TechSpot

Significance of impedance in headphones?

By macx
Oct 20, 2006
Topic Status:
Not open for further replies.
  1. Sent for a set of Sennheiser 280HD Pro headphones,
    came in today.

    Discovered on reading the manual that these are
    300 ohms impedance while the "normal" seems to
    be 64 ohms.

    What's the significance, what if anything will this do
    to the functionality?

    Can I use them with my Win XP and with my tv?

    This little item wasn't mentioned in the advertisement.
    Did I get sold something I can't use?

    BTW - my tv doesn't have a typical jack to receive the
    small plug - nor does my VCR. How to hook them up?

    Thanks!
  2. Rick

    Rick TechSpot Staff Posts: 6,304   +52 Staff Member

    Think of impedance as an item's ability to resist electrical current. This resistance is measured in ohms.

    In devices that deal with high frequencies, impedance mismatch can destroy electrical devices. For analog audio, I'm not sure what the immediate or long term effects would be for that difference in ohms.

    You see, analog audio uses relatively low wavelengths so I'm sure the headphones aren't going to melt your computer, headphones or your TV. You may receive a noticeable reduction in audio quality though, due something called reflection. Reflection is a result of the differences in ohms between connected devices. For audio equipment, it might present itself as a faint echo (ghosting) effect or other sound artifacts which could be pretty annoying. :)

    Your TV probably has a composite audio out/in. Look for male composite to female headphone jack adapters.
  3. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 25,948   +19

    The difference between 64ohm and 300ohm headphones is the volume will be slightly lower at any given volume setting at 300ohms than it would be at 64ohms. This is because 300 ohms has more resistance than 64 ohms and thus 300 ohms resists more current than does 64 ohms.

    This shouldn`t cause any significant problems and may actually be a good thing, Since there is less load on the amplifier, it is less likely to clip(distort).

    Higher grade headphones tend to have higher ohms. Your headphones are typical of the pro series of headphones.

    Your Sennheiser 280HD Pro headphones, are very good and should give you good quality sound, obviously depending on the source.

    I don`t think you`ve anything to worry about.

    Regards Howard :)
  4. jobeard

    jobeard TS Ambassador Posts: 13,412   +316

    the power equation for 100% efficiency is
    Pout (the amplifier) = Pin (the speaker-headphone)
    E = IR and P = EI, so P also = I^2*R
    equal impedance devices will transfer maximum power
    and a mismatch of R(impedance) will reduce Pin (perspective of the speaker/output device) by R1/R2.

    64/300 says you will have 21.3 % power delivered

    Understand, sound volume is measure in dB, not power or voltage -- so
    your volume will be 'lower', noticeable, but not 'massive'. the human ear can
    only detect changes > +-3dB
  5. macx

    macx TS Maniac Topic Starter Posts: 743

    OK! Thanks for the lesson.

    Just got them hooked up, I guess they sound pretty good.

    Surprisingly, though, not detectably better than my ~$20
    (or maybe less) old Labtec phones, at least to my ears.

    Listening to the same music, the cheapies actually seem to
    have slightly better "presence" in the mid range.

    (I'm "tuning" with Soundmax on XP and with an Asus board
    model something like PC400E Deluxe (don't remember exactly),
    2.8 Northwoods, etc.)

    Anyway, might that be related to the impedance thing, or are
    my ears just that bad?

    In other words, do you think the 64 imp. phones would sound
    appreciably better at moderate volume?

    Thanks again
  6. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 25,948   +19

    No, I don`t think the 64ohm version would sound any better, just slightly louder.

    Like I said earlier the quality you get depends on the quality of the source. That means the music files themselves and the quality of your soundcard. Onboard sound isn`t noted for it`s hifi quality, when compared to some separate soundcards.

    Regards Howard :)
  7. macx

    macx TS Maniac Topic Starter Posts: 743

    Well, at least that's a relief to a point.

    Didn't relish the thought of going thru a battle
    with the seller.

    Have plenty of volume, so - -.

    Anyway, next piece of information - what's a good
    Soundcard?

    Got the phones, might as well have the rest of the pieces!

    Thanks!
  8. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 25,948   +19

    That would depend on your budget. In any case I`m probably not the best person to advise you, this is because I use onboard sound. However, if I were to think about getting a good quality sound card, I think it`d be something like this.

    Regards Howard :)
  9. YosefM

    YosefM TS Rookie Posts: 66

    Been a while since I knew this, so please correct me if I'm wrong.
    64 OHM is normal for an analog headphone output on a consumer device, while 300 is normal for the monitor headphone out on mixers and other pro audio gear. If you really feel the need for best quality, you can hook an impedence matching device (in this case it would actually be a post-amp) in between, but as long as you're hooking a higher impedence device to a lower impedence output, there should be no problem. Hooking a high inpedence mic or instrument to a lower impedence line-in jack would require at least the impedence matching preamp.

    As for why the difference - doesn't higher impedence result in greater resistance to attenuation from cable length?

