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  • dneern
  • [*]
600 ohm headphone sanity check
I need to get myself some headphones, so I started looking at reviews and specs. I ended up finding a lot of information over at another forum I'm sure you all know about. I started looking into the information they were feeding me and after a little bit of research I find out they don't know what they're talking about.

So I find some more scientific and reliable sources of info, learn how to read most of the charts and graphs on headphone and amplifier test reports, and find a link to this forum from a nwavguy blog post. I look around a bit and find that people here generally have a better grasp of the science and engineering of sound.

Anyway, I'm still days new to this, so I need a little bit of a sanity check on the information I've gathered.

I'm interested in the Beyerdynamic DT880s. I don't want to buy an amp for them. I looked up the specs for my computer's sound card and it outputs 2VRMS at <24ohms. So for the sake of my calculations I assumed it would be operating at 24ohms. That's way more than 1:8 when compared to the 32ohms DT880s, so those are out.

Then I used this SPL calculator and plugged in the specs of my sound card and both the 250ohm and 600ohm DT880s because both of those exceed 1:8. This is what I got:


250ohm - 110.23dB SPL peak, 99.73dB SPL average
600ohm - 106.79dB SPL peak, 96.29dB SPL average

Here's the calculator I used:
http://reference-audio-analyzer.pro/en/amp-spl.php

Here's where I got the specs:
http://reference-audio-analyzer.pro/en/report/hp/beyerdynamic-dt-880-pro.php
http://reference-audio-analyzer.pro/en/report/hp/beyerdynamic-dt-990-600.php

I used the specs for the DT990 600ohm because it was the most similar headphone with the lowest measured sensitivity and highest measured impedance, so I could get the most conservative estimate as I could not find the measured specs for the exact headphone I'm interested in.

Anyway. It looks like I don't need any kind of additional amplification for either of these two headphones, but I need a sanity check after reading all the conventional "wisdom" over at that other forum. 106dB is hearing damage loud, isn't it? Why would you want to push it higher than that with a more powerful amplifier? So am I correct in thinking that either the 250ohm or the 600ohm version could get too loud with the output of my computer's built in sound card? Is everyone just running their headphones so loud that they're damaging their ears?

More to the point:  The characteristics of the two versions are pretty much the same. The distortion is all negligible, and the frequency responses are very close, which won't matter anyway after I EQ them as flat as I can get them. So what I really need to know is if that 3.44dB difference in average SPL is really a significant difference. Is 3.44dB a lot? Should I go with the 250ohm because they're significantly louder and so I could keep my system volume lower, or does it not make a difference since I'm going to be keeping the volume relatively low because I'm going to be using them for tracking and mixing over long periods of time?

Thanks for your help. I've already learned so much in my couple of days lurking this forum. You guys are the best, this place is awesome.

  • Rollin
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Re: 600 ohm headphone sanity check
Reply #1
Nwavguy recommended 110 dB SPL for peaks when playing music with high dynamic range. And he recommended to have source which is capable to give 5 V RMS for dt-880 600 Ohm
http://nwavguy.blogspot.ru/2011/07/o2-design-process.html
Quote
Music with a wide dynamic range is the most challenging to play loud because the peaks are much louder than the average level. Such music may not seem loud but the peaks can be seriously challenging for your audio hardware. For such music to approach live levels, you need to cleanly reproduce peaks of 110 dB SPL. If you want to know where that number comes from, see More Power?
Quote
Beyer DT880-600 – These need 43 mW at 600 ohms to hit 110 dB which is 5 V RMS. This is way beyond what most portable amps can manage.
  • Last Edit: 01 December, 2017, 04:51:06 PM by Rollin

  • eric.w
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Re: 600 ohm headphone sanity check
Reply #2
Innerfidelity has measurements on the DT 880 600 Ohm:
https://www.innerfidelity.com/images/BeyerdynamicDT880600ohm.pdf

They say 0.514 Vrms required to reach 90dB SPL.

I looked up the specs for my computer's sound card and it outputs 2VRMS at <24ohms. So for the sake of my calculations I assumed it would be operating at 24ohms. That's way more than 1:8 when compared to the 32ohms DT880s, so those are out.
If the specs say "outputs 2VRMS at <24ohms", it doesn't sound to me like they are quoting the output impedance to be 24 ohms, but I'm not sure. It's often not given in specs. What's the soundcard make/model?

  • dneern
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Re: 600 ohm headphone sanity check
Reply #3
It's the built in sound card for a MacBook pro Retina, so it's especially hard to find out the specs. I've seen a few places say 2VRMS at <24ohms, but because you asked me about it, I called apple and they don't even know the specs for their own machine. The guy I talked to said it could be 10ohms, or maybe 5-15ohms, but that's based on about the same amount, but less relevant info as I have for the <24ohms.

