I see a lot of posts stating this review isn't useful. I am sure there is a technical reason behind this view which I probably won't understand. However, I am able to understand the frequency response curve. So my question is, wouldn't this type of review, at the very least be able to expose poorly designed subwoofers?
Thanks
If you understand enough to ask the question, you can understand the answer, provided I - or someone else - are able to write it in a way that is possible to understand. So if it is not possible to understand, it is my fault.
First; the frequency response gives some information on quality and what frequency range can be expected to be useful. Roll-off at low and upper end, smoothness reveals resonances. But this type of subwoofer is almost impossible to make so bad that it shows significant faults in frequency response. It is a driver in a square box. For ported boxes, it could reveal a very bad tuning, or port resonances.
It would be more useful if it also showed phase, group delay and excess phase. But to screw up this, you would need something like what I make - with acoustic loading very different from the simple sealed box, it is indeed possible to end up with something bad, it is no longer a simple minimum phase system, there may be resonances.
The established way to present this is to do frequency response measurements at different spl levels, where you can see where compression starts, and at which frequencies. This gives useful information about maximum output capacity.
Distortion measurements are useful, like the one shown (1. page).
But all those graphs - compression, distortion - must have a reference, so that they can be compared to measurements of a different subwoofer. They must specify spl, at some given distance, in some known acoustic surroundings. The standard here is spl at 2m distance in 2pi surroundings. If the measurement is done normalised to 1m, that is fine - just subtract 6dB to compare. If they are 4pi, just add 6dB to compare. But this needs to be specified and calibrated.
Maximum output level is also a standardized measurement where distortion limits are defined with more distortion allowed for low order components, and more strict limits for higher order. This is specified in the CEA2010 standard.
Frequency response says nothing about how low the subwoofer can play, because at low frequencies you need enough output to make it useful, at 10Hz you need around 100dB just to be able to hear it (if I remember correctly).
Directivity is not important for anything you can buy in a ordinary shop, they are all omni. Some varations of dipole exist in the more exotic market, and some my own designs are acoustically large at mid and upper bass frequencies, and thus have some sort of directivity.
The in-room response of a subwoofer will be mostly determined by room and position of the subwoofer and the listener. Any high-performance bass-system need eq to give the best possible performance. Which means that the frequency response of the subwoofer itself is not important, because the system must be corrected anyway. Then you are left with maximum output capacity as the most important criteria for dimensioning your bass-system. And to be able to choose between subwoofers and determine how many you need, you need comparable numbers. You guess how loud you need down to what frequency, estimate room gain, and then you fill in enough capacity to meet this requirement.
How loud and how low you need depends on what you intend to play, and how you play it. There is a huge difference between playing movies at reference to bass support in a small room for classical music.
