IEM testing jigs

Andrew Broughton

Andrew Broughton

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Feb 2, 2011
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On the old forum there was a thread regarding methods for testing custom moulded IEMs. Dave said he got some putty from UE, someone else was talking about a tube adapter and yet another person had a link for an apparatus, but the link is broken now. UE says they don't sell anything like that. The thread was from a while ago and doesn't have any additional information. So...

Has anyone purchased or built a jig that can measure frequency response on custom moulds? Just looking for something to allow tests of IEMs against a known pair or against themselves over time, not for absolute frequency response, but repeatable and consistent measurement.

Thanks!
 
Re: IEM testing jigs

UE has never sold the putty. Naoi gave it to us right before he left UE to go back and run Jerry's new lab. We no longer attempt to measure them, too much work for not enough reward. I run pink through them to hear if all the drivers are working by holding the mould next to my head. If there is an issue we send it back to the lab. We've stopped using UE as have many of the other shows on The Strip and have gone to JHA.
 
Re: IEM testing jigs

That might have been me. The basic jig (unscientific as it was) was a 35mm film can with the closed end drilled out to accommodate a measurement mic, and then a bit of silly putty wrapped around that assembly. I put a small piece of soft rolled foam in the tube leaving a hole down the center, and silly putty used to "seal" the earbud to the other end. I tried to position the capsule so it was about 1.25" from the open end of the can, so that with the putty on the end it was about the same length as the human ear canal. Certainly far from perfect, but it was interesting to see the results between a bunch of different earpieces and packs.
 

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Re: IEM testing jigs

I've used a short piece of Gas hose. Don't remember if it was 1/4", 5/16", or 3/8"...but it fit my Earthworks just right, and let me get a seal w/ the business end of the molds. Far from scientific, but workable.

Kevin H.
 
Re: IEM testing jigs

would something like this enable me to measure SPL from my IEM's at specific belt pack volume levels? i'm now wearing my iem's an average of about 6 hours a week for rehearsals and performances and expect to do so for many years to come. i'd love to be able to quantify what my SPL is over time so i can guard my hearing...
 
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.
 
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Re: IEM testing jigs

thank you for your response. great things to think about.

i think for my practical application, your idea of matching pink noise in an ambient field [i.e. from a speaker cabinet] with perceived pink coming out of my in-ears and then measuring that could totally work. what i need is a reference point since i control the levels of my mix directly. just so you know my situation, i'm a retired live sound guy that now works at a church as the creative director. so i play on stage with in-ears. i also have significant control over my situation. that is, if it's too loud on stage or in my in-ear mix, i have the ability to change that.

i do know that ringing and temporary hearing loss are warning signs. and i don't think i'm there, although i do experience what seems like a very low level ringing when i'm in a very quiet environment. what i was really looking for was a way to objectively measure what i'm experiencing on a weekly basis playing there so that i can manage my exposure. i intend to be doing this for at least another decade or more and i want to make sure that i'm not one of those 60 year old tinnitus sufferers. i was very careful with my hearing during my 20 years in the sound business, and i intend to keep being careful.

thanks again for the response. great ideas all....
 
Re: IEM testing jigs

George Friedman-Jimenez said:
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.
Click to expand...

I wonder if it would be possible to do an impedance sweep of the IEM while in the ear to try to determine how it is behaving?

Jason
 
Re: IEM testing jigs

I finally got around to trying to build something. It ended up being absurdly easy to get usable results, not high fidelity but plenty good enough for testing.

I took a scrap of plywood, and drilled a hole through same diameter as the Shure nozzle (1/8" drill bit), and redrilled most of the way through for the measurement mic (Earthworks M30, 9/32" drill bit). Stick the earbud into the small hole on one side, and the measurement mic into the other. It's a decently snug fit but not very tight.

Plug the earbuds into an iPod playing music, plug the measurement mic into a mixer with headphones. I had to turn the input channel bass knob all the way up to get decent lows, and of course it didn't sound especially flat. But it does work, and aside from futzing around finding the right drill bit sizes it took all of 5 minutes to make.
 
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