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Junior Varsity
A few questions on Specs and equations.
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<blockquote data-quote="Phil Graham" data-source="post: 57240" data-attributes="member: 430"><p>Re: A few questions on Specs and equations.</p><p></p><p></p><p></p><p>Brian,</p><p></p><p>I'm not sure the thread you are referring too in regards to subwoofers, but hopefully this will clarify:</p><p></p><ol> <li data-xf-list-type="ol">Music, in the worst case of a hyperlimited CD will have an instantaneous peak to average ratio of about 3dB. Even with that, the long-term peak to average (level/voltage) ratio of said song will be about 6dB. A carefully crafted live mix, with plenty of compression, will double these two figures, or more.</li> <li data-xf-list-type="ol">Modern high performance loudspeakers typically start exhibiting substantial deviation (>1dB) from "cold" performance with long term average input power levels 4-6dB below the AES rating. Just because a loudspeaker will survive at the AES rating doesn't mean you'd want to use it there. 6dB below the AES input power is still a substantial level of input.</li> <li data-xf-list-type="ol">Loudspeakers mounted in most common LF enclosures exhibit highly reactive impedance, so the input power over a broad chunk of the low frequency is actually rather small. In the low frequencies where the average impedance is higher, the average cone movement is generally also higher, so there is some cooling aid from the cone movement.</li> <li data-xf-list-type="ol">Most loudspeaker heating takes place in the midrange, where the loudspeaker Z is near Rdc and there is little cooling from air flux through the voice coil assembly.</li> <li data-xf-list-type="ol">In the subwoofer range, there are (more or less) three places where the loudspeaker can trip up. The first is in simple over excursion. The second is in port compression, and the third is sub performance degrading from the shift in theile small parameters due to voice coil heating.</li> </ol><p></p><p>The average modern vented loudspeaker with good drivers will rarely be damaged due to mechanical over excursion. In similar fashion the same driver will rarely be damaged thermally with typical live sound performance material. The most common ill behavior from typical modern pro subwoofers is obnoxious noises and/or compromised performance due to port effects.</p><p></p><p>A second, longer term effect is the ongoing rise in steady state voice coil temperature over the duration of a session of extended output. This won't damage the loudspeaker system, but can hurt the tonality of the subwoofer system. This thermal change, as well as excessive excursion leading to IMD distortion components are two common tonality shift issues for subs.</p><p></p><p>One way that loudspeakers are damaged thermally is in the improper application of limiting! The well-meaning pa operator uses a compressor to "protect" their loudspeaker. Instead the compressor ends up increasing the average input power, and that destroys the speaker thermally. Removing "protective" limiting of this type can be a better way to protect the loudspeakers, especially if the amplifier has a good quality clip limiter.</p><p></p><p>Setting limiters (or unsetting them) is something that I do for clients. I wish I could say that there was a standard rubric I could post on how to approach this, but I've found it to be different in almost every setting due to the unique makeup of the gear in the system. It takes into consideration the details above, and usually combines a mixture of listening, measurement, and design simulation.</p></blockquote><p></p>
[QUOTE="Phil Graham, post: 57240, member: 430"] Re: A few questions on Specs and equations. Brian, I'm not sure the thread you are referring too in regards to subwoofers, but hopefully this will clarify: [LIST=1] [*]Music, in the worst case of a hyperlimited CD will have an instantaneous peak to average ratio of about 3dB. Even with that, the long-term peak to average (level/voltage) ratio of said song will be about 6dB. A carefully crafted live mix, with plenty of compression, will double these two figures, or more. [*]Modern high performance loudspeakers typically start exhibiting substantial deviation (>1dB) from "cold" performance with long term average input power levels 4-6dB below the AES rating. Just because a loudspeaker will survive at the AES rating doesn't mean you'd want to use it there. 6dB below the AES input power is still a substantial level of input. [*]Loudspeakers mounted in most common LF enclosures exhibit highly reactive impedance, so the input power over a broad chunk of the low frequency is actually rather small. In the low frequencies where the average impedance is higher, the average cone movement is generally also higher, so there is some cooling aid from the cone movement. [*]Most loudspeaker heating takes place in the midrange, where the loudspeaker Z is near Rdc and there is little cooling from air flux through the voice coil assembly. [*]In the subwoofer range, there are (more or less) three places where the loudspeaker can trip up. The first is in simple over excursion. The second is in port compression, and the third is sub performance degrading from the shift in theile small parameters due to voice coil heating. [/LIST] The average modern vented loudspeaker with good drivers will rarely be damaged due to mechanical over excursion. In similar fashion the same driver will rarely be damaged thermally with typical live sound performance material. The most common ill behavior from typical modern pro subwoofers is obnoxious noises and/or compromised performance due to port effects. A second, longer term effect is the ongoing rise in steady state voice coil temperature over the duration of a session of extended output. This won't damage the loudspeaker system, but can hurt the tonality of the subwoofer system. This thermal change, as well as excessive excursion leading to IMD distortion components are two common tonality shift issues for subs. One way that loudspeakers are damaged thermally is in the improper application of limiting! The well-meaning pa operator uses a compressor to "protect" their loudspeaker. Instead the compressor ends up increasing the average input power, and that destroys the speaker thermally. Removing "protective" limiting of this type can be a better way to protect the loudspeakers, especially if the amplifier has a good quality clip limiter. Setting limiters (or unsetting them) is something that I do for clients. I wish I could say that there was a standard rubric I could post on how to approach this, but I've found it to be different in almost every setting due to the unique makeup of the gear in the system. It takes into consideration the details above, and usually combines a mixture of listening, measurement, and design simulation. [/QUOTE]
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A few questions on Specs and equations.
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