1. ultrarunner2020's Avatar
    Hello;
    I have Moto G7 Optimo Maxx (Tracfone).
    I am considering a 'high-end' pair of wired IEM's to use with this phone.
    The IEM's have an impedance of 9.5 ohms. I was advised that in order to achieve the best sound from these IEM's, the source (headphone jack) impedance should be < 1 ohm.
    I doubt that the Optimo Maxx has such a low impedance, but would be interested to know what it is regardless.

    I have done many searches but come up empty.

    Anyone?
    Thanks
    Ultrarunner
    09-23-2021 03:32 PM
  2. Mooncatt's Avatar
    I won't claim to be an audio expert, but I've never heard of anyone being concerned with the impedance of the jack itself. That is just a solid electrical connection, meaning the impedance should be so low as to be virtually zero. In electronics, it's usually the load (speakers in this case) that determines the resistance.

    I'm curious who suggested this and why. If it was in an article, a link to it may be helpful. I'm wondering if you misunderstood something. I'd also be surprised if you find any info related to the jack impedance.
    09-23-2021 04:35 PM
  3. ultrarunner2020's Avatar
    Sorry, I should have used the correct term. What I am looking for is the output impedance of the headphone amp.
    09-23-2021 04:59 PM
  4. Mooncatt's Avatar
    Sorry, I should have used the correct term. What I am looking for is the output impedance of the headphone amp.
    Again, that doesn't make sense, as the amp only responds based on impedance. The higher the impedance, the lower the wattage it can output, though some headphone amps are designed to work with high impedance headphones. For example, the LG V-series phones can do this and will kick into high impedance mode if the headphones are over 50 ohm.

    That's why I asked if you had any links or extra info on where you got that suggestion. I think there is a misunderstanding going on, but I'm not sure what.

    In any case, I wouldn't worry much about it. Only the most discerning of audiophiles can pick up on those small details. Try them out and see if you like them and call it a day.
    Laura Knotek likes this.
    09-23-2021 05:06 PM
  5. ultrarunner2020's Avatar
    I have a pair of ATH-M50X with an impedance of 38 ohms, and a pair of Senn HD600's with an impedance of 300 ohms.
    The audio level from the phone is higher with the ATH than with the Senn's. That makes sense based on what you are telling me.
    So the much lower impedance of the Tri Starsea IEM's should produce higher audio levels... theoretically.

    I tried phoning Motorola earlier this evening. I actually spoke with a live person, but she couldn't give me any info at all.
    When I told her I wanted to speak with an engineer, she told me that they don't have any engineers...
    I guess I was speaking to one of those generic phone centers in India, so I wasn't really expecting to get any tech info.

    I could set up a test circuit with my oscilloscope and measure the audio level at different load Z, but that will take some time.
    In the meantime, I'll try to (re)educate myself on the relationship between source and load impedance in audio circuits to get a better understanding of what's going on and what to expect.
    09-23-2021 07:53 PM
  6. mustang7757's Avatar
    I have a pair of ATH-M50X with an impedance of 38 ohms, and a pair of Senn HD600's with an impedance of 300 ohms.
    The audio level from the phone is higher with the ATH than with the Senn's. That makes sense based on what you are telling me.
    So the much lower impedance of the Tri Starsea IEM's should produce higher audio levels... theoretically.

    I tried phoning Motorola earlier this evening. I actually spoke with a live person, but she couldn't give me any info at all.
    When I told her I wanted to speak with an engineer, she told me that they don't have any engineers...
    I guess I was speaking to one of those generic phone centers in India, so I wasn't really expecting to get any tech info.

    I could set up a test circuit with my oscilloscope and measure the audio level at different load Z, but that will take some time.
    In the meantime, I'll try to (re)educate myself on the relationship between source and load impedance in audio circuits to get a better understanding of what's going on and what to expect.
    Hi, curious what brand oscilloscope your using ? I use 2 for automotive a fluke and Pico but for different things CAN bus lines ,fuel injector duty cycle or fuel pump , ignition coil firing , static compression , cam and crank correlation,alternator ripples etc..i know for small circuit they use different oscilloscope you probably have 2 channel, mines 4 channel.
    09-23-2021 08:05 PM
  7. ultrarunner2020's Avatar
    I have a Siglent SDS 1104X-E 100MHz 4 channel scope.

    I found this very comprehensive discussion of audio impedance matching:
    https://www.headphonesty.com/2019/04...e-demystified/

    One thing I may be getting confused about is sensitivity. i was thinking that a higher number indicated less sensitivity, but that does not appear to be correct - according to this source. So sensitivity would be a measure of how loud the audio is when driven by some specific power?
    09-23-2021 08:20 PM
  8. Mooncatt's Avatar
    So sensitivity would be a measure of how loud the audio is when driven by some specific power?
    Correct, but don't confuse that with sound quality. You can have a high sensitivity speaker that is loud, but sounds like junk.
    09-23-2021 08:44 PM
  9. ultrarunner2020's Avatar
    I just watched a great YouTube vid showing a simple method of determining the output impedance of an audio amplifier. Simple enough. I should be able to get this done today. I haven't had the chance to do anything with my scope in a while, so it'll be fun.
    09-24-2021 08:09 AM

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