[Sir Tmotts III]

Just a little thing that has been in the back of my head for a time.

 

[proton007]

Quote:

Just a little thing that has been in the back of my head for a time.

 
I think IEMs that use Balanced Armatures typically have multiple drivers.
Basically, transducers based on balanced armature design don't need a lot of air to produce sound. Thats what makes them fit inside the ear an still work well. The drawback is that they're good at only the middle and high frequency regions, so a single driver cannot produce all frequencies by itself, especially bass, hence multiple drivers are wired through a crossover. In my opinion, it takes 2 drivers at least to produce good sound, one handling lower/mids, one higher/mids.
 
Full sized cans use dynamic drivers, like typical speakers. The frequencies that can be produced by a dynamic driver is related to the size of the driver. Too large and its good at producing lower frequencies, too small and its good at producing high frequencies.
I think headphones are somewhere in the sweet spot, a single driver can produce most frequencies reasonably well, so multiple drivers are not needed.
 
You might have noticed that studio monitors for instance, only use a woofer and a tweeter. The woofer alone can work well in the mid/lower parts, so no subwoofer is needed. It still uses a crossover because there are two drivers.
 
Apart from these, I think it also has to do with the circuitry. Balanced Armatures have very low power requirements, and the crossover can be made small enough to fit in the earphone. With headphones and multiple drivers, I think the crossover may be slightly bigger, and will take up space.
You'll also have to design and tune the crossover, so its an added complexity in a system where it might not be needed.
 
In a jist, whatever combination of drivers can produce the whole spectrum of sound is used. If a single driver can do it, well enough. Otherwise use a crossover + multiple drivers.

 

[xnor]

Some in-ears use only one driver, and some full-sized ones use multiple drivers.
 
It's basically a matter of the size of the driver, its frequency response and how "cleanly" it reproduces those frequencies at higher SPLs. For example a band-limited balanced armature driver could be used with two more of such drivers and two crossovers between them to cover bass, mids, highs. Additional drivers might be added to increase fidelity at higher sound pressure levels.

 

[Steve Eddy]

Quote:

Some in-ears use only one driver, and some full-sized ones use multiple drivers.
 
It's basically a matter of the size of the driver, its frequency response and how "cleanly" it reproduces those frequencies at higher SPLs. For example a band-limited balanced armature driver could be used with two more of such drivers and two crossovers between them to cover bass, mids, highs. Additional drivers might be added to increase fidelity at higher sound pressure levels.

 
I've been curious how the balanced armature drivers would do on a horn/waveguide. I hate listening with anything in my ears so don't use IEMs. But hear so many good things about them otherwise. Could perhaps do something like a coaxial with a dynamic driver handling the bottom end and a horn loaded BA for the top end. Perhaps multiples like those old Altec and JBL horns with 2, 3 and 4 compression drivers on them.

 
Y'ever heard of anyone using horns/waveguides on BA drivers?
 
se

 

[xnor]

I don't use IEMs for the same reason
I don't know of any such project, I'm not even sure it would be possible (to get high enough SPL). Also, I don't think reproducing high frequencies is a problem with todays tweeters. It's usually the low end that is problematic.
 
Obviously, big loudspeakers use multiple drivers that are optimized for their respective frequency range (like woofer for bass, tweeter for highs). If you had just one huge dynamic driver you'd get high distortion, especially intermodulation distortion. Also see http://www.linkwitzlab.com/frontiers.htm#J.
 
Headphone drivers are much, much smaller, don't need to move huge amounts of air, have a much smaller excursion etc. so full-range drivers work fine there.

 

[Steve Eddy]

Quote:

I don't use IEMs for the same reason
I don't know of any such project, I'm not even sure it would be possible (to get high enough SPL). Also, I don't think reproducing high frequencies is a problem with todays tweeters. It's usually the low end that is problematic.
 
Obviously, big loudspeakers use multiple drivers that are optimized for their respective frequency range (like woofer for bass, tweeter for highs). If you had just one huge dynamic driver you'd get high distortion, especially intermodulation distortion. Also see http://www.linkwitzlab.com/frontiers.htm#J.
 
Headphone drivers are much, much smaller, don't need to move huge amounts of air, have a much smaller excursion etc. so full-range drivers work fine there.

 
Tweeters? No no, I'm talking about a headphone, not a loudspeaker.
 
se

 

[xnor]

Oh, in a headphone. I think that could work.

 

[Steve Eddy]

Quote:

Oh, in a headphone. I think that could work.

 
Yeah. The question would be whether the horn/waveguide could acoustically load the BA driver similar to how it would be loaded when stuck in an ear canal.
 
Hmmm...
 
se