What determines the volume on headphones?

The basic principle is that power is voltage times current. Good headphones have heavily damped drivers, so they will stop moving quickly after a note is played. This allows them to resolve tiny details that would be muddy if they drivers were less tight. But damping down the drivers like that means that you will need more power to drive the headphones in the first place.

The volume on the headphones is determined by the voltage. Now, for a highly dampened pair of headphones, the manufacturer can design it to be current hungry or voltage hungry (V=IR). You need to be able to supply enough current and voltage for the headphone or it will not sound good. That's what amps are for. If your headphones are not loud enough they might be voltage hungry and need more amplification.

In your case, however, it might be because the 280's aren't considered that great to begin with.
 

The impedance will give you an idea of how much volume you need to drive the headphones. A typical full sized headphone would be around 30 Ohms impedance, but it's not uncommon for the nicer ones to go up to 300 or 600 Ohms, which necessitates more voltage. The impedance won't tell you, however, if your headphones are being underdriven from too little current. Some headphones are also more picky about amps than others, and require some attention into the synergy of the system to work well.

Quote:

Originally Posted by 88gal88 

What determines the output volume on a pair of headphones? I play mostly classical on my Digital Piano so bass is not a concern, I just want to be able to practice and do some recording to the pc.

 

I currently have and old pair of headphones, I think they are a Panasonic Digital Monitor (fairly cheap pair). There are no model #'s on it and I am thinking it is between 12-15 years old, maybe older. The sound and volume on these things are excellent but since I don't have the info on them I can't compare them to any new pair I am looking for. I bought the Sennheiser HD439 but when I plugged it in I had to crank the volume up on the DP all the way before I got any sound and what did come out of them was tinny and hollow at best. Went back to the store and demo'd the HD280's on the same DP as I have and got the same tinny low volume sound as the HD439's. When I am using the old pair, the volume control knob is at around 1/4 level.

 

The headphones sound great when plugged into the computer but when connected to my DP there is no comparison to my old Panasonics. The DP has a 1/8" headphone connection and so do my old Panasonics. I don't know what to look for now. I don't think I need a headphone amp since my current pair gives me the volume I am looking for. Any help you can give a noob would be appreciated.

Broken down simply, impedance, sensitivity, and efficiency.

Impedance effects how much power an amplifier like the one in your piano, can deliver to an output device like your headphones. Think of it as your headphones limiting the output power of an amplifier. The higher the impedance, the less output power an amplifier can deliver. Many non audiophile headphones are less than 100ohms and this allows an amp to deliver nearly full power.

In spite of what the previous poster noted, impedance definitely effects volume. When an amplifier gives it's power rating it is given at a specified impedance. That output rating changes depending on the impedance of the speaker. A 100mw headphone amplifier might only be able to deliver 16mw to a 600ohm headphone, but it might deliver 120mw to a 16ohm headphone if it's rating was for 32ohm load.

Sensitivity, this is how much sound pressure per volt that a headphone will produce at 1khz. Typical headphones can deliver 96-106db per 1volt at 1khz. Some are much higher, some are much lower. Voltage isn't really the best way to measure power but it's often how sensitivity is expressed in a headphones specification.

Efficiency, is how much work a headphone does (creating sound) for the amount of power it takes to drive them. This is arrived at by a combination of impedance, and sensitivity. The type of enclosure a headphone has can greatly effect it's efficiency. Closed backs tend to be more efficient than open. It is also impacted by things like barometric pressure, humidity, how well a headphone seals, and the size of the driver.

So in answer to your question, if you want the loudest volume for the minimum amount of power, you want to find low impedance headphones, say 32ohm, with a high sensitivity, say 102db+ and probably closed backed or IED.

That can at least get you started looking at specifications. Many cheaper headphones don't list their impedance (ohm) rating in specs so just assume around 80ohm unless otherwise specified.

Some of the more loud and efficient headphones in my collection are the Skullcandy Inkd in ears, and Sony MDR-V6 over ear.

The Ink'd can be had for $10-$15, and the V6 for ~$80

Most headphones rated for portable use should also fit the bill. These tend not to have 1/4" adapters with them, often have much shorter and thinner cables etc.

I recently picked up a pair of Sennheiser HD419's for $30 each that would fit your needs perfectly but they are a little bass heavy for piano work. If you don't mind in ears, try the Skullcandy.

Quote:

Originally Posted by obobskivich 

Impedance does not dictate power. It explains the relationship between voltage and current in an AC system. Many amplifiers have relatively lower power output into high Z loads because of design limitations (http://en.wikipedia.org/wiki/Nominal_watt). Impedance can relate to efficency in power transmission (http://en.wikipedia.org/wiki/Impedance_matching#Power_transfer), but it does not mediate "low power." It also doesn't dictate quality (e.g. a high Z headphone isn't better than a low Z headphone by virtue of being high Z). Also remember that even 16mW is a disgusting amount of power for most headphones.

Efficiency is not the "combination" of sensitivity and impedance, it has to do with power transfer - https://en.wikipedia.org/wiki/Loudspeaker#Efficiency_vs._sensitivity (efficiency of dynamic drivers is generally very low across the board - horns are a far more efficient design, but I've yet to see one in a headphone).

We are talking in laymens terms here. Impedance absolutely dictates output power though. An amplifiers given power rating is expressed as power in watts @ ohm.

A consumer stereo might say 100watt@8ohm, a Car stereo amp might say 400watt@2ohm 200watt@4ohm 100watt@8ohm. When you connect a speaker to an amplifier you are completing a circuit and the impedance of that circuit effects how much power the amplifier can deliver. This is a simplified explanation ignoring things like the power supply but it's basically true.

This image is from the FiiO E9 manual. Notice the highlighted section on output power. It produces 1watt of output power at low impedance, but just 80 milliwatt at 600 ohms.