There is common knowledge that many audio engineers are familiar with, such as subwoofers being supposed to be placed on the floor. How factual is that? Before we go into detail, let us define a subwoofer. 

What is a subwoofer?

According to Sony, a subwoofer is a speaker dedicated to reproducing low-pitched audio frequencies, commonly called bass. 

Subwoofers come in two types: passive and active (or powered). A passive subwoofer requires an external amplifier or receiver to power it, much like traditional speakers. It’s important to remember that passive subs need more power to effectively produce those deep, low-frequency sounds. On the other hand, an active or powered subwoofer is a self-contained unit, with both the speaker and amplifier built into the same enclosure. It takes a lot of load from the audio/ video receiver to just power tweeter speakers.

Why the floor is a good location for a subwoofer?

Putting your loudspeaker against a large plane (relative to wavelength) creates a half-space loading condition. It focuses the speaker’s energy from an entire sphere into a hemisphere, doubling the energy in that area and resulting in a 6 dB increase, equivalent to doubling the number of your subwoofers. Also, if the subwoofer is close to a tall stage face, the result will be another quarter of space loading, producing another 3dB, which doubles the subs.

The way you position your subwoofers can seriously affect their performance. For example, placing two of them in the corners of a room can boost the sound because the walls help bring out those deep, low frequencies. The arrangement enables the subwoofers to utilize the reflective surfaces to produce deeper and more powerful bass without increasing the number of units. This proves the theory factually, but what other things must you consider? 

The Inverse Square Law

As a sound wave moves further away from its source, its intensity decreases. 

This example from ProSoundWeb makes sense: during live shows, the distance from the subwoofers to the audience can cause big differences in how loud the bass sounds. For example, people sitting close to the subs might hear bass at 120 dB, while those far away might only hear 94 dB. That’s a huge difference of 26 dB! Maybe indoors, this difference isn’t as extreme, but it can still make the front rows uncomfortably loud.

Now, when subs and main speakers are far apart, something like subs on the floor and mains 25 feet high might create alignment issues. The sound from the subs and mains must arrive for it to sound right. The timing can vary depending on where people sit, causing the bass and mids to get out of sync. This mismatch creates dips in sound quality, especially around the crossover point where the subs and mains share frequencies. Different parts of the audience will hear these reductions in energy differently, so it’s tough to make it sound good everywhere.

So, is the floor the best spot for your subwoofers? The answer isn’t black and white—it’s a bit of both. Floor placement is ideal if you’re ground-stacking your entire system, as it minimizes physical offsets and effectively manages the inverse square law challenges. But if you’re flying your main speakers, it’s often wise to fly the subs for better alignment and consistency.

Sources:

https://www.prosoundweb.com/wp-content/uploads/2019/10/PSW_Subs_WP.pdf

https://www.sony.com/electronics/support/articles/00020675 

https://relationshipbetween.com/difference-between-d4-and-d2-batteries/ 

https://downhomedigital.net/home-subwoofers/powered-vs-passive/