In a 3-way design. If I would like to use 7" woofer.
The following two choices:
I. 7" woofer + 7" Passive Radiator
II. The two same 7" woofers are shunted in Vented box
I have known that using a passive radiator is another kind of vented.
So, what are the pros an cons of the two choices? (If the cost just a little different) Thanks for your help !
The different is, that you need approx. the twice of cabinet volume, if you will realize also a vented box in case of two same 7" woofers.
If you compare this two chassis variantes with the same volume, you must realize a closed box in case of two same 7" woofers. The different is now the acoustical slope of the resulting high pass function. Vented box create a curvature with 24db/oct and closed box only 12 db/oct.
If you sure, that you don't carry out an enhancement through a subwoofer system (e. g. because there is no enough room space), then the closed version is clearly to prefer.
In other case (as a transitional solution) vented box is to prefer, because in case of an exist/retrofitted subwoofer below 70 Hz you can enhance the reflex tuning frequency to an so called "boom box" (large enhanced level arround the tuning frequency of approx 70-90 Hz) include an electronical attenuation with help of passive components (additional passive high pass in series - 1x coil, 1x cap, 1-2 resistors for modelling curvature).
This I have carried out several times - have a look to the photos of my website www_tiefbassuebertragung_de.
By tuning frequencies of 70-90 Hz the surface of vented port is much more larger and more distortionless (and more efficiency) than by 25-40 Hz - very very important to know.
Therefore is by the use of low cabinet volume and low tuning frequencies at the same time a passive radiator the best compromise - unfortunately the efficiency is very low, i. e. low audible power.
Concerning the number of rails the best choice is the connecting in series or parallel both transducers, if the crossover frequency to the midrange is below 400-500 Hz (3-way).