IM Distortion, Speakers and the Death of Science


One topic that often comes up is perception vs. measurements.

"If you can't measure it with common, existing measurements it isn't real."

This idea is and always will be flawed. Mind you, maybe what you perceive is not worth $1, but this is not how science works. I'm reminded of how many doctors and scientists fought against modernizing polio interventions, and how only recently did the treatment for stomach ulcers change radically due to the curiosity of a pair of forensic scientists.

Perception precedes measurement.  In between perception and measurement is (always) transference to visual data.  Lets take an example.

You are working on phone technology shortly after Bell invents the telephone. You hear one type of transducer sounds better than another.  Why is that?  Well, you have to figure out some way to see it (literally), via a scope, a charting pen, something that tells you in an objective way why they are different, that allows you to set a standard or goal and move towards it.

This person probably did not set out to measure all possible things. Maybe the first thing they decide to measure is distortion, or perhaps frequency response. After visualizing the raw data the scientist then has to decide what the units are, and how to express differences. Lets say it is distortion. In theory, there could have been a lot of different ways to measure distortion.  Such as Vrms - Vrms (expected) /Hz. Depending on the engineer's need at the time, that might have been a perfectly valid way to measure the output.

But here's the issue. This may work for this engineer solving this time, and we may even add it to the cannon of common measurements, but we are by no means done.

So, when exactly are we done?? At 1? 2? 5?  30?  The answer is we are not.  There are several common measurements for speakers for instance which I believe should be done more by reviewers:

- Compression
- Intermodulation ( IM ) Distortion
- Distortion

and yet, we do not. IM distortion is kind of interesting because I had heard about it before from M&K's literature, but it reappeared for me in the blog of Roger Russel ( http://www.roger-russell.com ) formerly from McIntosh. I can't find the blog post, but apparently they used IM distortion measurements to compare the audibility of woofer changes quite successfully.

Here's a great example of a new measurement being used and attributed to a sonic characteristic. Imagine the before and after.  Before using IM, maybe only distortion would have been used. They were of course measuring impedance and frequency response, and simple harmonic distortion, but Roger and his partner could hear something different not expressed in these measurements, so, they invent the use of it here. That invention is, in my mind, actual audio science.

The opposite of science would have been to say "frequency, impedance, and distortion" are the 3 characteristics which are audible, forever. Nelson pass working with the distortion profile, comparing the audible results and saying "this is an important feature" is also science. He's throwing out the normal distortion ratings and creating a whole new set of target behavior based on his experiments.  Given the market acceptance of his very expensive products I'd say he's been damn good at this.

What is my point to all of this?  Measurements in the consumer literature have become complacent. We've become far too willing to accept the limits of measurements from the 1980's and fail to develop new standard ways of testing. As a result of this we have devolved into camps who say that 1980's measures are all we need, those who eschew measurements and very little being done to show us new ways of looking at complex behaviors. Some areas where I believe measurements should be improved:

  • The effects of vibration on ss equipment
  • Capacitor technology
  • Interaction of linear amps with cables and speaker impedance.

We have become far too happy with this stale condition, and, for the consumers, science is dead.
erik_squires
I never said measurements were arbitrary:

https://www.merriam-webster.com/dictionary/arbitrary

I said they are created by necessity to meet a specific need, as opposed to measuring everything humans can hear in all cases.

To reiterate:

What is my point to all of this? Measurements in the consumer literature have become complacent.

Erik wrote: "Don’t focus on distortion. Focus on us in consumer land (albeit educated consumer) having a limited number of measures and assuming we can’t have or use more."

I am confused.

Can you restate what you are looking for? I’m sure it’s clear to you, but I am not getting it. Are you looking for a plain-English translation of what a designer focuses on? 

Duke
@audiokinesis

The point was that we talk about a handful of measurements as if they were all we needed and all we should ever have, and we call this science.

It isn’t. It’s not science unless we are getting better and better at inventing measurements which reflect human perception. We cannot know from an (used correctly) arbitrary count of measurements everything about how we perceive it.

Imagine if as Bell’s assistant, I said "amplitude at 1 kHz is everything and all humans can perceive."

Well, clearly that’s not what we consider adequate, but it might be enough at this time in history when I’m trying to pick among 4 different diaphragm types.

The types of measurements we are using was not my complaint, it’s that we are happy with what we have.  From Bell's time to the 1970s/ 1980s the popular literature and the hobbyist expanded what we think of as the basic measurement suite.  When and why did it stop?

Best,

E
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@heaudio123

With all the advancements in compute, storage and data collection technology you'd think we could see many more dynamic tests being done, but in fact they are quite rare.

Best,

E