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I recently discovered that I can't use just any headphones with my Mbox Mini as it seems to have a somewhat underpowered headphone amplifier. I did this by buying a pair AKG K240 mkII headphones (which sound very very good on everything else, even the jack on the mac book worked) and discovered I couldn't head anything due to their 50Ω Impedance (which as I understand it isn't particularly high for a pro model).

I'm not sure what version of the Mbox Mini I have (its about 3 years old), so I can't be sure of the technical specification, but the 3rd Gen model has 20 mW into 32 R (so I'm not sure on the maximum impedance I can use, I assume <30Ω?, does anyone know how to work that out?).

So I have a dilemma where I need lower impedance headphones, but all I can find are consumer units. Question: Can anyone recommend some professional monitoring headphones (open or closed back) that will work with my Mbox Mini?

Note: I realise I can get a headphone amp, but is this the only option... I'd rather spend £100 on a pair of decent low impedance monitor headphones (if they exist).

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Beyer Dynamic DT 770 Pro 32 ohm ?

also worth exploring: Sony 7510 24 ohm

Re "working it out":

Read this and this.

At same sensitivity ("The sensitivity rating is usually for 1 milliwatt power input to the phones and a corresponding sound pressure level (SPL) output (usually 102 to 106 dB SPL output for moderate to high sensitivity rated phones)." source):

  • Power = volts times milliamps.
  • At the same voltage (amp output stage) more ohms = fewer milliamps (Ohm's law)
  • Thus more ohms (headphone coils+amp output stage) require more volts (amp output stage) to get the same milliamps to get the same loudness (same sensitivity, higher impedance)
  • Fewer ohms = potentially more sound coloration (source). But headphones are coloured anyway
  • (Sensitivity is likely determined by the magnets and the headphone membrane materials.)

Fewer ohms = higher current (same voltage), but remember the maximum current draw requirement of USB - <500mA. With Mbox Mini in question too high current is probably not an issue, but the max voltage available to the headphone amp is limited and the output stage likely has relatively high impedance. Re voltage USB offers 5V max (Firewire bus has 12+).

So to up the loudness your choices are lower impedance (=higher current) or higher sensitivity.

There are headphones with 24ohm (Sony above) and even 16ohm resistance. I'd stay at 32 minimum.

Also it's worth exploring the idea that you may be asking for too much loudness.

  • Thanks for the explanation. Accepted answer :) - I'm asking to be able to hear what I'm playing ;) – Mr Shoubs Feb 12 '14 at 12:23
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I did some reading, and I see several complaints that the headphone output on the Mbox mini is very weak. Depending on the version, 60mW or 20 mW into 32 Ohm. The Presonus Firebox, by comparison, can go ridiculously loud, and has 150 mW into 60 Ohm. An iPhone has 30 mW per channel.

Getting low impedance versions of headphones is one way to get louder output, another would be to buy a separate headphone amp, which might be a bit cheaper.

High impedance headphones are quite a bit higher than yours: For example, the Beyerdynamic 770 and 990 high impedance versions are 600 Ohm, the middle ones are 250 Ohm, which play at low to moderate levels on consumer devices (iPhone, Laptop outputs). The low impedance version is 32 Ohm.

I find it very strange that Avid decided to make the headphone output power of some mboxes lower than that of an iPhone! But even then, you should hear something, even if it's quiet. If you really hear nothing, you might have a different problem or defect.

  • Your right, I do hear something, but it VERY quite, it may as well be nothing. Maybe it was a marketing or budget decision to make sure people went for the higher model. Yeah, I didn't want to go down the headphone amp road, but if you have any suggestions on make/model, let me know. – Mr Shoubs Feb 3 '14 at 13:44
  • Could you post your references too please, it might help me find something in the future. Thanks. – Mr Shoubs Feb 3 '14 at 14:31
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    Make and model of a headphone amp very much depends on your budget: you can go from $20 to $several thousand. For that audio interface and headphones, I wouldn't spend more than $100 on a headphone amp. Among others, the Presonus HP4 comes to mind, you will surely have enough output power. I've found the info by googling different versions of "mbox headphone output" or "mbox headphone power", and replacing mbox with "firebox" and "iPhone". The mbox info was somewhere on avid.com – EMV Feb 4 '14 at 7:07
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+50

What are you comparing this low output on the headphone amplifier to? I realize that you say these K240's work fine on your laptop, but are you monitoring the same ProTools output on your laptop that you're trying to run through the MBox Mini? Have you eliminated everything else as the issue? Do you use the 1/4" monitor outputs on the back of the MBox Mini? Are they equally as quiet? Have you reinstalled the MBox drivers, opened the utility software and made sure that your software returns and L/R output are set at 0.0?

Once you're comparing apples to apples, and have determined that the hardware of the MBox Mini is your issue (which you very well may have already done), I'd reconsider your options. The AKGs are decent cans, and you know they function properly through using them with other sources. So I don't know if I'd lower the quality of what I'm listening to by buying lesser headphones in order to get the inferior headphone amp to suit your needs. If you're already willing to drop £100 on new cans, I'd consider replacing the Mini instead. The Firebox as EMV already mentioned or the Scarlett 2i2 are both similar in price to the Mini and are well reviewed.

  • The only thing I haven't tried is using the monitor outputs, but I use these for my monitors, so it isn't of use. They do sound very good, so it's a shame I can't use them. I agree, it may be time to find new hardware, however I've just blown my budget on the monitors, so I'll have to make do with something else in the mean time. I'm going to check out the 32 Ohm Beyer Dynamics DT770 headphones in the mean time. Have you any experience with these? – Mr Shoubs Feb 11 '14 at 9:46
  • I have not, but the DT770 PROs receive high praise around here sound.stackexchange.com/questions/61/… – Steve Urban Feb 11 '14 at 19:58
  • We'll find out if they work next week :) (+50 as your approach to problem solving is spot on). – Mr Shoubs Feb 12 '14 at 12:14
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Sony MDR-7506/V6's have served me, and many others, well for many years in this configuration.

  • but they are 63 Ohms, which is 13 more than the pair I was using, so I think you must be using a different version of the MBox. – Mr Shoubs Feb 11 '14 at 9:39
  • Despite not being fluent in electronics, I do know that those AKG's have a reputation for being extremely power hungry. I have AKG K701's and they are rated at 62 ohms but they are far far less sensitive than the 7506's. – Evan Feb 11 '14 at 17:05
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That's odd. I've got a Digi Mbox2 Mini which I use with a pair of 80Ω Beyer DT250's - it goes really loud.

Check the Mix dial is round all the way clockiwise?

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Two pair of Headphones that I love for monitoring are: Closed Beyer Dynamics DT770 and open Sennheiser HD 25 ii

Both work even when you plug them directly into your Laptop!

  • Both of those headphones have a higher impedance than the ones I tried. The problem is the mic amp on the mbox mini being underpowered. – Mr Shoubs Feb 3 '14 at 13:45
  • ah ok sorry couldn't help then – Tobias Schmidt Feb 3 '14 at 17:27
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    The 770 have a 32 ohm version. – georgi Feb 10 '14 at 20:33

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