Did you miss your activation email?

• February 18, 2020, 07:02 AM
• Proudly celebrating 14 years online.
• Donate now to become a lifetime supporting member of the site and get a non-expiring license key for all of our programs.

### Author Topic: Decibels, loudness, amplifiers, formulas...complete confusion!  (Read 11364 times)

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Decibels, loudness, amplifiers, formulas...complete confusion!
« on: December 09, 2014, 04:05 PM »
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.sengpiela...culator-loudness.htm

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

#### 40hz

• Supporting Member
• Joined in 2007
• Posts: 11,797
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #1 on: December 09, 2014, 04:27 PM »
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.

#### Target

• Honorary Member
• Joined in 2006
• Posts: 1,736
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #2 on: December 09, 2014, 05:18 PM »
never mind the quality, feel the width!!

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #3 on: December 09, 2014, 05:37 PM »
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
-40hz
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.hydrogena...php?showtopic=107678

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

#### Stoic Joker

• Honorary Member
• Joined in 2008
• Posts: 6,529
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #4 on: December 09, 2014, 05:44 PM »
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.

#### Stoic Joker

• Honorary Member
• Joined in 2008
• Posts: 6,529
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #5 on: December 09, 2014, 05:51 PM »
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.
-superboyac

LOL I've got a factory but very high-end sound system in my truck that subjected me to much the same experience. Understand I'm guessing a bit here, but... The newer music seems to be designed for equipment that has no baseline "white noise". Everything is digitally clear an sticks to frequencies that remain "comfortable" even when played at earth shattering db ranges. However, when one of my old school favorite songs came on, I found some parts of the guitar solo physically painful because it wasn't "designed" to be played that way over that kind of "new fangled" equipment.

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #6 on: December 09, 2014, 05:59 PM »
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.
-superboyac

LOL I've got a factory but very high-end sound system in my truck that subjected me to much the same experience. Understand I'm guessing a bit here, but... The newer music seems to be designed for equipment that has no baseline "white noise". Everything is digitally clear an sticks to frequencies that remain "comfortable" even when played at earth shattering db ranges. However, when one of my old school favorite songs came on, I found some parts of the guitar solo physically painful because it wasn't "designed" to be played that way over that kind of "new fangled" equipment.
-Stoic Joker
True.  I've had these raging debates also!
The  best conclusion I've heard, especially regarding the issue of the "loudness wars" is that things were just mastered differently before the digital age.  And that, compared to everything else I've heard, makes a whole lot of sense to me.  And I've listened to a few lectures from the master masterers, and they've pretty much said the same thing: that things are just mastered to be loud now, and before it was a different philosophy.  There's the usual curmudgeon like attitudes there also, but for the most part it sounds like things are being mastered for ipods now, whereas before they were mastered for living room players, or hifi stuff.

Eventually, I'm going to go after the whole tube vs solid state thing, too.  I'm both looking and NOT looking forward to that one.

#### 40hz

• Supporting Member
• Joined in 2007
• Posts: 11,797
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #7 on: December 09, 2014, 07:08 PM »
The big difference with analog is that distortion increasingly creeps in with increased loudness. So the name of the game was to saturate (we're talking tape here) your audio track with the levels just at the threshold where clipping began to occur. That got as much music as possible as far above the noise floor as possible without introducing too much perceived distortion. (Our ears actual seem to like a little grit with our music - so a hint of distortion is not automatically a bad thing.) With digital, we're talking digital "distortion." It's really not the same thing as analog distortion - but it sounds a lot like it. Digital distortion is fixed. IIUC it's a function of the quantization error whenever you attempt to mimic a complex natural sine wave with a calculated staircase wave. So with digital, you want to be as far above the fixed distortion floor as possible because - if you lower the level - the perceived distortion in the track actually seems to increase. Louder in this case better hides the distortion. And unlike analog, softer becomes more distorted sounding. That's a bizarre effect that doesn't occur in nature - so our ears and brain go nuts trying to deal with it. Apparently on some subconscious level we know what we're hearing is just plain wrong when it comes to digital sound.

Or so it was explained to me.
« Last Edit: December 09, 2014, 07:20 PM by 40hz »

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #8 on: December 09, 2014, 07:19 PM »
The big difference with analog is that distortion increasingly creeps in with increased loudness. So the name of the game was to saturate (we're talking tape here) your audio track with the levels just at the threshold where clipping began to occur. That got the music as far above the noise floor as possible without too much perceived distortion. With digital, we're talking digital distortion - which is fixed. So with digital, you want to be as far above the fixed distortion floor as possible because - if you lower the level - the perceived distortion in the track actually seems to increase. Louder in this case better hides the distortion. Softer becomes more distorted sounding. That's a bizarre effect that doesn't occur in nature - so our ears and brain go nuts trying to deal with it. Apparently on some subconscious level we know what we're hearing is just plain wrong when it comes to digital sound.

