Tough question, but a simple answer… NONE! For many years, 12” subs have been the highest selling subwoofer size. Why is this? I believe it is due to myths and consumers being misguided by sales people. I'm willing to bet that most people think a 10” sub cannot play as low or as loud as a 12” sub. I'll also bet that people think that 15” subs are the loudest and the clever people think that 15” aren't as “clean” or as “fast” as a 12” or smaller sub. Anybody wanna bet?

The fact is that this is all a bunch of BS, period! Let me ask a few question to get your gears turning… How many high-end home systems do you see with 15” subs? What makes a sub play lower, size or magnet or weight, or material or what? What makes a sub play louder, size or magnet or weight, or material, or does it even matter as long as you put it in a bandpass box?

Let's pretend for a moment that all subs were built exactly the same, out of the same materials and all parts will proportionate in size for the size of the driver… If this were true, then some of the myths would be true. The 15” would be louder due to its ability to displace more air, and it would have a lower resonant frequency. Since this is not the case, there are tons of variables that make all of the misconceptions full of poop!

Let's address output amplitude first. An average 10” sub has 50 square inches ( 50 in ^2) of cone area. A 12” has 75 in ^2. If a 10 has 15mm of xmax excursion capability, it will displace .017 cubic feet (ft^3). If the 12” has 10mm of xmax, it will displace the same .017 ft ^3. The 10” has 1/3 less cone area but it has 1/3 more excursion making the output of the 10” equal to the 12” . Now, what if the 10” sub handles more power? What if the 10” is more efficient? Or what if the xmax was more than 15mm in the example above? Just these 3 variables alone will make the 10” have more output volume than the 12” . This relationship can work between any 2 different size drivers.

But what about the application, specifically the enclosure? If we use the subs we just talked about in relative enclosures, the 10” may be a better choice. But what if we put the 10” in a small sealed enclosure, and we put the 12” in a properly engineered vented enclosure? Could the 12” outperform the 10” ? Possibly. It depends on the box design. EVERYTHING ALWAYS DEPENDS ON THE BOX DESIGN!!! If it were tuned low for bass extension, it would have more low bass, but maybe not more upper bass. Likewise, if is it tuned high, it may be louder than the 10” . What about a bandpass box? Bandpass boxes are the most difficult to understand. People tend to think that are the loudest type of enclosure possible. More BS! They have the capability of having a wide bandwidth and equal or lesser volume than a typical box. But some can be engineered to have a lot of gain, drastically increasing the efficiency! They normally sound like poop, but many people do not know what accurate sound is anyway. Another bad thing about bandpass enclosures is that people do not realize that not all woofers will work properly. In fact, many woofers will destroy themselves in a bandpass and you'll never hear it coming until it is too late…

Now, let's address low bass extension. Some woofers play lower than others. Some tiny desk top computer speakers actually play fairly low. Some 5” -8” subs in home speakers play very, very low. And yet some 15” or 18” pro audio speakers that musicians use do not play as low as an average 6” x 9” coaxial. This is 100% intentional by the manufacturer. Generally speaking, it takes more moving mass to play lower frequencies, which reduces the output volume. Like I mentioned above, EVERYTHING ALWAYS DEPENDS ON THE BOX DESIGN! Granted, a 4” woofer would have a real tough time playing as low as a 12” subs, but anything is possible. Look at Bose. At one point in time, they were probably using 70% or more 4” drivers in all of their loudspeakers.

Finally, let's talk about efficiency. First of all, take all of the specs you read and throw them out the window. Are some companies lying and inflating their specifications. You betcha! But others may manipulate the specification without being dishonest. For example, if a sub is rated at 90dB, where, when and how is it rated. Where meaning where on a frequency chart or at what bandwidth? Is that an average from 50Hz -100Hz? Is that at 100Hz only? Or is it 1kHz? Who knows? It could be anywhere. When meaning when what amount of power is applied. Is it with 1 watt at 1 meter (1w/ 1m )? Is it at 2.83 volts at one meter (2.83v/ 1m ) which is higher? As for How it's rated, sometimes I've even seen subs rated at ½ meter rather than the standard 1 meter which would obviously increase the specification radically! A bunch of marketing hype missed with the lack of a standard procedure and boundaries means that all specs are worthless and must not be considered since no accurate comparison can be made.

So, with all of this myth busting, what is my exact point? Just what I said in the first line… There is NO best size for a subwoofer. Some materials tend to sound better – I happen to like paper for sound quality due to the damping qualities. I tend to like smaller subwoofers due to their ability to sound big and for their transient response. On the flip side, I am currently rebuilding my truck with an R1-15, a 15” subwoofer with an aluminum cone, just to prove that it can be as snappy as a 10” woofer.

Well, there you have it… No woofer size is “the best” and the enclosure design is everything! On the down side, you probably did not get the answer you were looking for. On the up side, now you know you can use whatever size you want and most of the time, you can get the results you are looking for…