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deepthoughts last won the day on November 4 2016

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  1. Many thanks Josh for the extensive work involved in testing so many variables here. I'm happy to see so much interesting data collected by adding the iNuke3000DSP to the mix. From your testing, I generated the following set of EQ filters to flatten the single vent, 14.5Hz tuning option which can be used in any DSP that includes shelving filters, and doesn't require filters below 20Hz. An iNuke DSP or similar can easily implement this. For the 21DS115-4 as tested I have the following filters recommended: 1. BW 12 / 2nd order high pass at 20Hz (2nd order Q=0.7 filter) 2. A 2nd order Low Shelf at 20Hz boosting 6.0dB 3. A 2nd order High Shelf at 90Hz cutting 14.0dB This gives a response that is +/-3dB from 14-200Hz, and should be useful to around 12Hz in-room. Here is what I modeled up where this is just generic, so the exact shape may vary by a smidge:
  2. (4) Sealed 21": Funk Audio UH-21v1

    Promising and impressive results after all the work put into the project. I couldn't quickly find and answer, but are you currently running the SP2-12k off 120V or 240V power?
  3. I saw this in a local Dolby Cinema and was very impressed with the Atmos mix and overall sound, along with the movie as a whole. Are there specific scenes that really throttle the 20Hz range creating the spike we see in the graph?
  4. what makes a sub "sound good"

    The bag end device certainly works. I had long ago come across this and talked to one of the Bag End engineers about it's effectiveness at a SynAudCon event many years ago. I recommended this as an option to a friend with fairly exotic audio gear in his home demo room who wanted to have effective treatment for playing LP's without re-digitizing and something he could do for customers with the same preference. In playing with the Bag End solution in 3 different rooms and on a few occasions in the first room, I came to a few conclusions... The controls are way to coarse and low precision. Nudging and bumping a dial to get center frequencies to bump up a little higher or lower sucks. Similar to what we know about conventional bass EQ, you need to get the Fc and Q very accurate to the original problem to get the best damping results, and much like EQ you do not want to over-do it. It was hard to do "enough" where the audible benefit was dramatic without hearing some unwanted effects in the room. When set too aggressively you could hear the devices "speak back" while just talking in the room. They can be tricky to set and dial in. It's easier to make a modest improvement if you have 1-2 dominant and well spaced modes, so expectations should set be appropriately. While the active trap is effective, we are trying to correct the reproduced sound, where the microphone and filtering has poor selectivity. I would much prefer a input-based system that creates a cancelling signal in the subwoofer. A microphone does have the ability to better track the real variances and decay, but we are limited with what sort of problems and how many we attack, as they can even influence each other when using a microphone. We can also better measure and quantify the results from the specific stimulus of the speakers being used vs the listener, where the microphone-active systems will react to any sound produced in the room. When done digitally up front, we also add the possibility of simultaneously using a device as both a producer of desired output and as an active cancellation device. It seems a waste to have a good subwoofer location unavailable due to a device, or a cancellation location unavailable due to it being a worthwhile subwoofer location.
  5. Skipping the other silliness for the moment, In the rooms you have calibrated, has every room of differing size, construction, and acoustics subjectively sounded to have the same spectral balance just by adjusting for a flat magnitude response as measured by a sine-sweep? How about measured by RTA? If the answer is yes they sound the same beyond loudspeaker/subwoofer deficiencies, then there's not much to discuss. I don't know anyone with experience calibrating more than a dozen rooms who would answer yes to that question, and that gives us something to discuss.
  6. While you talk of first arrival, it's barely something that exists at the lowest frequencies in most of our listening rooms as you note at the beginning. While related, I would say the missing component from your study/experimentation is paying attention to decay and energy vs time. The ultimate litmus test is to create a correlation that translates the same subjective bass quantity from outdoor listening to a small listening room. Floyd Toole has written a few times about work with the Synthesis systems that getting the same subjective bass from a very large, leaky space to a small, rigid room can require a lift of as much as 10dB. We generally perceive loudness based on sound power, not just intensity, so it really is all about the intensity vs frequency vs time and finding a handy way to quantify different decay with respect to how much we hear as part of the original vs late energy. I'm sure this requires some form of variable time window, but confidence in such a correlation still remains elusive.
  7. Ricci's Skhorn Subwoofer & Files

