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Can someone explain to me what factors of the driver determines its maximum output?


I've always thought it is Sd and Xmax, but something tells me this isn't right.

According to this , the old SVS PB2-Ultra, with two heavy duty 12'' drivers with 28-30mm Xmax in a very large ported enclosure tuned to 20Hz can only produce 102.8dB at 20Hz with 9.4% THD in a 2m ground plane measurement.


Now fast forward 10 years, SVS's own PB12-NSD, a subwoofer with just one 12'' driver (a modified Peerless XXLS 12) with just 12mm of Xmax, is able to slightly exceed that level of output at 20Hz at 103.2dB with 9.3% THD in a 2m ground plane measurement.


Both subs are large ported subwoofers tuned at 20Hz. How does the PB2-Ultra, with at least double the enclosure volume, double the amplifier power, double the driver, each with more than double the Xmax, still produce less output? Since both subs are tuned to the same frequency, the only explanation I can think of is that Xmax and Sd are not the only determinants. Can someone enlighten me?


Thanks
 

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Quote:
Both subs are large ported subwoofers tuned at 20Hz. How does the PB2-Ultra, with at least double the enclosure volume, double the amplifier power, double the driver, each with more than double the Xmax, still produce less output? Since both subs are tuned to the same frequency, the only explanation I can think of is that Xmax and Sd are not the only determinants. Can someone enlighten me?Thanks

Your presumption that the /2 is a large enclosure is where you're mostly going wrong in how it relates to 20hz. SVS is constrained to enclosure size for a variety of reasons including the customer to a large degree. We see it over here in DIY, except not to the extent that SVS is forced to deal with.
 

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Quote:
Originally Posted by LowerFE  /t/1520381/what-determines-the-max-spl-of-a-driver#post_24424009


Since both subs are tuned to the same frequency, the only explanation I can think of is that Xmax and Sd are not the only determinants. Can someone enlighten me?
There's also the matter of sensitivity.

As for sensitivity, that's the result of a half dozen T/S specs along with the cabinet design, so you can't just look at xmax alone to compare the potential maximum SPL of two speakers.
 

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I think a likely explanation is that you are comparing apples to oranges. 103db for the pb12 is Max burst and the 102.8dB for the pb2 ultra is likely to be from a sweep (didn't read the whole thing so its an assumption). If you go to databass and look at the sweeps for pb12 you will find that it can do ~99.5db at 20Hz and is into heavy compression at that point. Look at the multi-series charts tab and extended charts tab. Also its not very reliable comparing measurements form two different sources. Their methods, equipment, technical skills and so forth might be more different than is revealed in the text.
 

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"I've always thought it is Sd and Xmax, but something tells me this isn't right."


add to that power handling and cab effects (horn, ported, etc.) and you should pretty much have it.
 
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