deciphering amp headphone compatibility - how do you do it?
Apr 4, 2010 at 7:04 PM Thread Starter Post #1 of 13

Br777

Headphoneus Supremus
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Hi all, I am wondering if someone can give me the most basic instructions possible regarding how decipher matching an amp to headphones and vice versa

in other words, various headphones are rated in things like ohms, resistance, milevolts or mileamps or milewatts.. (clearly i dont know what im talking about)

amps have power, ohm, wattage, voltage ratings too, but i can never tell how people figure out whats what and which ones go together

can someone break all this down for me, so that when i shop for cans, IEMS, or amps i can say .. ah yes, these iems would do well with an amp, and oh, this amp would be a good match, or ah yes these cans wont do any better with an amp, but oh these over here absolutely need a nuclear power plant to run effectively etc.. etc...

lets use some examples...

klipsch x10's - i dont think these require an amp.. but would they benefit from one how would i know

yuin ok1 - clearly require an amp b/c they say so, but what gives it away and how would i pick the right amp

hifiman he'5's - supposedly hard to drive - why? how would i be able to tell by looking at the specs of thees cans what type of amp they would need

stax - require a super duper special amp that could double as a generator for a small city.. why? how would you know what amp to get by looking at amp specs..

people are always commenting on how this amp is perfect for these phones, and that amp is not so good with those phones... ok i think you get the point..


I would really appreciate the most basic info possible..

thanks a lot ya'll
 
Apr 4, 2010 at 9:08 PM Post #4 of 13
General rule for telling the necessity of amping a headphone. If it has a high impedance (measured in Ohms) and/or a low sensitivity (there are different units used for this), you will want a amp.

In regards to the Stax specifically, you need a special amp to drive those because Stax headphones are different than most pair of cans that you're probably most familiar with. They are electrostatic drivers, meaning that they require much higher voltage swings and more current to even make sound. Now, you wouldn't even be able to plug these cans into a normal amp, because Stax and all other types of electrostatic headphones use a wildly different termination than dynamic headphones.
 
Apr 4, 2010 at 10:07 PM Post #6 of 13
Quote:

Originally Posted by logwed /img/forum/go_quote.gif
General rule for telling the necessity of amping a headphone. If it has a high impedance (measured in Ohms) and/or a low sensitivity (there are different units used for this), you will want a amp.

In regards to the Stax specifically, you need a special amp to drive those because Stax headphones are different than most pair of cans that you're probably most familiar with. They are electrostatic drivers, meaning that they require much higher voltage swings and more current to even make sound. Now, you wouldn't even be able to plug these cans into a normal amp, because Stax and all other types of electrostatic headphones use a wildly different termination than dynamic headphones.



what is sensitivity? what effects does it have on amp choice and headphone difference?

thanks
 
Apr 5, 2010 at 3:01 AM Post #7 of 13
High ohms (around 80-100+) = needs an amp.

Low sensitivity = need an amp, regardless of ohms. The K701 is the flavour of the year example. Only 64ohms, but very low sensitivity. Needs a high powered amp.

If it all gets too technical, then look at the plug on the phones. If it's full size, the manufacturer designed it with a decent set up in mind for optimum use, and that means an amp.
 
Apr 5, 2010 at 3:05 AM Post #8 of 13
so low ohms like denon 2000 at 25oms need an amp because they are low om high sensitivity

and real high oms like beyers that are 600 ohm need an amp because they are low sensitivity

and the ones in between like klipsch x10 that are 50 om and high sensitivity dont need an amp

so how do you then decipher amp ratings to match them to headphones
this is very helpful, thanks
 
Apr 5, 2010 at 4:41 AM Post #9 of 13
I do hope someone more technical could chime in here, but here's my thoughts:

Every headphone needs an amplifier, and every headphone plug has a amplifier - it just depends on quality. Some of the very nice headphones here, however, require much more voltage and current than the little amplifiers in the iPods and laptops can supply. It's difficult - the stuff in the thread is good, but not all the relevant specs are released - see the T1 thread, where one member had to e-mail Beyer directly to see if an amp could supply enough power.

Headphone/amp matching with regards to getting a pleasing combination isn't that simple. Because of all the design choices, getting the end result from an amp can be quite complex and you'd have to be quite well versed in amp design to know all the differences. Amps have different circuit designs. Some designs require a higher quality power supply. You also have to choose between solid state and tube, and the design requirements are different. SS amps can be opamp (and there are many, many opamps out there) based or have discrete circuits, tubes can be OTL, transformer coupled etc... In the end, it's a very complicated issue and specs can only help you so much, which is why most of us rely on hearing impressions, despite the many flaws with that method. The resources are here on head-fi, and the DIY forums around the internet are very helpful too. There's also an element of subjectivity, but I don't really want to wade into the thing about neutrality vs colors, that is covered far better in other threads.

So in real life, specs do help. We know why the HE5 sounds good with the EF5 is because the EF5 can swing a lot of voltage, more than most amps its price. But can we really say which amplifier out there is the best for the HE5 without a good round of listening? I doubt it.
 
Apr 5, 2010 at 6:30 AM Post #10 of 13
Impedance, measured in ohms, is how much current can flow through the cable.
The higher the impedance, the less current can flow through.

