I recently ordered a pair of ER20 "high fidelity plugs" from Etymotic, a universal-fit, low-cost option ($12.95) that the company claims to reduce sound by approximately 20dB in all frequencies. Have you ever tried them? I have also ordered a pair of custom-fit sleeves for my ER4s from ACS Custom. (When I was in the US, I went to an audiologist for my ear-canal impressions.) Because I had my impressions taken, I can also order a pair of custom-fit plugs with filters. However, they are more expensive ($185). Do you recommend the custom-fit ones?
Glad you enjoy the podcast! And I applaud you for protecting your hearing; I wish more people would do so. Sensitivity to loud sounds such as yours can be an unfortunate result of exposure to high sound-pressure levels called hyperacusis. Another potential result of such exposure is temporary or permanent ringing in the ears, technically called tinnitus.
I absolutely recommend custom-fit earplugs if you can afford them, but you're right, they are very expensive. When you add the cost of having an audiologist make the molds and the cost of creating earplugs from those molds, you're talking about several hundred dollars.
I use a pair of custom-fit plugs made by a company called Sensaphonics, which I chose because it uses a more durable material than that used by most other companies I've seen. As with most custom-fit plugs, mine accommodate interchangeable Etymotic filters (the round blue part in the photo of a custom-fit earplug above) that attenuate sound by different amounts; I use the filters with maximum attenuation, which is 25dB across the frequency spectrum.
I believe that custom-fit plugs provide better protection than universal-fit models because they form a more complete seal. Also, they exert greater control over the sound, so the attenuation can be flatter across the frequency spectrum, resulting in better fidelity. However, no earplugs are perfectly flat, since they can do nothing about bone conduction, which acts like a lowpass filter, allowing low frequencies to enter the inner ear more than higher frequencies.
If you can't afford custom-fit plugs, by all means use universal-fit onessomething is better than nothing! And the Etymotic ER20s are far better than the cheap foam plugs you can get at any drugstore, as I have verified myself.
I haven't tried using custom-fit in-ear monitors as earplugs, but I would think it might be somewhat inconvenient to have the wires dangling from them. Plus, I don't know if they provide as much protection as earplugs.
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