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[Easy back-loaded horn design formula] for Straight pipe horn
<01>
Va(liter) = Sd(cm2) ÷ 25
Air chamber volume [Va](liter) = Surface area of cone [Sd](cm2) ÷ 25
<02>
S1(cm2) = Sd(cm2) × Throat ratio
Throat cross-sectional area [S1](cm2) = Surface area of cone [Sd](cm2) × Throat ratio
[* Throat ratio optimum value = 0.7 - 0.9]
<03>
Sx(cm2) = S(x-1) × K
X-th tube - cross-sectional area [Sx](cm2) = "(X-1) tube - cross-sectional area" [Sx-1] × Flare factor[ K ]
***Example***
Second tube - Cross-sectional area [S2](cm2) = S1 × Flare ratio[ K ]
Third tube - Cross-sectional area [S3](cm2) = S2 × Flare ratio[ K ]
· · · · · · · · ·
X-th tube - Cross-sectional area [Sx](cm2) = [Sx-1] × Flare ratio[ K ]
<04>
Relationship of "flare ratio[K]" and "straight pipe volumes[Px]"
Five pipes[P5] > K = around 1.5
Six pipes[P6] > K = around 1.4
Seven pipes[P7] > K = around 1.3
***Please increase or decrease as needed flare ratio***
<05>
Relationship of low-frequency playback limit and horn length.
I can play somehow if there is a horn of 1/4 wavelength of the lowest frequency range you need.
For example, if you want to play is up to 50Hz,,,.
Wavelength of 50Hz = 340m (speed of sound) ÷ 50Hz (frequency) = 6.8m
6.8m × 0.25 (1/4 wavelength) = 1.7m
In other words, I will be playing of 50Hz can be expected if there is 1.7m horn length.
<06>
Horn length , it is not well be too long or too short.
I think about 1.2m - 2.6m is it safe.
Low-frequency limit is about 33Hz(2.6m)and from about 71Hz(1.2m).
At this time, the relationship between throat area and the opening area.
5 times back and forth in 1.2m, please have a target of about 8 times back and forth in 2.6m.
These numbers because they are empirical, but does not need to be concerned too much.
I think that if you design within the above range, big mistake and less.
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