Or so it was explained to me.
-40hz
oh yes!  I believe you have explained this before here and I've clipped it!
oy...it reminds me of this seindfeld scene:

"eating onions, spotting dimes!" lol

#### Vurbal

• Supporting Member
• Joined in 2012
• Posts: 635
• Mostly harmless
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #9 on: December 09, 2014, 07:44 PM »
I recently decided to download replacements for my trashed Jesus Christ Superstar CDs (Ian Gillan as Jesus FTW) and ended up finding torrents of 2 different versions. The first was from the same release I bought back in the 90s. The other was released within the last 3-4 years. I downloaded both, just to see if the new one had severe dynamic compression like I expected.

Not surprisingly, it did, and if you're at all familiar with the material,  you won't be the slightest bit surprised to know it sounded horrific. I wish I had saved a screenshot of the waveform comparison to demonstrate it. Of course, I deleted it afterward so I can't repeat it.
I learned to say the pledge of allegiance
Before they beat me bloody down at the station
They haven't got a word out of me since
I got a billion years probation
- The MC5

Follow the path of the unsafe, independent thinker. Expose your ideas to the danger of controversy. Speak your mind and fear less the label of ''crackpot'' than the stigma of conformity.
- Thomas J. Watson, Sr

It's not rocket surgery.
- Me

I recommend reading through my Bio before responding to any of my posts. It could save both of us a lot of time and frustration.

#### x16wda

• Supporting Member
• Joined in 2007
• Posts: 771
• what am I doing in this handbasket?
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #10 on: December 09, 2014, 08:50 PM »
Eventually, I'm going to go after the whole tube vs solid state thing, too.  I'm both looking and NOT looking forward to that one.
-superboyac

In the end it ain't what any numbers say, it's what your ears tell you. I had a friend who went through large sums testing every variety of tube, solid state, and discreet amps, tuners, D/A converters, and so many speaker systems it made my head spin. He took his reference material around with him to listen to equipment, and when he built his most recent house had his listening room configured to the most appropriate dimensions. He kept saying you don't need huge watts if you have good clean watts.

I have to say his system sounded very nice. However, my first rock concerts, at an early age, included Strawberry Alarm Clock and Black Sabbath, so I couldn't tell the difference. (Strawberry Alarm Clock was so loud, it rivaled the Saturn 5 static tests I used to hear when we lived in Huntsville, AL, during the Apollo years!) My old Denon system with the Philips speakers has worked plenty fine for me for about 25 years now.
vi vi vi - editor of the beast

#### TaoPhoenix

• Supporting Member
• Joined in 2011
• Posts: 4,640
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #11 on: December 09, 2014, 09:07 PM »
...I've written books on electrical engineering.
-superboyac

Impressive!

Meanwhile, I'll tell the doctors in the hospital their patients' vomiting symptom can be cured by turning off the BeeGees muzak : )

• Charter Member
• Joined in 2005
• Posts: 13,266
• Tell me something you don't know...
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #12 on: December 09, 2014, 09:48 PM »
I'm not really sure what your question is.

dB is just measuring atmospheric pressure difference (caused by sound) from a reference atmospheric pressure (silence).

There are different scales though.

The absolute difference is what you should use if you are measuring energy.

However, human hearing is limited, so there are A, B, and C scales (there are others as well). They all measure dB as it relates to human hearing, which is what you should use when you are interested in "hearing" the sound.

The absolute SPL is what you want to know when you want to know which song pumps out more bass and shakes the room more.

So, in short, dB is just a differential ratio, and in this context, it's about atmospheric pressure changes.

Does that sort of make sense?
Slow Down Music - Where I commit thought crimes...

Freedom is the right to be wrong, not the right to do wrong. - John Diefenbaker

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #13 on: December 10, 2014, 09:55 AM »
I'm not really sure what your question is.

dB is just measuring atmospheric pressure difference (caused by sound) from a reference atmospheric pressure (silence).

There are different scales though.

The absolute difference is what you should use if you are measuring energy.

However, human hearing is limited, so there are A, B, and C scales (there are others as well). They all measure dB as it relates to human hearing, which is what you should use when you are interested in "hearing" the sound.

The absolute SPL is what you want to know when you want to know which song pumps out more bass and shakes the room more.

So, in short, dB is just a differential ratio, and in this context, it's about atmospheric pressure changes.

Does that sort of make sense?
Thanks
The issue is this:
Supposedly, there's are calculations you can do to figure out which headphones will work with which headphone amps.  And it's all about volume, really, that's all there is to it.  Either it gets loud enough just right, or not loud enough, or too loud.
There are rules of thumb that are being used for this.  It works, for the most part.
But if you start wondering "Well, what if I don't use the rule of thumb and just do the full calculation?"
That's where you find all these electrical calculations, ohm's law.  However, then the db comes in.  And it's db, as in SPL (sound pressure).  And nowhere along the way does anyone do any calculation relating SPL to any electrical value like ohm, current, voltage.  So I have no idea how the SPL (which is loudness in a sense) to the circuitry.  So how can anyone figure anything out?

