frustrated with calcs

sparky3489 · 2005-04-19 9:32 pm

I can't seem to get a stable answer for a port length.

12" speaker
Qes = 0.38
Qms = 4.06
Qts = 0.347
fs = 25 Hz
Vas = 4.178 cu.ft.
Ze = 4 ohms
Xmax = 5.6mm
displacement = .12 cu.ft.

200 Wrms 600 max

wedge box

H = 16"
W = 14.75"
D1 = 9"
D2 = 12"

1.0 cu.ft box
0.82 after

Port dia. = 3"
tuning freq. = 42 Hz

What the **** is the length of the port?

I'll get anywhere from 8 in. to 11 in. I need a consistant calc.
or formula, plz.

ocool_15 · 2005-04-28 1:09 am

port length

I got 11.25" for a.82cuft box
if I'm supposed to minus the speaker vol from that its .7cu ft which gives me 13.69" long port. Assuming the normal flush one end and free end the other.
its not a flat response before rolling off its got about 2.6dB gain at 85Hz. IMHO i would go to a larger box and lower tuning freq.
there are differences from program to program partly due to more accurate modelling. Online ones are ok for approximations. Ive used WinISD(its free!!) most often but these numbers are from Bass Box Pro 6.

sparky3489 · 2005-05-05 4:49 pm

made hanges

I have since canged box size and tuning freq.

tuning freq 29 Hz
2 in. ports per chamber non-flared

W = 14.75"
H = 16"
D1 = 18"
D2 = 21"

Port length 8 13/16" for ea.

sound about right?

ocool_15 · 2005-05-05 6:58 pm

clarify

RE:
2 in. ports per chamber non-flared
Im assuming more then one 2" diameter port then, 1 flush 1 free end.

What internal volume do you have for the box before port ect.

(remember u have to minus port volume and speaker displacement in the final design).
from the numbers u gave me I wasnt getting close to your numbers unless you use 4 ports......

sparky3489 · 2005-05-05 8:18 pm

It's actually two boxes in one (center divider)

W = 28.75"
H = 16"
D1 = 18"
D2 = 21"

.75" MDF

2 cu.ft. per chamber
2 ports per chamber
non flared straight tube

Using WinISD .05a7

ocool_15 · 2005-05-05 8:40 pm

so 2 identical boxes/subs or like a 6th order bose?

sparky3489 · 2005-05-05 8:55 pm

Box Front Angle = Degrees 79.4
Gross box volume = cu.ft. 1.881
Net box volume = cu.ft. 1.847
Port Length = Inches 9.4 (square)
square port dimensions H=2.507 W=2.507
Port Area = Inches2 6.283
Port Volume = cu.ft. .034

The calc I used only supports square ports

sparky3489 · 2005-05-05 8:55 pm

sort of
going in my trunk

one big box with a center divider for seperation

ocool_15 · 2005-05-05 8:55 pm

area too small

as per
min port area your port area is too small. Port area is your friend especially if you are looking to do better speakers and dont want port noise.
o square that makes all the difference then its not as bad but its still a bit small

ocool_15 · 2005-05-05 9:10 pm

define gross/ net.
all I need are internal box volume after speaker displacement.
ports are by area shape doesnt matter. there is no major difference between square and round for your application. A single port per side will be more efficient as there is less surface area per port area. remember area for a circle thats same for port area pi r^2.

If you havent got any wood cut its usually alot easier to model what looks good(vol/ports) then define dimensions after that to give required volume. Thats how most programs are set up and people make boxes.

sparky3489 · 2005-05-05 9:51 pm

I'm using round ports
2 per chamber 4 in all
2" in dia.

When I put in the numbers using the "Vent Dimensions Calculator" link, I got 8.6" for port length

when I use Win ISD, I get 8.8"

should I compromise and go with 8.7"?

sparky3489 · 2005-05-05 10:05 pm

'Gross' volume is the internal volume of the enclosure before the port volume is subtracted. If you're using external dimensions and you set the wood thickness to something other than '0', the wood thickness will be subtracted.

