Zade08 Posted January 20, 2009 Report Share Posted January 20, 2009 Hey guys Iv been looking at subs. I always thought that more excursion meant more spl. But looking at my bl15s and the q15s. My bls only have 23mm xmax while the qs have 27mm xmax. Obviously the bls will get louder. Can some one chime in and explain to me exactly what high xmax does. Vehicle: 2001 Ford Escape Head Unit: Kenwood Kdc-x592 All out for a rebuild. New shit coming in the next 30 days. Link to comment Share on other sites More sharing options...
2000s-10 Posted January 20, 2009 Report Share Posted January 20, 2009 i belive its cause the Q is more of a sq sub and the suspension is softer. 1999 grand prix gt kenwood x994 head unit 1/0 big 3 all shok industry single run to the back New mid/highs coming not sure what Soundqubed q2200d at .5 (have) 2 soundqubed hdc3 12s (have) New box to be built.. sealed firing forward (yet to be designed) 200 amp alt not sure exact size or manufactor xs power batts Link to comment Share on other sites More sharing options...
Stephen Posted January 20, 2009 Report Share Posted January 20, 2009 From FLSPL Written by: Neil Middlemiss 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. you can cook bacon shirtless if you're not a pussy...lol not hatin, but am i wrong here it looks as if the amp is not grounded its hooked directly to the battery. it that the way it should be. DC POWER Link to comment Share on other sites More sharing options...
Zade08 Posted January 20, 2009 Author Report Share Posted January 20, 2009 I noticed the Q has 2 spiders while the bl has 3. But what does xmax do? Does it move more air and make more bass or just allow for a fuller range of frequencies? Vehicle: 2001 Ford Escape Head Unit: Kenwood Kdc-x592 All out for a rebuild. New shit coming in the next 30 days. Link to comment Share on other sites More sharing options...
Zade08 Posted January 20, 2009 Author Report Share Posted January 20, 2009 Stephen thanks for the copy pasta man. Realy cleared up alot of shit thats been swirling around in my head. Vehicle: 2001 Ford Escape Head Unit: Kenwood Kdc-x592 All out for a rebuild. New shit coming in the next 30 days. Link to comment Share on other sites More sharing options...
Ray Posted January 20, 2009 Report Share Posted January 20, 2009 In lamens terms the xmax rating is how far the sub can move before it loses 30% of its bl. (or motor force) xmech is how far its suspension can move not relevant to it's bl. 2008 California state record holder 157.2 Bassrace2009 California state record holder 157.0 BassraceRollin 50's 158.7db2009 King of Cali Bassrace2009 USACi score 160.5 @ 42hz Link to comment Share on other sites More sharing options...
Xplorer Posted January 20, 2009 Report Share Posted January 20, 2009 Wow, that was a really good read. thanks for postin' that up Stephen Link to comment Share on other sites More sharing options...
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