DevilDriver

I love Iron Laws. Why? Well, they are so succinctly and aptly named: they are infact, iron. Good luck breaking them! If you've been a browsing member of the online audio community for a while, you have no doubt heard about Hoffman's Iron Law. What's it all about? Well, it is quite simple. Forgive me if I am misquoting here, but I think JimJ put it best when he said: "You can have low end extension, high efficiency, or small enclosure size. Pick two." Please note that while many people use this statement related to enclosures, it applies to the speaker you're using as well So what does that mean? And why is that the case? Well, as you may have heard me say once before, speaker design and engineering is a game of compromises. The best speaker (if there truly is such a thing) is the one that has the lowest impacting compromises. Let's say you you drive a little Dodge Sprint or another vehicle with a relatively small cabin and little-to-no room for an enclosure. Of course, you're a bass head and you want to hear those lower notes banged out with some authority. To top it off, you're a cheap bugger and want a lot of sound without buying an expensive amplifier. You build your miracle enclosure, install everything, power it up, and surprise! Those low notes just aren't there. You tried to have your cake and eat it too, which just doesn't work in the real world. Naturally, you think there must be something wrong with the sub or amplifier. Now you have switched every product imaginable in and out. The good news is that an amplifier rated much higher than the RMS of your sub has given you that low end beat you're looking for. The bad news is that you just cooked a voice coil. And this is Hoffman's Iron Law at it's finest. If you want a low end monster, you had better step up the power or build a behemoth enclosure. If you want to keep your amplifier costs to a minimum, you had better build a huge enclosure or accept a very high rolloff with very little low end. If you want a small enclosure, be prepared to buy a big amp or give up that low end you love. What is the specific relation between these by-products? Simply put, the efficiency of any speaker system is directly proportional to the enclosure volume and the cube of the f3 (the frequency at which SPL is down 3dB). If you halve the efficiency of your speaker system, you may also halve the volume of the enclosure. However, if you decrease the f3 of your speaker system by a factor of two while retaining the same efficiency, you would have to increase the enclosure volume by a factor of 8 (2^3=8). Let's say you have an enclosure with an efficiency of 90dB/w/m that is 2 cubic feet in size. Suppose the f3 of this system is 30hz. However, you've decided you want a heavy bottom end and wish to drop the f3 to 15hz. Without decreasing efficiency, this change would require an enclosure measuring 16 cubic feet in size! That is quite a change, and hardly affordable in a vehicle. With a lot of preamble, I think that adequately explains how things work on the enclosure side. But as I mentioned earlier, this applies to a normal speaker prior to installation as well. I'll cover this when I get a chance, but to provide a starting point: where n0 = reference efficiency (% based) Fs = the resonant frequency of the driver (measured in Hz) Vas = Volume of air which, when acted upon by a piston of area Sd, has the same compliance as the driver's suspension (measured in m^3) Qes = electrical "Q" of the driver at Fs (unitless) n0 = (9.614 * 10^-7 * Fs^3 * Vas)/Qes * 100

CD vs mp3 Here's a comparison of the various LAME settings. I use v0 or v2 for anything lossy (the majority of my collection is in FLAC). You see that v0 is quite a bit smaller than 320kbps CBR but about as good.

The W7 is not always the best value but is always one of the top performers, surviving a decade filled with subwoofers designed to knock it off its perch. I've never used an Xcon but I'd never turn down a W7 at a price I could afford. Just because a product is mainstream doesn't mean it is any less deserving. Buy the best product that fits your budget.

Disclaimer The first thing I must make abundantly clear is that, though I feel all information listed below is highly accurate, it is possible I am wrong in certain areas. Let’s face it: I’m human. Though the concepts are well understood, much of what I discuss is my interpretation and opinion on a given set of circumstances. I come into this with absolutely zero bias and I feel that gives this more validity than other comparisons of a similar nature that you may have read. Above all, please read in the interest of gaining another viewpoint. Table of Contents 1.0 - Prelude 2.0 - Split-Gap 3.0 - LMT (Linear Motor Technology) 4.0 - Split Coil 5.0 - Efficiency/Flux Efficiency 6.0 - BL Linearity 7.0 - Inductance 8.0 - Power Handling 9.0 - Scalability 10.0 - Manufacturing Tolerances 11.0 - Manufacturing Costs 12.0 - Conclusion

