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Impedance/frequency response question.... Audio Interfaces
Old 7th September 2007
  #1
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Impedance/frequency response question....

Hi

I have a pair of Beyerdynamic DT-100s and I have just bought a pair of Sennheiser EH 250s. I always thought that the DT-100s were quite quiet but thought nothing of it. The Sennheisers are LOUD by comparison so I checked the impedance of the 2 pairs and the DT-100s are 400 Ohms (apparently there is a 16 Ohm version too) and the Sennheisers are around 30 Ohms.

The headphone output of my Fireface 400 and Voicemaster Pro are both around 30 Ohms so my two questions are.....

1. Is is true that the frequency balance is affected with impedance mismatching of this scale?

2. Where are these 400 Ohm headphones supposed to be plugged into?

Thanks for any help.

Paul
Old 7th September 2007
  #2
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nosebleedaudio's Avatar
 

Just make sure the amp can drive a 30 ohm load.
Old 7th September 2007
  #3


There may be a difference in frequency response under different loading conditions.

The 400 ohm cans need more voltage headroom, where the 30 ohm cans will need more current headroom. It's a bit of a crap-shoot with headphones unless you get a good amp with good voltage and current output.

Nobody seems to spec can amps at multiple driver impedances......

Just try finding a modern one that will drive the 600 ohm Koss cans I have well.



-tINY

Old 8th September 2007
  #4
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Cheers for the replies guys.

I suppose the only way of seeing whether the frequency response is true is to get a 16 Ohm pair of DT-100s to see what the difference is, although it is a bit weird that the 400 Ohm ones are on the market when there is nothing to plug them into though.

Onwards and upwards.
Old 10th September 2007
  #5
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ulysses's Avatar
Like you said, you were using the 400-ohm headphones without concern until you found out that some other headphones are louder. There's no reason you can't continue using them.

The primary frequency response variable is going to be the low-frequency cuttoff point, assuming the amp's outputs are capacitively coupled. The higher-impedance headphones simply will have a roll-off frequency 3 octaves lower than the 30-ohm headphones. If those coupling caps weren't big enough, you would hear a lack of low frequency extension in the 30-ohm headphones. Presumably, your amp is designed to have good wideband performance into the low impedancy load, and the higher-impedance headphones will simply be even better. No problem.

The larger issue is in how much signal voltage is required to deliver the same amount of power into a 400-ohm driver as opposed to a 30-ohm driver. But this is only part of the equation - the other part is the efficiency of the driver. So first you might consider how many milliwatts you need to deliver to the headphones to get, say, 85mW into your ears. That will depend not only on the efficiency of the driver, but also on the design of the headphones: How close the driver is to your ear. Doubling the distance to your ear means you need 4 times the power to get the same SPL into your brainholes.

As somebody else said, some amps might be better at driving the higher voltage level required for the 400-ohm headphones, while others might be better at driving the higher current level required for the 30-ohm headphones. Any reasonably well-designed professional headphone amp should be capable of delivering the necessary current, but there will be exceptions. When it comes to delivering significant voltage though, probably the ONLY headphone drivers that will fail will be those running off of low-voltage supplies, such as compact battery-powered devices like MP3 players and such. Even those will do fine if they're designed right.

So, basically, don't worry about it. You should use the pair that sounds better to you. If they're equal, then I would definitely take the 400-ohm headphones. They'll be far less likely to distort, and they'll be far less likely to damage your hearing.
Old 11th September 2007
  #6
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Thanks a lot for shedding so much light on the subject Justin.

One thing I didn't mention is that I do most of my mixing on headphones and so the frequency response thing is important - the DT-100s seem to be a bit more "bland" than my studio monitors and I have found on other systems that the upper-mids are more hyped when I've mixed on the Beyers.

Extremely good point about the hearing damage as well, and I think I'll be using the phrase "brainholes" quite a lot in the future if that's ok.
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