QotD: Can I Add a Second Subwoofer to Increase Volume?

A common question we get comes from people that have a subwoofer that is too small for their room. Sometimes they’ve moved and their new room is much larger. Others bought their subwoofer based on the size of the sub and not how much bass they needed. It doesn’t matter how they got there, they want to know one thing. If they add a second “too small” subwoofer, will that be enough to increase the amount of bass (or volume) in their room?

Answer: Not really.

Author’s Note: We are assuming you are adding an identical subwoofer. All the math goes out the window if you mismatch your subs. If they are two subwoofers of similar performance, you can assume that the math still holds.

Let’s Do Some Math

There is math involved here, but we’ll keep it simple. If you double the amplifier power you get a three-decibel increase in volume. If you co-located the subwoofers, you’ll get another three-decibel increase. So, technically, if you buy a second subwoofer, and stack it on top of your current subwoofer, you will realize an increase of volume by about six decibels (the room plays a part here but you’ll see at least 6dB).

No, co-locating doesn’t necessarily mean that they have to be physically on top of each other. When you see two subwoofers at the front of a room on either side of a TV stand, they are essentially co-located. If the subwoofer distance is within a quarter of the wavelength of the note it is playing (remember, a 20Hz wave is over 55 feet long), it is, as far as the sound is concerned, co-located. So, for the lowest frequencies, you will likely realize a six-decibel increase while you’ll only see three decibels at the higher frequencies.

If that doesn’t sound like a lot, you are right. If your “too small” subwoofer is struggling in your room, it is generally better to sell the sub you have and buy a new sub that is appropriate for your room size. As we’ve mentioned, dual subwoofers are about getting more uniform bass across all your seats. That means that each subwoofer needs to be able to put out enough volume and extension to fill your room with bass. By itself. Adding a second subwoofer that isn’t co-located with the first doesn’t increase volume by much or extension at all. It makes the bass more even throughout the room. Remember, extension is how low a subwoofer can play. Adding a second subwoofer with the same specs won’t make either sub play lower.

So, the good news is that you get to buy new subs! The bad news is that you can’t really do anything to make your old, too small, sub fit your room. Best bet is to place it in a room that is appropriate for its size and start shopping for subs that will work for your current room.

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