Donald A. Swanson
The program shown below can be copy and pasted into the editor window of the online BASIC interpreter. Click the RUN button to execute the program. Enter in the nominal driver size. There are 3 enclosure sizes to choose from. Width, height, depth values shown are the interior dimensions. Dv is the nominal vent tube diameter.
Calculate (Fs / Qes). If above 85 and the Qts value is 0.6 or less, then the driver is likely suitable for a vented enclosure. More expensive drivers usually show higher Vas values and will benefit from a larger enclosure size.
The back and sides of the enclosure should be lined with damping material. A small enclosure can be lined with 3-4 layers of craft felt. Consider rounding the backside of the cutout hole to allow air to escape from the backside of the driver.
15 rem Loudspeaker Enclosure Volume Calculator 20 rem Donald Swanson - das605813@yahoo.com 30 rem Online BASIC interpreter - https://www.calormen.com/jsbasic/ 40 clear 50 home 60 data 0.904,1.015,1.136 70 input "Enter nominal driver size (in) = ";dz 80 for i = 1 to 3 90 rem calculate width (wd), height (ht), depth (dp) 100 read s1 110 ds = dz * s1 120 wd = ds * 1.618 130 ht = wd * 1.618 140 dp = wd * (1 - (1 / (1 + 5))) 150 wd = int((wd * 4) + 0.5) / 4 160 ht = int((ht * 4) + 0.5) / 4 170 dp = int((dp * 4) + 0.5) / 4 180 rem calculate enclosure volume (Vb) 190 vb = wd * ht * dp 200 rem convert cubic inches to liters 210 vb = vb / 61.024 220 vb = int((vb * 10) + 0.5) / 10 230 rem calculate nominal vent diameter (Dv) 240 dv = ds / 3 250 dv = int((dv * 8) + 0.167) / 8 260 print"---------------------------------------" 270 print 280 print " ";vb;" (L)";" Dv: ";dv;" (in)" 290 print 300 print " ";"w,h,d: ";wd;", ";ht;", ";dp;" (in)" 310 print 320 next i 330 restore 340 print 350 input "hit enter to continue ";en$ 360 goto 40
Donald A. Swanson
The leftmost column in figure 1 shows the seven symbols used in the method. The left side symbol part is the base (+, N, Ø). The right side symbol part (+, -) is the modifier. Descriptions are names for the symbols. The symbols are usually hand-written with a forward slash "/" as a separator, for example: (N+ / + / Ø+). Symbol selection starts with consideration of (+, N, Ø) before moving up or down to the appropriate symbol. Memorize the symbols and descriptions. The rightmost column in figure 1 shows the matching Fibonacci numbers which will be used to calculate the weighted percentages.
| Symbol | Description | Weight |
|---|---|---|
| ++ | double plus | 21 |
| + | plus | 13 |
| N+ | neutral plus | 8 |
| N | neutral | 5 |
| N- | neutral minus | 3 |
| Ø+ | doubtful plus | 2 |
| Ø | doubtful | 1 |
The race is analyzed to decide which horses will be contenders. The handicapper will have some level of confidence that one of the contenders will win the race. A symbol is selected to represent the confidence level. Figure 2 shows the symbols and matching confidence levels. Symbol selection starts with consideration of (N+) before moving up or down to the appropriate symbol. Non-contenders get a (Ø).
| Symbol | Confidence Level |
|---|---|
| ++ | maximum |
| + | high |
| N+ | moderate high |
| N | moderate |
| N- | moderate low |
| Ø+ | low |
| Ø | minimum |
cp - contender percentage
nc - number of contenders
fs - field size
wt - weight
cp = (wt * nc) / ((wt * nc) + (fs - nc))
Four contenders in an eight horse field with moderate high confidence.
