Archive for February, 2014

Phones and Scones? I mean… Phons and Sones!

Since it’s been a while, I have received approval to write about phones and scones – yummy! Oh, I misread that… I can talk about phons and sones? Oh boy. I mean… hmm… uh…

Every so often, you get exposed to a term that you’ve never heard;  it seems like someone just made it up – and the more you learn about it, the more made up it seems.
(Disclaimer: I swear I didn’t make these up.)
Today, I will introduce you to two of these amazingly real terms, and do my best to explain why these terms exist… prepare to be amazed!

OK. Phons and Sones are two related terms in Psycho-acoustics that refer to how humans perceive the “LOUDNESS” of sounds. These are actual real concepts. (Stop laughing.)

Don’t we all perceive sound differently? YES!

So how can you have an actual measurement based on something that everyone perceives differently? EASY!

Take a bunch of people.
Play a 1Khz sine wave.
Play another frequency.
Ask them if it sounds just as loud.
Repeat. (No kidding.)

OK, this is over simplified…  Let’s start by setting some rules that make this a little easier.

For reference – whatever dB level that 1KHz wave is will be the reference for the whole group… compare a bunch of frequencies at different levels to 1Khz at 40 dB – and we’ll call all the ones that sound just as loud the “40 PHON Equal Loudness contour.”

Why? Because they sound just as loud as the 1kHz wave at 40 dB. (I’m not joking!)

Then compare a bunch to a 1KHz wave at 50dB and call all of those that sound as loud, (wait for it)
the “50 PHON Equal Loudness contour.”

Then 60dB, 70dB, 80dB… etc (see a pattern?)
Now, plot all of these from a bunch of people who hear pretty well… take an average and WHAMMO!!!

The PHON Equal Loudness contours!

Equal Loudness Contours.

ISO 226:2003 Equal Loudness Contours.

(To be fair this is the data from a bunch of 18-25 year olds who still have reasonably good hearing…)

Remember this is PERCEIVED LOUDNESS. The average of what the test subjects said “yeah, uh, that’s just as loud, Dude.”

It seems strange doesn’t it – that these aren’t nice straight lines? That’s because the human ear is constructed in such a way to be more sensitive to certain frequencies than others.

So according to this chart – a 1KHz wave at 40 dB sounds just as loud as 125 Hz at ~60dB and 3150 Hz at ~35 dB. (All on the 40 Phon contour.)

That’s Psycho-acoustics for you. (Wow.)
So if you’re an average person with average hearing, your bass perception is terrible and over 16KHz you’re basically – well… deaf.
But you hear really well from 2kHz – 5kHz!

Anyway… what’s the point?

Phons measure how loud the human ear perceives sounds at different frequencies. (TADA!)

FINE! –  then what are Sones ? To make this simple – Sones are relabeled Phons.
You start with 40 Phon being 1 Sone then double it every 10 Phon.

40 Phon = 1 Sone.
50 Phon = 2 Sones.
60 Phon = 4 Sones.
70 Phon = 8 Sones.
80 Phon = 16 Sones
90 Phon = 32 Sones
100 Phon = 64 Sones

(Hmm, thought that would be more complicated? It is – but that’s basically it in a nutshell.)

You will almost never see a phon or a sone. Bathroom exhaust fans and blowers are sometimes rated in Sones – to let you know how quiet they are… The problem is that no one actually knew how quiet that was until now!

I guess it sounds better to say –

2.5 Sones! Wow that's Quiet!

Quiet… Only 2.5 Sones!

“This bathroom fan operates at only 2.5 Sones!”

…Than it would be to say…

Quietish... Only loudish in frequencies you can't hear well. So it's not bad... Really.

Quietish… Only loudish in frequencies you can’t hear well. So it’s not bad… Really.

“This bathroom fan resonates at over 80dB,
but it’s in a frequency range that humans don’t hear very well,
so it sounds quieter than it actually is… no… really!”

Human perception of sound is very important to the development of acoustic products – Psycho-acoustics are not a joke.
(Why are you still laughing?)

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