    The part some might skip over is investigating ways to slice & dice the cabinets into pieces with fractional performance. Obviously the image above would be easy to slice in 1/2, but what about 1/3rd or 1/4 or even less? As you mention, sometimes drivers aren't so hard to find, and you increase the number of voice coils to split the power between. Separating boxes also gets around the issues of spreading the loading point along the horn path, although I suspect 2 with some careful spacing might even be beneficial to resonances, but that would require some testing... That gets to the other very useful reason to look at fractional designs. Proof of concept. If you have a design that looks very exciting, but you don't know how bends, real losses and Q's of resonances will be in reality, it can be very worthwhile and easier to test a 10-15" driver in a smaller package with the same acoustic design. The ultimate test is if a pack of the smaller subs is comparable to a single large sub, which it theoretically should be.
  8. Ricci's Skhorn Subwoofer & Files

    One way to up the challenge a bit is to dive deeper into these huge cabinet designs that are fun to model and every once in a while build. One great property about acoustics is the ability to scale things. Maybe burn some late nights working out what a sliced fraction of such a design would look like, what parameters are needed for a 15", 12", or even 10" driver to maintain the same response? Might any of those parameters be something you can find? The suitable smaller drivers might not have the same excursion, but things might get interesting if you can actually use multiple units. No matter the type of alignment I'd say that being able to scale most all the performance qualities to be an interesting challenge. Ricci mentioned the Bose boxes earlier, and ironically the 6th order bandpass was a now expired Bose patent. Sometimes looking at designs in a different scale or with different technologies we stumble on some fun possibilities. If you can make a $1 driver sound impressive in something the size of a briefcase, what can you do if that's the size of a refrigerator with high excursion parts? Similarly, maybe when scaled down there are parts from a different market or application that you wouldn't have bothered modeling, but in fact the math suggests it scales nicely in some interesting design. Personally I still would love to have the time to create my concept of a subwoofer system using 3 or more bandpass designs intended to blend together into a multi-way subwoofer with the ability to place each bandwidth in efficient locations. The upper 1/2 of the bandwidth really gets interesting when you look at small modules and bandpass designs with significant gain. Of course getting better results than just a pile of compact sealed subs always comes back to the execution. Excuse the diversion, back to big obscene subs.
  9. Is it possible to model port compression?

    LspCAD 5 includes an optional attempt at modeling port compression (can check a box to see with and without model). Unfortunately it doesn't really allow a simple model of a commonly flared port. Instead they have a model more akin to a flared vent that defines more of an hourglass shape with an effective, assumed radius greater than 1/2 the length of the port. Comparing straight ports and more significantly flared ports gives some interesting points of consideration. One thing overlooked in your assumption above is that as the port compresses, the driver excursion increases. This is seen very easily in the LspCAD models and can be estimated/correlated by comparing high level impedance sweeps around tuning, and comparing driver vs port near field measurements. With high excursion woofers you will often see the driver picking up a good bit of the output load as excursion increases in an exponential manner due to port compression. This actually reduces the observed output compression, so remember the port itself is even more non-linear than the total SPL compression suggests. As with most things, the models are overly conservative and compression isn't quite as severe as suggested, but it's a lot more than none. Long ago I recall Deon Bearden relaying on that in his testing and research most port designs start compressing anywhere past 10m/s. That's not to say the ports aren't useful past that point, but we should understand that behavior isn't linear, just as with real drivers well before the rated Xmax. The complicating factor is always the wide bandwidth, complex signal consideration. If a component of a complex signal pushes a port into severe compression, how does this impact the rest of the complex signal being produced at the same time?
  10. What kind of compressor do commercial subwoofers use?

    That all depends on what the designer, the DSP/electronic hardware/software capabilities or flexibility. The specific subwoofer design with respect to box, driver and amplifier limits all impact what sort of design is appropriate. Some give a lot of thought to the issue and do lots of experiment and listening. Some never bother or just quickly set a Voltage limiter using default settings. There is no all encompassing answer. Sometimes a simple Voltage limiter does the trick, as is the case with many sealed systems. The answer you are seeking is as clear cut as asking which subwoofer design is superior... sealed or vented?
  11. The patent is long expired now, but the real issue was always cost, engineering, parts sourcing and testing required to get the mechanics refined and durable enough. There is much more possible now with modern cone/surround design. Before Tom left ServoDrive, followed by myself and later Jeff (JTR), we did have a pretty cool 2nd generation prototype in testing. There was a concept for a preferred 3rd generation that would require more development and work with parts suppliers. Ultimately you need applications where high motor force and high excursion are needed for the advantages to outweigh the hurdles and cost, and/or you would need to have a custom built and optimized motor made. It does start to get interesting again when comparing to 6" VC's the motor strength and excursion required for 18-32" cones. If someone has $50-100k they want to gift away to get them to production I'd be happy to make it happen. -Mark
  12. Official SpeakerPower amplifier thread

