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Contrasseur last won the day on September 28 2016

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About Contrasseur

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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 wi
  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 ca
  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
  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. Aww that's a bummer. Do you have any plans to consistently carry a value driver? Your HT18 was the clear value winner among all drivers tested. The DS18 looked to have a nice edge on the Ultimax. In the absence of testing data, your track record shows that those impressive specs are likely conservative. Sure there's plenty of other cheap 18's on the market, but it's easy to trust something when it's passed Josh's super rigorous and thorough tests. Especially in a market with as much marketing BS as audio.
  7. Well for starters you should know that driver is discontinued and hard to get a hold of. It's replacement, the DS4, promises to be better in power handling and displacement. It's more expensive, but not by much. Other than that, there's not too much to know. That's a very straightforward box design with good drivers that will give you a lot of performance at a good value. Brace the box so it doesn't resonate and stuff it with a decent amount of filling.
  8. 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 TIM
  9. Same question here! I have a concrete floor. As you all know, there are tremendous efficiency gains and cost savings to be had for every octave of low end you sacrifice. Tactile transducers aside, how low can you really experience?
  10. When "Go big or go home" doesn't cut it, you call in Radulescu
  11. Let's look at Qts. Formulas drawn from Wikipedia. It's determined by Qms and Qes. With the exception of some dipole woofers and tweeters, Qes is much lower than Qms, so Qms is negligible for our calculation of Qts. Therefore we only care about Qes. Let's look at Qes. You can see it's (2pi*Fs*Mms)/(Bl^2/Re). Bl^2/Re is motor strength. We already discussed Fs and Mms for your enclosure, so we only care about motor strength right now. Let's look at motor strength. Increasing BL or decreasing Re does the same thing. If you look at 16ohm and 4ohm versions of the same driver, you'll notice t
  12. Fs only really has significant meaning in infinite baffle scenarios. Fs is driver free air resonance. When you put it in a sealed box, tapped horn, or ported box, it's not in free air anymore, is it? SYSTEM resonance is what matters when you're predicting the performance of a system. Now lets look at your particular usage case. You're looking at a tiny, tiny box. Assuming it's made of 1/2" plywood, your interior volume (before adding drivers) is 5.3L. This tiny air space isn't very compliant. Compressing a 5L space by 1L takes tremendously more force than compressing a 50L volume by 1L.
  13. 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
  14. 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?
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