# The calculation of the bass-reflex speakers

The bass-reflex with built-in head you can imagine with some simplifications, like an acoustic high-pass filter (HPF). The calculation is quite complex, as it requires consideration of a large number of parameters that provides the best uniformity of the frequency response of the loudspeaker.

For the calculation it is necessary to measure the displacement (SAG) of the voice coil head D (in millimeters) under the influence of the load of a nonmagnetic material with a mass M=0,2...0,4 kg, put the diffuser in place of the coil connection. Do it with strip scale-coordinate of paper brand H1 ("graph paper"), noting the removal of any marks on the diffuser from the ruler, put DiffuseMaterial. To measure the displacement of the diffuser should be used with great care, since it usually does not exceed 1...2 mm (for example, the diffuser head GD-RS is shifted under the action of a mass of 0.2 kg in just 1 mm). Then find the flexibility of a mobile system CR=10(-4)/DM (in Newton meters), the volume of the box the phase inverter V=0,875 CяD(4)eff (liters), where CE is the flexibility of the air in the box is equal to 0.7 SG. (in Newton meters), and Dэфф - effective diameter (in cm) equal to 0.76... 0,82 Dном. The length of the passage L is found from the relation (4L+3,4 (d)/d2= =ЗU2d2/4лVfo. where L and d are respectively the length and the diameter of the bass reflex tunnel (in meters), V - volume of the box (in cubic meters), fo is the resonant frequency of the head (in Hertz). When choosing the length L (Fig. 1), it should be borne in mind that the distance from the end of the tunnel to the rear wall of the drawer must be at least 40 mm, and the length L should not exceed 0.1 of the wavelength corresponding to the resonant frequency fo of the head, i.e. it is necessary to fulfill the condition: L(mm)<3400/fo (Hz). If the estimated length of the passage will be too large, given its smaller diameter, so that the above conditions are respected.

In the calculation on the calculator first record in program 1, and then are entered into the registers P1, P2, RZ, R4 and R5 raw data: the mass M (in kilograms), the mixing coil D (mm), the diameter of the diffuser Dном (cm), opening diameter d (mm) and the resonance frequency fo (Hz). Then press the keys V/O and s/P and after a few seconds is read from the display of the calculator the length of the passage, and from the register R6 extract volume the phase inverter in liters.

Example. To calculate the phase inverter. in running head HD-35 with a diameter of diffuser Dном=20cm and resonant frequency fо=65Hz. A weight of 0.2 kg is the displacement of the voice coil at a distance of D=1.5 mm., the diameter of the passage d is chosen equal to 0.05 m. Writing the program into the calculator, putting the source data in the memory registers: 0.P, 1.P, P, 0.P, P. Then press the key V/O and s/P and waiting for the cessation of calculation, read on the scoreboard the length of the passage: L=6.6 × 10 - 2 m. Check the condition: L<3400/fo. If the scoreboard shows the combination of "EGGNOG" (error). the condition is not met and it is necessary to reduce the diameter of the passage, if there was a number, then the condition is satisfied. Press s/P - on the scoreboard the number 52,3, it means that the condition is satisfied. From the register IP6 recoverable volume bass reflex V=13 l

**Literature**

Publication: N. Bolshakov, rf.atnn.ru