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Audeze LCD_4

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Sean Olive

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There is no headphone that wouldn't distort magnitudes higher than the UCX phones output. But if you want to the measure all parameters including very high SPL on insensitive phones then you indeed need a more powerful phones amp.
I could not find any information on the max power output of the UXC, only the output impedance (30 ohms).

Looks like the ADI‑2 DAC and ADI‑2 Pro have addressed this with low (0.1 ohm) headphone output impedance and stated max power output of 1.5 watts. That would drive most headphones to 110-115 dB except may some of the lowest sensitivity magnetic planars.

https://www.rme-audio.de/adi-2-dac.html
 
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MC_RME

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The UCX has an output impedance of 24 Ohm (the 30 Ohm in some older manuals was not accurate). As mentioned in the manual it also reaches up to +19 dBu. With a 300 Ohm headphone and the small voltage division 24/300 Ohm that still leaves +18 dBu unclipped, or around 130 mW.

With lower impedances the max output voltage is reduced by both voltage division (-6 dB for a 24 Ohm headphone) and the limited current capability of the (simple) phones output stage. For example with 32 Ohms clipping point is at around +10.3 dBu, which equals 200 mW.

And yes, our later interfaces reflect the change in headphone technology and costumer expectation.

Regards
Matthias Carstens
RME
 
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JIW

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Regardless of the power restrictions, since the impedance of few headphones does not vary with frequency, significant voltage division from a relatively high output impedance may well lead to significant changes in the measured frequency response. To ensure without knowing the frequency dependency of the impedance that the range of those changes remains within a given level difference, the ratio of the output impedance to the minimum impedance of the headphone has to be at most the voltage amplitude ratio corresponding to the desired maximum level difference less one:
Screenshot 2021-02-22 at 13.14.14.png


If both the minimum and the maximum impedance are known, the ratio of the output impedance to the minimum impedance must be at most the voltage amplitude ratio corresponding to the desired maximum level difference less one divided by one less the product of the voltage amplitude ratio corresponding to the desired maximum level difference and the ratio of minimum impedance to the maximum impedance:
Screenshot 2021-02-22 at 13.14.24.png


For a range of at most 1 dB, the output impedance must thus be at most 12.20 % of the headphones' minimum impedance, while for a range of at most 0.5 dB, the output impedance must be at most 5.925 % of the headphones' minimum impedance and for a range of at most 0.1 dB, the output impedance must be at most 1.1579 % of the headphones' minimum impedance.

Correspondingly, for a 24 ohm output impedance, the minimum impedance required to ensure a range of at most 1 dB is 197 ohm, while for a range of 0.5 dB it is 405 ohm and for a range of 0.1 dB it is 2073 ohm. In contrast, for a 0.1 ohm output impedance, the same required minimum impedances are 0.820 ohm, 1.688 ohm and 8.636 ohm, respectively, making the effects of voltage division probably negligible for nearly all headphones.

Assuming that the maximum impedance of the headphone is only twice the minimum impedance, only lessens the requirements by about a factor of one half. For a range of at most 1 dB, the output impedance must thus be at most 27.80 % of the headphones' minimum impedance, while for a range of at most 0.5 dB, the output impedance must be at most 12.60 % of the headphones' minimum impedance and for a range of at most 0.1 dB, the output impedance must be at most 2.343 % of the headphones' minimum impedance.

Starting from the formula for voltage division, the derivations are fairly straightforward and for any finite output impedance and any frequency dependent headphone impedance, the denominator in the second equation is always positive.
 

scott wurcer

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Are you saying the performance of the RME is not good enough to measure distortion of headphones? The output impedance is relatively high (30 ohms) and it probably doesn't have enough power to drive insensitive headphones.


Hopefully, will be getting something to replace it soon.

No I meant hardware like the B&K head and torso simulator, Helicopter was referring to some Python scripts that a couple of us did for plotting phono cartridge and turntable responses. I don't think any of that would help much with headphones.
 
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Sean Olive

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No I meant hardware like the B&K head and torso simulator, Helicopter was referring to some Python scripts that a couple of us did for plotting phono cartridge and turntable responses. I don't think any of that would help much with headphones.
Thanks. We do have a B&K 5128 as well as a KEMAR so we can and have measured headphones on those devices as well.
 

Jimbob54

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The steep notch at 9 kHz could be a reflection cancellation in the pinna. You see a smaller versions of these notches in the other two magnetic planars I posted. I need to confirm. The 45CA-10 is accurate to 20kHz.

Yes that is a lot of weight. You put it on you feel like your head is going to tip over. When you move your head, you can feel it shift on your head and you feel like it might fall off or your head might tip over. Comes with an optional neck brace.. :)

Impossible not to identify in a blind test even with your eyes closed.

I have the LCD XC which is even heavier (807g) . Oddly they arent the worst culprit for neck strain. That award goes to the Focal Clear (450g) but something about the way they sit on my head kills me . I actually dont mind wearing the XC.
 
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Sean Olive

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Regardless of the power restrictions, since the impedance of few headphones does not vary with frequency, significant voltage division from a relatively high output impedance may well lead to significant changes in the measured frequency response. To ensure without knowing the frequency dependency of the impedance that the range of those changes remains within a given level difference, the ratio of the output impedance to the minimum impedance of the headphone has to be at most the voltage amplitude ratio corresponding to the desired maximum level difference less one:
View attachment 114134

If both the minimum and the maximum impedance are known, the ratio of the output impedance to the minimum impedance must be at most the voltage amplitude ratio corresponding to the desired maximum level difference less one divided by one less the product of the voltage amplitude ratio corresponding to the desired maximum level difference and the ratio of minimum impedance to the maximum impedance:
View attachment 114135

For a range of at most 1 dB, the output impedance must thus be at most 12.20 % of the headphones' minimum impedance, while for a range of at most 0.5 dB, the output impedance must be at most 5.925 % of the headphones' minimum impedance and for a range of at most 0.1 dB, the output impedance must be at most 1.1579 % of the headphones' minimum impedance.

