Originally Posted by Soulburner
Well this has been a useful exercise. As stated above, we've landed on a couple of measurements that seem most reliable - FV25HP and F18. We have an explanation for the FV15HP. We do not have one for the FV18, so we're going to have to chalk that one up to sample and/or measurement variation and call it a fluke as it shouldn't be that close to FV25HP. So based on this we can scale the rest using Rythmik's own relative performance chart, and expand it to include even more information. It's useful to me. Maybe it is to you, too. Or, I'm just an analytical nerd who devotes too much time to this stuff. Thank you everyone for your patience and input.
And Brian, I don't think you need to adjust the FV25HP! I think things line up pretty well now.
• I didn't include FM8, L12 white, F12SE, or any other minor variation of the same sub.
• These charts only speak in terms of 20Hz performance and cost - nothing else. Desired max extension, finish options, and other considerations are a personal decision.
• FVX15 output was adjusted to be -2.5dB from FV15HP based on its product page instead of the main page figure of -3dB.
• Output figures of 2 subs at 20Hz is only valid if placed within a maximum of 14 feet of each other. If placed further apart, you will see +3dB instead of +6dB gain at 20Hz because you will lose acoustic coupling.
• The L series generally has the highest bang for the buck - because it forgoes some of the bass extension, finish options, and amp controls of the F series.
• All models increase in performance per dollar when buying duals - except for F8 and F12-300, because those models do not have a multi-sub discount, or the discount is currently extended to a single sub purchase.
• I can share the formulas if anyone is curious.
• Please let me know of any mistakes.
I also enjoyed the discussion and appreciate the value of these sorts of analytical comparisons. But, having used the term "value" in the preceding sentence, I think that determining performance value, as a ratio to cost, is a very tricky exercise. Although I think that the 20Hz frequency you picked is a very logical one (that is still the Dolby/THX standard), we pay disproportionately more for frequencies below 20Hz. So, even leaving size, features, finishes, and intangibles out of the equation, the performance/cost ratio will still vary depending on the specific low-extension goals of the individual.
It will be interesting to hear your reaction, if you move to ported subs. Everything is relative, but the Rythmik ported subs may sound more like sealed subwoofers, compared to some other ported subs. I will be interested to hear your observations in that respect. I thought it was interesting that Enrico added an FV25, and said it sounded like adding another sealed sub. That's pretty cool! (Well, apparently that's not quite what Enrico meant, but I still have a feeling these ported subs would sound a little smoother than most ported subs.)
There is one thing that I might point-out about your list of caveats. Acoustic coupling is a little more complicated than that. Subwoofers should couple acoustically at 1/4 wavelength of a particular frequency, and if they do, there will be a 6db gain. But, depending on room modes they might gain or
lose SPL at a particular frequency, beyond that 1/4 wavelength distance. Identical subwoofers, in the same room, should average 6db more SPL, across their entire bandwidth. But, there will be peaks and dips in the SPL, depending on room modes. The 6db gain will only be theoretically 6db, at every frequency, when the subwoofers are very close together. I keep saying theoretically for a reason.
Still another complicating factor is dependent on the room's longest room dimension, in a room with four walls. The diagonal dimension from corner-to-corner, and from floor to ceiling, times two (because the wavelength has to make a return trip) determines the frequency at which pressure vessel gain (PVG) occurs. Below that frequency, room modes no longer cause peaks and dips, and the room only gives back acoustically. The reason I mention that is because, in many rooms, PVG would occur at or before 20Hz.
Given the complexity of the issue of what frequencies may mutually couple in a particular room, I would just leave caveats like that one out of your helpful analysis.