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About DrWho

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  1. 20log(Sd/St) Where Sd = driver area St = throat area Conceptually, the driver moves one unit volume of air for a given excursion. When that volume of air moves through a smaller opening, then the velocity increases proportionally (because the same total volume gets displaced). The job of the horn flare that comes afterwards is to maintain as much of that higher velocity all the way to the mouth - where the surface area is even greater, and you're displacing even more air. In order for this to work, the horn needs to be long enough to allow the pressure to build up into a proper wave. If the horn flares too fast, or is too short, then the air "rushes around the corner" of the mouth / horn wall and yields a large pressure change. That pressure change creates an opposite polarity wave that travels in all directions, including back into the horn. That's why the quarter wavelength horn length is such a magic number. This is a horrible explanation for the concept of impedance matching, but I think it's helpful from an empirical perspective. The compression ratio basically sets your starting point.
  2. Hornresp is fairly accurate if you maintain the assumptions behind its equations. I use it as a best case first order sanity check. It's usually not too hard to calculate by hand when you're deviating from the ideal assumptions - I'll often manipulate the inputs to the tool to see the results of those deviations. You kind of have to put the full story together in your head after the fact....or just build it and measure. Hornresp is modelling the performance of a circular cross-section with the defined area expansion. Once you deviate from that, then hornresp is totally invalid. It's also assuming the wavefront follows the shape assumed by the exponential/conical/tractrix equations, which isn't reality either - even for circular horns. So from that perspective it's probably better to say that it's inaccurate for most systems. FEA (or BEM) is the way to go, but you're not going to get a nice interface like winISD or anything like that....and you can really muck things up if you don't get your meshes right. That or it will take weeks to solve the model.
  3. There is a big difference between comparing designs and comparing a working circuit against a circuit that was damaged or built improperly. Circuits behave the way they're built, not how they're designed.
  4. The reason it digs low is because the compression ratio is low. When the compression ratio is 1:1, then there is no acoustic gain. The driver excursion for a given SPL is the same. If the horn flare is narrow, then there is DI gain, but the total power is the same. This 12" driver has what, an 81 sq in Sd, and that's firing into a 49 sq in throat? That's a 2.2 dB max increase in power for an infinitely long horn. When the horn is shorter than infinity, then there is less gain at low frequencies. The shorter the horn, the higher that low frequency corner gets. What all that amounts to is a short flare horn like this is not much different than a direct radiator configuration, especially at the lower frequencies. This can be seen in hornresp if you setup a maxspl plot with very limited cone excursion and high power handling. 2.2dB at the top half of the passband isn't nothing, but it's a lot less than the 5.6dB gain over the full bandwidth of the Jubilee. That's why the Jubilee is so much longer. It starts with a smaller throat and loads to a much lower frequency. This isn't to detract from the design, but to point out why a small "horn" has a lower than expected low frequency corner. It's basically the direct radiator response of the drivers you're using.
  5. I have grown to believe the circuit topology has more influence than the type of active device employed. That said, the best topology for SS is likely different than the best topology for tubes. So it'll never be apples to apples. And SS is such a wide field....we talking BJT, MOSFET, JFET? They all behave very very differently and have their own design considerations. Then there's what, triode, tentrode, and pentode tubes? I feel like it doesn't make a ton of sense for audiophiles to have these discussions because there are both good and bad SS and Tube designs. How do you know what you're hearing is due to the active element, or certain design decisions? The point is that there are both good and bad implementations of each. Sure, there are in fact inherent limitations or flavors to the different active elements that do impart a common character to the sound. I think it would make more sense to try and understand those flavors - and find ways to describe what we're experiencing. The different characters detract differently from different types of source material and listening habits. But to really compare SS and tubes, then you're going to get into a very in-depth discussion that ultimately revolves around circuit design....and we're simply not equipped to cover those nuances on a public forum. Even the best audio circuit designers in the world are still learning more about how these devices behave. All that to say, SS is the best. Tubes should die along with vinyl and wax cartridges. They are archaic relics of the past that serve only nostalgic purposes. Haha (said totally in jest btw)
  6. Do you have a plot of the frequency response for each driver overlayed with the full speaker response? It would look a lot like the screenshots of your filter settings. This will give a good indication for how much summing you're getting at the xover frequency. One thing about phase is that it will change dramatically if you move the microphone around. Are you driving all three woofers in parallel? Didn't they do a tapered array in the passive xover? Are you sure you're not seeing polar lobing at 250Hz? Or is the mic within 14 inches of a reflective boundary? That could also be true of the speakers too. Is there a 28" path-length difference between the bottom and top woofer?
  7. Btw, have you seen this website? http://www.data-bass.com/data?page=systems&col=2&type=1&sort=desc&mfr=-1 That's a direct link to sorting by CEA2010 distortion numbers over a 10-63Hz bandwidth.
