I was still thinking about bass extension some time after I published Saturdays blog on how much bass is enough bass. The question occurred to me that while many of us audiophiles are in a relentless pursuit of a flat response curve, what actually happens once the music hits our ears and then more interestingly our brains.
And much like our individual perception of the color red really has no particular fundamental relationship to the frequency at which photons oscillate as they hit our retina, a sound as we hear it, really is just a metaphor our brains create to give us useful or even enjoyable clues about what´s going on in the real world. In fact I would be hard pressed to know if I would still recognize a, say, violin, if I heard it the way another human being might. I certainly can´t prove that your color red looks like mine.
Now this has of course been studied to a considerable degree and the interesting piece I came across was on the very particular topic of percieved loudness.
There are, you see, people who study the perception, note, not the physical energy of loudness and these people have long published something called “equal loudness contours”. These are plot lines of actual loudness for different frequencies along which people tend to hear sound at a similar loudness.
So there it was: The human brain is not flat at all. There is vastly more Sound pressure required for any of us to hear a 20Hz rumble as loud as we hear a 1000Hz ping. Several orders of magnitudes more, in fact.
Now given the outright tiny size of our eardrums, this may hardly be surprising, what was however intriguing to me is that if human hearing is so completely nonlinear, why do we audiophiles obsess relentlessly about the flatness of a particular response?
The easy answer is of course, because that is how we are used to hearing in the real world. But are we? When studying this topic deeper, I found the opposite to be just as true: we hear and interpret things with a strong bias to what is physically possible in the world of physics, and just how optical illusion rely on our brains preference to see the world in a way that makes sense to us, acoustical illusions are just as much of a possibility.
MP3 compression, for example, is built on such acoustical illusion, where two tones can be replaced by one single tone through a phenomenon called auditory masking, thus reducing the amount of data immensely. Now you can think of MP3 what you like, but the fact that it works as well as it does, actually does seem remarkable given the gross reduction of actual sound.
One other phenomenon that I became particularly fond of, is that of phantom frequencies also known as “missing fundamentals”. The human brain, you see is not one to easily accept the outright impossible and always prefers interpretations of sound that relate back to something we have learnt to be real. So say there are overtones that could only be generated by also generating a fundamental note, we can remove the fundamental and our brain will simply invent it back for us, not only that, in many cases it will also create the subfundamentals.
This is something that is very inherently used in those tiny loudspeakers and Bluetooth radios that surround us these days, which simply cannot produce the fundamental frequencies of a lower, pitched musical instruments. Such fundamentals are completely eliminated and our brains come to the admittedly partial rescue by substituting by perception what´s los in reality.
So what does that all mean for someone like me who builds loudspeakers for a living? Well thinking back on Saturday´s Blog on Bass, it became clear that if the brain can invent fundamental frequencies out of mid air, it can certainly also bring to life fundamentals that are in fact there albeit at a slightly lower loudness than one might consider ideal.
So for those willing to compromise a little on size and bass extension for the benefit good Spouse Acceptability Factor, a precise sound stage and great stereo imaging, a smooth bass roll off like the one found on a well designed quarter wave like our SoundSommeliers, is almost more important than a flat base response at the price of all entails in terms of price, complexity and size. This is because of our brains bias to invent the fundamentals and subharmonics that happen down below in the basses and even if they are not at full sound pressure level with the rest of the frequency range, as long as there is something and its congruent with the overtones, our brains will do their magic to make things sound the way they should.
Unfortunately many speaker designers are now looking too much at the overall lowest frequency they can express as an important marketing parameter that customers understand, and by tuning a normal bass reflex design too agressively, a dominant frequency is created that is then not in harmony with its overtone. This is a dreaded phenomenon called one note bass and it can really mess with our brains.
Now there is of course a place for everything and if a flat response down to 20HZ is your thing then that´s a wonderful technical challenge to strive for. Consider, however, that by the time the sound passes the pinna, tickles your eardrum and sends signals up your auditory nerve and on to your auditory cortex to create your particular perceptual metaphor of rising and falling air pressure around you, consider that by that time, all flatness is merely an idea. Or as aptly put it in his song "Consider me Gone": "To look for perfection is all very well, but searching for heaven is to live here in hell."