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| By: cplkittle on Sun, 30 Nov 2008 22:43:22
| | EBP (Efficiency Bandwidth Product):
used to determine best enclosure for specific subwoofer.
EBP = Fs / Qes
50 or less = Sealed / 4th order Bandpass.
50 - 90 = flexible enclosure options.
90 or greater = Ported / 6th order Bandpass
Best volume for sealed enclosure:
First find the value of X...
X = (0.70 / Qts)^2 - 1
Then find the enclosure volume
Vb = Vas / X
Vb will be given in same unit of measure as entered for Vas
To find the frequency of the box:
Box Freq= (0.7/Qts)Fs
The Golden Ratio:
Used for optimum sound in sealed enclosures
The ratio is the cubed root of the determined enclosure size in inches (x1), (x.7939), (x1.2599)
For example if your internal volume in cubic inches needs to be 2160^in or 1.25^ft.
Take the cubed root of 2160 (12.927) and multiply it by 1 to get side A
A=12.927
To get side B multiply side A by .7939
B=10.263
To get side C multiply side A by 1.2599
C=16.286
To double check multiply side AxBxC, and you should get within 1 of 2160
Tuning a ported box:
To tune a ported box to a desired frequency, use the following equation:
LV= [(1.463 x 10^7 x R^2) / (Fb^2 x Vb)] - 1.463xR
Fb - is the desired tuning frequency of your enclosure in Hertz.
Lv - is the length of your port in inches.
R - is the inside radius of your vent tube.
Vb - is the internal volume of your enclosure in cubic inches. To convert cubic feet to cubic inches, multiply by 1728.
Transmission line length:
First, find the length of the speaker’s Fs by dividing 1120fps (speed of sound) by the Fs of the speaker. (1120fps / 40Hz = 28’)
Line length = Fs wavelength / X
X= 4 (25% of wavelength gives you a 90degree phase shift)
X= 2 (50% of wavelength gives you a 180degree phase shift)
X= 1.333 (75% of wavelength gives you a 270degree phase shift)
Temperature, elevation, air pressure, and humidity all effect the speed of sound. If you wanted to get technical, plug these factors into winisd, and it will calculate sound velocity for you. Temperature is the biggest factor in sound speed.
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