Sub-Bass: The Frequencies Below 60 Hz, and Who Can Play Them

Where sub-bass sits

Human hearing runs down to about 20 Hz. The band from there to roughly 60 Hz is sub-bass; from 60 to about 250 Hz is the mid and upper bass most people mean when they say "bass". The split matters because the two do different jobs. Upper bass carries the punch of a kick drum and the pitch of a bass guitar. Sub-bass carries the weight underneath: the fundamental of the lowest piano and organ notes, the synth drops of electronic music, the size of a concert hall.

Not every recording has much down there. A string quartet barely reaches it; a lot of modern pop, hip-hop, film scores and electronic music live in it. Whether you notice a product that stops short depends heavily on what you play.

Why so many products roll it off

Reproducing sub-bass means moving a lot of air, and at the lowest frequencies the amount of movement needed rises steeply. A small driver has to travel a long way to do it, and when it cannot, output falls away below some point, or the driver distorts trying.

Headphones have an advantage speakers do not: the air volume is tiny and sealed against the head, so a well-designed driver can play flat to 20 Hz. The seal is the catch. Any leak - glasses under the pads, an IEM tip one size too small, pads that no longer press evenly - lets the lowest frequencies escape first, which is why fit changes bass more than any other part of the response.

Planar magnetic headphones are known for extending flat and clean into the sub-bass, because their thin diaphragm is driven evenly across its whole surface. Our reviews bear that out, with several HIFIMAN planars credited with linear extension to 20 Hz, and also show the exception: the budget HE400se is marked down for bass extension lacking below 60 Hz.

What extension means

Bass extension is how low a product plays before its output falls away. A specification quotes it as the frequency where output is 3 dB or 10 dB below the average, and a published "20 Hz to 20 kHz" range without a tolerance says almost nothing, because at some level of attenuation almost anything reaches 20 Hz.

Extension is also not the same as quantity. A neutral headphone can extend flat to 20 Hz and still sound lean beside a bass-boosted one that rolls off at 40 Hz, because the boosted one has more energy in the upper bass you hear most. The two words describe different things: extension is how deep, and emphasis is how much.

Sub-bass in a room

For speakers the room takes over. Below roughly 200 Hz, standing waves between the walls make bass levels swing by 10 dB or more from one seat to the next, so a speaker's sub-bass depends as much on where it and the listener sit as on the speaker itself. Floor-standing speakers and subwoofers exist to reach the lowest octave; bookshelf speakers usually hand it over to one.

Testing your own gear

A sine sweep is the quickest way to hear where your headphones or speakers give up. Play a slow sweep from 100 Hz down to 20 Hz at a moderate volume and listen for the point where the tone fades, starts buzzing or turns into a flutter rather than a pitch. The site's signal generator does this in the browser. Start quietly: sub-bass at high level is felt before it is heard, and a driver can be pushed past its limit before it sounds loud.