Originally Posted by jamiebosco
Just off the top of your head/back of the napkin calculations, what would the "ideal" cabinet size be (talking absolute performance) using 2 of your existing 18"s plus your current 1900w amp and ~12Hz tuning? I'm guessing over 20 ft³ ?? Where does the point of diminishing returns kick in here?
I know it sounds like a shrug-off but there really is no "ideal" size. Even limiting the scope of discussion to only objective performance there will almost always be metrics that degrade as other improve. I'm not going to detail all the checks and balances I've found most important over the years of course. However I have made a few points clear or tried too anyway.
1)Quasi-Anechoic data sets are important but only if we understand how they will correlate to a real world listening environment. In other words...an actual room.
2)CEA-2010 has value but to maximize it's value we have to understand it's limitations.
3)If you don't think mid and upper bass system efficiency has importance(i.e. focusing only on <25hz) you're missing the forest for the shrubbery. ( www.youtube.com/watch?v=69iB-xy0u4A
Of course the driver T/S will be a factor but not in the ways many assume and often not nearly as important as assumed. At least not in the simplistic "this driver has more claimed xmax it must be better than yours!!!"
Now, anyone starting a DIY idea like this might start with two ratios.
a)how much laminar port flow do I want relative to the driver compliment. In other words...one 10 in woofer doesn't require a eight in port tube. On the OTHER hand...dual high stroke/.high motor 21s?
b)Once you have the above ball parked then the minimum enclosure size is dictated to you because of the port size. I detailed this previously but the most effective, the most efficient port is straight, round, and thin walled(with adequate flaring on both ends). Any deviation from this is a compromise for other reasons.
c)Once you have the above, driver compliment matched to laminar port needs, matched to targeting tuning point...then you end up with a good ballpark on the effective internal volume requirements. At that point you now need to think about the most effective dimensions for performance, styling, and even a variety of considerations that may not be obvious. The best way to maximize a sheet of MDF for example(sometimes changing one dimension a fraction of an inch can dramatically lessen the "waste" per sheet).
So now you have the port width, depth, the driver compliment, and the minimum box size needed. Remember, the box size at this point is a NEED to have, not a design choice. If you want a big, straight port, the box size is *dictated* to you so you can fit it in the box. I mean, you can smoke stack it too...but that's not going to fly in a real commercial design
Probably before going any further one big decision is the exact port "tune". How low is low enough? 15hz? 14hz? 12hz? Where is the optimal balance? Believe it or not this will be a HUGE determiner for port length and by association box size. For example, use a generic big but not the ayatollah of rock and roller humongous box of say 12 cuft.
12hz tube with a 6 inch ID? 40 inch.
So now we have one dimension dictate to us and it needs to be 43-44 inch minimum.
14hz? A much more manageable 28 inch.
Okay, but let's look at that for a second. If the box size is staying at 12 cu-ft, what benefit would it be to us for reduce the port length from 40 to 28 inches?
Anyway, I'd be willing to bet that something 12.75hz to 14.00hz tune would score higher (all else being equal) than a 10hz design (literally)98% of the time in a listening session/GTG. Well, this assumes real music and real movie content. I'm not talking about looping 3 seconds of EoT which is really just the equivalent of running sine waves. If that's the end game test...meh...I'm losing interest in the whole thing pretty quick..
But go find some REAL movie scenes that do extend down to 15hz or 12hz or even 10hz...that's fine and expected of course. I'll attach a screen capture showing that even strong "10hz movie scenes" will almost always have 90hz of their content in the 20-100hz range.
So there you go. 10hz?, 12hz? 14hz? Choose wisely..
After that, you have the minimum box....long way to get to a simple answer I guess.
NOW, what are you gaining and possibly losing by increasing from the above minimum?
This is so intrinsically connected to cost and acceptable size for marketing purposes that I'm not sure how informative it would be to discuss them in a vacuum.
Bigger than minimum negatively affects both cost and potential market size. Increasing the cost(price) negatively affects potential market size in and of itself. But increasing cost AND size...that's a doub;e whammy. So any thought about increasing size above the minimums outlined above better have significant performance benefits associated with them. And in these specific examples(tune <15hz) the minimum size ends up being so big initially anyway(assuming you properly scale the laminar flow capabilities to the driver compliment) we're well into the whole diminishing returns thing regardless. In other words, you have say a 20x26x45 inch box that already weighs 200 pounds at whatever price point say 2650. Will you want to increase that to 20x30x48/240 pounds at say $3100 just to increase the cea-2010 score at 10hz a few dB?
You know what the man said...
Power Sound Audio