Wow, so much animosity.
So, as for physics. The -3dB measurements of a speaker are only part of the physics needed to understand the perceived bass extension. Of course, anechoically, a larger diameter driver and greater linear excursion contribute to lower and deeper bass. Each time you go down an octave your excursion requirements for the same driver go up by a factor of 10. This is basic theory, and there’s nothing incorrect about it. However, in a room, room modes matter a great deal. Having done a lot of measurements, +- 25 dB room modes is not uncommon below 40 Hz, so it may be quite impossible to get deep bass. Michael Fremer regularly complains about this, which is sad because it’s perfectly treatable. It may also be possible that the bass level is set by the peaks, not the average. As has been written by better acousticians than me, these room modes are completely untreatable by conventional (even digital) equalizers. There are some cool things being done with time-domain EQ’s though, I have not experienced them.
So, when I say that bass traps can extend the bass, I mean they can remove nulls, and flatten peaks. In addition, they can make speaker and listening locations more flexible. Lastly, they are the enabling technology for equalization (again, no matter if digital or analog). My concern, which you seem to have taken askew, is that most music lovers try to get bigger speakers, or more expensive speakers or subs without considering the room and room acoustics first. They spend thousands, if not tens of thousands of dollars on new speakers which may not end up being satisfactory. I prefer to suggest they consider bass traps and room equalization first. Of course, buy what you want. I’m just trying to suggest the most effective order of purchases.
Now, as for Vandersteen subs with built in parametrics. It’s much better than no EQ at all, that’s for sure. My preference for digital EQ’s such as Dirac Live or miniDSP comes from the flexibility and power of the measurements. Even with bass traps, some modes will exist. I can measure at six different locations, get an average, and then compute the exactly correct filter sets, upload them and bam. Done. In addition, being able to set delays to the main speakers (which are usually out in front), crossover slopes, and EQ of the entire combination are all features available via digital EQ’s or crossovers. Putting one before your DAC allows it to happen completely transparently.
My comment about "crap bass" is related to the end result I often hear. As you go down in frequency you are more likely to run into room modes. A smaller speaker, with a higher rated -3 dB cut off may in fact sound better. Focal famously added a subsonic filter to some of their subs for just such a reason. Of course, every room is different, and I’m not getting paid to do an in depth analysis of your room, so you should take this advice in context.
So, if you ask me what the recipe is for reliably getting the deepest, cleanest, and most musical and movie friendly bass, my suggestions are still measurement tools, bass traps, digital EQ and then a subwoofer, in that order.
By the way, you keep talking about having an octave overlap between the sub and the satellites. As a speaker designer myself, this sounds rather vague. I’m not sure how it’s possible with most speakers not to have this, so I’m clearly not understanding the specifics.
As for me liking Scanspeak and kits, yes I do. My point to all of that is, many good 2-way speakers can have much better and deeper sounding bass than most people realize. I use 6.5" ported versions in my mains, and for most music at volumes my neighbors will let me play is really great. I’m sure other brands can do the same in the right setting as well. I’m trying to encourage listeners to go for quality, not quantity. In addition, the phenomenon of room-gain can extend the -3dB point pretty meaningfully down in frequency, so a 2-way speaker that is rated to 40 Hz or so may play much better than you would think. Again, the lower you go, the more you can run into trouble. For more details on room-gain, look up Troels Gravesen's kits, where he compares the anechoic and in-room responses.
As I’ve written, I’d much rather have a $1,000 Hsu (very nice subs!) with bass traps and a miniDSP than practically any other sub without them. The quality of the room and integration between the sub and the room matters a lot more than the quality of the sub, and even more than the integration with the speakers. About 2/3rds of the time that listeners say they have speaker integration problems they don’t. They have room integration problems. This is why my generic advice is shaped the way it is. Does that apply every time? No, but for most it should be helpful.
Best,
Erik