#### 40hz

• Supporting Member
• Joined in 2007
• Posts: 11,797
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #14 on: December 10, 2014, 10:24 AM »
Wouldn't the SPL be a function of the frequency weighting and the transducer as well?

For example, my vintage Acoustic 18" folded horn bass enclosure has a sticker with a warning that it can produce ear damaging levels at even relatively low volume settings. That's because the folded horn increases efficiency by almost behaving like a focusing lens.

When tested with a sound level meter it showed the ability to produce dangerous sound levels with as little as 100 watts pushing it. Since the average stage bass head packs  200 watts and up, it's something you need to be aware of if you're using one.

#### Vurbal

• Supporting Member
• Joined in 2012
• Posts: 635
• Mostly harmless
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #15 on: December 10, 2014, 11:16 AM »
There is no universal conversion/transfer factor between electrical power and physical power (ie air movement) for speakers. In fact, just to add to what 40hz mentioned about bass cabinets, another common problem people have is understanding, at some point, any additional power may just be dissipated as heat instead of being converted to motion. For example, a cab may be capable of handling 400W or more of constant input, but will typically stop getting louder somewhere around 200W-300W.

I'm not saying that's going to be an issue very often for headphones, just that there are numerous physical issues which act as something of a brick wall for volume,even long before you come close to their electrical limits.
I learned to say the pledge of allegiance
Before they beat me bloody down at the station
They haven't got a word out of me since
I got a billion years probation
- The MC5

Follow the path of the unsafe, independent thinker. Expose your ideas to the danger of controversy. Speak your mind and fear less the label of ''crackpot'' than the stigma of conformity.
- Thomas J. Watson, Sr

It's not rocket surgery.
- Me

I recommend reading through my Bio before responding to any of my posts. It could save both of us a lot of time and frustration.

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #16 on: December 10, 2014, 11:35 AM »
Wouldn't the SPL be a function of the frequency weighting and the transducer as well?

For example, my vintage Acoustic 18" folded horn bass enclosure has a sticker with a warning that it can produce ear damaging levels at even relatively low volume settings. That's because the folded horn increases efficiency by almost behaving like a focusing lens.

When tested with a sound level meter it showed the ability to produce dangerous sound levels with as little as 100 watts pushing it. Since the average stage bass head packs  200 watts and up, it's something you need to be aware of if you're using one.
-40hz
I think that's precisely the problem I'm having.  As far as I know, there's no formulaic connection between sound levels and electrical circuitry (ohms, volts, current).   With a sound level meter, yes, you can measure the SPL or whatever it is that indicates loudness.

I'm pretty sure the problem is that the supposedly knowledgeable people do not clearly understand it themselves, especially the electrical engineering aspect of it, which is hard to understand anyway.  There's just no obvious, formulaic connection between the electrical circuitry elements and the loudness.  They are using rules of thumbs and using impedance values, but ultimately there's no direct connection.

I think the answer is simply:
I just need an amp with more juice.  The headphones have high impedance, they need more volts (since everyone is talking about voltage).
power = (voltage)^2/R
My R is larger than normal.  For the same amount of power driving low impedance phones, I need more voltage.  It's that simple to me.
for the headamp I want to buy, the max gain is 35.  I think that means if I input 1V, it will output 35V.
Unfortunately, the headamp has odd specs.  It shows specs for "Z" values, which indicate impedance, then gives the rating as watts, lol.
like this...
"Output Z: 10W"
lol, ok.

"How many apples you got in that bag there?"
"I got 30 oranges!"

and that's just one problem in this whole thing.

#### Stoic Joker

• Honorary Member
• Joined in 2008
• Posts: 6,529
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #17 on: December 10, 2014, 12:06 PM »
I think that's precisely the problem I'm having.  As far as I know, there's no formulaic connection between sound levels and electrical circuitry (ohms, volts, current).   With a sound level meter, yes, you can measure the SPL or whatever it is that indicates loudness.
-superboyac

Have you considered it may be due to the mechanical question mark in between them? Some of the electrical energy gets used accelerating the cone which is of an unknown weight and rigidity. Any drag caused by mechanical components making physical contact can also use/waste energy.

This is why vehicles have two different horsepower ratings, one at the crank, and one at the rear wheels. Because of the mechanical losses involved in getting the power from A to B (through the transmission, differential, clutch, and etc.).

