[bocast]

Just learning about headphones, and occasionally seeing reviews about amps that " may not do well with low impedance headphones.". Looking for some guidance as to how to recognize that based on build of headphones, rating on phones, and specs of the amp. ( A newcomer question, but that's what I am.)

I'm in my mid fifties, have some hearing loss but love a wide variety of music including small combo swing jazz, female vocals, electric and acoustic blues, and rock including classic and "indie rock.". Main system is a single driver speaker system driven with modwright SWLP preamp, and FirstWatt J-Fet amp. Turntable (Nottingham Dais....I love that 'table) with a Grado Reference Sonata provides most of the music, the rest from CD or a modwright modified transporter.

 

[cel4145]

The ohm rating for a headphone is the impedance. 16 to 32 ohm would be considered especially low impedance headphones.

 

[Sam21]

Impedance in a headphone's voice coil depends on three things:
 
(1) type of the conductor, Gold >> Silver >> Copper , Gold is the best naturally occurring conductor.
 
(2) How thick the wire is, thicker == more impedance
 
(3) How long the wire is, Longer == more impedance.

 

[davidsh]

^Silver is a better conductor than gold. Thicker wires is equal to lower impedance not higher

 

[bocast]

Thank you for clarifying what ohm rating would qualify as low impedence.  
 
Do some types of headphone driver mechanisms natyrally result in low impedence versus other designs?

 

[davidsh]

Not particularly as far as I know. Planars are often semi-low impedance

 

[pbui44]

Thank you for clarifying what ohm rating would qualify as low impedence.  

Do some types of headphone driver mechanisms natyrally result in low impedence versus other designs?

That is a very good question, though I wished someone had asked this a while back. There are many types of headphone drivers, though summed up in three types: dynamic, planar-magnetic, and electrostatic. Dynamic drivers range from 4 ohms (?) to 600 ohms, planar-magnetic drivers typically are around 8-64 ohms (depending on amp frequency), and electrostatic drivers are purely amp-based. I say amp-based because they require a specific amp for electrostatic diaphragms and will not work with regular headphone amps, but that is a different subject.

Dynamic drivers will stay close to their rating to ensure the coil in the diaphragm will remain stable, where planar-magnetic drivers will vary because of their electrical current will travel more evenly throughout the diaphragm and react to various magnets laid out in the diaphragm. Headphone amps also have their own ohm ratings, where the general rule is the lower ohm rating, the better (amp rating of 1 ohm or less qualifies it to be Class-A).

 

[manbear]

Dynamic drivers will stay close to their rating to ensure the coil in the diaphragm will remain stable, where planar-magnetic drivers will vary because of their electrical current will travel more evenly throughout the diaphragm and react to various magnets laid out in the diaphragm. Headphone amps also have their own ohm ratings, where the general rule is the lower ohm rating, the better (amp rating of 1 ohm or less qualifies it to be Class-A).

Dynamic drivers always have an impedance spike corresponding to the resonant frequency of the voice coil/diaphragm system. Planars, on the other hand, always have ruler flat impedance (I couldn't tell you why, but it's easy to verify through graphs on headroom or innerfidelity). 

The output impedance of an amp has nothing to do with whether it is class A--the class is determined by how the wave form is amplified. http://electronicdesign.com/analog/understanding-amplifier-operating-classes

 

[StanD]

That is a very good question, though I wished someone had asked this a while back. There are many types of headphone drivers, though summed up in three types: dynamic, planar-magnetic, and electrostatic. Dynamic drivers range from 4 ohms (?) to 600 ohms, planar-magnetic drivers typically are around 8-64 ohms (depending on amp frequency), and electrostatic drivers are purely amp-based. I say amp-based because they require a specific amp for electrostatic diaphragms and will not work with regular headphone amps, but that is a different subject.

Dynamic drivers will stay close to their rating to ensure the coil in the diaphragm will remain stable, where planar-magnetic drivers will vary because of their electrical current will travel more evenly throughout the diaphragm and react to various magnets laid out in the diaphragm. Headphone amps also have their own ohm ratings, where the general rule is the lower ohm rating, the better (amp rating of 1 ohm or less qualifies it to be Class-A).

Class A amps are a design, not an impedance designation.

 

[ProtegeManiac]

Quote:

Dynamic drivers will stay close to their rating to ensure the coil in the diaphragm will remain stable, where planar-magnetic drivers will vary because of their electrical current will travel more evenly throughout the diaphragm and react to various magnets laid out in the diaphragm. Headphone amps also have their own ohm ratings, where the general rule is the lower ohm rating, the better (amp rating of 1 ohm or less qualifies it to be Class-A).

 

Impedance and amplifier class have nothing to do with each other. (OTL) Class A amps can have high output impedance and many Class A/B amps (broadly defined, so that includes "Class A-biased op-amp-based" and "dynamically adaptive Class A/B") have low output impedance.