Originally Posted by blackjack616
How does the F15 compare to a higher end sub like the JL 13 or something of that price range?
JL is a company with very solid engineering. There are a lot of innovations (ie IP) on their drivers. But those are needed in order to be able to crank up high SPL in a SMALL enclosure using small diameter drivers with long excursion because thermal management (not to fry the driver), maintaining high BL value from a pretty big magnetic gap, and maintaining large excursion without the rubber surround becoming distorted are their top priority issues. So the key is SMALL enclosure, a desirable feature in car audio. If one does not need SMALL enclosures, those innovations may not be very valuable, a reason why we don’t them in our front speakers.
F15HP is designed with a different design philosophy. Our top priority is fast transient response(meaning low Q and high damping). To achieve that, we need to allow our subs to go down to 14hz with a separate rumble filter control. JL subs pretty much have that rumble filter engaged all the time. A rumble filter always adds ringing to the transient response.
Servo operation addresses another key problem in speakers (not just subwoofers)– memory effect. Memory effect can be explained as follows. If we have 4 notes A, B, C and D with different strength, the reproduced strength of each notes should not depends on the order they play. For instance, the note A strength should not be depend on if it plays as ABCD, DCBA, or DABC…etc. The ideal case that playback does not have memory effect is crucial to all audio gears. Its importance is even higher than distortion. For those who play pianos know not all of our 5 fingers have exactly same strength. A lot of piano practice is to add some compensation so that all 5 fingers appear to have same strength. Other instrument players face the same problem. We certainly don’t want audio gears to add their own memory effects. What are the factors giving arise to the memory effects in subwoofer? First one is the hysteresis of spider/surround of the drivers. Low compliance drivers (those with surround as hard as tires) just make the problem more serious because the spring force now mainly comes from surround/spider than the enclosure itself. The latter is much more linear with very low memory effect. We don’t see stiff surround drivers in our front speaker for a reason. It makes memory effect worse. The second is the voice coil temperature. Thermal behavior in drivers is very complicated. Each note of A, B, C, D leaves a different amount of thermal trace to the voice coil and whatever is played next depends on the history of previously played notes. That is a clear memory effect. There is a surge in high efficiency front speakers on this forum. One of the advantages they offer is they have lower thermal induced memory effect. Between these two sources of memory effect, servo operation reduces the first source by a factor of 3x(or 10db) and completely remove the thermal memory effect. Hope this offers a different perspective to your question.
PS. one may wonder why JL does not offer PR
-based subs. Well in one of the CES several years ago, Earthquake wanted to demonstrate their PR
-based subs can play 10hz. As soon as they did that, it was very apparent that sub was dancing on the floor and wanted to run away from the scene by itself at the same time. The company representative used his foot to pin that sub to the floor.