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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 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. 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 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.
  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 they have the same performance because they have the same motor strength. Changing Re means we also have to change voltage to get 1 watt comparisons, so let's only change BL to see the effect of changing motor strength. Let's look at BL. Taking the same T3-19 in a 100L enclosure, if we drop BL from 19.1 to 12.1, motor strength is cut by 60%. You can see from the impedance chart that Fb hasn't changed, so none of our previous discussions on Fb apply. Above Fb, sensitivity is decreased. No surprise there. At Fb, sensitivity is increased. Isn't this a good thing? Did our speaker become louder with a weaker motor? But when you look at the impedance chart you'll see the impedance has been reduced. The higher BL is creating more back-emf, and reducing the power draw. We need to know if the boost in sensitivity is bigger than the increase in power draw. We have to look at efficiency to see the real picture. As you can see, efficiency for the higher BL system is better at every frequency. Why would anyone recommend a high Q system for sealed systems then? Well look at the frequency responses. With a high Q, you can get a much flatter response. The low Q system requires a huge EQ boost in low frequency and will sound like garbage without it. Since you're using equalization, the stronger the motor, the better. This is the theory behind Powersoft's IPAL system efficiency. A low Q woofer will have better efficiency but sound terrible. A high Q woofer will have low efficiency but a nice frequency response. By EQing a low Q woofer, you get the best of both worlds.
  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. Your free air resonance (Fs) is determined by compliance and moving mass. So is Fb, but we have to include the box's compliance. The pushing on the cone of the Seas Prestige ER15RLY is equivalent to pushing on a volume of 15L (this is what Vas means- compliance equivalent volume). If you cram 4 of these into 5.3L, each driver has 1.3L of air space behind it. Now if you try to push on the cone of your Seas woofer, you're also compressing this 1.3L volume. See what happens here? Compressing a 1.3L volume by a certain amount takes more than 10 times the force to compress 15L by the same amount. The compliance of the woofer is negligible in this scenario. Let's take a look at moving mass. Lower masses are easier to move, and provide a better impedance match with air, i.e. they have greater efficiency. <see attached file #1> This is a simulation of a T3-19 in a 100L box. You can see the efficiency of the regular woofer (grey line), and if the woofer had a more reasonable moving mass of 400g (black line). The lower moving mass results in greatly improved efficiency overall. Look at the low end though. There's no gain to be had between 40 and 50Hz, and actual improvement to be had below 45Hz. Remember the response curve of these tiny sealed boxes? You have to use EQ to boost the bajeezus out of the low end to get a flat response, more so if you want a desirable, downward-sloping curve. So by the time you're done, you're dumping way more power into the low corner of your system. If your heavier system is 3 times less efficient at 100Hz, a 50% increase in 40Hz efficiency means you're using less power if you're pumping 10x the power into 40Hz as 100Hz. How can we gain efficiency anywhere by adding mass? Because it reduces Fb, pushing the impedance peak lower. <see attached file #2> As we just discussed, compliance cannot be changed because it's determined by the tiny box size, so we can only influence Fb by altering mass. Furthermore, have you checked out the Xmax Investigation thread? Ricci's data proves that Xmax is increased at and around Fb. You already know that the lower you go in frequency, the more excursion you need. If you're using a system down to 40Hz, wouldn't it be nice to have an excursion boost at 40Hz where you need it, rather than 60Hz where you won't reach the limits anyways? Distortion also increases below Fb. Look at the distortion charts for every one of Ricci's sealed systems. They all show marginal variation above Fb and all the way down to Fb, but below that, the motor starts fighting the compliance, and distortion increases. Ideally, your Fb will be at the very bottom of the bandwidth. Is this always a good thing? No. Like you saw, you're sacrificing massive efficiency on the top end for marginal gains on the low end. You'll have to do the math to see which alignment has lower power draw over the intended bandwidth (~40-300Hz), with the intended signal spectrum (music, which typically has a downward sloping power spectrum), EQ'ed to the desired frequency response (typically flat, 3db/octave downward slope, or somewhere in between). On the Xmax consideration, your airspace is tiny and your cones are light. If your Fb ends up at 100Hz, you might have to add an impractical amount of mass to get your Fb all the way down to 40Hz. If you can only get your Fb down to 60Hz, you're not gaining any extra excursion where you need it. You'll have to model the different options to see how well it works in your application.
  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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