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<blockquote data-quote="Phil Graham" data-source="post: 40120" data-attributes="member: 430">Re: Here&#039;s the picture you ALL have been waiting for&nbsp;Silas, Its not so much an ideal rolloff, as one that balances the excursion behavior of the cabinet. There&#039;s no sense in &quot;over&quot; rolling off the cabinet to the extent that the excursion below Fb is less tha an above Fb. Conversely, you don&#039;t want to &quot;under&quot; roll off the speaker below Fb have have a greater excursion maxima below Fb than above. You can simulate such things decently with a free program like WinISD, or you can use several more advanced pieces of software (e.g. SoundEasy, LSPCad, AkAbak, LEAP).Excursion of a horn cabinet like the LAB is pretty readily observable by simulation.Let me explain my thought process for high pass filtering on a hypothetical vented speaker. Lets say that Fb is 35Hz, and the -3dB point is 37Hz. For such a speaker, the highest driver excursion will be somewhere in the mid 40s or low 50s. Lets say that our hypothetical driver starts to sound bad after 10mm one way excursion. If we hit 10mm one way in the mid 40s, we don&#039;t want to go much above 10mm one way below the 35Hz Fb. For simplicity&#039;s sake, lets assume that the calculated excursion of the driver is 20mm one way at 25Hz. To cut the excursion in half to 10mm one-way, we need to reduce the drive level 6dB at 25Hz. That means our HPF must be 6dB down at 25Hz, and how we get there depends on the excursion rise between 35Hz and 25Hz.Distortion is related to the declining BL product, which in turn depends on the amount of excursion. The relationship is direct, but not linear. The Bl product is pretty consistent as long as the coil is fully in the magnetic gap, and then starts to taper off more rapidly as the coil leaves the gap.As for the amount of distortion that is acceptable, our ears are very insensitive to low order order harmonic distortion at low frequencies. Less than 10% THD is not readily audible, and nothing to worry about. Driver air venting and suspensions can produce a lot of anharmonic content, and that is often more audible and annoying than the drivers&#039; THD.</blockquote>

[QUOTE="Phil Graham, post: 40120, member: 430"] Re: Here's the picture you ALL have been waiting for Silas, Its not so much an ideal rolloff, as one that balances the excursion behavior of the cabinet. There's no sense in "over" rolling off the cabinet to the extent that the excursion below Fb is less tha an above Fb. Conversely, you don't want to "under" roll off the speaker below Fb have have a greater excursion maxima below Fb than above. You can simulate such things decently with a free program like WinISD, or you can use several more advanced pieces of software (e.g. SoundEasy, LSPCad, AkAbak, LEAP). Excursion of a horn cabinet like the LAB is pretty readily observable by simulation. Let me explain my thought process for high pass filtering on a hypothetical vented speaker. Lets say that Fb is 35Hz, and the -3dB point is 37Hz. For such a speaker, the highest driver excursion will be somewhere in the mid 40s or low 50s. Lets say that our hypothetical driver starts to sound bad after 10mm one way excursion. If we hit 10mm one way in the mid 40s, we don't want to go much above 10mm one way below the 35Hz Fb. For simplicity's sake, lets assume that the calculated excursion of the driver is 20mm one way at 25Hz. To cut the excursion in half to 10mm one-way, we need to reduce the drive level 6dB at 25Hz. That means our HPF must be 6dB down at 25Hz, and how we get there depends on the excursion rise between 35Hz and 25Hz. Distortion is related to the declining BL product, which in turn depends on the amount of excursion. The relationship is direct, but not linear. The Bl product is pretty consistent as long as the coil is fully in the magnetic gap, and then starts to taper off more rapidly as the coil leaves the gap. As for the amount of distortion that is acceptable, our ears are very insensitive to low order order harmonic distortion at low frequencies. Less than 10% THD is not readily audible, and nothing to worry about. Driver air venting and suspensions can produce a lot of anharmonic content, and that is often more audible and annoying than the drivers' THD. [/QUOTE]

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