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Contrasseur

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Contrasseur last won the day on September 28 2016

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  1. Modern voice-coil subwoofers are currently capable of maxing out the linearity of even the largest FEA optimized surrounds. They're much simpler to make and have far fewer moving parts. There's also no static friction to cause distortion at low levels, or kinetic friction to cause wear at high levels. Cost is much lower and reliability is much better. Plus they can often be useful over much greater bandwith due to less inertia. Danley's original ServoDrive transducers had 12-16mm xmax. Outstanding when 4mm was the norm, but pretty lackluster by today's standards. Surely a servodrive with modern materials and engineering methods would be quite impressive indeed, but the cost would certainly be unreasonable. I don't know how you could manage surround noise, let alone mechanical noise with such excursions. If Danley's patent expired, it's telling that no one has bothered to come up with a copycat product. If he still holds the patent, it's equally revealing that he doesn't bother making speakers with it while the idea is still protected.
  2. OK Josh (and other bass overlords), here's my hypothesis Underlying assumptions At such low impedance loads, neither amplifier's power supply can sustain max-burst levels for any significant period of time. The Speakerpower's power supply can produce more current and has greater output capacitance. The Powersoft's power supply produces much higher voltage rails. The drivers compliances have loosened up since testing with the K20. Rigorous testing also broke in the cones/spiders/dust caps, enough to shift breakup modes. This last assumption is a stretch, but it's the only explanation I can think of for the last conclusion. Explanation of max burst results - K20 wins on the high end At the high end, the max burst performance is voltage limited, not distortion limited. You estimated the K20 to be able to produce ~400v bursts. At system resonance, current draw is minimal, so the inferior current capabilities make no difference. Same at the high end where driver inductance drives up system impedance. Explanation of max burst results - SP2-12000 wins on the low end This is likely to be the breaking-in of the driver. Below system resonance, the compliance starts pulling the cone toward the center before the motor finishes pushing it all the way to it's peak positions. We already know that this is the main source of distortion at the extreme low end. The loosened compliance helped reduce distortion further, contributing to the higher achievable SPLs before breaking CEA-2010 thresholds. The lower system resonances also lowered the frequency of the impedance peak, reducing current and extending Xmax at a slightly lower frequency than in previous K20 testing. Better output capacitance could also prevent the rails from sagging, which could introduce some distortion in the K20 as well. Explanation of long term results - K20 wins on the high end Higher available voltage offers greater achievable SPL on the high end. Tightened compliance during these tests also helps high end performance. Higher impedance in the high end due to the impedance peak and driver inductance minimizes the effect of the lower-current power supply. Explanation of long term results - SP2-12000 wins on the low end More current capacity from the power supply offers more low-end maximum performance. Explanation of sensitivity measurements - SP2-12000 wins on the low end I don't see how this could have anything to do with the amplifers themselves. I think this is solely due to loosened compliance. Explanation of sensitivity measurements - peaks and troughs seem switched between tests Same with this anomaly. I don't see how going from one flat-response amplifier to another could cause any change here. I think the breakup modes have shifted. On both of these drivers, breakup modes are very mild, exhibiting well damped resonances that create soft lumps in the FR instead of sharp peaks. It doesn't look to me like the peaks have become troughs and vice-versa, it looks to me like all but one or two of the resonances have shifted lower in frequency. The one that I can't really explain is the blip around 150Hz. This can be seen in all your measurements of similarly sized boxes, which is sure to be a rear chamber resonance. I don't see how this could have moved if the enclosure is the same size. Maybe the damping material has settled, affecting speed of sound and therefore perceived depth of the rear chamber to the acoustic waves?
  3. If weight is evenly distributed, your suspension could probably handle it. If it sags slightly, there's no top plate for the VC to scrape into. If you've already bought the driver, give it a try and see what happens.