Correspondingly, for a 24 ohm output impedance, the minimum impedance required to ensure a range of at most 1 dB is 197 ohm, while for a range of 0.5 dB it is 405 ohm and for a range of 0.1 dB it is 2073 ohm. In contrast, for a 0.1 ohm output impedance, the same required minimum impedances are 0.820 ohm, 1.688 ohm and 8.636 ohm, respectively, making the effects of voltage division probably negligible for nearly all headphones.

Assuming that the maximum impedance of the headphone is only twice the minimum impedance, only lessens the requirements by about a factor of one half. For a range of at most 1 dB, the output impedance must thus be at most 27.80 % of the headphones' minimum impedance, while for a range of at most 0.5 dB, the output impedance must be at most 12.60 % of the headphones' minimum impedance and for a range of at most 0.1 dB, the output impedance must be at most 2.343 % of the headphones' minimum impedance.

Starting from the formula for voltage division, the derivations are fairly straightforward and for any finite output impedance and any frequency dependent headphone impedance, the denominator in the second equation is always positive.

Yes, fortunately the LCD-4 (200 ohms) and Sundara (38 ohms) I measured have essentially flat impedances across their frequency range, so the effect on frequency response would be minimal.

But the bottom line is that output impedance of the RME should be lower than 24 ohms to accurately measure and hear the frequency response of a range of different headphones that have lower, non-flat impedance curves.

I wonder if RME will allow a trade-in for one of their newer units with 0.1 output impedance? :)
 

jae

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Two planars I am curious about are the Ether 2 and Aeon RT Open. Bonus, they won't break your neck at 290/328 g respectively
 
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Matias

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Yes, fortunately the LCD-4 (200 ohms) and Sundara (38 ohms) I measured have essentially flat impedances across their frequency range, so the effect on frequency response would be minimal.

But the bottom line is that output impedance of the RME should be lower than 24 ohms to accurately measure and hear the frequency response of a range of different headphones that have lower, non-flat impedance curves.

I wonder if RME will allow a trade-in for one of their newer units with 0.1 output impedance? :)
I bet that if you take a selfie wearing headphones and holding an RME unit in your hand, and allow comercial rights for them to use that picture in ads, they would happily send you a new unit. Win-win situation! :D
 

JIW

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Yes, fortunately the LCD-4 (200 ohms) and Sundara (38 ohms) I measured have essentially flat impedances across their frequency range, so the effect on frequency response would be minimal.

But the bottom line is that output impedance of the RME should be lower than 24 ohms to accurately measure and hear the frequency response of a range of different headphones that have lower, non-flat impedance curves.

I wonder if RME will allow a trade-in for one of their newer units with 0.1 output impedance? :)

You could also use a stand alone headphone amplifier with low output impedance as a voltage buffer connected to one of the outputs of the UCX. @amirm has measured and reviewed plenty of those. However, his method overestimates the actual value of the output impedance.

Also, the ADI-2 line is not itself compatible with TotalMix and has no pre-amps built in so you would need an additional interface for that. Your UCX might be enough for that, though.
 
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Sean Olive

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You could also use a stand alone headphone amplifier with low output impedance as a voltage buffer connected to one of the outputs of the UCX. @amirm has measured and reviewed plenty of those. However, his method overestimates the actual value of the output impedance.

Also, the ADI-2 line is not itself compatible with TotalMix and has no pre-amps built in so you would need an additional interface for that. Your UCX might be enough for that, though.
That's a good point. The ADI-2 line has no microphone preamp inputs so I would still need the UCX for the GRAS 45 CA.

This device would solve all my problems as it has everything built into one box.

https://www.ap.com/analyzers-accessories/apx517/
 
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Sean Olive

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You could also use a stand alone headphone amplifier with low output impedance as a voltage buffer connected to one of the outputs of the UCX. @amirm has measured and reviewed plenty of those. However, his method overestimates the actual value of the output impedance.

Also, the ADI-2 line is not itself compatible with TotalMix and has no pre-amps built in so you would need an additional interface for that. Your UCX might be enough for that, though.
I also purchased the RME UCX 2.5 years ago for measuring and calibrating loudspeakers in rooms and it does a fine job for that, so I can't really replace it with a dedicated headphone DAC/AMP. Most recently I used the UCX for measuring and calibrating my 7.2.4 home theater system using Dirac Live.
 

JIW

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I also purchased the RME UCX 2.5 years ago for measuring and calibrating loudspeakers in rooms and it does a fine job for that, so I can't really replace it with a dedicated headphone DAC/AMP. Most recently I used the UCX for measuring and calibrating my 7.2.4 home theater system using Dirac Live.

I can't see where I may have suggested that you replace the UCX with a DAC/amp. To use an ADI-2 as a headphone output in your setup, you would probably have to keep the UCX anyways. As I have none of the devices in question on hand nor am affiliated with RME, I ask that you please consult with @MC_RME or RME in general for more information on that. However, I have owned the DAC and used its amplifier extensively and can recommend it as such.
 
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