m_ms

17 hours ago, SME said:

I would call the SKhorn a horn hybrid as it does behave like a horn in the upper end of its bandwidth and like a vented cabinet in the lower end.  But really, I think obsessing about terminology misses out on the important nuances.

Are you implying I'm "obsessing" about terminology? My point was simply to call for a comparison between the OThorn and SKhorn while having some tech background to possibly support the discrepancies found here, but apparently that's a touchy subject (or, granted, irrelevant). Oh, Mr. Ricci just confirmed the SKhorn isn't a horn at all, so there you have it..

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When you use the term "force multiplication", I think you are describing the increase in efficiency that occurs as a result of an increase in acoustic impedance of the air adjacent to the driver.  Put another way, the air near the driver is under more pressure than it normally would be without the "horn loading".  Truth be told, there are many ways to accomplish this acoustic loading.  One simple example that arises with subs in small rooms is placement of subs in or near a corner.  The corner placement actually increases the acoustic impedance of the air, loading the driver like a horn would.  Another way to increase acoustic loading is by placing multiple drivers next to one another.  These strategies can be combined.  For example, subs may be stacked in a corner in a floor to ceiling array, leading to an effective infinite line source and excellent acoustic loading.  These do exactly the same things that horns do, and if one is flexible in one's thinking, one can see how such arrangements *are horns* for all practical purposes.

Force multiplication, as it applies as a descriptor of the horn effect, to my mind is equally about effective air radiation area and how it couples to the air (what you mean by "acoustic loading"?). I've read of a number of cases where multiple direct radiating woofers, large ones at that (typically 18" or bigger), have been deemed to not better or even loose steam against horn-loaded bass augmentation - that is, where the latter used smaller diameter units in (much) fewer numbers. Following the need for nuance, as you pointed out earlier, I can't see how this's simply about efficiency dialed up via the horn. The horn being a megaphone as such also makes a given driver diameter appear much bigger at the horn mouth (and beyond it), but there's directivity at play as well and how this further affects how the sound is loaded or "carried" through the air, and ultimately perceived by the listener. Listening to direct radiators often feels like the sound looses energy and impact on its way to the ear/body vs. horn sound that somehow "latches on" to the air for a more visceral feel. More efficient direct radiating drivers alone wouldn't help to accomplish this effect.

So, in a sense the force multiplier is comprised in a threefold way: efficiency + air radiation area + acoustic loading (for a horn) and how this couples the sound to the air (the gradual impedance matching from throat to mouth). If there's a more or less precise numeric value for how to assess the increase of air radiation area from driver cone to the accumulated horn response in front of it, I take it the acoustic impedance matching, and what this means for sound "carriance"/directivity, adds yet another "amplification layer" of how the sound is actually perceived. Of course, all of this may as well be a giant pile of B.S.

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This makes me think of "waveguide theory", which basically provides a new set of mathematical tools to analyze and understand horns.  But at the time, horn speakers had a bad rep in audiophile circles for having screechy treble, so the people promoting the theory and speakers based around them insisted on calling their horns "waveguides", probably because the term was both less likely to sound offensive and more likely to sound sexy and innovative.  BTW, I hold waveguide theory in high regard and believe it has contributed to far superior horn designs, but I think it's still silly to call a "horn" a "waveguide" just because it was optimized using the better theory.

Every waveguide is a horn, but not necessarily vice versa - or something along those lines. I've owned 3 terminology-coined "waveguide" speakers prior to my current all-horn mains - from Amphion, S.P. Technology and hORNS (Polish) - and I was especially fond of the latter two. Going by terminology obsession and the supposed traits of waveguides, which I'm aware of, I should've gone from horns (that aren't waveguides) to waveguides, but the opposite is the case. Hmm.. That's not for lack of acknowledging the virtues of waveguides, but because the overall Tractrix + folded horn design with my current speakers sounded better to my ears.

Needless to say: if a pair of split-up SKhorns sounded better to my ears compared to some horn iteration (TH, FLH, whatever), of course I'd be going with the former. Going with the MicroWreckers, being tapped horns, instead of the SKhorn option comes down to two things: the MW's extending a bit deeper to cater to Blu-ray/UHD movie-playback, and being overall cheaper (cheaper drivers). Not least lilmike, just like Ricci, appears to be a very capable tapped horn, BP or other developer. Admittedly, being that I've had no opportunity to listen to either beforehand, I've been more intrigued with tapped horns than anything else (ports compress, sealed is boring (and inefficient), and all that jazz). 