#### CWuestefeld

• Supporting Member
• Joined in 2006
• Posts: 1,009
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #18 on: December 10, 2014, 01:16 PM »
I think Vurbal hits the nail on the head: given a given loudspeaker system - meaning that the efficiency of the driver, stiffness of the cone, dampening in the box, rigidity of the box, etc, are all held constant - then Ohm's law and all that other stuff will tell you how changes to the input will affect changes in the output. And that's precisely *why* it's expressed in db's - we don't know the actual absolute value, but we can still safely talk about relative values. So for your headphones, if you've got an amp design that produces X in your headphones, you (in theory) could tweak it to produce, say, 2X. But in real life you can't, of course, because that amp is a proprietary product, a black box to you, so you can't actually tweak it yourself.

As far as factoring in those values above, I think it's largely voodoo. There are rules of thumb, even things that pretend to be scientific and formulaic, but as far as I'm aware that's just formalizing those rules of thumb. They're as useful as high school physics formulas that assume point-masses and zero friction.

I also agree with the sentiment here that the final impression of the sound is determined largely by the music's mastering. It seems clear to me that the perception of the sound volume can be very decoupled from the actual sound energy being output. And generally speaking, it's that cleaner sound, even at higher "sound pressure", isn't perceived as loud, but when there's audible distortion, that quickly drives up the perception of loudness.

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #19 on: December 10, 2014, 02:56 PM »
i appreciate the theoretical discussion here, but I still think the question is simply "What do I need to get the headphone louder?" And I think that's a more simple answer than all the audiophile websites and discussions are making it seem.

I'm liking what this site is saying:
http://www.sengpiela...lculator-db-volt.htm
Note: Power gain (power amplification) is not common in audio engineering.
Even power amplifiers for loudspeakers don't amplify the power.
They amplify the audio voltage that moves the voice coil.

This means the ratios (db) are not for power, but for voltage.  So why do I care?  Well, when I'm doing ohm's law, I'm asking a seemingly paradoxical question "Do I need more power?  or more voltage?"  Well, the correct answer is both.  But the right way to think about it from the headphone's perspective is voltage.  The headphone needs more voltage.  So I need an amp that increases voltage (even though it will also increase power).  More importantly, I'd like to know what kind of voltage it is outputting!

#### Vurbal

• Supporting Member
• Joined in 2012
• Posts: 635
• Mostly harmless
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #20 on: December 10, 2014, 03:07 PM »
Given the information provided, it was a theoretical question.

That's not a criticism, but merely an explanation of the type of answers you got.
I learned to say the pledge of allegiance
Before they beat me bloody down at the station
They haven't got a word out of me since
I got a billion years probation
- The MC5

Follow the path of the unsafe, independent thinker. Expose your ideas to the danger of controversy. Speak your mind and fear less the label of ''crackpot'' than the stigma of conformity.
- Thomas J. Watson, Sr

It's not rocket surgery.
- Me

I recommend reading through my Bio before responding to any of my posts. It could save both of us a lot of time and frustration.

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #21 on: December 10, 2014, 03:14 PM »
Another good site with information:
http://shure.custhel...phone-specifications

The headphones come with this specification for rating, normally given in db/mW.  From that site, the db is indeed referring to SPL (sound pressure).  That's good.  Now we know that for my given headphone rating (96 db/mW), to get 96 db loudness, I need 1 mW.  The voltage for that is 0.78V.

But I want to be able to go hurtful loud sometimes, just so I know my equipment can handle it.  Most people say that 120db is way too loud to listen to for extended periods of time (or even short periods!).  Perfect!

The Headmp says it can do up to +35db in gain.  OK, that means:
96+35=131 db max

Well, that should do it!  So I'm going to get the headamp.

Now, let's do an experiment to see if I'm right or not.  This is it:
The knob can do max 35 gain.  So 0-100% is 1-35 db.
If I want comfy listening volume, like 100 db, where would the knob be?
(100-96)/35 = 11%, so almost a quarter turn of the knob.

Let's say I want 115 db:
(115-96)/35 = 54%, so the knob should maybe be about half turned.

Let's say I want to blow my ears out, 120db:
(120-96)/35 = 69%, so the knob is just about three-quarters turned.

We'll see!

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #22 on: December 10, 2014, 03:16 PM »
Given the information provided, it was a theoretical question.

That's not a criticism, but merely an explanation of the type of answers you got.
-Vurbal
No problem!  It's all useful for me.

#### CWuestefeld

• Supporting Member
• Joined in 2006
• Posts: 1,009
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #23 on: December 10, 2014, 03:36 PM »
I think that all you really need is an amp that goes to 11.

#### superboyac

• Charter Member
• Joined in 2005
• Posts: 6,195
##### Re: Decibels, loudness, amplifiers, formulas...complete confusion!
« Reply #24 on: December 10, 2014, 03:39 PM »
I think that all you really need is an amp that goes to 11.
-CWuestefeld

If it were a cartoon, I'd just write in "11" "12" and crank the knob a bit more!