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In Reply to: RE: Just how sensitve is our hearing? posted by PaulF70 on March 07, 2025 at 08:31:13
What do we hear with our ears?
The reason you rarely if ever see distortion spec's for loudspeakers is because that would not help sell them, in light of the numbers people are used to seeing with electronics.
Also, many had noticed that a measurement like THD may or may not indicate how it sounds.
It was pretty good when all there was were tube amps that behaved similarly, not so now.
The reason is we measure the entire range equally because with instrumentation that is easy. You don't want any preferred or shunned frequencies haha, same for a loudspeaker.
Examine the ear's equal loudness curve, if you are used to a "frequency response curve", invert that equal loudness curve shape and now you have a hearing sensitivity curve, that's the shape of it's frequency response..
Your ears ARE NOT flat in sensitivity. There are several ramifications to this;
Examining the curves again, you will notice that at 20Hz, it takes about 75-80dB SPL to reach the threshold of audibility while around 4KHz, around 0dB is the threshold.
What Dolby labs discovered in an early paper was given that sloped curve, that at the threshold of audibility at 20Hz, the 3rd harmonic of only 7% had an equal perceived loudness as the 20Hz signal.
One conclusion was there is no practical way to make a subwoofer with inaudible distortion.
Looking at the hearing curve inverted, one can see that when harmonics fall in the 3-4KHz range, that is where your ears are most sensitive to distortion. This is why at work with the Unity and Synergy horns I put an acoustic low pass filter between the mid range drivers and the horn throat. That attenuates the distortion above crossover that the drivers produce and would fall in that most sensitive range.
Why do loudspeakers sound bright, gritty etc when driven hard? ALL the distortion components add content 1,2,3,4etc octaves above the original signal.
Ok, this part was simple, the next part reminds me of what one of my audio hero's, the late Dick Heyser once said something like "we measure what we do because we can, not because these are the most revealing of what we are investigating". So many questions i would ask him now.
So actually a lot is known about how our ears work but it is the image painted by the kinds of measurements we can do and some of these show unexpected behavior, like how the ears shape and pinna responses were the missing detail of how we localize sound..
Doug Jones, former co-worker was one of the team that discovered these what look like flaws, position dependent notches in our hearing and then went on to make the LEDR recordings demonstrating these effects.
So far as distortion itself, an unexpected thing is called "perceptual masking" and this is the idea behind data compression, various degrees of don't count what you can't hear (easily).
Our hearing is apparently divided up into segments about 1/6 octave wide (called a Bark) and what one finds is that IF one has a single tone, that on either side of that tone is an area "masked off" or that you can't detect a second tone in that area until it's above this masking level.
Also, the even harmonics are musically related and in the recording process, it was either the white album or Abby road where they intentionally (new circuitry) added distortion to enrich parts.
A figure i remember was that a 2nd harmonic was inaudible as a flaw with music up to around 30% but with organic / natural sounds (not harmonic sounds ) that it was audible at around half that level.
An over driven woofer, maybe most drivers produce a 3rd harmonic the strongest and a familiar sound.
And then there is the top side of the sensitivity curve.
The falling hf sensitivity is why (in % numbers) we are comparatively insensitive to high frequency distortion. You can hear 20KHz and higher, it depends on how loud it is and if there is any other sound that masks it AND how far away you are as depending on temp and humidity 20KHz can be absorbed surprisingly fast by the air itself.
I find this to be an especially interesting area to investigate so if inclined, google some of these things.
Distortion measurements would help sell the speakers I listen to - Quad 63/988/2805s - because, at ~.1% across the audioband, the only dynamic speakers that can compete cost around ten times their price.
(And anyone can get a good used pair for ~$2,000.)
Mr. Servo
Your response reminded me of an astonishingly spec'd 0.009 THD preamplifier produced during the mid 70's solid state audio spec olympics by a highly regarded company.
The preamplifier had a variable Bass Contour control that offered me another level of welcome subwoofer control.
While I didn't doubt the companies THD figure the preamps overall presentation seemed overly sterile. Not necessarily a bad thing in the world of audio but as a Bassist a little dirt in the sauce seemed to be missing.
Great response, thanks.
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