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| Measuring distorting Etymotic earphones with an osciloscope |
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| RBBVNL9:
This week, I got annoyed by my favourite Etymotic earphones starting to sound distorted in one channel. I decided to use my lab equipment to see to investigate that distortion in mode retail. In this video you see how I did that both on an R&S RTB and a Siglent SDS2k scope: After making the video, I realised that I also could have exploited the fact that the SDS can do two FTT analyses at once! To do so, I took two identical microphones (Røde M5) and treated them with the same mic pre-amp settings, then connecting them to channel 1 and channel 3 of the SDS scope (pic attached). The result shows that the 'good' channel (Orange trace, green FFT) has fewer unwanted harmonics than the 'bad' channel (yellow trace, pink FFT). The dual FFT of the SDS is clearly an advantage over scopes that can do one FFT at the time only ;-) Next step is to try the audio analyser on the CMU200 to investigate the distortion… And to see whether I can get it repaired, perhaps by compressed air, as someone suggested! |
| wasedadoc:
No need for FFTs to see that level of distortion. :) Are the headphones purely passive or do they contain some active electronics? |
| RBBVNL9:
--- Quote ---No need for FFTs to see that level of distortion. :) --- End quote --- Absolutely, the waveform already gives away that the headphones do not reproduce a proper sine wave. But I was interested to learn how the distortion my ears experienced translated into harmonic content. I found it surprising that even the 'good' earpiece had a fair amount of harmonic distortion, but mostly uneven. Want to dig a bit more into that. --- Quote ---Are the headphones purely passive or do they contain some active electronics? --- End quote --- They are passive and have a single driver. After these Etymotic ER4 were introduced in the 1990s, many other brands followed with in-ear models, some single-driver and some multi-driver designs. But for me, as an former live sound engineer, the Etymotics always remained among my favourites! They always ship with individual frequency response graphs for the left and right earpieces you bought. Very nice. |
| switchabl:
--- Quote from: RBBVNL9 on February 18, 2023, 12:36:44 pm ---I found it surprising that even the 'good' earpiece had a fair amount of harmonic distortion, but mostly uneven. Want to dig a bit more into that. --- End quote --- I am not sure that you should draw any quantitative conclusions from this setup. The drivers are tiny and are meant to go into a sealed ear canal. I believe that if you place them in free space, radiation efficiency increases with frequency (something like 6 dB/octave, even though the proximity effect of the cardioid mics may offset this to some degree), so there will be a large emphasis on the harmonics. That's my understanding at least, I mean, after all acoustics is just a kind of scalar EM. >:D |
| tooki:
--- Quote from: RBBVNL9 on February 18, 2023, 11:22:35 am ---This week, I got annoyed by my favourite Etymotic earphones starting to sound distorted in one channel. I decided to use my lab equipment to see to investigate that distortion in mode retail. --- End quote --- Mode retail?? Anyway, do you not see the earwax filter sticking out of the lower one? I’d start there… |
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