'Net' volume is the internal volume after the port volume is subtracted from the gross volume. If your speaker needs an enclosure that's 1.5 cubic feet ported at 35Hz, the 'net' volume must be 1.5 cubic feet for proper operation.

no wood is cut yet and I've been using/trying so many diifferent types of calcs/programs and I'm frustrtated with inconclusive results.

Too much of inconsitancy.

WinISD beta stated I needed a port mach of >16 to prevent speaker "whistle" so I designed to where it had a mach of .07.
my 2" X 8.6" port (times 2) design

(after taking your suggestion of single/bigger ports)

The link you posted said I needed > 3.37" port so I used 3.5" (single port) @ 12.86" in length

WinISD alpha stated I needed 13.20 " length for the same 3.5" port

AAAAAAAAAAAAAARRRRRRRRRGGGGGGGGGGHHHHHHHHH!!!!!!!

STOP THE MADNESS!!

ocool_15 · 2005-05-05 10:14 pm

as I said before generally the better programs will use a more complicated model to give u a better result. You can always build the ports a bit longer and cut as needed. you building 2 so it should be easy to to a/b comparisons in car. You gain about 12db/octave below the tuning frequency of the car so the low end will be alot flatter in car then what win isd predicts as it is the box wo cabin gain.
tuning freq depends on the sub, desired output response and the vehicle. I would try in the range of 30-45hz. where a 45 would likely give you alot louder and boomier sound and better for like a smaller car like a honda crx. Lower freq for larger car and typically more sq application and more likely to require more power for a given ouput in the range of higher tuned enclosure.

sparky3489 · 2005-05-05 10:23 pm

so in other words, don't sweat the samll stuff, build and experiment.

last minute questions:

still, what is the disadvantage of (2) 2"X8.6" ports vs. (1) 3.5"X13.2"

what is "end correction" followed by 0.614 in WinISD

what's the difference between flush and free, I thought they were the same.

ocool_15 · 2005-05-05 10:57 pm

flush means the end is up against a surface like you would normally see on the outside of a box. free means the end goes into air with no obstructions around it. End correction is covered in the winISD help, as for the specific .634 I don't know how it comes up with the numbers I just work with it. I just do what the computer says for how that changes length. Ideally you want the largest area vs surface area.
s s area perim area/perim
2 8.6 17.2 21.2 0.81132
3.5 13.2 46.2 33.4 1.38323

so as always the larger port yeilds optimal. Square/round is therectically even better but harder to implement.

BTW when looking at win ISD look at the graph of cone excursion you will notice depending on the box you can easily damage a speaker below the tuning freq of the box without a sub sonic filter.

sparky3489 · 2005-05-05 11:18 pm

if I don't see anything in the cone excursion graph what does this mean?

ocool_15 · 2005-05-05 11:57 pm

up power

under the power of the sub change to what u will be running. If your designing the boxes seperatly then u will enter what that 1 sub will have for power to it. I cant remember what tab but i think its in the top left(default 1w) with 1m/3.28ft below that. the cone wont move much with 1w so thats why u dont see it

sparky3489 · 2005-05-11 4:11 pm

my own program

I've decided to write my own program to calculate a wedge with a port.

It is nothing special, it probably has a lot of errors, but I like it.

It was written in BASIC (stop laughing) and works fairly well.

Here it is.

5 CLS:SCREEN 9:COLOR 7
10 CLEAR
20 PI=3.141592653589793#
30 LOCATE 1

RINT "Volume of wedge speakerbox and port tube length calculator:"
40 PRINT "(All measurements are in inches)"
50 PRINT "Design is currently for single round ports."
60 PRINT
70 INPUT "Depth 1";DE1
80 INPUT "Depth 2";DE2
90 INPUT "Width ";W
100 INPUT "Height ";H
110 A1=7:B1=7:C1=7:E1=7:F1=7
120 IF DE1=0 OR DE2=0 THEN COLOR 4:GOTO 160
130 IF DE1=DE2 THEN COLOR 4:GOTO 160
140 IF DE1>DE2 THEN TEMP=DE2

E2=DE1

E1=TEMP
150 GOTO 910
160 INPUT "Box is NOT a wedge. Press <ENTER> to continue.";ENT
170 GOTO 5
180 INPUT "Wood thickness (0.75 default)";T
190 IF T=0 THEN T=.75
200 D1=DE1-(T*2)
210 D2=DE2-(T*2)
220 WI=W-(T*2)
230 HT=H-(T*2)
240 V=((HT*WI*((D1+D2)/2))/1728)
250 PRINT
260 LOCATE 5

