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Subwoofer myths exposed
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<blockquote data-quote="So Low iT Hz" data-source="post: 8213997" data-attributes="member: 658541"><p><a href="http:////forums/usertag.php?do=list&amp;action=hash&amp;hash=14" target="_blank">#14</a> It’s a bigger driver, then I need a bigger amp</p><p></p><p>Often times larger drivers require less amplification, that’s sort of the idea. The concept of bigger woofers need more power is not always true and plays right into the ever progressing misconception of car audio. What you should consider is the efficiency of the subwoofer. Efficiency will literally tell you how much acoustic output you will get given an amount of power (assuming linear limits of course). If the driver is bigger, has a larger motor and has a higher sensitivity, there is no mystery about it, you are going to get more SPL with the same amplifier provided the impedance is similar and the amplifier can produce high voltage at impedance peaks when the driver naturally draws very little current for a narrow range. If a driver is more efficient and has a larger voice coil, well you just got your cake and you can now eat it. Not only will it be louder, but it will have less thermal compression and ultimately more sound provided all else is equal (but such is not usually not the case). It’s often difficult to make voice coils larger and increase sensitivity too. This usually requires very large motors and expense. Sensitivity is most easily achieved by weight reduction usually from the cone surround and voice coil. Sensitivity is often a trade off of xmax and thermal compression limits.</p><p></p><p>However there are many larger drivers that don’t have ultra high sensitivity. A good pro audio subwoofer may have 6 to 10dB higher sensitivity over an average high excursion car audio subwoofer. That advantage makes them very capable with quite a bit less power at least for their frequency range which is usually above 40Hz. Likewise, SPL drivers ironically enough don’t need much power either! Let me repeat. True SPL drivers ironically enough don’t need much power! That’s because they are used in the higher frequency domain not limited by displacement and generally have great sensitivity numbers. They need this in order to get the excursion and ultimately SPL they need to win contests. High sensitivity and lots of power means lots of SPL provided the driver is still reasonably linear and does not physically break of course. Note: Strictly for SPL contest, drivers are normally burped at Fc (system resonance) which is the point of maximum current draw and minimum active driver displacement which is why excessive power must be used. Do not confuse that requirement with the much lower power requirements for sound reproduction outside that single SPL frequency. It’s important you know the TSP’s of the driver you buy, otherwise it could be the wrong driver for you! Who buys a car without knowing the horsepower? Just because a driver big and the manufacture claims pie in the sky RMS numbers doesn’t mean a thing!</p><p></p><p><a href="http:////forums/usertag.php?do=list&amp;action=hash&amp;hash=15" target="_blank">#15</a> Neodymium will lose its strength with heat</p><p></p><p>Of course it will, and so will ceramic motors too, but the fact is, under even extreme operating conditions, it’s not likely the motor will ever reach these temperatures. There is just too much steel to absorb the heat from the voice coil in almost any practical case. In practice, gradual demagnetization due to use simply does not occur. We have been making high power neodymium based drivers for many years now and we have never once measured a discernible number from heat.</p><p></p><p>While Neodymium is nearly 10 times as strong as a similar sized ceramic magnets, it can cost up to 50 times too which is almost exclusively why it is not used often. Also, traditional overhung motors, which account for more than 95% of all car audio designs, can get everything they need out of a ceramic magnet assembly and stronger neodymium would be perhaps unnecessary. If we could use neo more, we would, but because it’s a patented martial, it’s just not economically practical for most designs. Furthermore, in order the magnetize neodymium, A magnetizer with over twice as much power and energy needs to be used. Many manufactures lack the capabilities of even magnetizing neodymium, so it becomes impractical to not only use it, but to manufacture.</p><p></p><p><a href="http:////forums/usertag.php?do=list&amp;action=hash&amp;hash=16" target="_blank">#16</a> Its all about maximum displacement</p><p></p><p>A DIY’er favorite statistic, displacement / dollars. If you’re considering any bass above 40Hz then throw it out the door right now. Often times people assume that simply because one or more drivers have more maximum displacement over another type of woofer, than they will ultimately be the better performer(s). In many cases this is true, but it’s not true in general. Displacement alone does not guarantee SPL. In fact, SPL depends on not only displacement, but frequency range, sensitivity, box size, and BL product too. This is simply a matter of converting energy into acoustic sound pressure level and different devices work more efficiently than others for different frequency ranges. For subwoofers, it is generally accepted that BL product is the dominate factor that accounts for much of the performance or rather system efficiency, especially in a bass reflex or more complex system where there is a lot of air mass to displace. But keep in mind, depending on the type of system, size, frequency range, power and thermal limits, there may be even more critical and dependent variables that determine the overall performance of a system. None the less, high displacement is usually a good indicator that the subwoofer can excel in deep bass SPL. Of course there are other factors to consider depending on the system of system.</p></blockquote><p></p>
