Damn it, I initially wrote an extremely long post detailing why 119dB is impossible, but as I wrote and gathered evidence to make my case, I realized it is possible with a HUGE stretch. I still think it is impossible given what we know of that sub. However, 119dB is absolutely achievable with a 15'' woofer in that box size. I'll explain why later in this very long post.
But let's play devil's advocate for a second here. Pretend we're in a world where JTR subs didn't exist and the SVS PB13 is just announced. SVS claims the new PB13, with a 13'' driver, is capable of 110.6dB at 20Hz, 2 meter GP, with 5% distortion (right from Data-Bass). This would probably attract a lot of skepticism from people. Let's consider some examples:
PSA XV-30FSE, with *two* 15'' woofers in a massive cabinet: 109.4dB at 18% THD
2x Velodyne DD18+ with two 18'' woofers: 109.6dB, 26.8% THD
2x HSU VTF-15H with two 15'' woofers: 110.1dB, 31.9% THD
2x Reaction Audio PV-15X, again, two 15'' woofers: 110dB, 15.5% THD
How can a single 13'' have more output than much bigger double 15's and double 18's woofers in much bigger cabinets and power? Not only that, but with way less distortion? That's impossible! Right?
Back to this sub. Note that Thilo mentioned 119dB peak, so converted to RMS, which is what Data-Bass and most simulators use, it is only 116dB, and this is quite achievable if there is enough amp power.
The easiest proof? Look at the Data-Bass results for the TC Sounds LMSR12 Dual 15" VMP. This is a subwoofer with the 12'' LMS-R in a box with 2.4 cu ft of internal volume tuned to 18Hz. This little thing produced 109.6dB at 20Hz, 2 meters away (albeit with a LOT of power, way more than 1200W).
Now, given the picture of the sub, it seems reasonable that it could have 4.8 cu ft of internal volume. I'm choosing 4.8 cu ft to make the math simple, because that is exactly double the volume of the LMS-R 12 sub. If the enclosure size is doubled, efficiency goes up by 6dB. Therefore, for the same input power that produced 109.6dB in the LMS-R 12 sub, it would produce 115.6dB in a cabinet twice the size. The LMS-R 15'' has more cone area, more excursion (but excursion is not a problem at tuning), and better power handling, so it is actually possible to get more than 115.6dB, so 116dB is achieved.
But what about distortion? 2.4 cu ft is a very small amount of enclosure volume. The smaller the enclosure, the higher the distortion for a given output because the air stiffness increases with smaller enclosures, and a driver will produce more distortion because it has to try harder to overcome the stiffness of the air. Therefore, doubling the enclosure size would actually help a lot to lower the distortion.
What about port compression? Port compression just means as the driver's SPL output increases, the port SPL output does not increase the same amount. So it will just take more power to achieve a particular output because the vent velocity isn't high enough where it would limit the maximum output.
Therefore, with the bigger enclosure and higher power handling of the 15'' LMS-R, 116dB is definitely possible, just with a lot of power (around 6000W depending on how much thermal compression)
An analysis of the PB13's 20Hz performance for those interested. I originally wrote this to demonstrate how 119dB is impossible because the PB13U represents a 20Hz performance that is about as good as it gets for a 13'' woofer. However, turns out the amp isn't capable of much burst power. So with a very powerful amp, it is possible.
A lot of people don't know this, but the amount of output increase from porting a woofer can be drastically different. Four things affects the amount of output at tuning:
1. Amount of amplifier power
2. Amount of cabinet volume
3. Size of the port
4. The driver parameters (not Xmax), and most people do not know they even make a difference. Most people will be surprised how big of a difference it can make.
The two main driver parameters that make a difference are the suspension stiffness and the motor strength.
Motor strength is important, because subwoofers are generally in undersized enclosures. The stronger motor is better at overcoming the stiffness of the small air space. One thing worth mentioning is that motor strength is not simply a BL^2/Re figure. BL and Re are small signal parameters. These parameters will change drastically when the woofer is being operated at high excursion levels. For all woofers, the motor strength is reduced more and more the higher the excursion. Underhung woofers have a big advantage here because the motor strength decreases at a much slower rate as excursion rises (we call that having a flatter BL curve). However, underhung motors wastes a good amount of magnetic strength in order to achieve that, which is why most underhung motors use very large ferrite or neodymium magnets.
Generally, a higher suspension stiffness will result in more output gain from the port. This is the same as having a lower Vas. Again better at overcoming the stiffness of the air.
The amazing 20Hz performance from the PB13U is most likely attributed to the very high motor strength underhung motor that makes the woofer weigh 55 pounds. While there are no T/S parameters for the Ultra 13 woofer, it is very likely that it has a very stiff suspension. When you increase suspension stiffness, Fs goes up, and the only way to lower Fs is to increase moving mass, which lowers sensitivity. The lower sensitivity is evident in the relatively low upper bass maximum output despite a high motor strength that would increase sensitivity. What is even more impressive is that it does this with less than 1500W or so. The long term maximum output vs CEA 2010 maximum burst output showed just a 1.3dB difference. This means the amp's burst power isn't very high. Assuming the amp is capable of producing 1000W continuously, 1.3dB is just 34% higher power, so around 1340W for 110.6dB. Therefore, if one was to power the Ultra 13 woofer with a big 20,000W amp like Ricci uses, one would only need ~3.46x more power to hit 116dB, which is 4636W. The Ultra 13 woofer should have absolutely no problem handling 5000W for a very short period of time for the CEA2010 burst testing. Port velocity is under 20m/s, so no problems there. With a big amp it could probably even burst 120dB.
Last edited by bcodemz; 09-20-2016 at 09:03 PM.