This is a routinely asked question: "How long does the vent tube need to be if I use an n" flared port?" Granted, there are a few calculators out there that will calculate this for you, particularly if you're using some of the widely available manufactured ports. Here's a good example of a calculator available to you: http://psp-inc.com/psp-inc.com/public_html..._calculator.cgi But what if you have hand-formed your flared ends? Better yet, let's assume you are a dork like me and prefer to hand calculate a lot of things (believe it or not, the extra effort is worthwhile in the long run, but that's a rant for another day). Without getting too into depth on the actual derivation of the formula, here's what you need to know. Where: Lv = length of the vent tube (in meters) N = number of ports (unitless) c = speed of sound (in meters/second) Rm = mouth radius of the flare (in meters) Rt = throat radius of the flare (in meters) Rf = flare radius (in meters) Fb = frequency of port resonance (in Hertz) Vb = size of enclosure (in cubic meters) V = Volume of air in the flare Rm = Rf + Rt and V = pi*Rf*Rm*Rm - (pi*pi*Rm*Rf*Rf/2) + (2*pi*Rf*Rf*Rf/3) and for a vent with two flared ends: Lv = N*c*c*Rt*Rt / (4*pi*Fb*Fb*Vb) - 0.85*Rm - 0.613*Rm - 2*V / (pi*Rt*Rt) and for a vent with one flared end: Lv = N*c*c*Rt*Rt / (4*pi*Fb*Fb*Vb) - 0.85*Rm - 0.613*Rt - 2*V / (pi*Rt*Rt) I KNOW you are happy to have a lot of equations thrown at you, but this is actually relatively simple to sort out, as far as equations go. First, let's fill in the blanks I know the answer to in our simulation. We'll assume I have already measured or calculated the radius of the flare, throat, and mouth. Lv = length of the vent tube (in meters) N = 1 port c = 340 m/s at sea level Rm = mouth radius of the flare (in meters) Rt = 0.05m (approximately 2 inches) Rf = 0.025m (approximately 1 inch) Fb = 10 Hz Vb = 0.284m^3 (approximately 1 cubic foot) V = Volume of air in the flare As you can see, we are down to only three things that need solving! First, let's solve for Rm. As mentioned previously: Rm = Rt + Rf Rm = 0.05m + 0.025m Rm = 0.075m Now we move on to solving for V. This one is a bit more complicated, but still easy when we know all of the variables. V = pi*Rf*Rm*Rm - (pi*pi*Rm*Rf*Rf/2) + (2*pi*Rf*Rf*Rf/3) V = 3.14*0.025*0.075*0.075 - (3.14*3.14*0.075*0.025*0.025/2) + (2*3.14*0.025*0.025*0.025/3) V = 0.0004415625 - 0.000231084375 + 0.0000327083 V = 0.0002432 Ok, now we're getting somewhere! Let's get to solving for Lv where both ends are flared! Lv = N*c*c*Rt*Rt / (4*pi*Fb*Fb*Vb) - 0.85*Rm - 0.613*Rm - 2*V / (pi*Rt*Rt) Lv = 1*340*340*0.05*0.05 / (4*3.14*10*10*0.284) - 0.85*0.075 - 0.613*0.075 - 2*0.0002432 / (3.14*0.05*0.05) Lv = 289 / 356.704 - 0.06375 - 0.045975 - 0.0004864 / 0.00785 Lv = 0.81020 - 0.06375 - 0.04597 - 0.06196 Lv = 0.63852m Lv = 25.15" At last, we know how long the vent tube must be. There is one last step which you might find interesting. Let's say you model up an enclosure (who hasn't?). Using a straight port with a 2" radius, you notice that the vent speed is approximately 15m/s. What will be the new vent speed, now that we have flared ports? Using the values for Rt and Rm that we determined previously, we can easily calculate the change in exit velocity. Vt = 15m/s Vm = Rt*Rt*Vt / Rm*Rm Vm = 0.05*0.05*15 / 0.075*0.075 Vm = 0.0375 / 0.005625 Vm = 6.67m/s That's quite a change! From % perspective standpoint, that's a decrease of approximately 56%! Hopefully you enjoyed the little math lesson. Whether this is practical for you to learn in depth or not, it is definitely worth reading and maybe picking up some theory. If someone asks you any questions about calculating flared ports, you can answer intelligibly. Cheers!