RINT "Select speaker size:
270 PRINT " "
280 PRINT "The following uses approximate
290 PRINT "Air Volume Displacement (Cu.Ft.)"
300 PRINT " "
310 PRINT "1 - 8"CHR$(34)" "
320 PRINT "2 - 10"CHR$(34)" "
330 PRINT "3 - 12"CHR$(34)" "
340 PRINT "4 - 15"CHR$(34)" "
350 PRINT "5 - 18"CHR$(34)" "
360 PRINT "6 - Known Cu. Ft. "
370 A$=INKEY$
380 IF A$="1" THEN S=.035:SP=8:GOTO 460
390 IF A$="2" THEN S=.075:SP=10:GOTO 460
400 IF A$="3" THEN S=.13:SP=12:GOTO 460
410 IF A$="4" THEN S=.27:SP=15:GOTO 460
420 IF A$="5" THEN S=.33:SP=18:GOTO 460
430 IF A$="6" THEN INPUT "Air Volume Displacement";S:GOTO 450
440 GOTO 370
450 INPUT "Enter speaker size in inches";SP
460 IF SP+2=W OR SP+2<W THEN GOTO 500
470 COLOR 4:LOCATE 20

RINT "Your speaker is too large for your box, try again"
480 INPUT "Press <ENTER> to continue.";ENT
490 T=0:GOTO 5
500 V1=V-S
510 PRINT
520 INPUT "Desired tuning frequency(Hz)";F
530 INPUT "Desired port Diameter";D
540 CLS
550 L=(14630000#*((D/2)*(D/2)))/((F*F)*(V*1728))-(1.463*(D/2))
560 PRINT
570 PRINT "Gross volume of the box ="V"cubic feet"
580 PRINT "Net volume of the box ="V1"cubic feet"
590 IF L<0 THEN ER=2:GOTO 1070
600 IF D<=DE2-L THEN GOTO 610 ELSE FR=1:GOTO 610
610 IF D<=H-L THEN GOTO 620 ELSE VR=1:GOTO 620
620 IF D<=W-L THEN GOTO 630 ELSE SR=1:GOTO 630
630 IF D<D1 THEN GOTO 640 ESLE DR=1:GOTO 640
640 IF FR=1 AND VR=1 AND SR=1 THEN COLOR 4

RINT "The port will NOT fit this box":ER=1:GOTO 1070
650 IF DR=1 AND FR=1 AND VR=0 AND SR=1 THEN COLOR 4

RINT "The port will NOT fit this box":GOTO 1070
660 IF FR=0 AND VR=1 AND SR=1 THEN COLOR 14

RINT "The port will only fit horizontally (from the front)":ER=3:GOTO 790
670 IF FR=0 AND VR=1 AND SR=1 THEN COLOR 14

RINT "The port will only fit horizontally (from the front)":ER=3:GOTO 790
680 IF DR=1 AND FR=0 AND VR=0 AND SR=1 THEN COLOR 14

RINT "The port will only fit horizontally (from the front)":ER=3:GOTO 790
690 IF DR=0 AND FR=0 AND VR=0 AND SR=1 THEN COLOR 14

RINT "The port will only fit horizontally (from the front) or vertically":ER=3:GOTO 790
700 IF DR=0 AND FR=1 AND VR=0 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the side) or vertically":GOTO 790
710 IF DR=0 AND FR=1 AND VR=0 AND SR=1 THEN COLOR 14

RINT "The port will only fit vertically":GOTO 790
720 IF FR=0 AND VR=1 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the front or the side)":ER=3:GOTO 790
730 IF FR=0 AND VR=1 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the front or the side)":ER=3:GOTO 790
740 IF DR=1 AND FR=0 AND VR=0 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the front or the side)":ER=3:GOTO 790
750 IF FR=1 AND VR=1 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the side)":GOTO 790
760 IF FR=1 AND VR=1 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the side)":GOTO 790
770 IF DR-1 AND FR=1 AND VR=0 AND SR=0 THEN COLOR 14

