It would seem that the discussion has digressed into nothing more than who has the highest SPL at the lowest frequency. Certain brands are being cited based on test results as being a better value because they are loudest under those test conditions.
Maximum SPL at full extension is only one of many criteria and not necessarily the most important.
The aforementioned brand also requires a 3” greater driver diameter, a passive radiator, and a volume of nearly 8750 cu inches, 1.78 times the volume of the f112 at 4925 cu inches, to get the high SPL at the frequency extension quoted. In reviewing the list of tested subs, one should note that farther down is a 12” model by the same manufacturer that only produces 105 dB.
There are trade offs with using such a design to satisfy the high SPL/extension goal. Passive radiators operate as pneumatic devices that have issues with compressible fluid flow.
Compressibility of the air used to drive the passive radiator will generate phase discrepancies between the active and passive drivers with the passive lagging the active driver as pressure builds up to move the passive driver which also has greater inertial mass than the mass reactance loading that air in a port would. Coupled with internal reflections and exacerbated by the storage of elastic strain energy from deformation of the passive driver, the air pressure will then be forced back into the cabinet in an accordion effect. All this must be engineered carefully to avoid any detrimental acoustic effects.
The measurements quoted in support of one product’s superiority over another are
in room measurements at 2 meters. In reality, such measurements are of a somewhat limited value as a comparator between products as it is more a measurement of the room than of the products in question. Corner loading will be the most likely to excite room modes and it is unclear as to the level of
precision executed in the test. Many questions, some significant and some minor, are not addressed such as:
What are the room’s actual dimensions and shape? At this volume, were the ceilings level or vaulted? Length, width, height, and shape will all affect the room response.
Was the room an open or closed room? If a closed room, were any doors consistently opened or closed for all tests?
Where precisely were the subs placed in relation to the walls, what are the dimensions?
Was every sub placed in the same corner, each with its acoustic center located identically in three dimensional space for every measurement?
Where was the measurement microphone located in relation to the walls?
Was the measurement microphone located in precisely the same spot in three dimensional space for every measurement?
Did the technician see fit to rearrange any objects of significant size such as furniture that would alter reflectivity over the course of what is likely an extended measurement period as it is unlikely he had all the subs at the same time?
Did the technician do any other redecorating that might change the ratio or locations of absorptive to reflective surfaces such as add a rug, take out carpeting, or change whether the drapes were open or not from test to test?
The test results provided have a significant amount of missing data whose absence supports questioning the precision and thoroughness of the testing.
We now know how the technician’s testing room performs, not actually how these subs perform.
Do not confuse this testing methodology with frequency response. A more reliable methodology to evaluate actual output from each sub, and not variations in room acoustics, placement, and measurement technique, would be anechoic or quasi-anechoic measurement of frequency response at various dB levels for power compression.
Based on the approximate room volume and assuming a rectangular closed room with an 8’-0” ceiling height, I have evaluated some possible room modes for a similar room volume using a spread sheet calculation provided by a major manufacturer that includes graphics to help illustrate the issue.
If we place the sub at 1 meter from each wall at the corner and measure at 2 meters from the sub along the room length, knowing that 1 meter = 3.28 feet, the microphone is at 9.84 feet near a dropout centered on 28 Hz at 10 feet in the first scheme. If the microphone is placed 2 meters away along the width, the dropout is at 28 Hz at 10 feet.
Place the sub at 1.5 meters from the walls. Now the microphone is at 3.5m = 11.48 feet, we have a potential 24 Hz dropout in the width of scheme 1 or length of scheme 2.
The above is just a hypothetical exercise to illustrate the point. We really do not know the actual room dimensions, where the subs or microphone are located, or even if they are in the same spot for every measurement. Throw in variability of room shape, contents, and surface conditions and we have no idea what the measurements may mean.
Interestingly enough, the Fathom subs have an extreme low frequency (ELF) control that can adjust output between –12dB to +3 dB at 25 Hz to correct for this sort of troublesome room business.
Also of interest is that the review of the f112 that corresponds to these measurements is very favorable and comes to similar opinions as to the depth, power, and accuracy of the f112. The review goes so far as to say that the f112 easily outperformed his similarly priced reference sub by a wide margin.
Review of the frequency response in figure 2 in the measurement section will show the sub goes below what certain readers and tests have suggested, measured at levels that will not cause permanent hearing damage,
Occupational noise exposure. - 1910.95, section 1910.95(b) (2).
I will now point out that in real world use depth is not a problem, the f112 is very accurate with exceptional dynamics, transient response, and detail. This translates into an intense listening experience in a category with only a few products.
JL Audio, from my observations, is an engineering driven company that goes to great lengths in designing their products. I have come to this conclusion, not only from what has been said in advertising literature, but in discussion, at some length, with several engineers and project managers in charge of designing the Fathom subs. Considerable engineering effort has been spent on the linearity of the Fathom drivers in terms of mechanical, thermal, and electromagnetic behavior. Look at the number of patents in the engineering design of these subs.
The engineering mindset can also be witnessed by having a look at the following video on JL Audio’s site:
The results to this level of engineering and attention to details in driver linearity are outlined in some of the editorial notes I inserted in the review. But it comes at a cost. The level of control the f112 exerts over the cone and level of musicality and finesse are what you pay for.
The Fathom also comes with a number of features, signal processing and room correction controls that the other sub does not: automatic room correction to trim off the worst modal peak, variable phase, balanced inputs/outputs, grounding/isolation, and master/slave connectivity for controlling multiple subs with the settings on one. All this will improve real world performance but increase the discrepancy in cost.
The Fathom subs are
not bang for the buck products and that is stated in the review. Diminishing returns will have its way with cost for the improvements, but money is spent here on the engineering, materials, and construction quality of this product which will make it very competitive with other products that are
also not bang for the buck, in terms of musical sound quality as well as output.
If one is looking to purchase a new subwoofer and is interested in SPL only, I am quite sure that one can find a model to satisfy that singular goal. It may not be listenable, but there will be plenty of it. With this type of mentality, do not forget to take advantage of the room modes as well to make the sub even louder.
For the record, I would drive an Aston Martin over a Camaro any day. The driving experience and road feel would not be the same despite what 0-60 mph and lateral skid pad test might say.
Sometimes, one gets what one pays for.
