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DevilDriver

SSA Tech Team
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Everything posted by DevilDriver

  1. DevilDriver

    Prototype Big Boy SPL Motor

    Can I make any guesses on what that piece of paper is covering in the gap? From the rear of the driver, I think I like the direction your cooling approach is heading.
  2. DevilDriver

    I figure I will be the guinea pig

    I could care less about what means what, but I think the source for the BL's name is hilarious. Mind you, I've heard there is something interesting about all the names Scott has had for Fi and when he was with RE as well.
  3. DevilDriver

    Copper or Aluminum?

    Sorry, I think I've been missing a key part of your question: does Audioque offer the HDC3 with either copper or aluminum coils? If that is the case, I would probably just get the aluminum coil since the copper coil will likely add significant mass to a driver that will already have enough low frequency extension for most. For your purposes, the aluminum coil is probably preferable.
  4. DevilDriver

    Copper or Aluminum?

    The setup you have listed should be manageable. I was mostly speaking from an engineering standpoint. For most consumers, looking at individual aspects (like voice coil material) is a pretty fruitless adventure.
  5. DevilDriver

    Copper or Aluminum?

    Nope. Copper is 1st, then Aluminum, then Stainless Steel. Yes, this is something that is a bit misunderstood. Forgive me, as I have hardly studied thermodynamics, but.... Thermal conductivity refers to how well an item conducts heat. On the other hand, we also have Newton's law of cooling. I will save you the math, but the general premise is that the greater the difference between the body and its environment, the greater the rate of heat loss for that body. Simple conclusion: 1) Copper is a better conductor of heat than aluminum. As such, copper can get hotter, quicker than aluminum. 2) Because copper can get hotter, quicker, it also presents a larger difference between the temperature of the body (the copper) and the temperature of the environment. As such, copper cools more quickly. This is the "dissipating heat" part that was referred to. With a speaker, the material chosen will vary depending on what you (as an engineer) seek and the geometry of what you end up using. In some cases, copper will be more preferable....in others, it will be aluminum. Or, for those who prefer, you could do Copper Clad Aluminum or any one of the less popular alternatives.
  6. DevilDriver

    Death Penalty 21" Pics!

