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About minimum amp requirements: impedance & power (applying general stuff)

post #1 of 5
Thread Starter 

I opened a thread before because I was thinking of getting the HD's 650 or the DT 990. But I changed my mind after reading about the HE-4. The problem is that even being a pretty low impedance cans (38 Ohm), they seem to be pretty hard to drive properly. More concretely I've read about the Fiio E7 not being able to drive them (sounding muffled and not better than Sennheisher's HD 580) in comparison to a wonderful sound using a EF-5.

 

I have a Cretive Titanium HD soundcard with the following headphone output: 

 

Headphone (330Ohms): 1Vrms,117dB

 

And I'm worried thinking if it would be able to drive them correctely too. The E7 impedance limit is 300Ohms, so the problem wasn't about that. Power I suppose?

 

Ok, the E7 characteristics:

 

Output Power: 150mW (16Ω); 16mW (300Ω)
 

Now if I want to compare both amps (I will assume that those mW from the E7 are rms! although I'm not sure!):

 

Titanium HD: Power = V^2/R = 1/300=3mW (@300Ohms); P=1/16=63mW (@16Ohms)

 

So, much less than the E7 (edit: and less than an E5! 12mW-150mW @16-300Ohms. And the E9 gives 1W @16Ohms with just 2Vrms. There's something wrong... Those Watts in E7/E9 specifications aren't in rms and are just peak values?).

 

Am I right? If that's the case I assume that buying those headphones in order to use with my soundcard is out of the question and I need the EF-5 or at least an E9.

 

Thanks in advance!

 

PS: I do not know if there's any way to use this to make an idea, but the efficiency of the HE-4 in the specifications is 86 DB.

 

Original post what I reffer before:

 


Quote:

Originally Posted by cnk15 View Post
(...)

 

Setup

 

I have listened to the HE-4's in 2 different setups.  The first setup is from my PC to FiiO E7/E9 via USB connection and the second setup is via my PC via Creative Labs X-Fi Titanium Fatal1ty line out to the HiFiMan EF-5.

 

Listening Impressions

 

With the FiiO setup, I had to put it on high gain and to me the HE-4's didn't really sound any different than the 580's besides requiring the higher gain setting.  If anything, the sound was a bit muffled.  I don't experience this with the 580's so I was a little disappointed at first. 

 

I then switched over to the EF-5 setup.  Wow!!  What a difference.  The sound was crystal clear and I could hear details in the music that I couldn't hear before.  The bass hits low and the highs are not ear piercing.  I was actually quite surprised that the HE-4's were that much better than my 580's.  The sound stage is broader as well and I just feel more enveloped in the music. 

(...)

 

Follow Up

 

I decided to take the E7 out of the picture to make it more of a apples to apples comparison.  Here's what I found after listening to a variety of songs back to back.  The E9 can drive the HE-4's just fine, but there is a small difference with the EF-5.  The EF-5 brings out just a little bit more detail and sounds a tiny bit fuller.  So it appears that the muddiness I was hearing was due to the E7 DAC.  If I didn't have both to compare back to back, I would say that I would be happy with the E9.


 
post #2 of 5

I have the HE-4s, and yeah, despite being low impedance the HE-4s aren't efficient and hard to drive. Coming out of my iPod only the left driver actually emits sound. But I think that though it might not drive the HE-4s in the sense that they will sound their best, your soundcard will make the headphones usable at least. I would highly recommend an amp though. My EF-5 sounds great, and I hear the E9 can drive them fairly well too.

post #3 of 5

another option u mite wanna take a gander at is driving them directly offa home amp speaker taps. one can easily pickup a decent low power amp (20w rms is plenty fyi) for wayyy less than a $100 - more like $20-50. i drive my HE5-LEs directly off a vintage Sansui integrated amp & its sounds freakin awesome! actually the headphone jack also sounds pretty spectacular with a 600ohm AKG K240 Sextett, a 150ohm PK1 & a 30ish ohm HD238 too.

 

& u can even power your room speakers too! cheap, multitasking & sounds good to boot...wot a concept! prolly wont appeal to "real" headfiers cos they need an nice expensive "dedicated" headamp or it wont be headfi! hmmmmm...........................

post #4 of 5
Thread Starter 

Thanks for the comments! But hum, there should be a way of knowing if the power is enough (ok, having a good sound or not no, but at least to be able to know if "theoretically" an amp has enough power to move the headphones -even when is not only about giving X peak power in a moment, but to being able to give it again just after a very short time-).

 

The soundcard has 1Vrms output, while the E9 gives 2Vrms. That's the only think that I see it could be more different, and it's a factor 2. The E9 seems to be fine, my soundcard could be between E7 and E9... (I didn't find output rms voltage of E7).

 

I'll continue searching for a guide about this, and if I find something I'll write it here because I think it's important, and seems that not very understood in general (I usually just see comments about enough impedance or not, or direct tests once people have the cans and amps to hear and compare).

 

For sure if I buy something like the E9 or EF-5 it will be more than fine, but it's out of my budget, considering that I've just bought the soundcard few weeks ago thinking of getting just a good pair headphones in addition. I'm affraid I could hear much better the HD650 or DT990 250Ohm than the HE-4 :-(

post #5 of 5
Quote:
Originally Posted by gtrevize View Post

Thanks for the comments! But hum, there should be a way of knowing if the power is enough (ok, having a good sound or not no, but at least to be able to know if "theoretically" an amp has enough power to move the headphones -even when is not only about giving X peak power in a moment, but to being able to give it again just after a very short time-).

 

The soundcard has 1Vrms output, while the E9 gives 2Vrms. That's the only think that I see it could be more different, and it's a factor 2. The E9 seems to be fine, my soundcard could be between E7 and E9... (I didn't find output rms voltage of E7).

 

I'll continue searching for a guide about this, and if I find something I'll write it here because I think it's important, and seems that not very understood in general (I usually just see comments about enough impedance or not, or direct tests once people have the cans and amps to hear and compare).

 

For sure if I buy something like the E9 or EF-5 it will be more than fine, but it's out of my budget, considering that I've just bought the soundcard few weeks ago thinking of getting just a good pair headphones in addition. I'm affraid I could hear much better the HD650 or DT990 250Ohm than the HE-4 :-(



Well, you could start with correcting the bit about the E9 putting out 2 V RMS.  That's just the line out, and 2 V is standard (although many wimpy devices today can only manage 1 V).

 

You also need to understand the difference between Volts RMS and voltage swing.  Basically, you need to use Volts RMS for power calculations, and Volts RMS = (Peak voltage) / (2)^(1/2)  Peak voltage is half the voltage swing.

 

Also, you have to consider the maximum voltage and current capabilities of the amp when calculating power at a given impedance.

 

 

But the truth is, there is no and can be no simple hard-and-fast rule for determining if an amp is enough.  It depends on a lot of things - in particular, even if an amp can get "loud" enough, is peak power for transients.  You can of course make approximate estimations, but it still requires work, especially with the limited information most manufacturers give.

 

 

Oh, and for the other guy trying to run the HE-4 out of his iPod - that's because the 3.5 mm jack is for balanced amps only.  You'll need a 3.5 mm balanced to 3.5 mm stereo adapter (TRRS to TRS) like the one Hifiman supplies with one of its IEMs, or a 6.3 mm to 3.5 mm adapter for the other cable.


Edited by BlackbeardBen - 3/10/11 at 2:12pm
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