Head-Fi.org › Forums › Equipment Forums › Sound Science › Approximating Headphone Volume Output (dB)
New Posts  All Forums:Forum Nav:

Approximating Headphone Volume Output (dB) - Page 4  

post #46 of 57
Quote:
Originally Posted by xnor View Post

---

 

Regarding the other questions, maybe you can take something useful from http://www.head-fi.org/t/668238/headphones-sensitivity-impedance-required-v-i-p-amplifier-gain

 

What is "dBL"? Measuring RMS voltage with a multimeter is not very accurate. Some only work properly with 50/60 Hz signals. My old Fluke is specified to measure more or less accurately up to about 500 Hz. I have no idea how it would deal with anything but single tones.

 

Thanks for the useful comments and reference. I'll check it out.

dBL as in:

"Unweighted sound pressure level is called "linear sound pressure level" and is often written as dBL or just L"  (wiki info).

I didn't measure the rms voltage with a voltmeter. I wrote an application which uses a high-end sound card and samples at 24bit/96kHz and computes the real rms voltage and calibrated with a precision voltage source. It seems to be accurate (~ 10%) up to 20kHz.

post #47 of 57

Oh okay, so the Vrms figure is more or less accurate, but that doesn't necessarily translate well to perceived loudness or measured weighted SPL. There's also still the problem with headphone frequency response.

post #48 of 57
Quote:
Originally Posted by xnor View Post

Oh okay, so the Vrms figure is more or less accurate, but that doesn't necessarily translate well to perceived loudness or measured weighted SPL. There's also still the problem with headphone frequency response.

Yes I agree with that. I think the only useful comparison (and it is only at one frequenc so is really of limited practical use and give a very rough idea of overall "loudness") is the spec'd dbSPL at 1 kHz for either 1 mW or 1Vrms. Being a Physicist, I like to "assume it's a sphere" :-)  

post #49 of 57

Interested in these things but still confused.

 

First, I am feeding my music through an Apex Glacier which says the following in Maximum Output : 3.3V RMS into 15 Ohms; 2.14V RMS into 33 Ohms. Anyone care to decipher what that means and also which numbers can I extract as information?

 

The Apex Glacier manual also stated that each step on the wheel is exactly 2 dB so is it correct if I assume this to be linear instead of logarithmic in the calculation? (there are 32 steps, I listen at around 10 to 16 steps)

 

Also I have a headphone with 102 dB SPL/mW, 60 ohms impedance if anyone would kindly help me find my loudness number biggrin.gif.

 

Thanks guys!

post #50 of 57

Specs on ttvj website say:

Maximum output: >2.6V RMS into 150Ω; >1.7V RMS into 32Ω

Maximum gain:  0dB, 10dB, or 20dB, ±<0.5dB

Maximum input level: 2V RMS

 

So with a 2V source you don't need any gain (0 dB) in order to reach (close to) max output into 60 ohms.

 

102 dB SPL/mW = 114 dB SPL/V

 

so at full volume: 120 dB SPL (+6 dB because of 2V source)

at step 29: 114 dB SPL (120 - 3*2)

at step 16: 88 dB SPL (120 - 16*2)

at step 10: 76 dB SPL (120 - 22*2)

 

 

This is with a full-scale 1 kHz tone. Real music will have a lower average SPL, but can have short term peaks reaching close to those numbers.


Edited by xnor - 8/1/13 at 9:11am
post #51 of 57
Quote:
Originally Posted by AbsoluteZero View Post

Interested in these things but still confused.

 

First, I am feeding my music through an Apex Glacier which says the following in Maximum Output : 3.3V RMS into 15 Ohms; 2.14V RMS into 33 Ohms. Anyone care to decipher what that means and also which numbers can I extract as information?

 

The Apex Glacier manual also stated that each step on the wheel is exactly 2 dB so is it correct if I assume this to be linear instead of logarithmic in the calculation? (there are 32 steps, I listen at around 10 to 16 steps)

 

Also I have a headphone with 102 dB SPL/mW, 60 ohms impedance if anyone would kindly help me find my loudness number biggrin.gif.

 

Thanks guys!

