I tend to reference the power level back to 8 ohms, as that's the specification used for many amplifiers. VituixCAD supplies the voltage to the load, and the actual dissipated power is computed on that basis.
So i think this is the best i can do, another question, SBB4 or QB3 or SC4? I don't understand the diference between them
It should run 330w o 450w max. Any advice before i start the wood cut?
The SBB4, QB3, and SC4 represent different low-frequency alignments that can be achieved with a given driver. They result in different frequency response shapes, giving different transient responses. The more rounded frequency response curves can be regarded as having a "better" transient response, but they do sacrifice low-frequency output and low-frequency extension.
When considering a woofer's response function, I tend to prefer the QB3 alignment, as it seems to strike a good balance between low-frequency output, low-frequency extension and bass-reflex transient response. However, for a subwoofer application, the additional effects of the low-pass and high-pass filters also need to be considered. If trying to achieve the lowest possible −3dB cut-off frequency for the subwoofer, then the SBB4 or SC4 alignment may prove better than the QB3 alignment. The differences should become evident in the simulations.
In VituixCAD, when using the PD.18BR40 driver, you can see the frequency response change as you select between the SBB4/BB4, QB3/SQB3, and SC4/C4 alignments. If you click on the Enclosure tab, you will see that VituixCAD has automatically altered the enclosure volume and vent tuning frequency in order to set up the chosen alignment.
The SBB4 alignment produces Vb = 135 litres, Fb = 30 Hz, and f3 = 51.1 Hz.
The QB3 alignment produces Vb = 127 litres, Fb = 37.2 Hz, and f3 = 45.6 Hz.
The SC4 alignment produces Vb = 126 litres, Fb = 33.3 Hz, and f3 = 48.3 Hz.
As you can see, the enclosure volume stays roughly the same for each of the three alignments. The frequency response curves are adjusted by changing the vent tuning frequency, Fb, to suit.
Below is a set of three responses corresponding to the three possible alignment settings. The solid line corresponds to the QB3 alignment. As you can see, the QB3 alignment produces the flattest response in its passband, with the lowest −3dB cut-off frequency (f3=45.6Hz). However, it can also be seen that the −10dB cut-off frequency (denoted by f10) of the QB3 alignment is the highest of the three.
When considering a woofer's response function, I tend to prefer the QB3 alignment, as it seems to strike a good balance between low-frequency output, low-frequency extension and bass-reflex transient response. However, for a subwoofer application, the additional effects of the low-pass and high-pass filters also need to be considered. If trying to achieve the lowest possible −3dB cut-off frequency for the subwoofer, then the SBB4 or SC4 alignment may prove better than the QB3 alignment. The differences should become evident in the simulations.
In VituixCAD, when using the PD.18BR40 driver, you can see the frequency response change as you select between the SBB4/BB4, QB3/SQB3, and SC4/C4 alignments. If you click on the Enclosure tab, you will see that VituixCAD has automatically altered the enclosure volume and vent tuning frequency in order to set up the chosen alignment.
The SBB4 alignment produces Vb = 135 litres, Fb = 30 Hz, and f3 = 51.1 Hz.
The QB3 alignment produces Vb = 127 litres, Fb = 37.2 Hz, and f3 = 45.6 Hz.
The SC4 alignment produces Vb = 126 litres, Fb = 33.3 Hz, and f3 = 48.3 Hz.
As you can see, the enclosure volume stays roughly the same for each of the three alignments. The frequency response curves are adjusted by changing the vent tuning frequency, Fb, to suit.
Below is a set of three responses corresponding to the three possible alignment settings. The solid line corresponds to the QB3 alignment. As you can see, the QB3 alignment produces the flattest response in its passband, with the lowest −3dB cut-off frequency (f3=45.6Hz). However, it can also be seen that the −10dB cut-off frequency (denoted by f10) of the QB3 alignment is the highest of the three.
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