Re: 600 ohm headphone sanity check
Reply #4
Innerfidelity has measurements on the DT 880 600 Ohm:
https://www.innerfidelity.com/images/BeyerdynamicDT880600ohm.pdf

They say 0.514 Vrms required to reach 90dB SPL.



That means that 5.14 volts Vrms would be required to hit 110 dB, presuming that the headphones are linear at those SPLs. 

I seriously doubt that there are a lot of consumer computer sound cards that can provide 5+ volts rms into a headphone load.   It would have to run off of a +/- 8 volt or 16 volt or higher power supply.

However some pro audio type interfaces may be able to provide 5 or 6 volts at digital FS into 600 ohm loads. Others can produce only 4 volts and some can do no more than 2 volts.

In most operational computer or audio signal level processor environments, a separate power supply or a DC-Dc converter would be required.

I think the classic NWAVGUY O2 ("Objective 2") headphone amp or something like it could be recommended.

All things considered, 110 dB SPL short-term instantaneous peaks is not as extreme as it may seem if wide dynamic range music was being listened to.
  • Last Edit: 02 December, 2017, 08:21:19 AM by Arnold B. Krueger

  • schmidj
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Re: 600 ohm headphone sanity check
Reply #5
Just because the output impedance of your sound card is 24 ohms doesn't mean it will perform properly with a 24 ohm load.  It probably wasn't designed to do that.

Matching the load to the source impedance gives maximum power transfer.  Not, or not significantly, loading the source at all (10K load on your 24 ohm output) provides maximum voltage. 

Most modern circuit designs are designed to be run with little or no load (power amplifiers driving speakers excepted, and even there modern amplifiers have a much lower output impedance than the rated impedance they can drive.

I would be surprised if your soundcard will perform acceptably driving 600 ohms (and I assume we are talking about the "line" output, not a headphone jack).  There should be a spec for "minimum output load" or something similar telling you what the minimum impedance is it should be connected to.  Loading it with a lower impedance will probably result in it not meeting one or more specifications.

Also output impedance is frequency dependent.  Probably specified at one frequency, 400 Hz, 1000 Hz or something in the middle of the audio frequencies.  For instance if there is a coupling capacitor after the output stage of the card to block DC, it might well be of a value designed to work well with a 10K ohm load.  Its impedance at 400 Hz might be quite low, but at 20 Hz, much higher, resulting in a distinct lack of bass.

You should strongly consider getting a headphone amplifier to connect between your sound card and the headphones.

  • eric.w
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Re: 600 ohm headphone sanity check
Reply #6
I have a MacBookPro10,1 (the first 15" retina model from 2012), and I measured the output impedance to be 1.1 ohms.
Quote
60hz sine
691mv loaded
699mv unloaded
101.9 ohms dummy load
AN8008 True-RMS multimeter

As far as maximum voltage, I got the following:
Quote
1kHz sine (prepared in audacity, amplitude 1.0), unloaded, 100% volume: 1.394 Vrms
60Hz sine (prepared in audacity, amplitude 1.0), unloaded, 100% volume: 1.397 Vrms

  • Audible!
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Re: 600 ohm headphone sanity check
Reply #7
Quote from: Arnold B. Krueger
That means that 5.14 volts Vrms would be required to hit 110 dB, presuming that the headphones are linear at those SPLs.

I seriously doubt that there are a lot of consumer computer sound cards that can provide 5+ volts rms into a headphone load.   It would have to run off of a +/- 8 volt or 16 volt or higher power supply. 

It's really an interesting situation these days, as mother board manufacturers are try to differentiate their products. Certain high end motherboards feature onboard headphone opamps that are explicitly billed as being able to push 600ohm loads. The TI NE5532 on that ASRock motherboard seems like it might reasonably do so:

Quote from: TI spec sheet
Peak-to-Peak Output Voltage Swing 26 V Typ With VCC± = ±15 V and RL = 600 Ω
...
Number of Channels (#)    2  
Total Supply Voltage (Min) (+5V=5, +/-5V=10)    10  
Total Supply Voltage (Max) (+5V=5, +/-5V=10) 30  
  • Last Edit: 02 December, 2017, 05:44:17 PM by Audible!

  • dneern
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Re: 600 ohm headphone sanity check
Reply #8
Alright, so thanks to all of the new information I've learned from yous guys, and because of the reading I did over at nwavguy's blog, I've decided to go with the O2 as I'm certain it will perform well, and it's inexpensive.

So now I have a few new questions:
Is JDS a good manufacturer for this choice? It's affordable, it looks nice, and I know it's made from the open source design I like.
Is there another manufacturer you would recommend instead?