  4. Metal would require lots of tooling. Folding, welding, maybe even casting, just way too much for probably no net benefit. If wood won't cut it for you, then you need composites. 1/4" carbon fiber or fiberglass with epoxy is damn tough. Even 1/8" will go a long way. They can be laid up in the final shape, with virtually no tooling required. Adding bracing would be elementary. Some people even consider it easier than woodworking once you get the hang of it. Just carve out a foam mold, glass the whole thing, then remove your foam. Cost is quite reasonable also. For such a small enclosure, the materials cost will be miniscule compared to your current $2.5k electronics and transducers budget. Useless in the workshop? Draw it in Solidworks or SketchUp and send that bitch to a 3D printer. You can brace it within an inch of its life for no extra work or money. Put gussets on top of gussets inside your gussets. You only pay per gram in 3D printing. You'll probably be using ABS or something. Fiber reinforced plastics can be stronger than many metals, but I don't know if they're printable.
  5. Really shows the output/size advantage in ported subwoofers over folded horns. The OS-LFU wins in efficiency and top end to no one's surprise, but a WHOLE OCTAVE of extra low end extension in a slighty smaller package? I'll bet the folks at JTR are justifiably bragging about this one!
  6. I think you can still do the PR just fine, but SME's right, you have to account for time domain issues. Group delay is related to the curvature of your final SPL. This means that it's treating say, 35Hz very differently from 40Hz. Intuitively, ask yourself "How is it going to tell the difference between these two frequencies, and how is it going to attenuate one but not the other?" This is the exact same concept that gives rise to the Heisenberg Uncertainty Principle. Knowing frequency with 100% precision requires infinite amount of time. Makes sense right? Frequency is cycles PER UNIT TIME. Now your system sees an input curve. As voltage rises, it doesn't know if it's going to be a 40Hz sine wave, a gaussian function (bell curve), a 39Hz sine wave, or any other infinite number of shapes until your 40Hz sine has completed it's full cycle. That's 1/40th of a second, or 25 milliseconds. Let's say our sine wave stopped at 25.6ms. It was a 39Hz sine wave. A perfect brickwall 40Hz filter would eliminate it, but it wouldn't be able to tell the difference until that last 600 microseconds. Such a slope is so steep that 40Hz frequencies would be delayed infinitely until it could be certain there was no 39.99999...Hz content, then the 40Hz tone would pass through unadulterated and any <40Hz tones would be eliminated. Real systems aren't perfect brickwalls, but attenuate by a certain amount. To attenuate power by 16x (12db) for every octave, we've created a second order rolloff. Sealed systems eventually progress to this steepness. A ported system will eventually have a 24db/octave slope. These slopes (and therefore delays) will stack with whatever active processing you add to it. Option 1 Eq flat to 40hz with only a 4th order rolloff. This means no high pass. Loud notes below 35Hz will fart, but you'll still only have your 4th order rolloff and time domain behavior will be quite acceptable. Option 2 Soften the corner of your final slope. Think Bessel filter, Zaph's quasi-EBS/QB3 alignment, Ricci's 25Hz ported BMS 18N862 system etc. i.e., a gradual increase in slope the further you drop in frequency. Response will be flat to say ~60Hz, slowly roll off to maybe -6dB at ~40Hz, then your high pass filter drops frequency response below tuning. Now all frequencies from 30-60Hz are delayed, but no frequency is delayed by more than one cycle, so time domain behavior will be acceptable. You can keep your high pass filter to eliminate below-tuning farts, you won't hear any ringing at the low corner, but 40Hz output is reduced. Option 3 Eq flat to 40Hz and put in your 40Hz high pass filters. No farts, no reduced 40Hz output, but very high group delay. Maybe as much as 1.5 cycles, maybe more. Now let's throw another wrench in the system. Room effects. Room effects will add all sorts of peaks and valleys everywhere in the low end. Even if Option 3 had barely acceptable group delay before you put the speaker in the room, it probably won't afterward. That's why a lot of speaker designers opt for Option 2 or Option 1. You'll have to decide where you want the tradeoffs to land.
