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4X8" DIY Mid-High
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<blockquote data-quote="Peter Morris" data-source="post: 208646" data-attributes="member: 652"><p>18 Sound use - "Linear Math. Xmax is calculated as(Hvc-Hg)/2 + Hg/4 where Hvc is the coil depth and Hg is the gap depth." Which is probably the point at which distortion and non - linear behaviour starts to rise, but it can depend a little on the drivers design.</p><p></p><p>With the 8NMB420 it has an RMS power of 280 watts, but the continuous program power is only 400 watts not 560 watts. If you use the program power for your calculations what you find is that the is the 420, 650 and the 8NDL64 all make about the same SPL (based on the manufactures Xmax) the 8NDL51 makes about 3 dB less but goes lower.</p><p></p><p>The reason I chose the 650 was that it had a stiffer cone and as you can see from the frequency response it operated in the piston range up to about 1200 - 1500 Hz. You can get a rough idea where this happens by looking at the off axis response compared to the on axis response. For a line - array and coupling between drivers this is important and if you read the spec's 18 sound say that its recommended for line array applications.</p><p></p><p>B&C also specify Xvar which is a good indication of the useful Xmax </p><p></p><p>"Evolution is a process that affects not only products, but also their technical specifications. Constant advances in research provide more and more precise methods to measure the performance of loudspeakers, and describe their features. Thiele – Small parameters have become the universal language for describing loudspeaker behaviour in the small signal domain. Nevertheless, they comment little on the working limits of loudspeakers in the large signal regime.</p><p></p><p>These limits are customarily indicated by Xmax, the maximum linear excursion. This value is typically measured according to the AES2-1984 standard, corresponding to a maximum of 10% total harmonic distortion (THD) with a sinusoidal signal (though most manufacturers, including B&C, now typically provide data for Linear Mathematical Xmax, not measured Xmax). Recent research shows that this method can yield ambiguous results, and even different numerical values for the same loudspeaker. The main limit of this measurement is that it looks at the output signal instead of the physical features of the driver itself. On the contrary, the most up-to-date instruments for distortion analysis can measure the variations in loudspeaker parameters when they are fed with high-level signals. In this way, an excursion limit can be fixed, beyond which the parameter’s variation becomes excessive.</p><p></p><p>The “X var” value reported in our data (generally after the traditional “Xmax” value) is measured this way. Beyond this excursion limit, the magnetic field seen by the voice coil, or the total suspension compliance, or both, drops to less than 50% of their small signal value, producing high distortion levels, strong variations from small signal behaviour and power compression. The new technique yields different results from the standard measurement based on THD. B&C Speakers believes that this added information gives a more accurate and reliable description on loudspeakers behaviour in actual operating conditions."</p><p></p><p></p><p>See ... <a href="http://www.bcspeakers.com/resources/faq-frequently-asked-questions/" target="_blank">http://www.bcspeakers.com/resources/faq-frequently-asked-questions/</a></p></blockquote><p></p>
[QUOTE="Peter Morris, post: 208646, member: 652"] 18 Sound use - "Linear Math. Xmax is calculated as(Hvc-Hg)/2 + Hg/4 where Hvc is the coil depth and Hg is the gap depth." Which is probably the point at which distortion and non - linear behaviour starts to rise, but it can depend a little on the drivers design. With the 8NMB420 it has an RMS power of 280 watts, but the continuous program power is only 400 watts not 560 watts. If you use the program power for your calculations what you find is that the is the 420, 650 and the 8NDL64 all make about the same SPL (based on the manufactures Xmax) the 8NDL51 makes about 3 dB less but goes lower. The reason I chose the 650 was that it had a stiffer cone and as you can see from the frequency response it operated in the piston range up to about 1200 - 1500 Hz. You can get a rough idea where this happens by looking at the off axis response compared to the on axis response. For a line - array and coupling between drivers this is important and if you read the spec's 18 sound say that its recommended for line array applications. B&C also specify Xvar which is a good indication of the useful Xmax "Evolution is a process that affects not only products, but also their technical specifications. Constant advances in research provide more and more precise methods to measure the performance of loudspeakers, and describe their features. Thiele – Small parameters have become the universal language for describing loudspeaker behaviour in the small signal domain. Nevertheless, they comment little on the working limits of loudspeakers in the large signal regime. These limits are customarily indicated by Xmax, the maximum linear excursion. This value is typically measured according to the AES2-1984 standard, corresponding to a maximum of 10% total harmonic distortion (THD) with a sinusoidal signal (though most manufacturers, including B&C, now typically provide data for Linear Mathematical Xmax, not measured Xmax). Recent research shows that this method can yield ambiguous results, and even different numerical values for the same loudspeaker. The main limit of this measurement is that it looks at the output signal instead of the physical features of the driver itself. On the contrary, the most up-to-date instruments for distortion analysis can measure the variations in loudspeaker parameters when they are fed with high-level signals. In this way, an excursion limit can be fixed, beyond which the parameter’s variation becomes excessive. The “X var” value reported in our data (generally after the traditional “Xmax” value) is measured this way. Beyond this excursion limit, the magnetic field seen by the voice coil, or the total suspension compliance, or both, drops to less than 50% of their small signal value, producing high distortion levels, strong variations from small signal behaviour and power compression. The new technique yields different results from the standard measurement based on THD. B&C Speakers believes that this added information gives a more accurate and reliable description on loudspeakers behaviour in actual operating conditions." See ... [URL]http://www.bcspeakers.com/resources/faq-frequently-asked-questions/[/URL] [/QUOTE]
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