  8. There is an assumption that "horn loaded systems" have less driver excursion than direct radiator systems. It's a nice thought, but that simple remedy is simply not true across the board. You see this in both simulation and measurement world. This becomes the reality when the horns are undersized, which is the case for very low frequency devices. Also, if we're talking about "impedance matching" - which is one way to talk about horns, then you can't talk about "impedance matching" without first understanding the load you're trying to drive. The load in this case is the listening room - and specifically the wavefront that arrives at the listening position. The source in both cases is the driver. If you crank through the math, then you will find that a "classic horn" is not the best way to couple the wavefront to the listener at the listening position for a "typical" home environment, especially if you're dealing with an "undersized horn" in an acoustically "small room". A "classic horn" assumes radiation into free space. You get more power per displacement using other methods in a "small room". Not that this is an example of quality reproduction, but there's a reason you don't see horns in the car audio subwoofer SPL drag races. It's the same physics at play - just that the room is even smaller. I'm putting quotes around these terms because they are loosely defined concepts that can have an effect on these conclusions depending on the specific situation. Anyone claiming that a horn automatically has less modulation distortion is drinking kool-aid. Can it have less? Yes. Can it have more? Also yes. It depends on the design and implementation. The thing is - you're going to get more bang for the buck avoiding the classical horn route for very low frequencies. It's just how the physics play out. Anytime you make the horn bigger to give it more advantage, then you can always add more drivers and end up with a smaller total footprint that meets the same SPL requirements. And even if you make the horn bigger, it's the compression ratio that determines your best-case excursion reduction. Make the compression ratio higher and the horn has to get much much longer for the same pass-band ripple. It's more volume-efficient to use multiple drivers to achieve the same excursion per SPL at the lower frequencies (and you have a perfectly flat passband). This is why pro-sound touring companies use direct radiators for their subwoofers. At high frequencies, horns are always better. Our rooms are acoustically large at high frequencies (so the free space assumptions are valid) and we're getting very large compression ratios because there is enough space for the horn to be appropriately sized and couple well. At low frequencies, we have small rooms and the horn isn't big enough to get the energy out of the horn. The frequency response ripple in an undersized horn is the result of "room modes" inside the horn. Designs that are undersized but appear to have less ripple are converting energy to heat inside the horn (which is still energy not getting out). On top of that principal, inside a small room, the direct radiator gets coupling benefits from the room itself. That "room gain" provides more gain to the direct radiator than the horn firing into the same location. A lot of that impedance matching work of the horn is duplicated by the room - the thing is, you can't get a double benefit from impedance matching. Anyways, that's not to say that you can't get a good sounding horn loaded subwoofer. It's simply going to be a larger cabinet than a comparably performing direct radiating setup. And by comparable, I mean same bandwidth, spl, and excursion requirements.
  9. Just to clarify, I was recommending to purchase the IB drivers, but don't install them in the walls or ceiling. You can put them in a classic speaker cabinet of your choice. Start with the drivers and then figure out which cabinet alignment meets your current needs best.
  10. There is no science in the world backing up this aversion to direct radiating bass...especially for a narrow bandwidth subwoofer. There are measurements however that disagree with the claims presented thus far, which also lines up with the science. I'm not going to debate it though because these guys have drunk too much kool-aid. I have always been a proponent of audio purchases aligning with long-term goals. If you want to go the IB route in the future, then perhaps you might consider investing in the IB drivers now, and installing them in a slightly different cabinet alignment. That can be hard with the IB drivers, but would be something worth investigating I think. Plenty of guys on the AVS forum to help hash out the details. What kind of amplifier will you be running for the sub?
  11. LTSpice is free btw - and also my simulator of choice: http://www.linear.com/designtools/software/#LTspice The tool is fairly straightforward, but adding parts is a major pain.
  12. ces

    Interesting - where are they located? Hidden behind that grill going down the sides?
  13. ces

    The JBL 2226H uses a 4" voice coil and extends beyond 1kHz... https://www.jblpro.com/pages/pub/components/2226.pdf That's what, a 25 year old design? I'm sure there are plenty more examples - I hope it's not poor form to mention a JBL driver here. Do they count as "low mass" drivers?
  14. ces

    I was just thinking - if we're really using different words to describe the same thing, then perhaps we can throw some numbers on the table? When I hear low mass 15" driver in a sealed cabinet of that size, then I'm expecting an acoustic F3 somewhere between 50Hz and 70Hz, which is basically lascala territory. It's interesting that PWK noted 50Hz in that article @dwilawyer posted, so I'm probably not too far off. Is it too early to release numbers like that? Is it possible you've achieved better THD numbers at the expense of increased frequency modulation distortion? PWK had a lot to say on that subject...
  15. ces

    " I am talking about the speed in which a driver can go from rest to excursion and back to rest. " *sigh* That's also called frequency response. Honest.