Why Don’t Larger Subwoofer Drivers Play Lower
When you start shopping for subwoofers, it’s easy to look for shortcuts. More expensive surely means more better. Bigger driver probably means it can play lower? Ports suggest louder? A few minutes into your research and you’ll learn that none of those are universally true. You can find sealed subwoofers that can play very loud. There are fairly inexpensive subwoofers that can outperform others that cost much more. The most confusing one, however, is when you find a subwoofer with a smaller driver with greater extension than a sub with a bigger driver. Why don’t larger subwoofer drivers always play lower than smaller drivers? Let’s discuss.
Sum of the Parts
The easy and correct answer is that subwoofers are not just a driver. If the driver were the defining factor of a subwoofer, then larger drivers would probably be able to play consistently lower than smaller drivers. A subwoofer’s performance isn’t just determined by its driver size. There is the enclosure, the amp, DSP, and many other factors that will determine how a subwoofer performs.
Drilling down even further, a driver isn’t just the size of the diaphragm. There are lots of parts of the driver that will determine how it performs. When SVS was developing their 2000 series subwoofers, they went through dozens of prototypes before they settled on a driver with the right performance. If diaphragm size were the most important performance factor, all subwoofers with the same driver size would play just as low.
Subwoofers are Designed to Hit Performance Metrics
When you shop for a car, you have specific features in mind. Maybe it is the engine horsepower, the number of seats, color, type, or make. You probably have a couple of these in mind. For example, the last time I shopped for a car, I was using it for work. I needed specific towing capacity, four-wheel drive, and a few other features. Now that I no longer use my vehicle for work, I don’t need all of that. I’m stuck with a vehicle with crappy gas mileage and a bunch of features I no longer use.
Subwoofers are the same. When the design team starts, they have performance metrics in mind. They want to hit a specific extension, fill a specific volume of air, and often have a maximum price point in mind. With those metrics in hand, the designers have to come up with a design that will fulfill all those at the same time. Sometimes they can do that by slapping a massive driver in a huge box and calling it a day. Other times, they have specific size requirements that will limit what size drivers they can use. Suddenly, they need to find a way to make a smaller driver play lower than other subwoofers with the same size drivers.
Back to SVS, when you look at their 3000 Micro subwoofer, you have a subwoofer with smaller drivers performing similarly to another sub with much larger drivers. Of course, the 3000 Micro subwoofer has two drivers instead of one, but it still plays as low or lower than other subwoofers with dual drivers that are larger.
Not Everything is Designed for Max Extension
The extension of a subwoofer is a very important metric that people often take for granted. They think that just because home theater people care about maximum extension, all subwoofers are designed with extension in mind. That’s not the case. In many instances, the goal of a subwoofer is to boost the low end of music (think live venue subwoofers) where extension past 30Hz really isn’t important. What is important is output. These subwoofers will be designed to play very loud down to 30Hz with no meaningful output past that point.
Home theater enthusiasts, trained that infrasonics are important (they aren’t), will be baffled by such a design. Humans can hear down to 20Hz. Why would your subwoofer NOT play those notes? Well, in music there is exceedingly little (if any) content that low. Creating a subwoofer that can play that low would just make it more expensive for no real-world performance gains.
In all hobbies, there are “rules of thumb” that more knowledgeable people know are wrong. Carbon fiber bikes aren’t always the best, cars with larger engines aren’t always faster, and larger subwoofer drivers don’t always play lower. In all those examples, people are chasing a single spec instead of looking at the whole. Once you can look at a subwoofer as a system and not simply at the driver size, you’ll be able to find the right product for you.