Explain why flat response sounds better than flat attenuation

When you research "flat attenuators" you will see that they are only flat in a small range in the middle frequencies. Carefully observe the far reaches of the bandwidth, and you will find very aggressive changes, steeply sloping drop-offs, to the frequencies above 6KHz (where musician's really need the signal).  Remember, middle C is approx 256Hz, and a good amount of the ensemble comes from the low frequencies.  

I have heard this phrase duplicated so often, that I don't think anybody gives it a second thought anymore…..

"flat-response attenuators have a frequency response that follows the shape of the natural frequency response of the open ear, but at a reduced level."

The phrase…."follows the shape of the natural frequency response of the open ear" is what I don't think makes any sense. It implies that at some point, someone graphed out the ear's natural resonance…..say at 65dB SPL (conversational level). So, it is being suggested that the shape of the ear canal response (resonance), at a 65dB SPL Input, produces a certain effect in the brain, a certain loudness across frequencies, which is the shape that all loud music should adhere to. Hmmm

This is where I get lost (if I haven't lost you already).  We all know that our ears are not linear. As we turn up the volume control, we become more sensitive to differing frequencies. Loudness Growth curves (Fletcher-Munson) right? Most audio engineers are still with me here.   A simple example here, as you raise the volume on your home stereo, don't you need to change the equalizer on the stereo to keep the sound "natural" or "pleasant" or "warm"?   It is clear that listening to music at a soft or normal level is much different than listening at a loud level.   

So, the assumption I am trying to verify (disprove) is:

         That "following the shape of the natural frequency response of the open ear," by measuring what sounds "normal" to the normal ear canal resonance and at normal speaking volumes, and keeping that shape for wide bandwidth composite signals such as music, and with the intensity of a loud environment will also sound normal.

Let me ask a basic, simple question….."If I liked the way things sounded with an open ear canal resonance…..why in the world would I need earplugs?" We need the earplugs EXACTLY for the reason that our open ear resonance does not sound good at loud inputs. It clips our uncomfortable limits at different frequencies, and at different intensities which do not match the open ear resonance. A flat attenuator could only make loud music sound normal, if the response curve of your discrete UCL's (uncomfortable level at each freq. ) matched the natural ear canal resonance AND we were attenuating enough to bring the SPLs below UCL. Input + Attenuation + Ear canal resonance = SPL at the eardrum.

I want my loud music to sound loud, just not hurt or cause damage. Loud music sounds different than conversational speech, and it sounds different at different levels. This probably has a lot to do with the amount of energy traveling through the skull via bone conduction, compared to what normally comes through. I suspect that a lot of headphone manufacturers put merit in the richness of bass due to bone conducted energy.  A little about this topic can be gleaned from a study done by NAL (National Acoustic Laboratories) in Australia, probably the leading research clinic in the world in regards to hearing instrument sciences.  NAL did a study, and nobody really knew what to do with the data once they discovered what they did not expect.   Simply placing an earplug in the ear, changes the wearers perception of the low frequency energy by an additional 10dB.   I'm not saying the earplug was a 10dB attenuator either.   I'm saying that the wearer thought they were being plugged up even more than they actually were, but this effect was only in the low frequencies.    Now my own experience with this phenomenon was as a young drummer, I used to put in earplugs, and then turn the volume up on my headphones as I practiced the drums to get back some of that richness.  After mentioning this to other drummers and musicians, I am surprised how many people have done this.   Put in earplugs, and then turn up the volume!    An earplug not designed with the musician in mind, is an earplug that will find its usefulness negated by the wearer, one way or the other.

Sure, we are trying to protect our hearing, but the physiological truth here is that the open canal resonance is not being "followed" at all. Once you have a resonating cavity, and you put in an earplug, especially if it begins to occupy the outer part of the ear, and the pinnae effect changes, your directional ability to locate sounds also changes. Most filters occupy the outer part of the ear, or at least block some sound to the pinnae.  Music is composite, and location cues are critical. I have seen studies that show musicians have a greater ability to locate in noise.  We can't take that for granted.  

I also don't understand how those triple flange filters "teach" sound to only go down the center of that tube where the filter is…..is that magic? I mean, what keeps sound from going around the filter / stick portion and entering the ear through the flanges?  Ok, I digress.

Again, how important is "following the ear canal resonance" when that resonance was designed for the primary benefit of amplifying speech, in particular speech between (1KHz-6KHz)? This is the unvoiced range of consonants…..eg…(whispering "shhhh, there's a bear over there."  Our ears weren't designed for the post industrial revolution Les Paul / Marshall stack of amps era. (My apologies to the Creator, as He must have had a plan for a better earplug….revealed below).

I humbly suggest, that comparing the natural ear response at conversational level, and saying that shape should yield an acceptable earplug at loud levels, is something we should reconsider. I just want everyone to think about this …. and understand that they have options if they don't like the customs or the stick in the ear style.

Certain multiple flange earplugs and filters (custom or generic) have had a great run, and they are far better than any foam plug or non-filtered device, as they will protect your hearing if properly inserted. Maybe this is a poor argument, but they have been available for nearly 20 years, and they have failed to achieve significant adoption rates, and that tells me something, as I personally know so many musicians that just decided to take their chances unprotected rather than wear them.

Different manufacturers can build them differently, with different depth both in the outer ear, and inside the canal, and that can have a huge effect on your $200 pair of custom plugs.   Even one in four people have such considerable jaw motion in their canal that will cause the earplugs to loosen or cause dull ear aches after a short while rendering them as part-time systems. Further, if you have particularly small ear canals, the air/mass parameters required by the nominal (standard) filter they put in your custom earmold, will not be sufficient to give you the flat response attenuation curve which they claim.  Realize, your filter is produced on a production line, and the custom plug is different from person to person.   They can only hope that your ear canal resonance was within the range expected to achieve the acoustic mass requirements of the entire system to achieve the results intended.   Whew….that's a mouthful.  

In closing, as I am arguing for a generally flat frequency response filter versus a flat attenuator. A flat frequency attenuating  filter may generally preserve the effects of the ear canals open response (disregarding location cues)…. BUT that is the beast we are trying to tame. We just don't need an 18dB "resonator" (the ears natural resonance / gain at 2700Hz) in a 93dB environment. We need it for the soft phonemes, not the Ramones! Earasers fix these problems - all of the ones mentioned above. Earasers are a flat frequency response earplug (not flat attenuator) and through our website, they come with a 100% money back guarantee which no other earplug will offer.   I wonder why?

Hears to you!