarea x port length, or 24in^2 x 20.5in = 492in^3 or 492in^3 / 1728 = 0.28ft^3

 

So the internal volume of the enclosure after driver and bracing displacement needs to be 2.92ft^3 + 0.28ft^3 = 3.2ft^3 or 2.92ft^3 with an external port.

 

I hope that sheds some light on the topic.

Edited August 18, 2013 by stefanhinote

[ncc74656 2]

i need to relearn order of operations here... i have hte base numbers but the total area that i should have is another question that i need to figure out.

 

i was told that i need 438.85 of port area for this band pass on the caraudio forum calculator. on here another guy said i would want 877.7 of port area for this bandpass so im not sure what is hte correct answer here for minimum port size.   when i built my last box the calculator said 227.78 area but i went with 99 port area instead to stay more inline with what Fi had on htere cut sheets. so idk if any of this is accurate.

 

do you have any input on what my port area should be in this kid of box?

 

by my math i have 15310.08 cubic inches of volume (VB).  and 11.941 radius.  on top of that i think i want a 45 ish tune on the vented part no? 

[shizzzon 461]

unfortunately i'm not fond of BP requirements but some others here i believe are.  Hopefully they'll see your post.

[ssh 924]

I should have read your first post better. This type of enclosure alignment is not suited for your goals.

 

Regardless of what enclosure alignment you do use, I'm extremely skeptical that the driver will be able to be used up to the 90hz region with good results.

 

If you truly want a flat response and wide FR than stick with sealed or ported enclosure with low tuning. Model the driver in multiple sealed enclosures within Fi's volume recommendations, do the same with ported enclosures and low tuning, and see which appears to meet your goals (flat frequency response, output).

[ncc74656 2]

assuming i use the minimum port area by the online calculator and if i have read up on order of operations correctly and didnt screw up the math then i believe my port should be 67.2858" long.

 

does this sound right?

 

i have no clue how i could ever fit a 67" port and this number is way off from what ever other calculators ive used.

 

1.463*10^7*(11.941)^2/(45^2*15310.08)   those were the numbers i used.

[ssh 924]

assuming i use the minimum port area by the online calculator and if i have read up on order of operations correctly and didnt screw up the math then i believe my port should be 67.2858" long.

 

does this sound right?

 

i have no clue how i could ever fit a 67" port and this number is way off from what ever other calculators ive used.

 

1.463*10^7*(11.941)^2/(45^2*15310.08)   those were the numbers i used.

Select port area based on port speed--not some minimum port area calculator you found online that doesn't show it's formula or source.

 

Order of operations is PEMDAS, do everything in parenthesis first, then exponents, then multiplication, then division, then addition, and lastly subtraction.

 

I didn't check your math, but in your post you don't show the last part of the formula: -1.463*R

[ncc74656 2]

i just did the final procedure and got: 49.816117"   so thats better. i did the -1.463R last as it was outside of the close bracket.

 

so if this box will not give me up to 90 (and maybe i dont need that),  i know i want my sub to sound more like it did with my old box so by the math that box would have peaked at around the 75hz mark.

 

ill throw my box into winisd and see what the air speed comes out to.

[///M5 2,833]

Stay with a 4th order ported, your goals do not at all match a 4th order BP.

[ncc74656 2]

wait a miniute... a 4th order is one sealed and one vented chamber in a box with a cross over on the sub no? what is a 4th order BP?

[ricksi30 923]

wait a miniute... a 4th order is one sealed and one vented chamber in a box with a cross over on the sub no? what is a 4th order BP?

Wrong 4th order refers to the roll off, and does not have to be a band pass enclosure,

[ncc74656 2]

ok wait a min now... the orders reffer to DB slope of the cross over fall of? so 24 is 4th order and 6 is 1st order?

 

i read this, but also read 1,2,3,4th order BOXES so im very confused here.

 

a bandpass is a box with 1 sealed and 1 vented enclosure right? so that means i want a 4th order bandpass setup to maximize my chances of getting the results i want.

[ssh 924]

ok wait a min now... the orders reffer to DB slope of the cross over fall of? so 24 is 4th order and 6 is 1st order?

 

i read this, but also read 1,2,3,4th order BOXES so im very confused here.

 

a bandpass is a box with 1 sealed and 1 vented enclosure right? so that means i want a 4th order bandpass setup to maximize my chances of getting the results i want.

What you are describing is a 4th order bandpass, and it is the wrong alignment for your goals--as previously stated.

[ncc74656 2]

now when you say alignment, do you mean its the wrong box or is there more meaning to it than this?

 

from what i read a bandpass can give me lows from sealed and high from ported. logically this makes me think that it would fit me better than a straight vented. 

 

where am i going wrong in my conclusions? do i not understand this properly?

 

what would you say would be "my box"? a vented with a higher tuning?

[ssh 924]

now when you say alignment, do you mean its the wrong box or is there more meaning to it than this?

 

from what i read a bandpass can give me lows from sealed and high from ported. logically this makes me think that it would fit me better than a straight vented. 

 

where am i going wrong in my conclusions? do i not understand this properly?

 

what would you say would be "my box"? a vented with a higher tuning?

I mean any 4th order bandpass enclosure is wrong for your goals listed in the first post.

 

A 4th order bandpass enclosure is going to have a limited bandwidth with a steep rolloff.

[ncc74656 2]

so i want to make sure i understand this. your saying that the sealed box is going to give A-B frequency and sharply cut off leaving B-C frequencies dead and then the vented side would pick up at C-D in a limited range on the high end before dipping off into a dead zone?

[///M5 2,833]

You understand crossover slopes so then apply it to a box. Let me help clarify one other thing. What you call ported is actually a 4th order vented enclosure, what you are calling 4th order is actually a 4th order bandpass enclosure. A bandpass in nature will have rolloffs on BOTH the high frequencies and low frequencies, ie it only allows frequencies in the passband to play.

There are some applications for 4th BP boxes, but they are few and far between and you have shown us NOTHING that makes them logical for your choice. Yes you can steer the width of the BP in the enclosure via design as you can watch the skarbage FL guys attempting to do, but this yields a "one note wonder" that in reality only buys you a shitty sounding enclosure. Of course you can steer the enclosure the other way as well, but good luck getting it right on even the third iteration. And even when right the standard 4th order ported enclosure will most likely give you a better response and fit your needs better.

[jonbearsmt 919]

sure will make it hard to put the flames out!