[haslaughz]

Hi all - was wondering if anyone could tell me why it's so uncommon to see Thiele-Small parameters for headphone drivers.

 

[Mython]

I suppose one aspect would be the fact that headphones are so often configured as open-backed, so Thiel-Small parameters (other than free-air resonance) are perhaps considered to be of less significance.
 
Furthermore, the volume of air being displaced by a small headphone driver is so much smaller than that by a loudspeaker woofer, that there might be a degree of complacency on the part of headphone driver manufacturers.
 
Or, perhaps Thiel-Small parameters become less accurate at very small volumes?
 
I'm only offering suggested possibilities; nothing more.
 
I'm interested to hear others' thoughts on your question!
 
 
.

 

[ForceMajeure]

Thiel-Small parameter works in relation to a specific closed enclosure volume to an open space with no reflection of sound back that can affect the diaphragm...
 
With headphones and earphones it's much more complicated, because the driver is close to the ear and usually in a closed enclosure of various shape (for headphones) the diaphragm reacts differently. The bass return from the back of the driver affect the bass response of the driver, the interaction of the soundwaves with the shape of the outer ear are also a factor.
For IEMs with their on seal, the ear canals shapes which differ for everyone, is a big factor also.
 
There are other things that don't comes to my mind right know that surely make Thiel-Small parameter not relevant for headpones/earphones. I think Tyll from innerfideliy mentioned recently somewhere a book that had equations (a lot more than Thiel-Small) that tried to make it easier for a designer to predict the diaphragm response. 
 
Edited PS: I found where Tyll talks about it from 35:45

 
I suggest to view the all episode, very interesting stuff.

 

[solderer]

It would seem that headphones and loudspeaker systems are like apples and oranges. For example, frequency response range of a loudspeaker system is very problematic, usually requiring at least two drivers (woofer and tweeter) in order for the system to pass as being a full frequency range transducer. Yet very often a single headphone driver can apparently easily have frequency response on the order of 30 Hz to 20 kHz.
 
Another point, open air headphones can reproduce down to 20 Hz, yet getting a loudspeaker to reproduce that low, let alone not severely restricting the bandwidth of the speaker, is not at all easy. An open-back loudspeaker system or dipole won't naturally reproduce bass frequencies.
 
In other words, for reasons I don't know, the acoustics of headphone drivers must be very different from that of loudspeaker systems, and so a Thiele- Small analysis must not apply to headphone drivers. A headphone driver looks to be a tiny loudspeaker, so you would think that the physics of reproduction would be the same.
An important difference between loudspeaker systems and headphones is that the loudspeaker radiates into free space while the headphone driver acts on a captive volume of air of the ear canal.
 
 
Regards,
S.