The first graph below shows the measured output levels of two loudspeakers driven to the maximum limits of their capabilities. In other words, this shows exactly how loud they will go between 20Hz and 200Hz. The blue line shows the BASSBOSS SSP118. The brown line shows the JBL SRX818SP.
The second graph shows the frequency response graphs of the two speakers when they are not being pushed to their maximum levels. So, when you're not pushing them to their very limits, this is an indication of the difference in how they will sound. The BASSBOSS is intended to sound warm and deep and big. It was designed with the sound character in mind, rather than with being able to meet a high SPL as the priority.
The test signal is swept sine wave from 200Hz to 20Hz. The calibrated microphone was placed 1m from the speaker grill with both the speaker and the microphone on a flat concrete surface. The microphone and speaker were located 50' from the nearest obstruction or reflecting surface.
The tests indicate that in the range above 65Hz, the two boxes produce very nearly the same maximum level however, below 65Hz the BASSBOSS SSP118 provides more output, showing a 3dB advantage at 55Hz, a 5.5dB advantage at 50Hz, a 6dB advantage at 40Hz, a 5dB advantage at 35Hz and a 3dB advantage at 30Hz. It can be concluded that it would take 2 of the JBL SRX818SP to equal the 40-50Hz output of the BASSBOSS SSP118 and that greater output above 50Hz would be achieved by 2 JBL SRX818SP.
It is evident that the performance of the SSP118 is focused on the lower range of the spectrum and that even at the very maximum limits of its output, it maintains the character of a subwoofer. The SSP118 can also be seen to deliver 130dB output as specified, and does so at 50Hz.
The JBL is specified to produce 135dB, which, from this measurement we must conclude is a "peak" specification. Actual measured continuous output is 127.5dB at 65Hz. From there, peak output is calculated to be 133.5dB.
I'm sure a test could be devised that would create a result of 135dB peak output, but for the sake of comparing apples to apples on the same day in the same place with the same mic, the same electricity and the same test procedure, this is an accurate comparison.
BASSBOSS SSP118: 130dB continuous. 136dB peak. Peak output frequency: 50Hz
JBL SRX818SP: 127.5dB continuous, 133.5dB peak. Peak output frequency: 65Hz
For those of you familiar with the relative energy associated with dB, a 3dB increase is effectively double the output. 6dB is 4x the output. Therefor a 2.5dB increase is approximately 85% more output. In the range between 40Hz and 50Hz, the SSP118 delivers approximately 400% of the JBL's output. Looking at it from the other side, the JBL delivers approximately 25% of the SSP118's output between 40 and 50Hz.
One JBL SRX818SP is less expensive than one BASSBOSS SSP118. If you were to use 2 of the JBL SRX818SP, together they will deliver more output than one SSP118, but only very little more where you really want it and feel it. When getting back to comparing cost, two of the JBLs would be more expensive and would be twice as much gear to carry around. In the long term this costs you in time and effort as well as money. In normal operation, it's possible to get effectively the same amount of heavy bass from one SSP118 as two JBL SRX818. The two boxes are very nearly the same size, with the JBL being slightly lighter.
The BASSBOSS box and electronics are designed and made in the USA. The BASSBOSS amp and connectors are safely recessed into the back of the cabinet. The BASSBOSS has 2 steel bar handles and a grab point at center rear.
The JBL box is designed in the USA and made in Mexico. Electronics say assembled in Mexico. The JBL has the amp flush with the back surface so the connectors extend behind the box. The JBL has 4 plastic handles.
Please let me know if there is anything I can clarify or expand upon.
Thanks for your question!