4 / 8 / N+
N+ / N+ / N+ / N+ / Ø / Ø / Ø / Ø
8 + 8 + 8 + 8 + 1 + 1 + 1 + 1
cp = 32 / 36 = .889
cp = (8 * 4) / ((8 * 4) + (8 - 4)) = .889
Races with two or more contenders will use one to three factors which must be arranged from left to right in order of importance, for example: class, form, distance. Factors can be two-part compounded, for example: form-surface, jockey-trainer, form-age, distance-surface.
The (N) symbol can be extended to (NN) making the neutral base symbols (N+, NN, N-). The factor symbols are the right side symbol parts (+, N, -) matched up with Fibonacci numbers 8, 5, 3 respectively. Figure 3 shows the six factor symbol combinations and weighted percentages. A symbol combination is chosen that indicates the relative importance of each factor.
| Symbols | Percent | Doubled |
|---|---|---|
| N N N | 33,33,34 | 66,34 |
| + N N | 44,28,28 | - |
| N N - | 38,38,24 | 76,24 |
| + N - | 50,31,19 | - |
| + - - | 56,22,22 | 56,44 |
| + + - | 42,42,16 | 84,16 |
Weighted percentage calculation for the (+ N -) combination.
8 + 5 + 3 = 16
8 / 16 = .5
5 / 16 = .3125
3 / 16 = .1875
Factors can be doubled, for example: speed, speed, form making a two factor race. The factor symbol representing the doubled factor must be duplicated in the combination as shown in figure 3. A single factor can be tripled (N N N) making a one factor race.
Two contenders in an eight horse field with high confidence.
cp = (13 * 2) / ((13 * 2) + (8 - 2)) = .813
Three factors are chosen: class, form, distance with the (+ N -) combination.
8 + 5 + 3 = 16
(8 / 16) * .813 = .407
(5 / 16) * .813 = .254
(3 / 16) * .813 = .152
Each contender gets three symbols one for each factor as shown in figure 5 second column.
| Horse | cls / fm / dst | Weights |
|---|---|---|
| #1 | + / N / N | 13 / 5 / 5 |
| #2 | N- / N+ / + | 3 / 8 / 13 |
13 + 3 = 16
(13 / 16) * .407 = .331 (#1)
(3 / 16) * .407 = .076 (#2)
5 + 8 = 13
(5 / 13) * .254 = .098 (#1)
(8 / 13) * .254 = .156 (#2)
5 + 13 = 18
(5 / 18) * .152 = .042 (#1)
(13 / 18) * .152 = .110 (#2)
Sum the three percentages for each contender.
.331 + .098 + .042 = .471 (#1)
.076 + .156 + .110 = .342 (#2)
Sort the percentages (pct) in descending order before converting into odds.
odds = (1 / pct) - 1
(1 / .471) - 1 = 1.123 (#1)
(1 / .342) - 1 = 1.924 (#2)
Select the increment (inc) for rounding off.
if odds < 0.3 then inc = 20 elseif odds < 1 then inc = 10 elseif odds < 2 then inc = 5 elseif odds < 5 then inc = 2 else inc = 1
odds = (int ((odds * inc) + .5)) / inc
(int ((1.123 * 5) + .5)) / 5 = 1.2 (#1)
(int ((1.924 * 5) + .5)) / 5 = 2 (#2)
Convert rounded odds into fractions.
n = 0.5 // numerator d = 0 // denominator while int(n) <> n d = d + 1 n = odds * d end print n,"/",d
Finished calculation shown in figure 6 with percentages and fractional odds.
| 2 / 8 / + | cls / fm / dst | + N - | |
|---|---|---|---|
| #1 | + / N / N | .471 | 6 / 5 |
| #2 | N- / N+ / + | .342 | 2 / 1 |
Figure 7 is a two factor race with the distance factor doubled.
| 2 / 10 / + | cls / dst | + - - | |
|---|---|---|---|
| #1 | N+ / N / N | .552 | 4 / 5 |
| #2 | N- / Ø+ / Ø+ | .213 | 7 / 2 |