Also:
I'm quite happy with the audio quality of my laptop's sound card through my powered studio monitors. it outputs 24bit/96kHz which is more than I need, and I don't hear any problems with the quality of the audio it produces. I've been able to reliably produce masters that sound great on every system I play them through.

But I'm wondering if there's some reason that it might not perform just as well with the amplifier and headphones that I hope to use them with. I'm new to this, so I'm not sure if there's something about headphones or headphone amps that might not be totally  compatible/useful with my sound card.

Essentially what I'm asking is, would I be able to use them without a separate DAC?

  • schmidj
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Re: 600 ohm headphone sanity check
Reply #9
Audible, a 5532 connected properly will easily drive 600 ohms.  Be aware that you may need rails at +/- 15 to 18 volts to get enough output level for many professional uses.  I've noticed that almost all USB powered audio boxes don't provide input or output clip points anywhere near the +22 to +24 dBu needed for true professional installations.  Apparently they can't suck enough juice out of the USB power to power the boxes to produce those levels.

Dneern, there is no reason your laptop's sound card would perform any worse driving a headphone amplifier than driving powered speakers.  I am not familiar with different make headphone amplifiers, but I'd expect any unit with decent specs would perform pretty well. 

Headphones, like speakers, all sound different.  You might want to listen to a demo pair somewhere before you buy, unless you have a clear OK to return them if you don't like them.  There are also considerable differences in comfort, fit and durability between brands.  There are also both "open" headphones which do not block outside sounds, and "closed" phones which provide some (but not complete) isolation from outside sounds. 

As you may know, headphones provide exaggerated separation between left and right when listening to stereo.  Headphones provide binaural listening, not stereo.  Most music is mixed in stereo.  Google the terms to educate yourself on the difference.

  • dneern
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Re: 600 ohm headphone sanity check
Reply #10
I use binaural panning in my music extensively, so I always spend a great deal of my time listening to the crappy headphones I have. That's why I need to get some real headphones. It's a huge pain in the ass.

I'm primarily interested in open headphones. Sound leak and isolation are not an issue for me. I just want a good soundstage so that I can at least appreciate my own music the way I intend people to hear it.

Also, I don't have a lot of money, so I have to make my equipment last a long time, and Beyerdynamic stuff is affordable, easy to repair, there's a lot of solid chunks of metal in the construction, and you can buy any of the individual parts of any of their headphones if something fails or breaks. That's much better for me than having to buy a whole new set of cans because some crappy plastic part snaps or the cable fails, or the detachable cable ports fail. That's my main concern in how I'm choosing headphones.

I'm in a kind of small city, so my options for auditioning headphones are pretty limited, but I could try on a set of dt770s or dt990s to see if they're comfortable. I've called around and I know those are available for such purposes.

Besides that, I'm perfectly happy to select the headphones based on a graph. I don't care about how they sound subjectively to me. It's not really about what I prefer. I care that they're close to flat on a graph. I'm going to EQ them as flat as I can, and then I can become accustomed to whatever the sound of the headphones is and learn to be able to produce a solid master from that knowledge.

That's what I'm doing now with my monitors because my apartment is a pretty terrible space when it comes to acoustics. It's not a big deal though, it's like how you get used to how yellow tungsten lighting is when you're indoors at night and it just starts to look neutral, it just sort of happens eventually without you having to do much about it. I mean I EQd them, but they're placed off center of the room, too close to a wall in a small, totally untreated room. It's not ideal but it's my only option, and I'm so used to my set up at this point that I've figured out how to reliably produce something that sounds good on every system I've been able to try.

That's good news though about the sound card. I was a little worried that I was going to have to spend even more money on a DAC. The people over at head-fi were saying some stupid, self-contradictory, unscientific things that had me thinking that I was getting myself in over my head and shouldn't even bother, just stick with my shitty apple headphones and continue to struggle.

I'm so glad I discovered nwavguy and that they pointed me over here. I've learned so much from reading old threads over the past couple days. So much interesting knowledge about physics, acoustics, engineering, mathematics... This place is my shit.

  • Audible!
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Re: 600 ohm headphone sanity check
Reply #11
Quote from: schmidj
Audible, a 5532 connected properly will easily drive 600 ohms.  Be aware that you may need rails at +/- 15 to 18 volts to get enough output level for many professional uses.  I've noticed that almost all USB powered audio boxes don't provide input or output clip points anywhere near the +22 to +24 dBu needed for true professional installations.  Apparently they can't suck enough juice out of the USB power to power the boxes to produce those levels.

Sure, that makes total sense. Without at least a high current "charging" USB port, power could certainly be a concern.

However, in this particular case the TI opamp is soldered onto the motherboard proper, meaning it has access to 24/12/5/3.3V rails at the very least. Given the board marketing it would be rather surprising if Asrock did not in fact supply the opamp with sufficient voltage to drive Beyer Dynamic 600ohm cans.