Have you ever completed an enclosure that was a touch too small? Your low end sounds cramped but you don't want to or can't build a brand new enclosure. You throw in some polyfill and are blown away by the improvements. Then you go online to talk about it and everything gets confusing. You don't know why it works or what it really did, but you know that it sounds better. Maybe it's time you learned more about it! Firstly, there are a few primary types of fill that are used. This includes polyester fiberfill, fiberglass insulation, and long-fiber wool. Of these three, polyester fiberfill is perhaps the best option, and also the origination of the term "polyfill". These products can easily be found in several stores, including Wal-Mart, Home Depot, or a local crafts and fabrics store, and all are extremely affordable (typically less than $2/pound). It is also very easy to apply to the inside of your enclosure: simply staple or glue it to the inside of your enclosure. How does it work? Stuffing a box with polyfill makes it seem larger and it all relates to thermodynamics. When polyfill is added to an enclosure, it changes the behaviour of the airspring in the enclosure from "adiabatic" to "isothermal". The term "adiabatic" implies that there is no heat transfer occurring. An isothermal process occurs once the polyfill has been added. As the air passes through the polyfill, the fibers wiggle and cause some of the energy created by the airspring to be dissipated as heat. This heats the surrounding air molecules warmer, causing the air to become less dense. Being that sound passes easier through a denser medium, the speaker interacts with your enclosure as if it is larger than it actually is. The effective increase in enclosure size can be as much as 40%! This has some very obvious benefits that are inherent of a larger enclosure. Firstly, it becomes more efficient (a larger enclosure is always more efficient than a smaller one for any given driver). Second, the f3 (or the frequency at which SPL is down by 3dB) will be lower, providing a little bigger bottom end. While these are both great advantages, they decrease the effective damping of the speaker as well, meaning the speaker can be more likely to bottom out or over-excurt itself. Naturally, this is speaker, frequency, and power dependent. If used in a ported enclosure, you will also see the Fb (or the resonant frequency of your port) drop lower. There are some additional worthy considerations. Adding polyfill to an enclosure can be a great choice. However, too much polyfill can be a bad thing. At a certain point, the stuffing becomes too dense and the fibers no longer wiggle. At this point, not only have you taken away the size benefit of adding polyfill, you have actually decreased the effective volume as the polyfill is now taking up room inside your enclosure. It is also worth mentioning that polyfill is not as effective in a large enclosure. Let's combine these two thoughts into two simple rules: 1. If the enclosure is less than 2.5 - 3.0 cubic feet in size, you should use no more than one and a half pound of polyfill per cubic foot available in your enclosure. 2. If the enclosure is greater than 2.5 - 3.0 cubic feet in size, you should use no more than one pound of polyfill per cubic foot available in your enclosure. Specific examples of polyfill's effects on various enclosure sizes (with varying amounts of polyfill in each size) can be found in The Loudspeaker Cookbook by Vance Dickason or in an article written by Tom Nousaine for the March/April 1995 edition of "Car Stereo Review". There is one last point that you will hear from time to time regarding polyfill: that polyfill stops standing waves in an enclosure. When referencing an enclosure for a subwoofer playing a fundamental frequency that falls in the typical range, this is simply false. A standing wave in this range of frequencies would be several feet long and, thus, unlikely to occur. However, higher order harmonic distortion is possible, and can potentially colour music. Being that these higher order harmonics will be progressively shorter (in terms of wavelength), polyfill can be effective for this purpose. However, audibility, particularly at high SPL, can be quite minimal. Using polyfill in an effort to absorb standing waves or various distortion is most effective in large enclosures for your midrange and is not particularly effective for a subwoofer. Hopefully you now have a greater understanding of what polyfill does and doesn't do, while also enjoying the opportunity to absorb some scientific content as well. If you're still undecided, be wild and adventurous: put some polyfill in your enclosure right this minute!

