Guide to Subwoofers

Subwoofers, also called subs, are speakers designed to reproduce audio or bass frequencies as low as 15 hertz. They are separate from ordinary speakers because they are capable of transmitting very low sound frequencies normally not recognized by other speakers.

Subwoofers are usually connected to stereos and home theater systems to provide the ultimate video-watching experience. They make movies seem more real, as they accurately reproduce the lowest bass sounds. They are available in five types: sealed, ported, bandpass, passive radiator, and transmission line. 

Sealed subwoofers

Sealed subwoofers are the simplest systems. They consist of a sealed box and a driver installed on one side. They are smaller than the other subwoofers. They offer good transient response and low frequency power handling. They play extremely low sounds.

Sealed subwoofers have a wide range that can reach 28 hertz. They have aluminum cones that allow fast transient responses and offer excellent pitch while extending low. However, they have lower sensitivity and increased cutoff points.

There are two types of sealed subwoofers: air suspension (AS) and infinite baffle (IB) subwoofers. AS subwoofers have small enclosures with air compliance lower than driver suspension compliance. IB subwoofers have larger enclosures with air compliance higher than driver suspension compliance.

Ported subwoofers

Ported subwoofers are made with an open port and a driver installed on one side. The open tunnel allows air to flow through the subwoofer that adds to the system’s output especially at low frequencies. They offer high power handling, low distortion, and reduced cutoff frequency.

When the driver becomes unloaded, distortion increases below the intended frequency cutoff. They are more sensitive to skewed parameters than sealed subwoofers. Their speaker binding posts can be coated with gold and shaped to fit round cones.

Bandpass subwoofers

Bandpass subwoofers consist of a sealed enclosure and an acoustic filter installed in front of the driver. They offer lower frequency cutoffs. They are larger than most subwoofer types; however, some manufacturers use isobaric configurations to make their enclosures smaller.

The ports of bandpass subwoofers, which can be flared or have large diameters to reduce port noise, release the system’s outputs. Some systems produce out-of-band noise that shatters perfect bandpass responses; however, notch filters can be installed to lower the noise.

One type of a bandpass subwoofer is the Sixth order bandpass. It has vents for tuning the front and rear volumes. It has a lower transient performance compared to the other subwoofer types. It is ideal for situations that do not require excellent audio such as non-critical multimedia applications and sound reinforcements. It is also prone to out-of-band noise, but it can be installed with a low-pass filter to reduce it.

Passive radiator subwoofers

Passive radiator subwoofers are similar to the ported types, but they use a drone cone or a passive radiator instead of a port to lengthen low frequency responses between 20 and 100 hertz.

Their drivers are similar to the ported systems. They emit similar responses except they have higher cutoff frequencies at about -3 decibels and deeper cutoff slopes due to the notches in their frequency response. The notches are found beyond the system’s passband, hardly affecting their overall sound.

Passive radiator subwoofers have electronic crossovers between 70 and 100 hertz, and a phase control between 0 and 108 degrees. They come with input level controls and preamp level inputs.

Transmission line subwoofers

Transmission subwoofers use waveguide systems to reinforce low frequencies between 40 and 90 hertz. They have special guides that turn the driver’s rear output phase around to reinforce frequencies. They are one of the larger subwoofer types.

Transmission subwoofers provide unique sounds and extended low end responses. They are ideal for Fs values, 0.3 to 0.4 Qes, and low Qts drivers between 0.25 and 0.4.