Sensitivity, measured in dB, is how much the drivers can move the air (make sound) with a certain voltage.
The higher the sensitivity, the more volume the drivers can make with a certain amount of power (volts).

High impedance means the headphone is getting less power. If the headphone has ridiculously high impedance, it might not get enough current and needs to be amplified.

Low sensitivity means the headphone does not make as much sound with a certain amount of voltage, which means it needs more power to make a sound. The lower the sens, the more an amp helps.

Eg.
16 ohms, 125 dB sens: VERY loud, no amp needed.
64 ohms, 100 dB sens: Softer than ^, probably doesn't need an amp, but it will help.
250 ohms, 100 dB sens: NEEDS an amp, not enough current is getting through, so you have to increase the voltage per current.
64 ohms, 50 dB sens: Needs an amp with tons of power to make a sound.

CMIIW, I'm a highschool student.
 
Apr 5, 2010 at 6:47 AM Post #11 of 13
Quote:

Originally Posted by Ypoknons /img/forum/go_quote.gif

Headphone/amp matching with regards to getting a pleasing combination isn't that simple. Because of all the design choices, getting the end result from an amp can be quite complex and you'd have to be quite well versed in amp design to know all the differences.



Getting enough power for a given power hungry phone is one thing; matching for a pleasing combination (provided the first need is met) is another, and is the very realm of audio subjectivity.

Someone might have a very good amp that provides a phone exactly what it needs, yet not like the sound. Trouble is, most people here are trying to rely solely on specs and opinions to choose an amp - so all the understanding of amp design is pointless, as technical and specs understanding won't tell anyone a thing about the sound itself.

So for people trying to choose an amp for a phone that needs one, it's best to make sure the power needs are met, and then buy to your budget. It might not be perfect, but at least one variable has been met, and if the sound isn't pleasing, then they can try another, similarly powerful amp and try another flavour.

Some of us are lucky enough to access a headphone store and cut out all this stuff.
 
Apr 5, 2010 at 4:05 PM Post #12 of 13
Quote:

Originally Posted by Trysaeder /img/forum/go_quote.gif
Sensitivity, measured in dB, is how much the drivers can move the air (make sound) with a certain voltage.
The higher the sensitivity, the more volume the drivers can make with a certain amount of power (volts).

High impedance means the headphone is getting less power. If the headphone has ridiculously high impedance, it might not get enough current and needs to be amplified.

Low sensitivity means the headphone does not make as much sound with a certain amount of voltage, which means it needs more power to make a sound. The lower the sens, the more an amp helps.

Eg.
16 ohms, 125 dB sens: VERY loud, no amp needed.
64 ohms, 100 dB sens: Softer than ^, probably doesn't need an amp, but it will help.
250 ohms, 100 dB sens: NEEDS an amp, not enough current is getting through, so you have to increase the voltage per current.
64 ohms, 50 dB sens: Needs an amp with tons of power to make a sound.

CMIIW, I'm a highschool student.



Pretty good description, I'll make one correction though. Sensitivity is measured against power input (in mW) not voltage.

I.e. to properly compare them you need to consider impedance and consider the sound level at a fixed voltage; which is perhaps the more useful measure since the voltage is related to the volume setting on almost all amps.

E.g.

Denon D7000, 108dB/mW, 25ohm
Senn HD-650 103dB/mW (at one volt), 300ohm

For the Denon case; 1v corresponds 40mW to which means that you need to add 16dB (10*log(40)) to get sound preessure level (SPL) at one volt; 124dB at 1 volt.

For the Sennheiser case; 1v corresponds 3.3mW to which means that you need to add 5dB (10*log(3.3)) to get SPL at one volt; 108dB at 1 volt.

I.e. at the same voltage (volume setting), and on an amp that can drive either satisfactorily the Denons should sound considerably (16dB) louder.

As to the original question, the ratings of amps do not really matter rather than at the extremes. E.g. very high impedance (need a lot of voltage) or very low impedance (need a lot of current). (The latter is the case with my 25ohm Denon D7000's, not all amps are rated to drive these).

What should you look for with an amplifier;

Recommended impedance range (i.e. the range of impedances that the manufacturer states that the amp can drive adequately).

Gain : some amps can have a low gain which may mean that you cannot get as loud an output as you would like (many people complain that this is the case with Meier amps for instance).

Output impedance; the lower the better, especially with low impedance 'phones.

Maximum output power (or voltage). This should be very much higher than normal listening levels to ensure that music peaks are undistorted. I would assume something like 30dB (1000x power) headroom should be about right (if someone knows of a better accepted recommendation please shout). I.e. for the senn HD-650, assuming that normal listening level is c80dB, then this represents c0.08v. To get 30dB headroom you will need a minimum of 2.5v RMS, which then corresponds to +/- 3.5 for the maximum voltage. (I will make note that no one should be listening at these (continuous) levels since hearing damage will occur - they are only needed for the short peaks that occur in music).

The above numbers are for determining how to match headphones and do not define quality.

However, all the above said, most amps will be sufficiently good 'in the numbers' (including those that define quality) that one does not need to worry unless your 'phones are at an extreme end of the sensitivity or impedance ranges.

Use the above for a quick check on matching, but otherwise better to base decisions on what people have reported on hearing the amp.
 

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