This is always an interesting and controversial topic. Every couple of weeks, a debate rages regarding the relevance of high Xmax and whether it is truly valuable to achieving SPL scores. Perhaps the greatest argument is that Digital Designs Audio drivers, who have a very impressive track record in SPL competition, have been routinely tested to show below average Xmax numbers. How is it possible that a driver with limited linear excursion can still be amongst the loudest? The answer is simple and complex all at once: Xmax is relevant to SPL and it's not. Now that I've confused you, let's proceed. I'll touch on how a speaker makes sound and how it's interpreted at a later time, but let's skip to some ground works. Acceleration is a critical component of creating SPL. The higher the rate of acceleration, the more pressure that can be created. Let's figure out how to get there. If you've been through any high school physics classes, you're probably very familiar with this equation. F=m*a Hey, that looks like Newton's Second Law of Motion. In short, it states that the net force of an object is equal to the product of it's mass and it's rate of acceleration. Of course, we can re-write the simple formula to better suit our needs. F/m = a After our spinning, the formula reads that the rate of acceleration is equal to the net force of an object divided by it's mass. Let's apply this to speakers for a moment, shall we? The force of an speaker is determined by the two factors: 1. BL - the combination of the magnetic field strength (B ) and the length of the voice coil in the gap (L) 2. i - the level of input current Taking that information and our above equation, we can easily translate this to a speaker relevant equation. (BL* i)/m = a Let's make some logical conclusions from this formula. 1. Increasing the magnetic field strength (B ) or the length of the voice coil in the gap (L) will increase the rate of acceleration 2. Increasing the level of input current (i) will increase the rate of acceleration 3. Increasing the mass of the driver will decrease the rate of acceleration Naturally, the inverse of these conclusions holds true as well. For example, if you decrease the moving mass of the driver, the rate of acceleration will increase. Simple stuff, me thinks. Now we have our foundation for understanding why Xmax is and is not relevant to SPL. We know what we want to have a really loud driver, don't we? Huge BL, ability to take a lot of power, with extremely low moving mass. When looking at thiele/small parameters, we are looking for something with a high BL^2/Re, high power handling, and low Mms. It's odd that Xmax isn't factored into that equation, don't you think? Ahh, but it is, in a sense. Once we apply current to the voice coil, it moves. Based on the Understanding Power Compression thread, we know that as the voice coil moves out of the gap, BL decreases. It stands to reason that as the voice coil moves out of the gap, BL decreases, and based on our previous conclusions, so does the rate of acceleration! In this sense, high Xmax is a good thing because it means the driver is capable of moving further without an alarming decrease in BL. In this sense, high Xmax is a great thing. A driver that can move great distances while keeping BL very linear can make for a very good, very loud driver. This is handy for competitions like Bass Race, where everyday music is played for longer durations. With that said, there is another aspect of SPL competitions where high Xmax may not matter so much. In DBDrag style competition, high Xmax is not always critical. Typically, a competitor plays a short burst sine wave near the resonant frequency of the port(s) used in their enclosure. This excites the air mass in the port, causing it to become the primary source of our pressure. Meanwhile, the driver that is exciting the air mass is relatively stationary; it is not excurting itself very much at all. If your driver is only moving +/- 2mm, what is the difference in BL between a driver with 16mm of Xmax and a driver with 100mm of Xmax? Not much at all. There is one more important consideration in the "high Xmax vs. SPL" equation. Again, looking back at that original equation, we know that high moving mass decreases our rate of acceleration. Let's pretend I'm engineering a driver for a client who wants high Xmax using conventional designs (more on this another day). How do I do so? Quite simple: I add length to the voice coil. There is, however, a caveat to adding length to your voice coil: more wire (be it copper, aluminum, etc) adds mass to the driver as well. This is not a good thing from an SPL standpoint. As we can clearly see, high Xmax and SPL are not necessarily mutually exclusive; in fact, sometimes they go hand in hand. At the same time, some situations call for very little Xmax. This is why companies like Fi Car Audio deserve more credit than they receive: there is no one answer for every question, but we'll allow you to customize our answer to suit your question. The point comes back to a daily engineering focal point: where can I afford to make sacrifices for the application? And that ultimately brings us to Newton's Third Law: For every action, there is an equal and opposite reaction. Cheers!