Assuming roughly that at 60 ohm load, we have ~ max output voltage of 3.3Vrms, then here are some results:

 

A 2 dB step per volume increment means the output voltage factor is reduced by a FACTOR of 0.794  (or the POWER is reduced by a factor of 0.631).  So, these are the output voltages (pure sine wave) and assuming Z(1 kHz) = 60ohm with 102 dBSPL/mw or 114 dBSPL/1Vrms @ 1 kHz:

 

  10 setting:  21 mVrms      (22 dB below max setting)  giving  80 dBSPL at 1 kHz

  16 setting:  82 mVrms      (16 dB below max setting)   giving 92 dBSPL at 1 kHz

 

Result using this calculator:   http://www.jensign.com/S4/calc.html

post #52 of 57
Quote:
Originally Posted by xnor View Post

Specs on ttvj website say:

Maximum output: >2.6V RMS into 150Ω; >1.7V RMS into 32Ω

Maximum gain:  0dB, 10dB, or 20dB, ±<0.5dB

Maximum input level: 2V RMS

 

So with a 2V source you don't need any gain (0 dB) in order to reach (close to) max output into 60 ohms.

 

102 dB SPL/mW = 114 dB SPL/V

 

so at full volume: 120 dB SPL (+6 dB because of 2V source)

at step 29: 114 dB SPL (120 - 3*2)

at step 16: 88 dB SPL (120 - 16*2)

at step 10: 76 dB SPL (120 - 22*2)

 

 

This is with a full-scale 1 kHz tone. Real music will have a lower average SPL, but can have short term peaks reaching close to those numbers.

 

 

Quote:
Originally Posted by Jensigner View Post

Assuming roughly that at 60 ohm load, we have ~ max output voltage of 3.3Vrms, then here are some results:

 

A 2 dB step per volume increment means the output voltage factor is reduced by a FACTOR of 0.794  (or the POWER is reduced by a factor of 0.631).  So, these are the output voltages (pure sine wave) and assuming Z(1 kHz) = 60ohm with 102 dBSPL/mw or 114 dBSPL/1Vrms @ 1 kHz:

 

  10 setting:  21 mVrms      (22 dB below max setting)  giving  80 dBSPL at 1 kHz

  16 setting:  82 mVrms      (16 dB below max setting)   giving 92 dBSPL at 1 kHz

 

Result using this calculator:   http://www.jensign.com/S4/calc.html

 

Thanks guys for the calculations, I am starting to understand these things currently.

Now I can calculate for my other headphonesin my inventory, cheers!

post #53 of 57
Quote:
Originally Posted by AbsoluteZero View Post

 

 

 

Thanks guys for the calculations, I am starting to understand these things currently.

Now I can calculate for my other headphonesin my inventory, cheers!

Glad to help out in some way. Related to audio level, I recently have built some basic gear to verify audio specs (typically "A-Weighted in a 20 kHz BW" noise and S/N) of some audio equipment I have. This is a very interesting area and opinions are strong (as you can see from the references I include):  http://www.jensign.com/AWeight/

post #54 of 57
Quote:
Originally Posted by tinyman392 View Post
 

I originally posted this on another forum (iFans) here: http://www.ifans.com/forums/showthread.php?t=364522

 

I do think that it is an important concept to get down for a headphone forum, so I am going to repost here as well.  Some disclaimers before I begin, I have double checked the units and they do add up to dB when multiplied out (stage by stage), so that part is accurate.  However, I still have to warn that these results may not be 100% accurate and will only give you a ballpark estimate at your actual listening levels.  The best way to get the actual number would to get a dummy head and an SPL meter (kind of expensive).  This method requires a calculator, and a little understanding of high school physics.

 

On the other forum I did include a quick and dirty command line program (Windows only, sorry Mac and Linux users) that would calculate it for you granted you inputted correct information.  I don't know what the rules are like here concerning executables, so I won't upload it here.  It is uploaded on the other forum if you need it (it comes with source code to be compiled for other machines; use a C-based compiler).

 

Again, no guarantees of 100% accuracy, but it will get decent numbers to give you a good estimate.  Let me know if you have any questions.  This guide also assumes that your volume bar increases voltage at a parabolic rate (what I found most devices to do: phones, iPods, laptops, etc).

 

Quote: Tinyman392
I don't know how many of you actually pay attention to this. However, a large volume output can really damage your hearing, even further, anything over ~75-85 dB can cause your ears to tune out low and high frequencies. This in turn can actually decrease the quality of your music (Inner Fidelity). Anything over 90 dB can damage your hearing if exposed too long.

Ideal listening levels should be around 60-80 dB. I generally listen myself around 70 dB (calculated). So how exactly do we calculate this (estimated) listening level? Well it's simple, first we need some information though:
  • Maximum voltage output of your device (search google for this), the iPod Touch 4G puts out a maximum of 1.110 v (60 mW max or 30 mW per channel).
  • Headphone specs (specifically the impedance and the sensitivity ratings) - Find it on the box of your headphones, or online through the manufacturer's website (or even the reseller's site sometimes)
Disclaimer: this guide will not get you exact numbers. It will merely give you a ballpark estimate of how loud you are actually listening. To get actual numbers, obtain a mic, dummy head and test your own headphones.