6 hours ago, Ricci said:

TH's have a harmonic spike in what is commonly considered their bandwidth which can end up causing issues. If the TH is tuned low it moves the placement of this spike down in frequency until it can end up in the critical bandwidth you want to use the sub in. Bass guitar and kick drum range...As the TH becomes more and more undersized it exaggerates the spike in response even more. The more the tuning is lowered the greater the TH will be undersized effectively. There are tricks that can be done with the design to minimize this harmonic spike and a very well damped driver helps somewhat. You can also attempt to address it with EQ. However if it is bad enough it will always be audible. In my opinion TH's work the best when only extending to 25-30Hz at the lowest due to this. This allows you to keep that harmonic above 100Hz and above the usual low pass for the sub. This is why I quit pursuing big TH's that extend deeply.

Other designs can be made to sound excellent over a wider range much easier. Sealed, IB, ported, FLH, or BP variants. In my opinion for HT powerful headroom down to the 15-16Hz range gets most of the content. It's greatly diminishing returns below that point. For music I consider 25-30Hz the minimum for good reproduction without missing out on the "heavy" notes.

Thanks for this run-down - indeed interesting info. It seems to confirm I'm hitting a compromise with the MicroWrecker, tuned some 5Hz below the OThorn(and SKhorn?) and 5Hz above the lilWrecker and similar TH "company."

Attached is a simulation of the B&C 15TBX100 in the MW at 200 watts, 1pi measurement. Sensitivity sits at approx. 97dB's with this unit. There's a clear 80Hz spike, but I'm not sure how that'll translate to the actual real-world performance. I'd like to experiment with a 100Hz low-pass to relieve my all-horn mains from some bass duties, but maybe that's a bit optimistic. 

Being that the SKhorn is not really a horn (not even a variant of sorts?), does that mean the fitted driver is not "force multiplied" as would otherwise be the case via a typical horn loading? How for example would one section (with one 21" driver) of a spilt-in-two SKhorn fare against a single 21"-fitted OThorn (let's just say using the same driver, B&C 21SW152, to make comparisons easier)? Since pressure from both sides of the cone is also used in the SKhorn (though without being horn loaded in a similar fashion at one side as in a TH like the OThorn), I imagine they're not that far apart. Also, looking at the innards of the SKhorn it does seem there's a short loading at the front side of the cone. 

Reading up on this thread one gets the feeling that a "low corner" below some 25-30Hz for subs used for music augmentation - TH's, FLH's and 6th order BP perhaps in particular - may even be inadvisable if the most "musical" and best-integrated sound (with the mains) is sought. Is there any truth to this?

Tapped horns are said to be particularly bandwidth limited, so that the likes of Ghorn, LOWAR horn and lilWrecker TH's (all tuned at or below 20Hz) have a hard time reaching 100Hz without being EQ'd here. However, for as long as they're used within their "safety zone" in the upper region of their frequency span (say, up to 60-80Hz), not least high-passed accordingly, does that necessarily place any hindrance for them being excellent as music subs? Or is there an inherent flaw - typically, at least - with subs that are tuned below 20Hz, or maybe even higher, that makes them less than ideal for music?

Of course, if music is the primary source why bother with <20Hz reproduction, save perhaps organ freaks and their desire to reach into infrasonics? Cinema subs for the home environment are often preferred when having strong 10-20Hz output, which rules out a lot of horn varieties or other high(er) sensitivity pro-style options (like the SKhorn). Although, I may have to reassess the need for ULF-capabilities for Home Theater use when taking into account that most commercial cinemas use steep high-pass filters below 35-40Hz (except IMAX), and then suddenly strong bass reproduction down to 25Hz, as seen with the OThorn and SKhorn, isn't so bad after all.   

As is I'm going with a pair of MicroWrecker's of lilmike, hopefully finished by the end of next week, because they seem to give me both one and the other; strong reproduction to 20Hz (tuned to 22Hz) and up to some 100-120Hz (perhaps with slight EQ needed), to serve both music and films well. Still I'm wondering if I'm pushing a bit too far towards 20Hz to maybe compromise music reproduction. Maybe the lesson learned is to avoid both/and here, and instead seek either/or - with all that entails. The SKhorn is a close runners-up as a music-mostly sub, split up in two, but maybe that's the next build to embark on some years ahead..

Oh, perhaps I need to reveal that my priorities in regards to music and films (Blu-ray/UHD) is some 60/40. So, I do prefer having the subs dialed in for music first and foremost, but the added weight, physical presence and palpability of having reproduction capabilities down to 20Hz (or even lower) with films is quite addictive.

/Mikael