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Topic: Frequency responses of IEM's with different devices (Read 5958 times) previous topic - next topic
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Frequency responses of IEM's with different devices

I have the Ultimate Ears Triple.fi 10 Pro IEM's.  I've noticed a significant difference in frequency response when used with different audio equipment.  The sound is similar when plugged into my iPod as it is when plugged into my Mbox.  However, the higher frequencies are greatly diminished when plugged into my Mackie analog mixer, with a dedicated headphone amp.  I believe I'm dealing with impedance matching problems, as the phones are rated at 32 ohms, which is an order of magnitude less than many other headphones.

When I use the adapter with my iPod, the high frequencies are *diminished* significantly, and the iPod has a hard time driving the phones (have to crank up the volume).

When I use the adapter with my mixer, the high frequencies are *increased* significantly, and the sound is somewhat similar to what I get with the iPod and Mbox without the adapter.

I suppose by using the adapter with the mixer, I'm better matching the impedance of the phones to the output stage of the mixer.  I suppose that the iPod and Mbox are better equipped for driving low impedance headphones.

Is there a more thorough explanation that someone can offer that could help increase my understanding of impedance matching?

Frequency responses of IEM's with different devices

Reply #1 –
Impedance mismatch could explain what you are hearing.

The phones' impedance could be 32 ohms for low and mid frequencies, but due to inductance, rise to higher impedance at high frequencies.

If you drive this with a low impedance source then the phones will draw less power at high frequencies and the response will roll off (which may be what the manufacturer intended).

If instead you drive them with a high-impedance source then all frequencies will be less sensitive (requiring that you turn the volume up) but there would be less roll-off of the high frequencies, so the high frequencies will sound louder.

Frequency responses of IEM's with different devices

Reply #2 –
Quote from: LocrianGroove on
I have the Ultimate Ears Triple.fi 10 Pro IEM's.  I've noticed a significant difference in frequency response when used with different audio equipment.  The sound is similar when plugged into my iPod as it is when plugged into my Mbox.  However, the higher frequencies are greatly diminished when plugged into my Mackie analog mixer, with a dedicated headphone amp.  I believe I'm dealing with impedance matching problems, as the phones are rated at 32 ohms, which is an order of magnitude less than many other headphones.

When I use the adapter with my iPod, the high frequencies are *diminished* significantly, and the iPod has a hard time driving the phones (have to crank up the volume).

When I use the adapter with my mixer, the high frequencies are *increased* significantly, and the sound is somewhat similar to what I get with the iPod and Mbox without the adapter.

I suppose by using the adapter with the mixer, I'm better matching the impedance of the phones to the output stage of the mixer.  I suppose that the iPod and Mbox are better equipped for driving low impedance headphones.

Is there a more thorough explanation that someone can offer that could help increase my understanding of impedance matching?


The impedance curve of  UE 10 Pro earphones is provided at http://www.ultimateears.com/_ultimateears/...Stereophile.pdf. I'm not sure that these are exactly your phones, but yours are probably similar.  The impedance curve shows a low frequencyl impdance  of about 14 ohms, with a broad 2 ohm rise at 1 KHz, a broad 4 ohm dip at 8 KHz, and then  rising back to reference at 30 KHz followed by more rising.  This is going to provide potentially audibly nonuniform response with any source that provides a source impedance of more than a few ohms.

If you pick a common source impedance like 16 or 32 ohms as one extreme, and a very high source impedance (100's of homs) or a very low one (1 ohm or less) then there may be mildly audible differences between those and the typical source.

In the comparisons you mentioned, you didn't say that you tried to precisely match levels. I'd do this by playing a test tone and adjusting gain so that the voltage across the phones is some predetermined constant like maybe 100 millivolts. Since you didn't match levels, the differences you heard are more likely to be due to level mismatch than the relatively small differences that might be due to source impedance.
 

Frequency responses of IEM's with different devices

Reply #3 –
I agree with PDQ.  I suspect your Mixer has a high output impedance.  Since the impedance of your IEMs varies across the frequency range (it seems all Multi-driver IEMs are like this), this has an interaction with the high output impedance of your mixer.  This can audibly change the frequency response.  Adding a impedance adapter (resistors?) will only make the problem worse.

You can see examples of this here

The output impedance of IPODs is fairly low so this is typically not an issue.

The solution is to just get a really cheap headphone amp.  I need to see some RMAA tests, but I suspect that even a Fiio E5 will do.

Finally, you shouldn't be trying to match the impedance of your device with your IEMs.  Your source/amp/device should have an impedance that is as close to zero as possible.