So let's start by calculating the actual voltage that comes out of your headphone jack. When you push up on your volume, you actually don't increase in a linear, straight manner. Instead, it's squared. To get the voltage your increasing use this formula below:

Actual Voltage (volts) = Max Output Voltage (volts) * (volume level fraction)^2*

The volume level fraction is actually the amount of the total volume you are outputting. So if you listen at half the max volume of the iPod, your volume level fraction is 1/2 = .5. If you listen to it at 30%, then the fraction would be 30/100 = 3/10 = .3. If you listen at 3/8, then your fraction would be 3/8 = .375. It's important that you keep this a fraction under 1.

The next thing we need is actually the current going through your headphones. The current is generated using the formula below for current through a parallel circuit.

Current = Voltage * (1/R1 + 1/R2 + 1/R2 + 1/R4...); where R1, R2, R3, etc are resistors. Your headphones have two of these both rated the same. So we can simplify that whole statement to:

Current (amps) = Voltage (volts) * (2/R); Where R = Impedance rating (ohms) of the headphones. Thusly, we get the equation:

Current (amps) = Voltage (volts) * 2 / Impedance (ohms)*

With the voltage and current we can calculate power generated by your device at a given volume level. This is why we calculated the current and voltage. So use the equation below:

Power = Current (amps) * Voltage (volts)*

Or if you want the long one:

Power = (Voltage (volts) * 2 / Impedance (ohms)) * (Max Output Voltage (volts) * (volume level fraction)^2)

Now to get the actual sound pressure level (SPL) coming out of your headphones (note this is in Pa), we can use the formula below:

SPL (Pa) = Sensitivity * Power*

Or the long one:

SPL (Pa) = Sensitivity * (Voltage (volts) * 2 / Impedance (ohms)) * (Max Output Voltage (volts) * (volume level fraction)^2)

Now, this number is going to range anywhere from 0 to 15 (maybe higher if you have special headphones). We need to convert this number into one we can use. To convert the SPL (Pa) to SPL (dB) to get the decibel rating we want you can do one of two things:
Use this converter*

Or you can use this formula:

SPL (dB) = 20 log(SPL (Pa) / (2*10^-5)) / log(10) (dB)
*We are stating that the log has a base of ten when we divide by log(10). On any given calculator, the log button has a default base of 10 (check this for your self), that is, log(10) = 1. Ln is the natural log which has a base of e. In the equation above, log can be replaced with ln, but you'll have to divide by ln(10) still since ln(10) is not 1.

So we get the final equation as:

SPL (dB) = 20log(SPL (Pa) / (2*10^-5)) dB*

Plugging in what SPL (Pa) is, you get the long equation:

SPL (dB) = 20 log(Sensitivity * (Voltage (volts) * 2 / Impedance (ohms)) * (Max Output Voltage (volts) * (volume level fraction)^2) / (2*10^-5))

^^If you do this equation, don't type it in wrong And double check your work).

Please note you'll get more accurate results (since you'll make less human errors) if you just calculate each thing and right down the number it produces and plug those into the small equations (which are marked with a star, *, at the end of them.. The big equations scare me (especially the last one)... If you are using the bigger equations, just skip to the final equation; plug and chug it all down and hope you didn't type anything in wrong

And there you have it, the actual listening level you are listening at (approximated). Now let's see how scary your numbers are... Happy (safe) listening everybody.

 

Sources used: http://www.innerfidelity.com/content/loud-music-sucks

 

 

I haven't read this whole thread, but I see a potential flaw in this calculation.  If you use all the variable and figure out your decibel level that you are supposedly listening to, how do you determine the level of the music as well?  In other words, the result of this calculation tells you the potential max db level you're listening to, but some songs are quieter than others.  If you change nothing with the volume, but switch to a quieter track this calculation won't reflect that (unless I missed something).  So if track two is 20db quieter than track one, how do you know how loud either track is?  Is this formula based on listening to a song that is a wall of 100% db of noise?  Just curious...

post #55 of 57

His old calculations were completely wrong. It's best to ignore them.

post #56 of 57
Quote:
Originally Posted by xnor View Post

His old calculations were completely wrong. It's best to ignore them.
Is there any way to know your db without a measurement device?
post #57 of 57

Add to the sensitivity specified as x dB SPL/1 Vrms the following: 20*log10(V)

 

That's peak. For a more realistic average see http://www.head-fi.org/t/668238/headphones-sensitivity-impedance-required-v-i-p-amplifier-gain (scroll down).

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Sound Science
This thread is locked  
Head-Fi.org › Forums › Equipment Forums › Sound Science › Approximating Headphone Volume Output (dB)