Why do planar headphones often have low reaching mostly linear bass while dynamic drivers often have heavy roll-off?

[Soria Moria]

What is the mechanical reason for this?

 

[_thelaughingman]

My uneducated guess is that the planar magnet does not have a moving coil which leads to linearity in bass.

 

[DVDdoug]

Why do planar headphones often have low reaching mostly linear bass while dynamic drivers often have heavy roll-off?

Is that true?

What do you mean by "linear"? Flat frequency response? The Harman preference curve actually has boost in the lowest audio frequencies. It's not flat. There are dynamic headphones with that boost (or close).

Mechanically, both should go down to zero Hz. If you've ever connected a battery to a speaker you can see it move in or out and hold as long as the DC voltage remains. But you'd need a perfect seal around the ear to maintain the pressure. The regular dynamic drivers MIGHT have more of a tendency to resonate in the mid-bass range, causing a bump, but I don't know.

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[markanini]

What is the mechanical reason for this?

What if it's from tight front volume sealing? On other words it can be more down to implementation than driver technology. Marketing and heresay will tend to attribute it falsely to planar tech alone, but the driver is not doing any "heavy lifting" whether planar or dynamic.

 

[Soria Moria]

Is that true?

I'd say so yes. Why though I don't know hence the thread. By linear I mean not sliding curving heavily off the end like this. I don't know if I have ever seen this in a planar but several times with dynamic ones.

 

[InfiniteJester]

I'd say so yes. Why though I don't know hence the thread. By linear I mean not sliding curving heavily off the end like this. I don't know if I have ever seen this in a planar but several times with dynamic ones.

Not as pronounced, but it isn't that uncommon.

 

[ugur38]

I think this is the answer:

acoustically dynamic headphones similar to a shelf speakers 6-8", and to make a flat low-mid area, HD650 needs to keep the driver resonant at 100hz, sacrificing the sub-bass. A planar or ES driver doesn't have a resonant there(actually, 0.5-2um has no resonant across the audio range at all, only local chambers resonant), and usually, planars sub-bass always goes lower vs dynamic one but the efficiency of a dynamic driver is way higher.

 

[oratory1990]

Nowadays, planar magnetic headphones are usually designed with a VERY compliant (meaning: low-stiffness) membrane.
This means that the system's stiffness is mostly determined by the stiffness of the pressurized volume of air, as opposed to being dominated by the stiffness of the membrane itself.

Remember, stiffness is the force that determines the excursion of the membrane (at a given driving force).

This makes headphones designed that way more leakage tolerant: When the front volume is not perfectly sealed, the stiffness of the pressurized volume of air will drop (at low frequencies), allowing the membrane to excurse further (at low frequencies). This additional excursion creates higher sound pressure (at low frequencies). Of course the imperfect seal will also allow sound pressure to leak out through the leakage path, which lowers the sound pressure (at low frequencies).
If designed well, then the lost sound pressure ("loss of bass") will be almost entirely compensated by the membrane simply excursing further, so the resulting sound pressure as it enters the eardrum will be the same as if no leakage was present (e.g. via a perfectly sealing earpad).

This is what allows headphones with compliant membranes or diaphragms to be more "leakage tolerant" (=not losing as much SPL in the presence of a leaky front volume), and it's what allows typically designed planar magnetic headphones to have an essentially flat frequency response at low frequencies.