    http://incriminatoraudio.com/update/index....age=3&cat=2
  7. DevilDriver

    Plug on BL pole vent

    I see the BL has vent holes at the sides all around. But how do other subs do their cooling since they do not have side vents but only pole vent? i believe that is the conventional way of cooling the voice coil First, let's just think about how a pole vent would help cool the driver. It would have to either draw cool air up or push hot air down. This will work in either of two ways: 1) The heat from the coil is absorbed by the pole, then air traveling over the inner wall of the pole piece carries that heat out of the pole. 2) The heat from the coil must manage to get off the coil, through the former, and down into the pole piece, at which time you count on convection to take the air out of the pole. If you think about this logically, I think it should be very obvious that either approach is not going to do a whole lot. In fact, if #1 is the preferred method, then a smaller pole vent is often preferable because you can achieve higher air velocity and there is more steel to absorb the heat (steel absorbs heat a lot better than air does). So what is a better approach? Firstly, I think there are a few things that we should target. 1) Get the heat off the coil - It should be easier to move heat off the coil and into another region with increased air velocity. What you really need to find is the balance between air mass and air velocity, at which the most heat can be removed from the coil. The pole vent is generally a low velocity, high mass method of moving air and is not particularly effective. The method we will review is more of a high velocity, medium mass approach. 2) A short path to move the heat along - Obviously the shortest path will be the most effective. 3) A place to put the heat - Once we have moved the heat off the coil, we want to move it to a place that will be absorbed. The approach for many is to try and move this into the surrounding atmosphere (ie. the air in the enclosure), but as I already mentioned, the air is not very thermally conductive. Some clever engineers use deposits of aluminum or copper in the motor to absorb some of the heat; for the sake of comparison, the aluminum is about 10,000x more thermally conductive than air, while copper is about 16,000x more thermally conductive than air. How thermally conductive the steel is in the motor will depend a lot on the grade, but it is always much more thermally conductive than the air around it. Anyways.... The pole vent approach is just dumb. First, you remove steel from the pole: the pole is just a short jump from the coil, and is also a good place to put heat. Not only that, but removing steel means you have less steel to carry flux and, potentially, lower flux density, lower BL, lower efficiency, lower SPL, etc. Second, you have to move a large mass of air quite a distance (from the top of the pole out the vent). Ask yourself: if the goal is to move the heat into the surrounding atmosphere, isn't there a shorter path we can do this with? Hopefully the answer is obvious: yes! Hell, the coil (which is where the heat is coming from) sits just a few cm from the surrounding atmosphere if we go up through the top plate instead. We can also avoid taking steel out of the motor (which is good for all of the above reasons), and the steel top plate and basket (of whatever material) are right there to absorb heat as well. So we've found narrowed down a more effective path and an equally (or more) effective place to put the heat. In order to get the heat off the coil, we are going to want to draw air at a high velocity across the top plate and down into the gap (where the coil resides). Via convection, we can now pass heat into the steel pole piece, the surrounding magnets, the steel top plate, or draw it back out of the gap and into the basket (or, to a lesser extent, the surrounding atmosphere). We can also add aluminum or copper inside the motor to provide even more mass to absorb the heat (a thick copper or aluminum ring on the ID of the magnets might be quite effective). To make the drawing of air into the gap most effective, we can add a spacer between the basket and the top plate; we can also machine channels through which air is drawn down into the motor. The size and shape of the channels will vary for the application, but this is a very effective method. What I have described is, in essence, exactly what Fi is doing. There are a number of small tweaks you can make (adjusting the geometry of the pole or the top plate), but this is way more effective than the traditional pole vent method. In fact, if moving heat out of the rear of the motor is your goal, it is often better to utilize a series of holes drilled into the back plate that allow you to vent heat out of the rear of the gap (rather than out of the pole). Other companies are starting to figure this out (very slowly), but the vast majority do not do this (or even understand it). Part of the problem is that consumers don't really understand it either, so we have the blind asking for the blind to give them something neither of them can see (metaphorically speaking). That's why it is so important to share what we know with others.
  8. DevilDriver

    Welcome to the IHoP

    <-- currently reading Dracula For fun? Not a bad book...must read for those of us who love vampires.
  9. DevilDriver

    MJ18 Measurements

    Very interesting results....thanks for sharing. The symmetry on the BL curve is excellent, although a little more extended plateau might be preferable. Le(x) reflects the lack of a shorting ring, while the compliance symmetry could definitely use some work. Still a great value driver at that price.
  10. DevilDriver

    Fi BTL 18 T/s parameters

    So there were no improvements or changes made then? Well thats a relief This is not the case and all box programs are wrong. Any insight on what Thiele and Small's models are doing incorrectly?
  11. DevilDriver

    "Advice"

    Question everything.
  12. DevilDriver

    Recording Audio changes source's frequency

    How were you recording this? With a microphone and mic pre-amp? What soundcard was this with? More info would help.
  13. DevilDriver

    Woofer parameter tester

    The WT3 is a fine option. The real advantage to it is the quickness with which you can take Thiele/Small measurements. http://audiojunkies.com/blog/1016/wt3-woof...ew-dayton-audio
  14. DevilDriver

    Welcome to the IHoP

    It's Shay Laren. Here's something nsfw.
  15. DevilDriver

    Welcome to the IHoP

    It's like science for rockets....
  16. DevilDriver

    Welcome to the IHoP

    Really quite tired this evening. Funny, don't have a job at the moment but am working harder now than I had to before. Definitely looking forward to school again in the Fall.....
  17. DevilDriver

    How does a sub play 10 hz when..