Bottom line is that the prohibition of something so physiologically harmless would just add to the business of the violent black market that prohibition has already created. It's also a question of liberty.

I've been meaning to do this for a while but haven't had a chance yet. 15" Icon Home Sealed Lower power - 4-5.5 cubes Higher power - 2.5-3 cubes sealed Home Ported Music - 4 cubes tuned to 30 Hz Home Theatre - 5 cubes tuned to 20 Hz (can tune lower if wanted) Vehicle Sealed 2-2.5 cubes sealed Vehicle Ported 3.5-4 cubes tuned anywhere from 28-35 Hz Any of those should work just fine. It's very important that you match your enclosure to your application. If you do so, you'll be very happy.

I have seen some very good ones lately, but I have to recommend The Prestige. Christian Bale and Christopher Nolan are an unbelievable team. I have read the book and Bale plays a very good Alfred Borden. The film is shot very well and the plot is very circular, which I love. I saw it twice in theaters and downloaded the dvd a few weeks ago; just got a chance to watch it again last night. What are some movies you have seen recently that everyone else must see?

Don't pay $400 for it. You can find Brahma's for less on caraudio.com, or you can buy similar products from Exodus Audio or Creative Sound Solutions.

Having a large magnet means you have a lot of potential flux in the system. You must have enough steel to carry the flux while still making sure the steel is saturated (ie. can't carry any more flux). Air has greater reluctance (resistance to carrying flux) than steel, so keeping the gap tight ensures you have the most flux possible in the gap (since the coil is closer to the steel). Any time you're able to increase BL, you're able to increase efficiency. There is no strong correlation between the amount of magnetic material in the motor and the power handling of the driver (note that talking about power handling and cooling is essentially the same thing). The steel in the motor does play a role, but the dominant factor is always the coil. The goal is to get the heat off the coil; in the past, the idea has been to get as much air moving in the motor as possible, which is, in part, one of the reasons the pole vent has been used. In reality, we just need to get the heat off the coil, so moving it anywhere else will be useful. So instead, you have a lot of steel in the motor, add some copper or aluminum shorting rings, and design the motor such that air is drawn down into the top plate, over the windings, and then passing the heat into the shorting rings below the gap or into the steel above the gap. The pole vent is still useful for relieving pressure under the dustcap, but it is best to keep as much steel as possible, in my opinion. Keep in mind that another dominant factor in efficiency is the mass that is being moved (Mms). The longer the coil, the greater the inductance. Since the inductance and resistance of the coil acts as a first-order (6 dB/octave) low-pass filter, it is preferable to have inductance that pushes the corner frequency (at which response begins to roll-off) above the bandwidth in which you'll be using the subwoofer. For SPL, you typically want a lot of windings in the gap (for both power handling and BL), so inductance is often higher.

x = x0 + vt x = 4" x0 = 0" t = 1 second/30 cycles = 1s/60 Solve for v. I divide the time by 60 as there are two 4" movements per cycle; as an alternative, you could set x to 8" and leave t as 1s/30 cycles. As I've mentioned several times, Le is the dominant aspect of transient response, while Mms (and other factors) play a lesser role. Note that there is a relationship between the time domain and the frequency domain.

Can I ask you guys why you bought DD buds and not someone else?

I think the point is mostly that the number of slugs is irrelevant. We can take about how tall the stack is or how wide, but using the number of slugs stacked tells us nothing at all. The most important thing about the magnets is that they saturate the steel with flux. You can use stacked magnets to gain more clearance (which is easier from a production standpoint), but all that really matters is that the magnets saturate the steel that your project requires.

Id like you to buy the AQ2200 and do an actual comparison with the BXI 2607. Someone needs to do this atleast. What about a drop in comparison between 9500s and BTLs. I say that needs to be done before anything can be said. And which one of DD's fart cannons are you going to compare with the Fi Q since the thread is comparing the two companies? Has DD ever made a SQ orientated sub? 9100's are supposed to be (underhung), but there is no evidence to confirm that they are.

