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Decibels, loudness, amplifiers, formulas...complete confusion!

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superboyac:
OK, I just admitted something really embarrassing in another forum, thought I'd share it here.
As a music nut, musician, engineer (electrical at that), all around nerdo geek...I don't understand decibels as it relates to loudness.  More so than that, I don't get it in relation to amplifier circuitry and the formulas used.

This all started when I began researching types of headphone amps to get for my home studio.  This is really embarrassing to admit...I've written books on electrical engineering.

All the circuitry (obviously) uses volts, amps, currents.  Fine, I am comfy with that.  But then, somehow these numbers are magically turned into decibels!  How the f?  Now, decibels is not a unit I enjoy using.  First of all, for loudness, the unit it uses is called SPL, which is a measure of sound pressure.  But decibel in itself is dimensionless; it's a ratio of one unit over another number of the same unit (i.e. they cancel out).  So a inputted values for decibels can be volts, ohms, watts, spl, mattresses, bicycles, whatevers.

On top of all that, I have to sort through all the audiophile pseudo-science, snake oil nonsense.

Am I crazy?

Here's a fun chart:

from here:
http://www.sengpielaudio.com/calculator-loudness.htm

I don't know what is going on there, but it looks helpful if I did!

40hz:
It gets crazy because the human ear doesn't perceive loudness in a linear or strictly physical manner. Check out this article if you want to really start pulling your hair out. As one EE from MIT who was the most knowledgeable sound engineer and circuit designer I ever met told me: It's not just science, It's psychology.  :tellme:

Target:
never mind the quality, feel the width!!

superboyac:
It gets crazy because the human ear doesn't perceive loudness in a linear or strictly physical manner. Check out this article if you want to really start pulling your hair out. As one EE from MIT who was the most knowledgeable sound engineer and circuit designer I ever met told me: It's not just science, It's psychology.  :tellme:
-40hz (December 09, 2014, 04:27 PM)
--- End quote ---
Here's the problem I'm having, and why I'm going through this.  I have a pair of 600 ohm headphones.  They're very good headphones, but the high impedance makes them difficult to drive in this ipod age of unamplified playback devices.  Apparently, a long time ago, high impedance was used with professional hifi equipment.

But I still want to use the headphones.  So instead of buying new lower impedance headphones, I said let me make use of it by just getting an amp.  So I got one as an experiment, and I even asked around to make sure it could drive those headphones.  Everyone's like yea yea, and gave me the formulas backing it up along with the specs of the headphones and amp, etc.  So I was convinced.  I got it...it's ok, but it "feels" not loud enough because everything is cranked to the max.  So while I hear it fine, I'm uncomfortable with maxing all the knobs out, including the volumes in my software and audio drivers.  I'd like to have some top room remaining, like 25% or so minimum. 

So I'm now left wondering which amp I need.  I'm 90% convinced that this thing, the Aphex Headamp 4, is the way to go.  I'll test it out later this week.  The reason why is because in it's marketing video, it says this:
Decibels, loudness, amplifiers, formulas...complete confusion!

If you really want to follow the technical discussion, you can do so here:
http://www.hydrogenaud.io/forums/index.php?showtopic=107678

But I'm reserving this thread for my more intimate, less polite venting.

Stoic Joker:
How loud something is perceived to be is directly proportional to how acceptable the sound is to the listener. (i.e.) To me it is impossible to play AC/DC's Shoot to thrill to loudly ... Even if I'm bleeding from the eyes...I'll still be digging to music. Conversely, anything from the BeeGees, will make me vomit immediately...if it played audibly enough to recognize.

I've heard racing engines with open pipes redlined inside of a small shop that were loud enough to be physically painful unless you opened your mouth to equalize the pressure ... And I still responded Oh fuck me, do it again!!! ...Because I freaking loved it... Due to the intense pressure waves tickling the happy place in my soul.

So subjectivity is pretty much where it's at.

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