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IEM testing jigs
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<blockquote data-quote="George Friedman-Jimenez" data-source="post: 41077" data-attributes="member: 1115"><p>Re: IEM testing jigs</p><p></p><p>I am skeptical about the validity of frequency response measurements of IEMs, and therefore about SPL measurements. The FR of an IEM depends a lot on the very individual geometry of the external ear canal of the user and the seal and fit of the IEM, not just on the IEM hardware itself. The unobstructed external ear canal, which is about an inch long, acts as a bandpass amplifier with resonance around 3,000 Hz and gains have been reported on the order of 10-20 dB relative to other frequencies below 400 Hz and above 9,000 Hz. The resonance frequency and magnitude depends on the length, volume and specific geometry of the external ear canal. The IEM massively changes all of these, and compensates to some degree by having a complementary frequency response that gives a (very roughly) flat overall system response of the external ear canal with the IEM inserted. Seal of the IEM, and geometry of its internal canals, are additional factors that can affect the resonant frequencies and resultant SPLs at given frequencies. </p><p></p><p>I certainly support your interest in limiting the potential for the IEM to cause hearing damage. Given the variables I just mentioned, rather than try to measure SPLs inside the external ear canal with the IEMs in place, you may be able to approach the problem in several ways.</p><p></p><p>1) Try to set up an approximate subjective SPL scale by matching perceived loudness of pink noise or music using the IEM at a given setting and perceived loudness at a measured acceptable SPL (eg, 85, 90 or 95 dBA depending on expected duration) during sound check in your venue.</p><p>2) If you experience ringing in your ears or seem to have any hearing loss after the event, the SPL was too high and SPL or duration needs to be reduced in future events. You can actually get tested for temporary threshold shift by getting your hearing threshold measured before and after an event, as an objective aid to confirm or rule out a temporary shift in your hearing threshold that would predict permanent hearing loss. There are approximate do-it-yourself hearing tests available that can give you a very rough relative measure of your hearing threshold at standard frequencies, which you can do and compare before and after an event.</p><p>3) Regardless of whether you do your own hearing testing or not, I recommend regular hearing tests by a knowledgeable audiologist in your area, and occasional consultation with an ear, nose and throat specialist with interest and expertise in prevention of noise/music induced hearing loss. This is yet another reason to try to get health benefits from your union or employer, although paying out of pocket for many consultations over your lifetime would still cost less than paying for one set of hearing aids later in life.</p></blockquote><p></p>
[QUOTE="George Friedman-Jimenez, post: 41077, member: 1115"] Re: IEM testing jigs I am skeptical about the validity of frequency response measurements of IEMs, and therefore about SPL measurements. The FR of an IEM depends a lot on the very individual geometry of the external ear canal of the user and the seal and fit of the IEM, not just on the IEM hardware itself. The unobstructed external ear canal, which is about an inch long, acts as a bandpass amplifier with resonance around 3,000 Hz and gains have been reported on the order of 10-20 dB relative to other frequencies below 400 Hz and above 9,000 Hz. The resonance frequency and magnitude depends on the length, volume and specific geometry of the external ear canal. The IEM massively changes all of these, and compensates to some degree by having a complementary frequency response that gives a (very roughly) flat overall system response of the external ear canal with the IEM inserted. Seal of the IEM, and geometry of its internal canals, are additional factors that can affect the resonant frequencies and resultant SPLs at given frequencies. I certainly support your interest in limiting the potential for the IEM to cause hearing damage. Given the variables I just mentioned, rather than try to measure SPLs inside the external ear canal with the IEMs in place, you may be able to approach the problem in several ways. 1) Try to set up an approximate subjective SPL scale by matching perceived loudness of pink noise or music using the IEM at a given setting and perceived loudness at a measured acceptable SPL (eg, 85, 90 or 95 dBA depending on expected duration) during sound check in your venue. 2) If you experience ringing in your ears or seem to have any hearing loss after the event, the SPL was too high and SPL or duration needs to be reduced in future events. You can actually get tested for temporary threshold shift by getting your hearing threshold measured before and after an event, as an objective aid to confirm or rule out a temporary shift in your hearing threshold that would predict permanent hearing loss. There are approximate do-it-yourself hearing tests available that can give you a very rough relative measure of your hearing threshold at standard frequencies, which you can do and compare before and after an event. 3) Regardless of whether you do your own hearing testing or not, I recommend regular hearing tests by a knowledgeable audiologist in your area, and occasional consultation with an ear, nose and throat specialist with interest and expertise in prevention of noise/music induced hearing loss. This is yet another reason to try to get health benefits from your union or employer, although paying out of pocket for many consultations over your lifetime would still cost less than paying for one set of hearing aids later in life. [/QUOTE]
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