[tfarney]

When they are there, they confuse me. In the world of amps that are measured in watts (rms) into ohms and speakers that are measured by load (ohms) and sensitivity (which will give you a pretty good indication of the overall power requirements of the thing), I can sit here on the internet, where most hifi shopping must be done in a retail world gone wile with HT, and get a pretty good idea of what speakers might be a decent match to what amps. I'm not talking about synergy here - warm speakers/cold amp, that sort of thing - I'm talking about a basic match that says that amp will be strong enough to drive that load with sufficient headroom.

But here in the HP world, where ohms range from near zero to 600 or more, amps are measured in milliwatts and those milliwatts are rarely related to a load (which makes them useless to me), and where sensitivity ratings almost never exist...what am I missing? How does one navigate this world? Can someone show me the map?

Tim

 

[Herandu]

Headphones are resistance controlled, not mass-controlled like loudspeakers.

The international standard on audio interfaces, IEC 61938 calls for an intermediate impedance source of 120 ohms and a source voltage of 5 V rms, which provide reasonably satisfactory performance (sound level, frequency response, distortion) with headphones of any impedance over the range of 32 to 600 ohms at least.
The problem is that few headphone amp designers stick to these two rules. Most amps don't have the 120 Ohms in series with the headphone output socket, or put out a 5Vrms voltage. According to my crude tests, the equivalent of a 8W 8 Ohms audio amp would be needed to drive a HD650 to its full 200mW level with its 300 Ohms impedance. But you would probably go deaf within 5 minutes at such levels.

 

[odigg]

I know very very little about electronics and headphones, so if what I'm telling you is wrong, my apologies in advance.

According the FAQ on headwize, headphones with a sensitivity over 100 db SPL can be run without a dedicated amp.

As for the amp/headphone match, I'm only guessing how this works. Take a look at this page.
HeadWize - Technical Paper: Understanding Headphone Power Requirements by Dennis Bohn

Let's take the DT990PRO. According to that the max power is 80mw. The impedance is 600ohms. So, for the sake of argument, let's say to make those headphones as loud as they can go, an amp needs to be able to power 80mw at 600ohms.

Let's take the CK2III amp. The specs say that it can deliver 0.15W into 330Ω or 1.4Wrms into 33Ω. That looks to me that if the impedance is divided by 10, then the watts is multiplied by ten (well almost ten). As Impedance goes up (assuming resistance is constant), wattage goes down.

Let's convert this to 150 milliwatt (0.15w x 1000) into 330Ω. If I go simply by ratio, the amp should be able to give out 75 milliwatts into 660Ω. So It should be able to give out around 80mw at 600Ω which seems good enough for the DT990PRO.

As for matching the "sound quality" of the amp and the headphones, nobody has that answer except your ears. I don't even own an amp so I can't even tell you what I think.

Hope this helps (and is correct).

 

[davisac]

I have an older Carver receiver does anyone know how that is on the headamp?

 

[Jaska]

Quote:

Originally Posted by davisac /img/forum/go_quote.gif I have an older Carver receiver does anyone know how that is on the headamp?

Did you actually mean to post this here? Sorry, but I don't get it.

 

[jcx]

headphones:
HeadWize - Technical Paper: Understanding Headphone Power Requirements by Dennis Bohn

http://www.head-fi.org/forums/f4/db-...lly-go-168037/


Headphone Amplifiers don't have uniform standards of power output specification so you need to use some electrical power and dB relations to adjust/guess when they give some info that is incommensurate with your headphones

all amplifiers will have limited peak output V and peak output I, which limit is the 1st limiting factor depends on your Headphone Impedance (~= R in Ohms)

from P=I*V and V=I*R you should be able to get:

P = (I^2)*R = (V^2)/R

add in the fact that audio I,V,P will be RMS values which work out in the above equations but peak I,V are sqrt(2) larger than RMS I,V and peak Power is 2*Prms

 

[oicdn]

My advice as a consumer is not to pay any attention to any of it. Specs are useless for the most part. Reality of it all is subjective at the end anyways.

How so? A predator is supposedly able to drive HD650's properly, yet, another portable amp of the same output "cannot". A bit conflicting isn't it? Anything can drive a headphone into loud volume and the almighty "volume doesn't equal quality" comes back into play. Spec sheets are not the end all, and IMO are mostly worthless.

Like said, some people say the Predator (or insert another example here) drives an HD650 well, when, mathematically speaking, it doesn't have the physical output to be able to, but some think it sounds good, and that's really all that matters right? What it boils down to is how well YOU perceive it to be and if it's pleasing to YOU. Go based on what is KNOWN to synergize if you're that concerned about buying the wrong product(s) and it not being able to drive something. Or, do like me and experiment with combinations like nobody's business and find out what YOU like. After all, that's what this hobby is about, finding and listening to what YOU find pleasurable.

 

[jcx]

I do take issue with the deliberate "anti-technology"/anti-science/innumerate position exemplified above

no simple set of specs captures everything but peak SPL capability without clipping does establish a quality floor that everyone should be aware of and be capable of determining from published specs - if we could convince amp manufacturer's to publish usable specs

I see recommendations of amp/headphone pairings that are simply wrong

135 dB/V sensitive iems really need high quality step down impedance matching transformers much more than amplifiers with V gain of 5-10 - unless you like listening to hiss

an amp optimized for 32 Ohm, 98 dB/mW headphones like the GS Lite isn't capable of driving K601,K240, or 250 Ohm DT770 with the same dynamic headroom

split supply “9V” battery powered amps with op amps that current limit at 20-30mA and can’t swing to within 2 V of the supply rails are simply not as technically competent to drive many headphones as the iPod’s they are supposedly “improving”


it is actually hard to "just listen" in an objectively meaningful way - instrumentation/measurement is required to level match to <1%, many psychological factors are known to interfere in our subjective comparisons of audio experiences - long term memory is severely limited for fine sensory discrimination

so we should welcome simple measurement/calculations that do illuminate at least one meaningful dimension of audio quality

 

[nikongod]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif I do take issue with the deliberate "anti-technology"/anti-science/innumerate position exemplified above ... so we should welcome simple measurement/calculations that do illuminate at least one meaningful dimension of audio quality

i sort of agree, and sort of disagree with different parts there.

i think that oicdn's point could have been better stated this way:
once you have passed a certain threshold of "adequacy" the numbers matter less. depending on standards this threshold is different for different folks, but unless you are looking for something very specific will be met by many combinations.