    What on earth does any of that mean? How do you hear accuracy with your ears?
  18. DevilDriver

    Just for FI....

    The BTL is the most efficient driver and at any power level, it will be the most efficient driver. Efficiency, in the simplest sense, is the ratio of input vs output, ie. in a highly efficient system, there will be more output for a given input. So what affects efficiency? In a very general sense, we are looking at two primary factors: mass and BL (or for comparison's sake, BL^2/Re). We know mass will not change at 1 W or 10,000 W. We know the B (flux density in the gap) will not change (within reason). And the L (length of coil that cuts the flux) will only significantly change once we approach Xmax. The BTL's coil also happens to be capable of handling more power before the resistance increases, so we know the BTL will be most efficient at any power level. Now....does this necessarily transfer to loudness? First, we need to look at the bandwidth (range of frequencies) that the subwoofer will be covering. Yes, the BTL is more efficient than the Q, but will it be louder at 20 Hz for a given input? There are many factors and, at the risk of oversimplifying, the answer is no. This is the tradeoff that is Hoffman's Iron Law (look in the Tech Area on this site). However, through most of the bandwidth that is typical of a subwoofer, the BTL will, in fact, be louder than any other Fi driver. No speaker "needs" a certain amount of power.....the only time you need more power is if you're not satisfied with the output you already have. So why not just buy the BTL? Well, there are different applications for each driver. Some drivers are more linear than others (generate less distortion), some drivers have better low frequency extension, and some drivers will meet your needs at a much lower cost than buying the big boy BTL.
  19. DevilDriver

    i wish our president had the balls to say this

    This is nothing short of horse shit. Plain and simple. I hope no Canadian honestly believes any of this (I don't know of many who would), especially since we tend to take pride in our multiculturalism. Up here, it is seen as an asset rather than a detriment. Explains a lot about the current state of the US, mind you.
  20. DevilDriver

    4th order banpass build Log

    All enclosures are just filters.
  21. To answer the question about what specifically causes subwoofers to sound sloppy, people look for a lot of reasons but it really comes down to what happens in the frequency domain (ie. frequency response). Flat response in the subwoofer range, especially transitioning into the midbass, is really what is key to good, even performance from your subwoofer. A common mistake people make is to allow the low frequency performance of a driver to practically swamp the response above 50-60 Hz (particularly when we consider the transfer function/cabin gain of your vehicle). The primary negative detractors will be the inductance of the voice coil, the enclosure, the vehicle's transfer function, the power on tap, and the midrange/midbass driver's own performance. All of these things need to be managed appropriately to achieve the response you're looking for. There are secondary detractors (like mass, BL, and others) but these can easily be accounted for or even avoided if the primary detractors are taken care of.
  22. DevilDriver

    surface area

    For linear displacement, look at the Thiele/Small parameters.... Vd = Sd * 2(Xmax) The radius would be one half of the diameter of the cone plus 1/3 the width of the surround (not 1/2 as is often claimed). Then you can use this radius to calculate the effective surface area using the methods described above.
  23. DevilDriver

    Welcome to the IHoP

    Double LOL.
  24. DevilDriver

    Welcome to the IHoP

    Congress was really giving it to them. One congress woman would not even listen to what the Exxon VP had to say. Their argument is that the company is making 40+ billion dollars and should lower their gas prices. Exxon countered that the amount they are making hasn't changed, but that the reason the price is going up is because crude oil has been going up (which is true). Still, the congress was convinced that Exxon should be willing to take a cut in their profits in order to help consumers out. I understand congress' argument, but I think it is Exxon's right to free enterprise and capitalism...if the consumers are tired of paying for gas at that price, they need to stop buying it.
  25. DevilDriver

    Sound Transmission Loss- LL/LLP

    www.noisedead.com/vbp Thanks. I give you credit for full disclosure. Why this type of stuff isn't first and foremost for companies like Anthony's is beyond me. Actually, I know why they do it....I just can't stand it.
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