[QUOTE="So Low iT Hz, post: 8213997, member: 658541"] [URL="http:////forums/usertag.php?do=list&action=hash&hash=14"]#14[/URL] It’s a bigger driver, then I need a bigger amp Often times larger drivers require less amplification, that’s sort of the idea. The concept of bigger woofers need more power is not always true and plays right into the ever progressing misconception of car audio. What you should consider is the efficiency of the subwoofer. Efficiency will literally tell you how much acoustic output you will get given an amount of power (assuming linear limits of course). If the driver is bigger, has a larger motor and has a higher sensitivity, there is no mystery about it, you are going to get more SPL with the same amplifier provided the impedance is similar and the amplifier can produce high voltage at impedance peaks when the driver naturally draws very little current for a narrow range. If a driver is more efficient and has a larger voice coil, well you just got your cake and you can now eat it. Not only will it be louder, but it will have less thermal compression and ultimately more sound provided all else is equal (but such is not usually not the case). It’s often difficult to make voice coils larger and increase sensitivity too. This usually requires very large motors and expense. Sensitivity is most easily achieved by weight reduction usually from the cone surround and voice coil. Sensitivity is often a trade off of xmax and thermal compression limits. However there are many larger drivers that don’t have ultra high sensitivity. A good pro audio subwoofer may have 6 to 10dB higher sensitivity over an average high excursion car audio subwoofer. That advantage makes them very capable with quite a bit less power at least for their frequency range which is usually above 40Hz. Likewise, SPL drivers ironically enough don’t need much power either! Let me repeat. True SPL drivers ironically enough don’t need much power! That’s because they are used in the higher frequency domain not limited by displacement and generally have great sensitivity numbers. They need this in order to get the excursion and ultimately SPL they need to win contests. High sensitivity and lots of power means lots of SPL provided the driver is still reasonably linear and does not physically break of course. Note: Strictly for SPL contest, drivers are normally burped at Fc (system resonance) which is the point of maximum current draw and minimum active driver displacement which is why excessive power must be used. Do not confuse that requirement with the much lower power requirements for sound reproduction outside that single SPL frequency. It’s important you know the TSP’s of the driver you buy, otherwise it could be the wrong driver for you! Who buys a car without knowing the horsepower? Just because a driver big and the manufacture claims pie in the sky RMS numbers doesn’t mean a thing! [URL="http:////forums/usertag.php?do=list&action=hash&hash=15"]#15[/URL] Neodymium will lose its strength with heat Of course it will, and so will ceramic motors too, but the fact is, under even extreme operating conditions, it’s not likely the motor will ever reach these temperatures. There is just too much steel to absorb the heat from the voice coil in almost any practical case. In practice, gradual demagnetization due to use simply does not occur. We have been making high power neodymium based drivers for many years now and we have never once measured a discernible number from heat. While Neodymium is nearly 10 times as strong as a similar sized ceramic magnets, it can cost up to 50 times too which is almost exclusively why it is not used often. Also, traditional overhung motors, which account for more than 95% of all car audio designs, can get everything they need out of a ceramic magnet assembly and stronger neodymium would be perhaps unnecessary. If we could use neo more, we would, but because it’s a patented martial, it’s just not economically practical for most designs. Furthermore, in order the magnetize neodymium, A magnetizer with over twice as much power and energy needs to be used. Many manufactures lack the capabilities of even magnetizing neodymium, so it becomes impractical to not only use it, but to manufacture. [URL="http:////forums/usertag.php?do=list&action=hash&hash=16"]#16[/URL] Its all about maximum displacement A DIY’er favorite statistic, displacement / dollars. If you’re considering any bass above 40Hz then throw it out the door right now. Often times people assume that simply because one or more drivers have more maximum displacement over another type of woofer, than they will ultimately be the better performer(s). In many cases this is true, but it’s not true in general. Displacement alone does not guarantee SPL. In fact, SPL depends on not only displacement, but frequency range, sensitivity, box size, and BL product too. This is simply a matter of converting energy into acoustic sound pressure level and different devices work more efficiently than others for different frequency ranges. For subwoofers, it is generally accepted that BL product is the dominate factor that accounts for much of the performance or rather system efficiency, especially in a bass reflex or more complex system where there is a lot of air mass to displace. But keep in mind, depending on the type of system, size, frequency range, power and thermal limits, there may be even more critical and dependent variables that determine the overall performance of a system. None the less, high displacement is usually a good indicator that the subwoofer can excel in deep bass SPL. Of course there are other factors to consider depending on the system of system. [/QUOTE]
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