Basically, his point was this: Speakers are highly inefficient. A moving speaker generates back EMF. The counter-voltage that is induced (back EMF) subtracts from the voltage supplied to the windings. Now because of how inefficient a speaker is, the suggestion is that the counter-EMF is especially problematic with low current inputs. This is, to an extent, true, but you must remember that at high-outputs we also lose output from non-linearity and thermal power compression. To be clear, I don't believe in this fallacy of "it requires X amount of power to get moving", and will not until someone shows evidence to the contrary. I have seen several measurements of a particular speaker's response vs frequency vs amplitude where output doubled with every doubling of power up to about 400 watts, after which the increase became increasingly small. If your theory were to be true, I would expect to gain maybe 1-2 dB for the first few doublings, then closer to 3 dB, then falling off again after that, which I simply have not seen. Further, it is an inductance-related problem (though not necessarily solvable with what we're doing now). More on this a bit later.

Are the mids the newer ones with Split Coil topology, or the older XBL^2 drivers? Either way, you'll be limited to the 1.7-2.0 kHz region on the mids. Where you cross the tweeters over will depend on where you position them and level differences. You will likely have to scale back the power on the tweeters a bit, both for safety and a smooth crossover. You'll probably have to underlap a bit.

So you are saying that folks who hear differences in various amplifier topologies, have either bad hearing or not very smart? What I'm saying is that ACTUAL differences between amplifiers are completely quantifiable...there is no magic pixie dust. Now, in terms of interpreted differences, I am saying that our ears and brain are not very smart. We have very poor memory for sound, and are unable to distinguish what is actually driving a difference between a variety of physical properties. We don't hear what happens with each component in the chain separately...we hear their summation. Even then, we are often unable to determine when a change is favourable or unfavourable (if the goal is accurate reproduction): instead, we hear how it relates to a personal preference. This is, of course, ignoring the whole philosophical argument of perception. We can only understand and compare against what we already know...what we've already perceived. No person here has ever heard a system that was a perfect reproduction of a song, and it is doubtful that we were there for the original production of our recordings; as such, it is impossible to state with a high degree of certainty using only our ears what level of accurate reproduction the system is achieving.

Tell me more. I haven't met anyone with a complaint about them... Well for starters, the RF T15k gained CEA compliance even though it doesn't do near the continuous power it is rated for.

Just wondering what you meant by this statement. I have been finding a ton of drivers I have been using lately sealed, will not get above 63hz. I need something that will get to around 72hz. Is this possible with the Havoc? Also, I think I have asked this before, but do you know the Le? Keep in mind....the enclosure behaves as a highpass filter; with both sealed and bass reflex (ported) systems, the enclosure only has an effect on low frequency performance. If you are having a perceived problem with upper frequency performance, you need to address the vehicle acoustics by eq'ing down the bottom end or by selecting a driver with less inductance and inductance variation.

I'm not completely sure I understand what the guy you spoke with is talking about. Can you get him to expand on it a bit? No, not all amps sound the same. Mind you, all amps that measure the same (whether that is by default or as a result of modification) will amplify the signal in the same way, and thus will often sound the same. The "sound" argument is greatly confused by our rather imperfect ears or, more specifically, our rather imperfect brains. Note also that there is no such thing as "RMS" watts. RMS current, yes....RMS voltage, sure. But what we're really talking about is average power....average watts.

Now that is a good idea.

I would venture a guess that Dan doesn't care that much. The Adire split was bad....if I were him, I wouldn't waste my time making a legal case....just more mess. RU has the parts now and at least they're staying (relatively) true to their purpose.

CA.com isn't that bad. This forum vs. forum stuff is junk, in my opinion. SSA is a whole different world, and I suppose that's something to be proud of. For me, there are less opportunities for educating here as of late (whether that be audio related or something else...say...maybe US politics) and that is just the nature of each site's traffic. I read maybe 2% of the threads there, but they usually leave an opportunity to help another person. It is hard to keep telling people to read the enclosure and power recommendations on Fi drivers somedays.