RINT "The port will only fit horizontally (from the side)":GOTO 790
780 IF DR=0 AND FR=0 AND VR=0 AND SR=0 THEN COLOR 2:ER=3
790 PRINT "Port length = "L"inches"
800 PRINT:COLOR 7
810 B=DE2-DE1
820 S=H
830 C=(S^2)+(B^2)
840 HYP=SQR(C)
850 PRINT "hypotenuse = ";HYP"inches"
860 X=S/HYP:ON ERR GOTO 890
870 RAD=ABS(ATN(X/SQR(-X*X+1))-PI/2)
880 DEG=(180/PI)*RAD
890 PRINT "Front angle of box ="90-DEG;

RINT CHR$(248)
900 A1=4:B1=14:C1=5:E1=2:F1=1
910 DP1=DE1*1.25

P2=DE2*1.25:WD=W*2.5
920 LINE (350,190)-((350+(DP1*5)),190),A1
930 LINE (350,190)-(350,(H*5)+190),B1
940 LINE (350,(H*5)+190)-(350+(DP2*5),(H*5)+190),C1
950 LINE (350+(DP2*5),(H*5)+190)-((350+(DP1*5)),190),F1
960 LINE (350,190)-(350+(WD),190-(WD)),E1
970 LINE ((350+(DP1*5)),190)-(350+(WD)+(DP1*5),190-(WD)),7
980 LINE (350+(DP2*5),(H*5)+190)-(350+(WD)+(DP2*5),190-(WD)+(H*5)),7
990 LINE (350+(WD),190-(WD))-(350+(WD)+(DP1*5),190-(WD)),7
1000 LINE (350+(WD)+(DP1*5),190-(WD))-(350+(WD)+(DP2*5),190-(WD)+(H*5)),7
1010 IF T=0 THEN GOTO 180
1020 LINE (200,196)-(200,209),4:LOCATE 15,27

RINT "= "DE1"in."
1030 LINE (200,252)-(200,265),14:LOCATE 17,27

RINT "= "DE2"in."
1040 LINE (200,224)-(200,237),5:LOCATE 19,27

RINT "= "H"in."
1050 LINE (200,280)-(200,293),2:LOCATE 21,27

RINT "= "W"in."
1060 LINE (200,308)-(200,321),1:LOCATE 23,27

RINT "= "HYP"IN."
1070 IF ER=1 THEN LOCATE 12:COLOR 4

RINT "An error occured in"
1080 IF ER=1 THEN PRINT "your port length. "
1090 IF ER=1 THEN PRINT "Try raising your tuning"
1100 IF ER=1 THEN PRINT "frequency or decreasing"
1110 IF ER=1 THEN PRINT "port diameter. Port was"L"inches."
1120 IF ER=2 THEN LOCATE 12:COLOR 4

RINT "An error occured in"
1130 IF ER=2 THEN PRINT "your port length. "
1140 IF ER=2 THEN PRINT "Try decreasing your box"
1150 IF ER=2 THEN PRINT "size or use a larger "
1160 IF ER=2 THEN PRINT "speaker. Port was "L"inches.
1170 IF ER=3 THEN LOCATE 9

RINT "If using port in front, it will have to be cut at a "90-DEG;

RINT CHR$(248)" angle and will"
1180 DR=PI/180
1190 ARC=DEG*DR
1200 AC=(D/2)*TAN(ARC)
1210 IF ER=3 THEN PRINT "need to be ";:COLOR 2

RINT AC+L;:COLOR 7

RINT " in. long to be flush with the front of the box."
1220 LOCATE 18:COLOR 7

RINT "Do again?":T=0
1230 A$=INKEY$
1240 IF A$="Y" OR A$="y" THEN GOTO 5
1250 IF A$="N" OR A$="n" THEN GOTO 1270
1260 GOTO 1230
1270 SCREEN 0,0,0:SYSTEM

known issues:

This program will only work in full screen mode, it freezes if you attempt run it in a window (Win2K Pro, other OS??)

sparky3489 · 2005-05-11 4:15 pm

oops

replace the

with a colon followed by D

sparky3489 · 2005-05-11 4:46 pm

bored

changed some things

frustrated with calcs

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