BEST 18" Sub for a folded horn enclosure!

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Wow, that sounds like fair summary and fresh air to my wisdom. Exactly what I was looking for (and expected).

That way I could propably stay with BR, because box volume and weight is the thing what drives my decision. Also highest power output density under 50Hz (SPL per cubic measure), so BR or even pasive radiator design is what I seek for then.

Thank you for clarification.
 
Hey guys.
Firstly, when I set some strict box volume, I never see compact TH outperform BR where I need it - under 50 or 40Hz.

The way I tend to look at (and this will mostly echo what JAG said), efficiency and enclosure size are very closely tied together. The issue is that the standard ported box design as we tend to think of it (A relatively large box with a resonant port that does not take up a dominant portion of that volume) does not really realize those gains when you scale it up. Quarter wave resonators like tapped horns/pipes and even regular horns do realize those efficiency gains from being scaled up much more effectively. But just like a ported box is not the most effective choice at large scales, the advantages of horns mostly disappear when you build them at small scales.

That said, I think you can start to have a whole different discussion about why bass reflex/ported boxes might be becoming less favored due to how strong modern drivers are. Those low qes high bl pro drivers seem to waste some potential in standard ported boxes. More innovative alignments like bandpass and TH can more effectively utilize their strengths. I think that change is pushing the break-even point between choosing a tapped horn and a ported box for a given size toward smaller sizes.
 
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Then there is all that sensitivity and power talk, and efficiency, but NOONE looks at it from the impedance and real loading and power level angle of view.

Probably because there is no need to do so. Basically all power amplifiers these days can be considered as voltage sources (up to their rated power output, of course), so the speaker's voltage sensitivity is a much more useful parameter for determining the loudspeaker's output capability. Of course the amplifier has to be rated to drive the loudspeaker's rated impedance (or the combined rated impedance if multiple loudspeakers are connected to the amplifier).
 
zettairyouiki: I see.
The favoring of more "accoustical impedance loading" designs is rather difficult to sort out. There is "cool" factor to it on DYI forums, "changing SPL for frequency range" thing, which is very common (very little amount of people go for range under 35-40Hz), there is "changing SPL for directivity" and there is even more. So it´s not easy comparison. At ALL. That way I´would most likely stay away from some superiority claims.

Low Qes high power drivers only seem to waste its potential, unless you understand how to use it even in this enclosure. BL is the king, and if you look at impedance curves, you´ll see that the driver can do a lot more if driven properly. The main problem is low impedance around the bassreflex tuning frequency, and bassreflex size (efficiency when driven by large signals).

I´ve heard 4 BH760s though (and saw non-empty drinking cups thrown from benches on the ground), so I see how it scales up nicely, and do better job when large.
 
Brian Steele: There is no need for everyone. But there is the need for these who strive for more "power density". I.E. SPL in frequency domain per cubic measure.
Most of current power amplifiers indeed are voltage sources. The question is "Is that the rightest right"? Cannot it be different way? And it can. So the speaker´s voltage sensitivity can be neglected, and true POWER efficiency can show up. In third milenia with all that processing power, SMPSs and D-Class amps, it is possible. I believe B&C and powersoft tries nicely with IPAL.

But I wasn´t really talking about certain system design. I rather noted how I don´t like all these claims about efficiency, when it´s not measured appropriately. Efficiency is efficiency, and should be claimed the way it is. Not by the voltage sensitivity, which is very different parameter, on which you cannot really trash another system.
 
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