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this 42" tall coupler imo was a good performer dynamically speaking with high output capibility with low cone excursion and no visable offset effects. (there's ~no midrange gain vs direct radiator so getting giddy with coupler might not be good)what doesn't seem to be known is how far down the apparent front pipe's cross-section can be pulled vs Sd and whether front tuning can be lumped and examined by looking at the 3rd Z peak. (a 32" high box with 8CF bulk and no front shelf had 3rd Z peak @195Hz vs K15 @~155Hz)
what are practical front chamber aspect, bulk constraints and tuning ratios for effective couplers?
how might one put Poppe's paper to useful work?
front view 18K (~12% larger in bulk than K15)
input Z with vent set to side gapped position
Follow Ups:
Greets!Not sure what you're getting at, but these are BPs, so a basic one would be a type 2. Using an old version of LspCad and Altec's 604E's published specs I did a typical K alignment at 75 W rated power with 19 mm thickness vents. Note that the front vent ~ = Sd and that cone excursion doesn't exceed Xmax and that if an extra resonant chamber was added between the two tuned to ~70 Hz, then it would be well below Xmax and the roll-off would be more linear, just as you've seen/measured.
Anyway, as the front vent is reduced in area, the 3rd peak shifts lower in frequency/higher in amplitude, flattening the response and of course, vice versa. If each resonant chamber was increased in length to bring 1/4 WL damping to the vents, then they could be bigger for a given duct length, with even higher driver damping.
Did this answer your Q?
GM
hi GM - very nice program (WinISD won't work for me anymore and AJ seems to not have series BP capability) - IIRC, that particular coupler above exhibited a bit of rise and its curved reflector made for rougher graph with mic at ground perspective than another coupler variant wihc was ~32" tall (and around 190Hz 3rd Z peak - - from these programs it appears tuning F would be described a bit lower than that Z peak)re:"extra" chamber - are you referring to the partitioning of K's back chamber with the rear lowpass shelf?
re: 1/4 wave damping - lets say one wants the front tuned in 120-135Hz range --- what might be the effective height of the slotted coupler and what might be practical crossectional area vs Sd? - it has some building constaints.re:"BP"-ha- CN wouldn't like that :^)
these things could/can be made to perform pretty well.
Best,
FIgraph 1/24 octave >
Greets!Right, the K15 has the driver rear chamber venting into a low pass filter, which vents into another low pass filter, which vents into the front driver chamber, so while you can get by with just venting the rear driver chamber into the front like in the sim I did, adding the two interstage filters will of course perform better. If CN can't see that this is a multi-chambered BP, then that's his problem. Then again, neither he nor any of the others called me on it when I posted it on the K forum some years ago, so deep down that's an admission of agreement to my way of thinking. ;^)
Never tried 1/4 WL loading a BP, but I'd start with the obvious, ~3390"/135 = 25.1" to see how it measured, figuring the end correction will lower it some. The calc'd chamber Vb won't change though.
GM
might take 25" above the driver? - hahaha - but CN has a multitude of CNC-ed panels and math galore including k-coupler portions (must be top seKret info...) I'd like new coupler and maybe ~tapped horn subs.
Greets!Well, I didn't say he couldn't have derived something that works, but to do it without understanding the basics seems pretty far-fetched to me. Could be he just doesn't want folks to figure them out.
Anyway, the 25" would be chamber's total height.
hey GM - here's what I've seen for 3rd peak. dunno 'bout CN - seems to take stock in wing flare (and supposed release distribution) alot. CN will take 4 sets of tapers, pick best-set, possibly adjust that set, then try for a better coupler.the fun (or torture) with one of these things would be to achieve "acceptable" response (including sonics), minimal peaking, most output ability overall with least amount of excursion and somehow pick the best aspect and layout to to this stuff. (Moray likes K-TL - I'm really ignorant on TL and not sure how to work that for high spl withput something weird)
I've reached reasonably high spl with very little cone motion and K sound far cleaner than reflex imo. I can't get heavy B&C 15 to sound like doing much other than resonant flab/flapping on drums (might have to live with those in ~aperiodic)
Best,
Freddy(all height dims external)
25.5" high K12 per July 1958 Popular Mechanics areticle - 3rd Z peak 235Hz
27" high Acoustic Control box - VBf ~0.9CF, 3rd Z 224.6Hz
28" tall RCA-Fan X15 size - 3rd Z peak ~195Hz - if board above baffle if perpendicular and theres no reflector so that probabably accounts for somewhat lower tuning than X15 & 115BK
32" tall K box 6.3 cubic feet - 3rd Z peak 195Hz
32" tall 6.3 CF k-box - add 20 liter stub to top of front pipe via 2" x19" slot - 3rd Z drops to maybe 130Hz
response effect of a lightly poly-damped 20 liter add-on stub at top of front pipe keeping back chamber fixed at 85L - driver in both cases a 5% efficient 18" (not the 2.3% se in that other 18 coupler)
adding more volume (45l) to the same coupler seems to de-tune as BP theory would predict - but is the stub a legit thing to do with K's in first place? what is the best configuration for an Ultra-Fidelity type?
Impedance of 32" k/6.3CF with 45l stub on top of front chamber really droppped the 3rd Z peak
In-room graph of 45 liter cavity-stub vs none - looks to be de-tuned condition losing energy around 80-85
BP sim of 45 liter add-one cavity experiment above
33" high Stock K15 - 3rd Z comes in ~155Hz even if tuned like exemplar
32" tall K-box 8 cubic feet - no front nor rear shelf 3rd Z 190Hz - why is it so much higher than K15 (or vice-versa?)
Greets!Yeah, I've noted before that the vent's shape has some bearing on tuning, just nothing like Karlson hawked.
I wasn't aware Moray had done a TL loaded K, this is what I suggested quite awhile back as an easy way to somewhat mimic a K.
By 'heavy', I assume you mean a higher Qts driver. If so, then it needs to be in a bigger cab tuned lower over a narrower BW, so may make a good K-sub.
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