Why Do Subwoofers Have Holes?

Subwoofer designs are different and unique. These days you’ll find most subwoofers with hole-like designs on them.

This seems odd at first encounter especially for those that do not know why those holes exist on the sub.

 I’m therefore going to explain what these holes on a sub are meant for and what they actually do so that you stop wondering and start learning.

It’s important to know your equipment well because this allows you to get the most out of it.

With that said, why do subwoofers have holes?

The holes on subwoofers are called ports. If you open the subwoofer you’ll notice that these holes are not actually holes but tubes.

These ports/holes are, by design, a way of utilizing the rear side of the woofer driver in the effort to extend the frequency response in the lower frequency range.

Simply put, these holes or ports reinforce the driver’s output by combining the front wave with the rear wave coming from inside the cabinet as the cone moves back and forth.

Resonance

Like I’ve mentioned the hole is essentially a tube which has air inside that has a given mass when the sub is playing.

This mass will, according to its area, length and volume of the box, cause resonance.

For example, If you blow air into a bottle, you’ll notice that the smaller the bottle, or the more water or juice there is in the bottle, the higher the pitch of that sound, and vice versa.

The tube in your subwoofer box works the same way, the only difference is that the woofer driver is what triggers the resonance, and not the turbulence from the blowing air across the opening of the bottle.

Port Role

These holes in subwoofers or any bass speaker are meant to allow the lower frequencies that often get trapped in the back to be enhanced.

When your speaker is working, the vibrations inside compress air in the front and back, which can become unbalanced.

Therefore, Bass reflex systems have these holes, so that no bass is essentially lost.

Is a bigger port better for subwoofer?

A big port size combined with reasonable port length can maximize  the potential of the system.

In most cases a bigger ported subwoofer will get louder, but will roll off quicker because it will have a narrower frequency range compared to a smaller subwoofer box.

As general advice, it’s worth knowing that round ports are essentially better for music, while slot ports are better suited for movies.

Does it matter which way the port faces?

Its better to have the ports away from nearby walls. Ports essentially relieve the pressure inside your subwoofer and make it easier for the woofers to move.

The ports push air out when the woofers move back and suck air in when the woofers move forwards.

Ports basically fire sound out in whichever direction they face.

Therefore, rear ports with a wall behind them will essentially bounce the sound back to you.

Slot port size

The best slot port size would ideally be 3 ¾ inches wide by 14 ½ inches tall.

Can a port be “too big”?

Larger diameter port ultimately means a longer port.

The longer the port, the lower the port resonance.

The lower the port resonance, the more likely it gets into a frequency range of high energy which is essentially difficult to absorb with internal damping materials like sound absorbers.

Small ports

If the port is too small in diameter you can get a chuffing sound from the air flow turbulance in and out of the port. That is why ports sometimes have beveled edges added to reduce that effect.

This chuffing sound is called port noise, usually caused by straight ports with no contour at both ends.

Final Thoughts

Ports or “holes” essentially redirect sound from the back of the cone and add it to the sound coming from the front, making the bass louder.

This increase in efficiency lets you use a smaller amp than you would need with a comparable sealed box to play at a similar volume.

For the best sound quality, it’s best to have your subwoofer placed with the speaker facing out to the room, and the port away from the wall.

Bass waves tend to travel in all directions, however it’s important to have the speaker facing your main listening area.