Resource to calculate, building and measuring Hi Fi Loudspeakers and more... Home Email Links Forums Tips "How It's Made"  Something about Espresso  Disclaimer For Sale Calculators Loudspeakers Projects My System My System CD Master Clock Generator Components explained  Recommended Records  Measurement Software  Calculate Tonearm/Cartridge Capability Phono Cartridge Specifications Acoustics About Acoustics Acoustical Measurement Basics  Acoustic Calculations Acoustic Glossary Absorbtion factors(Excel) Specials

 donderdag 20 september 2018 336 users online

 A vented loudspeaker is analogous to a 24dB/octave cutoff high-pass filter, characterized by an enclosure having an open tunnel or port which allows the passage of air in and out of the box. At low frequencies, the vent contributes substantially to the sound output of the system. It does so however, by increasing the acoustc load at the rear of the cone, reducing cone motion, and the output of the driver. As such, a vent only adds as much as it subtracts. Compared to closed-box systems, vented enclosure posses several unique characteristics: A: Lower cone excursion near the box resonance frequency. B: Lower cutoff using the same driver. C: In theory, a +3dB higher efficiency for the same volume closed-box system. On the downside, vented enclosurs are much more sensitive to misaligned parameters.This factor makes the vented box loudspeaker somewhat more difficult for the inexperienced homebuilder.

 Just like at closed boxes nearly everyone Qts-waarde can be used, although generally only values between 0.2 and 0.5 will lead to a good reproduction.

 f-3 -3dB half-power frequency. fs resonance frequency of driver fc resonance frequency of the closed box system Q ratio of reactance to resistance (series circuit) or resistance to reactance (parallel circuit) Qts total Q of driver (woofer) at fs, considering all driver resistance. Qtc total Q of speaker system at fc, including all system resistance. Vas volume of air having the same acoustic compliance as the driver suspension. Vab volume of air having the same acoustic compliance as the enclosure. Xmax peak linear displacement of driver cone. Sd effective surface area of driver cone. Vd peak displacement volume of driver cone. Vb net internal volume of enclosure.

 Parameters: Vas = 57,2 Liter fs = 42,5 Hz Qts = 0,32 Calculation Vb: Vb = 15 * Vas * Qts2,87 = 32,6 Liter Calculation f-3: f-3 = 0,26 * fs / Qts1,4 = 54,5 Hz Calculation fb: fb = 0,42 * fs / Qts0,9 = 49,8 Hz Port : Sv = 72cm² Lve = ((10*3432*Sv)/(4*3,142*fs2*Vb))-0,825*wortel(Sv) Lve = ((84707280)/(2322280,88))-7 = 29,5 cm

 Parameters: Vas = 57,2 Liter fs = 42,5 Hz Qts = 0,32 Calculation Vb: Vb = 17,6 * Vas * Qts3,15 = 27,8 Liter Calculation f-3: f-3 = 0,3 * fs / Qts1,33 = 58 Hz Calculation fb: fb = 0,42 * fs / Qts0,95 = 52,7 Hz Port : Sv = 72cm² Lve = ((10*3432*Sv)/(4*3,142*fs2*Vb))-0,825*wortel(Sv) Lve = ((84707280)/(1980350))-7 = 35,8 cm

Firstly, calculate the Efficiency Bandwidth Product: EBP = fs/Qe.

 Fs [Hz] Qe [] EBP[]
 If EBP is around 100, this indicates that a vented box would be a better choice. If you have Qe and Qm, you can take external resistance into account when calculating Qts. Qts = 1/((1/Qm) + Rs/((R+Rs)Qe)) where R is the resistance of the wiring, typically 0.5 ohm. Alternatively, use Qts as specified in the TS parameters.

Basis for the recommended housing size Vb and tuning frequency Fb is the Qb3-B4-C4-Tabelle for Ql=7 ("normal" losses).

Fs [Hz] : Qts [] : (0.1 - 0.8) Vas [l] :

Vb [l] : Fb [Hz] : F3 [Hz] : Ripple [dB] :

Dv [cm] : Lv [cm] : Pa [cm2] :

If you change the pipe diameter [Dv], click on 'Port' to recalculate Port length.

 Vb [l] - Net volume of the box in liter (without the volume for the bass reflex pipe) Fb [Hz] - Tuning frequency of the Port F3 [Hz] - Frequency, where the level at the lower end of transmission dropped around 3dB Ripple [dB] - Ripples at the lower end of the transmission range (-0 to +Ripple dB) Dv [cm] - Diameter of the bass reflex pipe Lv [cm] - Length of the bass reflex pipe Pa [cm2] - Area of the bass reflex pipe