    The ideal manner is to peel back the jacket from the 4 conductor cable and use 3 pieces of heatshrink to dress the split. Use a smaller and longer piece on each leg, with a larger diameter piece put over the split and overlapping the legs last. As Josh posted, there are many ways to split, and you can even bring 2 separate 2 conductor cables into 1 connector.
  13. ZOD Audio M.A.U.L. Test Results and Discussion

    You can also get some interesting results by getting a little more LF loading with longer slots by tapering down where effectively the "port" is the in one dimension of the path, but narrows slightly, and ideally opens again near the exit. I've landed at the same point from both directions of starting with a chamber and port that kept growing to be the same cross section as the end of the chamber, to starting with a longer line/horn that you reduce the horn segments to model it like the line/column it really is. When I last experimented Hornresponse couldn't load 2 of the same drivers at different points on the pathway, so it was an average and a double check with models from each separate location to insure acoustic resonances don't line up. It does open up some interesting options if you can direct all the output from a large box to a relatively modest sized opening. Slot ports certainly work, they just need a little compensation as the aspect ratio increases. The one hurdle they all face is noise/turbulence near the small ends. Of course it's then a question of do you really care if it lets you get 6dB more from larger area or a tuning you might never build with round ports. The big bandpass designs can work well, with the caveat that any non-linearity in the high frequency system sets in motion all sorts of gross response modulation. In my early investigation with the Terraform design I first spent a lot of time making sure I got a handle on why there were so many bad sounding examples of bandpass designs. Shift the BL and Cms on a driver in a bandpass design and you can quickly see what happens to those short Xmax, long Xmech pro drivers which used to be so common. Next look at an undersized port and the changes that occur and you can get an idea of what is happening dynamically. Most of it isn't a big deal below 30Hz, but at 50-100Hz, it's highly audible, with some driver non-linearities probably responsible for 6-10dB high-Q peaks if they are producing that range when the driver gets past Xmax. Having free tools like the recent incarnations of Hornresponse opens up possibilities which would have been largely guesswork not that long ago.
  14. ZOD Audio M.A.U.L. Test Results and Discussion

    Hi Josh, That looks like quite a fun and highly effective design you've brought to life... so long as you have others around to move it. Thanks for posting the with/without for comparison. For those curious about using such design, this is ultimately what determines if you've done something useful with the front chamber. While trickier to compare, as it requires a bit more back/forth adjustment in models, matching either the SPL or excursion at a few frequencies in the loading range let you know if you are just gaining sensitivity (still worthwhile) or if you are also seeing some useful acoustic loading. I've played with many variations on this sort of 4th/6th order loading, and you can almost always get a smoother result from sort of front pathway than a classic chamber w/small port, and you don't suffer from the huge mess caused by a small port's dynamic behavior in the upper bandwidth nor the out of band peaking... as your simulation shows. You also hit on the other benefit with such high motor strength woofers in your later post about the under-sized ported box. With a little creativity in the chamber size, length, and tapering it is easy to push some of the upper bandwidth efficiency down into the heart of the operational range and achieve a response which would require a very heavy or hard to build woofer. Using 2 woofers at different offsets along the chamber can also help stagger notches and any resonant issues with the front pathway. Thinking back, I believe the pro subwoofer cabinet Acoupower put together to demonstrate their woofers used a higher tuned, non-opposed variation on this design. Congrats on the results aligning with predictions and how well it appears to have come together. I know how much planning and head scratching must have gone into bringing this to life!
  15. I haven't looked at the exact unit and specs yet, but you should be able to get decent info for sine wave testing over shorter duration. You would have to check if it can look at peak or some sort of sustained maximum current to measure shorter bursts. I'm not really sure it will give you all that much more info other than being able to see how the amplifiers draw power from the wall at the same output level, which gives you insight into the real world efficiency. Ironically a couple big pro amps dump a lot of power into cooling fans if the temp gets hot which can significantly affect efficiency of a class D design. This shouldn't be an issue in home use though.