Too Low Impedance?
Mar 7, 2006 at 4:03 AM Thread Starter Post #1 of 9

DarkLongboarder

New Head-Fier
Joined
Mar 7, 2006
Posts
1
Likes
0
Is it possible for headphones to have an impedance that is too low for my mp3 player. In the manual for my Toshiba Gigabeat under "Headphone jack" it states a load impedance of 16 Ohms, it doesn't say if it is a minimum or the impedance of the stock earbuds or what. I'm planning on buying some Ultimate Ears Super.fi 3 that have an impedance of 13 Ohms. I know from my experiences with car audio that running amps below their rated impedance is bad, is it the same deal with mp3 player's amps?
 
Mar 7, 2006 at 4:16 AM Post #2 of 9

TheSloth

Headphoneus Supremus
Joined
Aug 3, 2005
Posts
2,377
Likes
13
The chance of damaging either the amp or the headphones is rather slim, however a very low impedence headphone is very difficult to drive. I know specifically for the iPod for example that the bass from 50hz begins to roll of very significantly as the impedence decreases from 32ohms.

It will work fine, however you will not be getting the best out of it. Problem is, if you add a relatively inexpensive 'portable' amp to go with it, you'll have to put up with quite a lot of hiss.
 
Mar 7, 2006 at 5:14 AM Post #3 of 9

Gino

500+ Head-Fier
Joined
Apr 2, 2003
Posts
515
Likes
44
I need enlightenment too. My Sennheiser Px200 (32ohms) can be driven well by my Cmoy amp. My Altec IM716 (16ohms) however gets distorted. I have tried this on two Cmoys built by different people and there is still distortion.
 
Mar 7, 2006 at 7:01 AM Post #4 of 9

MonkeyA**Sucka

Head-Fier
Joined
Feb 25, 2006
Posts
55
Likes
0
Mar 7, 2006 at 7:23 AM Post #5 of 9

jSatch

500+ Head-Fier
Joined
Dec 30, 2005
Posts
701
Likes
10
As per TheSloth, lower impedances can cause a more rapid roll-off at low frequencies. He observes a noticeable roll off below 50 Hz at earphone impedances below 32 Ohms. Good ears! At the other end, lower impedance equates, for the most part, with lower resistance. Thus, the phones may sound louder, but may also exhibit hiss if the impedance drops too low. Simply adding a volume potentiometer (eg, from Radio Shack) should increase the impedance a bit and reduce the hiss a bit. The Ety ER4S is approx 100 Ohms, and was originally designed for home stereo systems, not portables. The ER4P, for portables, is approx 27 Ohms.

Unfortunately things are not so simple. Impedances are not static, but can vary across the frequency spectrum. Phase will generally vary inversely to impedance. Crossovers will also impact these parameters, usually negatively.

As per the iM716, I wish it were 16 Ohms, like the Ety ER6i. They’d be a bit more sensitive. I measured the DC impedance of the iM716 at approximately 68 and 37 Ohms at HD and Bass modes, respectively. These values were confirmed by kwkarth. The impression has been that the difference between the HD and Bass modes is simply moving a set of resisters in or out of line. The paradigm for this concept is based on the Ety ER4P (27 Ohms) to ER4S (100 Ohms) converter simply being the addition of a set of resistors in-line.
 
Mar 7, 2006 at 7:27 AM Post #6 of 9

jSatch

500+ Head-Fier
Joined
Dec 30, 2005
Posts
701
Likes
10
Quote:

Originally Posted by MonkeyA**Sucka
jSatch measured the DC resistance of the iM716 as 68 Ohms in HD mode and 37 Ohms in Bass mode.

http://www6.head-fi.org/forums/showp...&postcount=186




Sorry for repeating the info you posted MonkeyA**Sucka. I got sidetracked watching Jon Stewart/The Daily Show (repeat, drat!) before submitting post.
580smile.gif
 
Mar 7, 2006 at 8:47 AM Post #8 of 9

fewtch

Headphoneus Supremus
Joined
Jul 23, 2003
Posts
9,559
Likes
31
Quote:

Originally Posted by Gino
I must have read wrong. Thanks for the new figures. And what would the relationship of impedance to the distortion I am experiencing on the Cmoy?


Cmoys are unbuffered and thus better for high impedance cans IMO... depends on how well the chosen opamp is capable of directly driving headphones (most are not especially good). Using a very low gain (like 2 or less) should cut down on hiss with high sensitivity cans.
 
Mar 7, 2006 at 7:30 PM Post #9 of 9

jSatch

500+ Head-Fier
Joined
Dec 30, 2005
Posts
701
Likes
10
Quote:

Originally Posted by Gino
I must have read wrong. Thanks for the new figures.



Gino, the 16 Ohm figure was originally given by PCMag.com, along with their reviews of the iM716 and iM616. Maybe you saw it there. I think this was a misprint and that the iM616, purportedly based on the ER6i, may be 16 Ohms. The iM616 is reported to be easier to drive than the iM716, so it makes sense that this may have been mixed up.

Don't know what a Cmoy is, fortunately fewtch does. Is the distortion more apparent in the Bass (37 Ohm) mode than the HD (63 Ohm) mode? As fewtch states, an unbuffered opamp, depending on the opamp, might mate better with the higher impedance setting (although in home systems, even the 63 Ohms of the HD setting is still low).

These may seem obvious questions, but is there distortion in both channels, and only with the Cmoys?
 

Users who are viewing this thread

Top