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Topic: Calculating Loudness from Efficiency/Sensitivity (Read 37250 times) previous topic - next topic
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Calculating Loudness from Efficiency/Sensitivity

Reply #100 –
Quote from: xnor on
Onboard, especially the connectors on the backpanel, are technically line-outs with high output impedance but are normally fine with low impedance loads. The onboard implementation may only put out <1 V into a high impedance. In the worst case the output impedance is >100 ohms and the voltage would almost be divided in half into 150 ohms. Add some EQ that needs headroom or the guy just really wants to blast his ears .. I can see how he could run out of volume.

Wouldn't having a high output impedance means the damping factor is worse with low impedance headphones, meaning more power is required the lower the damping factor? Which do you think would be harder to drive on onboard... HD800s (103db/Vrms, 97db/mw) or HE400s (107db/Vrms, 93db/mw)? My guess is that both would be too much for onboard. Nwavguy primarily noted clipping as the side effect of improper powering of a headphone. I'm assuming that with either insufficient voltage or insufficient current, clipping is the result. Is it just clipping or are there other distortions that occurs?

Quote from: xnor on
Yes, that is a power supply and usually opamp (the small integrated circuits that do the amplification) limitation.

Assume you have a power supply with +/- 10 V, so if the opamps were perfect they could output 20 V peak-to-peak, or 10 V peak, or 7 V RMS (Vpeak divided by square root of 2).
P = V^2/R

As you increase R, the power drops.

Hmm, what is the power supply of the O2? With a USB powered amp, it pulls 5v, so that's 3.533v max theoretically. But the plug for O2 varies depending on location (http://www.jdslabs.com/pdf/O2_Power_Adapters.pdf). (I'm talking about running it off the wall, not on batteries.)

Calculating Loudness from Efficiency/Sensitivity

Reply #101 –
Quote from: Dark_wizzie on
Wouldn't having a high output impedance means the damping factor is worse with low impedance headphones, meaning more power is required the lower the damping factor?


Yes.  In which case you should get a better device. 

Quote from: Dark_wizzie on
Which do you think would be harder to drive on onboard... HD800s (103db/Vrms, 97db/mw) or HE400s (107db/Vrms, 93db/mw)?


Probably both would be fine unless its very bad or you want to go relatively loud. 


Quote from: Dark_wizzie on
Nwavguy primarily noted clipping as the side effect of improper powering of a headphone.


(Analog) clipping just means you tried to drive the voltage to level it couldn't remain linear at for a given load. 

Quote from: Dark_wizzie on
I'm assuming that with either insufficient voltage or insufficient current, clipping is the result. Is it just clipping or are there other distortions that occurs?


There are others.  He discusses this in detail in his articles.

Quote from: Dark_wizzie on
But the plug for O2 varies depending on location (http://www.jdslabs.com/pdf/O2_Power_Adapters.pdf). (I'm talking about running it off the wall, not on batteries.)


Pretty sure there is an entire article discussing this.

Calculating Loudness from Efficiency/Sensitivity

Reply #102 –
O2 is +/- 12 volts, output reaches about 10 volts peak.
"I hear it when I see it."

Calculating Loudness from Efficiency/Sensitivity

Reply #103 –
Quote from: stephan_g on
Ah, the trusty Mastech M-830B in its numerous incarnations. *chuckle* Call it "My first S^Wmultimeter". They actually are surprisingly capable for the less than 10 bucks that they cost and always handy to have floating around, but as mentioned, totally unsuited for low-level AC measurements.


Great to have around for things like testing batteries, but one must be aware of their limitations, the worst of which for audio is their frequency response. Good AC frequency response for general AC measurements can be a distraction by picking up HF noise that is irrelevant to the measurement at hand -  like is my power line voltage OK?

If you don't know better, the meter in your hand turns into a pumpkin around 400 Hz.


Quote
One would have to splurge on a fancier unit with low-level AC ranges here, with "TrueRMS" capability (with a frequency range extending to at least 2 or 10 kHz) being highly recommended. The latter costs about 10 times as much as a lowly '830B at the very least (I think an UT61E is the very cheapest option),


I use my UT61 a lot even though I have a Fluke 85 on hand. It lacks the utter refinement of a Fluke - for example mine was giving me screwy readings in AC and then I squinted at it and saw a battery icon that suggested to me that a new 9 volt was in order. It was and it resumed operating reasonably. If memory serves, my Fluke  makes a weak battery a far bigger issue, as any good meter should.

Quote
and if you want 100 kHz, the price quickly doubles. Something like this also fares better in terms of accuracy, build quality, input protection and electrical safety though.


A Uni-Trend meter still doesn't handle like a Fluke, but many people will be able to live with it after a look at the price tag of a Fluke 87 V...


I tested my UT61E with the output of my E-Mu 0404 and find that they are jointly about 0.5 dB down at 80 KHz.

Re: Calculating Loudness from Efficiency/Sensitivity

Reply #104 –
Quote from: Dark_wizzie on
[...]
Some more calculations if you care to doublecheck them:
He-6 is 50ohms.
Here... He-6's power requirements using Hifiman's efficiency numbers (83.5db/mw):
105db:
10^((105-83.50)/10) = 141w
110db:
 446mw
115db:
1412mw

Using Innerfidelity's pessimistic measurements on He-6 instead of Hifiman's rated efficiency:
105db:
622mw
110db:
1959mw
115db:
6225mw

I know this is an old thread, but thread's initial question remains unanswered. The difference between Tyll's measurements and manufacturer specs are way much different. I found this thread after I was reading Tyll's measurements for HE6 headphones and I realized myself that something might be wrong.

SDark_wizzie's calculations seems to be done well and the difference between 1412mw and 6225mw to get these babies to 115dB is huge, like almost 4.5 times manufacturer specs, so my question would be: who's wrong here Hifiman or Tyll? :)

Thank you,
Raul.

Re: Calculating Loudness from Efficiency/Sensitivity

Reply #105 –
I don't know...  The manufacturer's don't usually divulge the measurement techniques/details and I haven't checked into the other measurement methods.

Manufacturers often "fudge" the specs, but I'd expect the SPL spec to be close to reality (under the specific measurement conditions).

It could be a different simulated head/ear with different microphone positioning, or maybe the measurements are made at different frequencies with some normal measurement and part-to-part variation/error thrown in.

Re: Calculating Loudness from Efficiency/Sensitivity

Reply #106 –
The InnerFidelity measurement conditions are specified and described in some detail on their website. Are the measurement conditions used by the manufacturer documented publicly somewhere?