    As for soundcard - my situation is gaming in the living room. No room for the surround speakers, and no wish to compete with the other entertainment in the room. I also wanted to keep the 2.1 onboard sound running through my GuitarPort. I bought the USB Mentor surround headphones. Since the headphones are the sound card, I've eliminated looking for one.

    My recommendations for a sound card depend on the desired use, X-Fi Fatal1ty for gaming only, or AuzenTech XPlosion 7.1 if usage is for HT & gaming. The other X-Fi models have issues switching from gaming to entertainment modes.
  10. krismeister

    krismeister TS Rookie Posts: 25

    http://www.creative.com/products/welcome.asp?category=1
    For me creative is the only manufacturer to consider for audio cards.

    Like Yosef said if you play games and have the budget get the X-Fi fatal1ty.

    Too bad you didn't feel there was much difference from your old headphones, those Sennheiser are ultra sweet. You should test with a DVD, especially if you have PowerDVD or another player which has 5.1/7.1 simulation for headphones. The nice thing about DVD's or games is the sound is 24bit audio, while CD's are 16bit.
  11. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 7,286   +24

    Try this sound card. It's a great one for the price and Diamond are a good company when it comes to sound. Creative are best I know, but quite a bit more pricey, especially when u compare this particular Diamond model against a similar Creative one.
     
  12. N3051M

    N3051M TS Rookie Posts: 2,800

    I think i'll drop in now :D
    The reason why you're not hearing much difference is dependant on 3 things:
    1) The source sound/device (ie soundcard, player)
    2) the music/sound and how its recorded. eg: Good CD/DVD quality sound verses one recorded using a cheap dictaphone etc.
    3) The speakers/headphones itself. The sennheiser headphones are top quality and most likely have a much more broader range of frequency it can reproduce than your old one, (eg my HD215 is 12Hz-22KHz) cheaper ones probably only in the 22Hz - 20KHz (average human hearing). Thats probably why you're getting a better mid range (800Hz to 1.2KHz) response, since the cheap one's working with less range. Some pro audio heaphones (your's is probably classified in this area) try to replicate a "true" sound by giving it a more flat EQ response. But note all these can be changed with a bit of a EQ adjustment on your media player :)

    i think you got this bit already....

    Impedance/Ohms i guess everyone's covered it.. it doesn't hurt your gear by using one or the other, just that you have to remember to turn the volume or amp down a bit if your using the consumer stuff or you'll blow it, pro stuff can take a good beating (electrical wise to a point, but it doesn't mean you can just mistreat it) before they blow.

    BTW.. wouldn't 300Ohms need a lot more juice to run than 64Ohms?

    Creative X-Fi series are pretty good consumer/amature recording level gear, i'd reckon 100x if not more better than onboard sound. If you can't afford the X-Fi, then the Audigy series are better than nothing, and since they're the older series to creative you may find some on the bargain bins at the shops maybe.. although older they're still pretty good. You can get the internal modules or external module sets with both Audigy and X-Fi series, depends what you want and how much $$ you got..

    i think this has more to do with how the speaker's made (the coil & magnet that drives the speakers back and forth) and the energy it needs to create that sound rather than the cable (even if length of cable does add some resistance to signal going through). I'm not 100% sure and i can't remember (memory blank :|).

    If you want to go pro audio cards, there are some.. but i think its gonna be pure overkill for you :D
  13. jobeard

    jobeard TS Ambassador Posts: 13,412   +316

    the 'weak link' in all systems are the transducers on inputs ;
    eg: a microphone, tape head, phonograph pickup ---
    and the output device; eg: the headphone or speaker system

    the subjective 'quality' is actually the frequency response of the device --
    how faithful is the signal reproduced (ie fidelity). when shop for output devices
    in particular, you first attempt to match the impedance of the device to that
    of the amplifier; then you *pay* for the frequency response curve you 'believe' you need.
    sound is a goofy subject -- the actual information content is in the 100-400 cps,
    but the low(10-100) and high ends (400-17k cps) adds all the color and
    harmonics that allow you to tell the difference between a horn, clarinet,
    violin and the human voice.

    btw: hi power in the 10-100cps range is where hearing losses are generated,
    not hi power in the highend.
  14. jobeard

    jobeard TS Ambassador Posts: 13,412   +316

    per the equations above, yes, the amplifier would need more
    output to create the same volume level

    cable length and wire guage size would only be important in a commercial
    application where they drive very large speakers for hugh room volume --
    eg: auditoriums, movie theaters. for any reasonable length, the impedance
    of the wire is nil.

    a speaker is a CURRENT driven device; current in the voice coil in the presence
    of a (strong) magnet creates the motion of the cone -- more current - more motion.

    the boom-box boys that buy 800w amps and wire their cars with a trunk full
    off bass speakers are only obliterating their own hearing --
    I can drive you out of a room with less than 100w of amp power and have
    cables no bigger that an A/C line cord! a fool and his money are easily parted :knock:
  15. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 7,286   +24

    Hey, enough of the tech talk already! :D
  16. jobeard

    jobeard TS Ambassador Posts: 13,412   +316

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