  7. When "Go big or go home" doesn't cut it, you call in Radulescu
  8. Ah I see it now. Without it you don't really get that full 100Hz extension on the top end. I guess you could have just angled the baffles, but then you're sacrificing some of your force cancellation. Not a great tradeoff when your total moving mass is nearly 10lbs. I'll bet those 4 woofers could walk a 500lb cab if they were all facing the same direction
  9. Josh, when you made the slot, why did you choose to make that slight horn profile? It looks to me like weight, volume, and construction time could have been (barely) reduced by having the baffle run straight from the bottom to the top. The baffles would then be pushed toward the hatches a little, and the whole rear-chamber extension under the front chamber wouldn't be necessary. Was it to make more room for hatch bracing?
  10. Dig around as in eBay or dig around as in back alley dealer who probably stole them?
  11. I found this part to be particularly brilliant when I was playing with your Hornresp model. The slot loading adds so little volume gain everywhere above 18Hz! No front chamber ports needed. Sure it ruins your response above 100Hz, but that huge 12" rear chamber port already did that, so nothing lost. The extra sensitivity means this setup could easily be wheeled outside (with a crane) for PA use. Plus, when you equalize it to flat (or downward sloping curve like most will do) the upper band distortion gets stupid low. All of the upper band distortion spikes caused by out-of-band resonances vanish!
  12. Not at the size enclosure you're using, and the frequencies you intend to use them at. The distance between woofers is acoustically small. Even at 300Hz, the woofers are just about quarter wavelength of each other. The lower you go, especially down to 40 and 30Hz, the distance between sources, even wrapping around the cabinet, is negligible compared to the wavelength they produce. They will be pushing in phase unless you wired one wrong. Again, each woofer will eat up a little internal volume. Your proposed enclosure is ABSOLUTELY TINY so even going neodymium might have a measurable effect on the interior dimensions. Still, maximum output will be increased for the reasons previously discussed.
  13. I can't be the only one amazed at how simple this is! I saw "Horn" on the description and tried to imagine the 4th dimensional hyperspace fold you worked out, and it's not much more than a bandpass. A bit anticlimatic Really showcases the brutal power of these RFs. Distortion is unreal. Great build quality and optimization for size and performance! I love it. I also look forward to the extra 3dB of sensitivity thread! Looks like it's going to be another good one!
  14. What does this mean for your enclosure? Below Fb, you will see no gains in sensitivity. Adding more woofers will give you more displacement and power handling. This is where the increased maximum output comes from, and can only be achieved with the application of proportionally more power. Comparing Ricci's 21SW152-4 single driver to double driver systems, sensitivity is only increased above 60Hz. Fb will go up in frequency. Adding more woofers gives each woofer less air space, so each one's air spring is stiffer, yielding a higher resonance. Notice Ricci's 21SW152-4 single driver system has an Fb ~50Hz, but the dual opposed is 65Hz despite adding a little more volume. This means you won't see any of the Fb efficiency gains until a much higher frequency. If you look at the Xmax Investigation thread, you'll see that Xmax is also increased at Fb. A driver can often remain relatively linear all the way up to it's mechanical limits. If your single driver system was getting an Xmax boost at 40Hz, your quad driver system might not get the boost until 70Hz. Ricci's 21SW152-4 data show only a 2dB gain in CEA-2010 burst performance around 50Hz going from one driver to two. Everywhere else, a 5dB gain can be seen. At Fb your maximum performance will increase by adding more drivers, but it will not be double. Above Fb, you will see great gains in performance and exactly the kind of scaling you'd hoped for. Josh has said many times that this punchy midbass can be perceived as low sub-bass. In reality, it's just extra midbass. Without EQ an undersized system will be very punchy and top-heavy. After flattening the response, your sub-bass will no longer be overshadowed by the mids and you'll notice all the rumble your system is capable of.
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