Have you guys seen these yet? I think they've been around for a couple of years now.
David Gunness / Fulcrum Audio have a line PASSIVE cardioid speakers. The size / weight / dB output per watt is sort of amazing, considering how inefficient and large most active cardioid subs are. Gunness is obviously one of the really talented audio guys out there, but still the specs on these subs look WAY better than they should.
Specs below, but I'm wondering if there's any way a DIY guy (Not me, but a really knowledgable engineering type) could design something similar?
In addition, you'd need to figure out the DSP that's going on. Sounds daunting to put it mildly, but this might be a new bar to reach for, at least with BR subs.
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Check out, for instance, the 2x12" Fulcrum Audio CS212L. (They also have similar subs with larger drivers)
The sensitivity is only 95 dB, with a power limit of 700w per driver at 8 ohms, yet they claim a max continuous SPL, @ half space of 132 dB.
I don't see how that's even possible.
They also claim 8 dB of rear-rejection across the entire usable bandwidth, with (from what I can see) no lobing on the sides. - which is also sorta' hard to believe.
Mind you the retail cost is over $2800 for a single 2x12", and I THINK you need to run them in pairs, plus you need a qualified processor to run his TQ dsp.
This is making me wonder if I should even bother building a new version of my current 2x12" boxes, or even try a small TH.
David Gunness / Fulcrum Audio have a line PASSIVE cardioid speakers. The size / weight / dB output per watt is sort of amazing, considering how inefficient and large most active cardioid subs are. Gunness is obviously one of the really talented audio guys out there, but still the specs on these subs look WAY better than they should.
Specs below, but I'm wondering if there's any way a DIY guy (Not me, but a really knowledgable engineering type) could design something similar?
In addition, you'd need to figure out the DSP that's going on. Sounds daunting to put it mildly, but this might be a new bar to reach for, at least with BR subs.
Check out, for instance, the 2x12" Fulcrum Audio CS212L. (They also have similar subs with larger drivers)
The sensitivity is only 95 dB, with a power limit of 700w per driver at 8 ohms, yet they claim a max continuous SPL, @ half space of 132 dB.
I don't see how that's even possible.
They also claim 8 dB of rear-rejection across the entire usable bandwidth, with (from what I can see) no lobing on the sides. - which is also sorta' hard to believe.
Mind you the retail cost is over $2800 for a single 2x12", and I THINK you need to run them in pairs, plus you need a qualified processor to run his TQ dsp.
This is making me wonder if I should even bother building a new version of my current 2x12" boxes, or even try a small TH.
Fulcrum Audio's subcardioid subwoofers are able to control directivity far better than I would have thought possible before I heard them at the 2017 Orlando InfoComm. The rear rejection was quite amazing for the size, bringing pattern control to low frequencies in cabinets that can be handled by one person and have good sensitivity.
The sub DSP does not look to be daunting, but the rest of the design would be 😉.
David Gunness (Fulcrum Acoustic,LLC) Patent No.: US 10,123,111 B2 from November 6, 2018 is a good introduction to the current state of the art in passive cardioid technology.
https://www.fulcrum-acoustic.com/wp-content/uploads/2019/10/Passive-Cardioid-Speaker-Patent.pdf
Hydrophobic acoustically resistive cloth as used in cell phone mic protection helps make the calibrated resistive element process repeatable (around 38:55):
It appears the CS212L spec sheet claiming 101dB half space nominal sensitivity is +6dB over what it should be.
The
"Equalized Maximum SPL 6 (half / whole space)
134 dB / 128 dB peak
128 dB / 122 dB continuous"
specification looks OK, given Dave's explanation:
David Gunness wrote on 4/10/14, post # 18:
https://soundforums.net/threads/9905-Compact-Power-Subs-for-Stick-mains
OK, here we go. Once more into the breach. The reason I hate this is that in the process of explaining how our industry does specs, it appears that I am justifying practices that I actually don't agree with.
One of the reasons I don't like peak SPL specs is that "SPL", at least in textbooks, is defined as the RMS sound pressure (referenced to 2x10-5 pascals). So theoretically, there is no such thing as "peak SPL". OK, maybe that's too pedantic: we could interpret it as "peak sound pressure, expressed in units of SPL". Let's go with that.
The point is that "Peak SPL" as it is treated in the professional loudspeaker industry, is peak pressure, not "highest reading of an SPL meter" (SPL meters only measure RMS; even if there is a peak hold function, it is the "highest rms reading observed", and that includes the selected averaging time). Anyway, peak pressure is calculated using the peak voltage of the amplifier. With non-powered systems, the assumption is that a user will supply an amplifier with twice the power rating of the loudspeaker, and that the peak voltage of the amplifier is 3 dB higher than that, because amplifiers are rated with sine waves. Hence, the peak pressure should be 6 dB higher than the maximum continuous SPL.
Keep in mind that maximum continuous SPL is a survival rating, not a useability rating. Of course what would be more useful is "maximum useable SPL", but that would be signal dependent and would have to be subjectively determined. So we're stuck with a calculated value that serves only as a point of comparison: "This one's red line is 2 dB higher than this one's red line."
