Originally Posted by qguy
Hopefully Salk sounds reads this part of the thread so he can comment on why he added the passive radiators. Would be interesting to see graphs of the ported vs the passive radiator version
It is almost same between the two except the passive radiator has an Fs and the output of the sub at that Fs point is null (that is, 0, or zip), meaning the radiator and the active driver has exactly same output magnitude, but with 180 degrees phase difference. Passive radiator, by name, means it can only transmit energy, not generate energy (not like the active driver with current passing magnetic field and therefore generate active force that pushes the cone). If you want to further draw parallel between the port and the radiator, the collective mass inside the port plays the same role as the moving mass of the passive radiator, except the passive radiator has a spring. As you can imagine, we want to make the passive radiator as compliant as possible (with negligible spring force). It will be no fun of the Fs of passive radiator is at 20hz. We actually want them to be at least at 10hz or even lower, say 5hz. It is not easy to design a passive radiator to do that.
The PR version of the SALK sub uses the same servo amp as our FV15HP except there is no multi-tune. They share the common servo feedback network. In other words, we treat these two configurations as the same one.
On the subject of bandpass subs, Gedde is the expert of bandpass subwoofers. He wrote an AES paper covering at least 10 different kinds of bandpass. First category is with two port tuning chambers (like the Boss). The trade-off in this type of bandpass is the efficiency is affected by the "bandpass" bandwidth. If you want to have a bandpass extended from 20hz to 100hz, the efficiency is will be low. The second category of bandpass is very simple. Hide the active driver and let the passive radiator do the work. But my view on this type of bandpass subs has always been similar to my view towards Isobarik: why hide the active driver when it can actually be exposed to outside and contribute to the real output?