I was rooting around on Salk's site, sort of comparing Phil3s to SS8s & SS10s. I have a little understanding of passive radiators, and a little of folded transmission lines, but not much. It seems people often generally equate the sound of the Phil3s to the SS8s, but it appears the design is quite different.
Just wondering about the advantages or disadvantages of each. (I'm really wondering why Jim chose passive radiators and Dennis chose FTL.
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The reason is size and practicality.
A passive radiator speaker is a tuned enclosure, pretty much identical to a properly sized ported enclosure, although the bass rolls off about 6 db steeper than for a port as a rule.
A properly designed folded TL can be designed to give low Q non resonant reproduction. Properly done the quality and realism of the bass is remarkable. .
Now F3 for F3 the TL is going to be a much larger structure. In addition there is a fairly narrow range of T/S parameters that make for a really impressive TL. One thing you need is low Fs. This generally means a large driver. The lower the operating range of the pipe the longer it is. The higher the VAS of the driver the more volume the box must have. This is also true of ported and ABR. However the TL starts from a higher volume to start with. Now if you put in two drivers, the volume of either design is doubled. The TL though starts to become a massive and formidable endeavor.
In Dennis's design there is one nice 8" woofer going down to the mid 20s. (Fs 21 Hz) However his enclosure is very large for one 8" woofer. If he had used two to increase power handling the enclosure would have been twice the volume.
So if Salk had used a folded TL for the SS8 then his enclosure would have been much bigger and the same for his 10" woofer which goes to the low 20s.
So really powerful TLs going to the 20 Hz range or below are going to be the preserve of the DIY community I feel. The practicalities imposed by the physics of the situation make for limited commercial applications to say the least on grounds of size and cost, especially if the consumer is focused on F3.
The fact is that smaller lines actually sound very good and are better than just a look at f3 would suggest. a ported enclosure rolls off 24 db per octave below F3 and an ABR generally 36 db. On the other hand a properly designed folded TL will roll off 12 db per octave below F3.
The other confounding problem is that I think consumers have become accustomed to resonant bass reproduction at least to a degree. Listening to properly damped TLs is disarming at first encounter for many, until they realize that the bass really is true to life.
When a 32 ft stop in a cathedral in the UK is just ever so lightly sounded against the choristers, the sound is just truly amazing. It becomes not how loud the bass can be (and TLs will do that too) but how light and soft it can be. The bass is just so clean without boom or overhang. Once you have experienced it for a while you will never go back to resonant reproduction.
My lines are truly formidable constructions. The bass lines have 2 10" drivers with Fs 20 Hz. That is the same as having one 15" driver in each enclosure.
Even so the shear size of these speakers is still to a large extent concealed by the architecture of the room.
The other thing I would say, if you do want to use a smaller TL and want to use a sub with it, to really get the benefit the sub also needs to be a TL in my view. Without taking that step the magic is to a large extent lost.
In those speakers there are two lines half an octave apart which act in synergy. So in my view a totally integrated full range design makes the most sense. Because of active circuitry the LFE channel is fully captured and integrated.
As a commercial venture I would not see many takers. As a DIY design it is absolutely worth it to me and brings untold pleasure.