As for the TS215ac, here is the math (with one more significant figure than the whole numbers on the spec sheet):
Equalized Sensitivity: 99.2 dB
Maximum Peak Voltage of the Amplifiers: 150 V
"Peak Power" into 2 ohms (actually two channels driving 4 ohms each): 11,250 W
Peak Power, expressed in decibels: 40.5 dB
99.2 dB + 40.5 dB = 139.7 dB, which rounds to 140 dB
Note the unprocessed TS215 is 95dB at 40Hz, the CS212L is only 88dB, though the impedance is much higher in the low frequency range and the cabinet smaller.
Having heard one of Dave's subcardioid subs, that part of the spec seems completely believable.
Art
I'm glad you actually heard these, Art.
The efficiency surprises me because some amount of power has to be "sacrificed" in order to create the phase-cancellations.
Anyway, do you recall at all if you were impressed with the overall sound? (Tightness, cleanliness, "fun factor," etc?)
Also, as above, do you think it's beyond the scope of DIY to even consider trying to design something like this?
The efficiency surprises me because some amount of power has to be "sacrificed" in order to create the phase-cancellations.
Anyway, do you recall at all if you were impressed with the overall sound? (Tightness, cleanliness, "fun factor," etc?)
Also, as above, do you think it's beyond the scope of DIY to even consider trying to design something like this?
The efficiency is less than a good 2x12" bass reflex. The JTR Captivator 212 is only slightly larger, but it's 1w/1m sensitivity is about 97dB at 40Hz, 102 at 100Hz, compared with only 88dB at 40Hz, 98 at 100Hz for the CS212L. You don't get something for nothing..
The listening condition was a noisy open convention center floor at a relatively low SPL, so other than the drop off in level to the rear of the cabinet, I don't have any other lasting impressions- it sounded like a good sub in front, and almost like it had been turned off when I walked behind.
I don't think anything in the design or construction of a sub-cardioid subwoofer is beyond the scope of DIY, but it won't appeal to most DIY builders, throwing out 8dB in front to loose 6dB at 40Hz behind takes double the cabinets and amps to keep up.
Considering you use multiple cabinets and amp sides already, you could go cardiod with a 2 forward 1 back arrangement and probably get better results with no monetary investment, and make the appropriate choice for the type of gig.
Art
I know manufacturers love to play with numbers, but then how is Gunness claiming 132 dB continuous in half space with 1400w?
Just at 100 Hz? I must be calculating wrong.
I'm not arguing with you (that would be foolish 🙂 ) - only trying to understand. Besides, I EXPECTED the cardioid sub to be less efficient. I was just surprised when it seemed otherwise.
I gotta' look at the numbers again for that 2x12" you designed for me.
Of course, guys with permanent install PA's (unlimited power) and home theater types might want to look into this design.
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That's an interesting idea, especially as I'll typically be carrying three 2x 12" cabs. Plus the main time I'd need all three for volume is outdoors, where having cardioid is much less important (for me, not the surrounding businesses) so this might be feasible idea.
The downside is that, without fancy DSP, you can't get true cardioid. (heck, not EVEN with fancy DSP, from what I've seen.) There seems to always be some lobing or whatnot on the sides.
Still, this might be a very good idea to play around with.
Is not fancy dsp just delay , phase flip can be done at the driver flipping the cables, just the delay.you need to adjust till you get the maximum cancellation at the back.
And of course whatever LP and HP filters settings that you apply to the forward cabinets you do for the back firing one, just that one need to be delayed .
I just got one of these to have fun delaying my subs for cardiod experiments and to align my horn subs with BR ones and sometimes to align the tops with the horns when cause where the subs was did not align properly acoustically speaking.
BSS ACTIVE SIGNAL MANAGEMENT TCS804 4 channel delay unit
https://prg-proshop.com/products/item/1163/bss-tcs804-delay
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132 dB Nominal continuous, based on a nominal sensitivity of 101 dB, which is only reached above 400Hz.
Note 4 "Nominal Sensitivity" does not specify the band limit of the pink noise signal.
The band limited EIA-426-B signal looks like this:
The FA CS212L is about 5.4 cubic feet gross (exterior dimension), the FA US212 is 4.1 cubic feet gross, and specs a nominal sensitivity of 102dB.
The charts show what you need to know about sensitivity vs frequency and impedance, the US212 is about +6dB more sensitive at 40Hz.
I didn't actually design anything for you, but made comments about Jerry McNutt's box suggestions.
Don't know the size or details of what you actually built, but Jerry's 2x12" Kappalite 3012LF sim indicated the 5.2 cubic foot (Vb, or Vb total?) 39Hz Fb box 1w/1m sensitivity would be about 94dB at 40Hz rising to 100dB at 200Hz.
Your box sensitivity should be very close to the FA US212 up to 100Hz (less above), and quite a bit more sensitive than the FA CS212L, but not as sensitive as the 44Fb 6.25 cubic feet gross JTR Captivator 212-Pro.
We could add sub-cardiod to Hofmann's iron law: low, efficient, small, pick two.
Art
https://prg-proshop.com/products/item/1163/bss-tcs804-delay
That's why Fulcrum's response looks so impressive. And passive, no less.
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Art -
Yeah I built Jerry's basic design, (and he was incredibly helpful) but used your small changes to box tuning and port size.