WHAT IMPEDANCE SHOULD I CHOOSE FOR MY HEADPHONES?
What’s going on?! The high-quality over-ear headphones with an impedance of 600 ohms that received rave reviews online from all the experts sounded fantastic in the store when you tried them out but now that you’ve connected them to your smartphone you’re hearing a quiet whisper instead of a full and rich sound. Are your new headphones already broken or is your smartphone on its last legs?
The most likely explanation is that your headphones’ impedance might be too high for the music source in question. It’s entirely possible – and many users aren’t aware of this issue when deciding which model to purchase.
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Where does the term “impedance” come from?
Here comes the science bit: impedance (measured in ohms or Ω) is an electrical engineering term and denotes the electrical resistance of voice coils in the transducer of wired headphones. It is tested during production with a standardised audio signal so that headphones achieve their intended “nominal impedance”.
What does headphone impedance denote?
To understand this better, we need to take a closer look at how headphones are designed. Headphones use diaphragms, which cause air molecules to vibrate, to create sound waves. These diaphragms, which are located in the transducer, are moved by an electromagnet. The critically important factor in all of this is the copper coil (voice coil) which is connected with the diaphragm. The lighter the coil (and therefore the thinner the wire), the clearer and more precise the transducer will sound.
However, a lighter coil involves greater resistance, i.e. higher impedance. The type of device that the headphones are going to be connected to is therefore important as not every source is able to provide the necessary voltage to overcome the headphones’ resistance and cause the diaphragms to vibrate properly.
How does impedance affect volume?
Put simply, the higher the impedance, the more voltage is needed for the headphones to sound loud enough. Most smartphones and notebooks don’t provide as much power as a modern hi-res player or a stereo system. Headphones below 100 Ω are therefore really designed for mobile use. Headphones above 100 Ω, on the other hand, are great for stationary systems with a headphone amplifier or can be used in professional settings.
High impedance won’t cause a well-equipped stereo system any bother or cause any issues in the studio as the devices used here usually supply enough voltage. However, the situation is completely different when it comes to smartphones and tablets as headphones with high impedance will often sound too quiet. Headphones designed specifically for mobile use such as the XELENTO remote will produce a full and rich sound here – even when you’re out and about and on the go.
The rule of thumb is therefore that headphones with higher impedance often produce a higher-resolution sound. Headphones with lower impedance are therefore better suited to mobile devices such as smartphones and tablets.
Example calculation
For illustrative purposes, it is worth comparing the DT 770 PRO (80 ohms) and DT 990 Edition (600 ohms) headphones using a simple example calculation. If you connect both models to the same smartphone, you will notice that the resulting power (P) is considerably different. The output voltage at the smartphone’s jack connector was assumed to be 1 volt, so as to simplify matters.
The power is calculated as follows:
- DT 770 PRO: P = (1 V)2/80 Ω = 12,5 mW
- DT 990 Edition: P = (1 V)2/600 Ω = 1,6 mW
The results show that, when connected to the same smartphone, the DT 770 PRO headphones, which have lower impedance, can supply almost eight times the power (P), which in turn leads to a higher volume. In order to achieve the same power with the 990 Edition headphones, you would have to increase the voltage of the playback device, which can be pretty tricky with mobile playback devices, though an amplifier can help here.
Online impedance calculator: Calculate power and sound pressure level:
You can use this online calculator to calculate the power (P) that your headphones can supply.
To calculate the maximum sound pressure level in dB, please also fill in the field corresponding to your headphones’ nominal sound pressure level in the “Optional details” section. The other details required for the calculation can be found in your headphones’ relevant data sheet.
These data sheets can be found in our download area.
You can classify the calculated sound pressure level using the chart provided.
What levels of impedance are there?
Broadly speaking, we differentiate between high and low impedance. Commonly, the low impedance range covers the increments 18 Ω, 32 Ω and 80 Ω. A common value for high impedance is 250 Ω. If you want to get the most out of your system (and it can supply the relevant power), opt for a model with 600 Ω such as the DT 990 Edition.
How do the PRO X headphone series models differ from the classic models?
Headphones with impedance of 32 ohms would be louder than 48-ohm headphones with the same signal voltage because there would be more power on account of the lower load resistance – provided that the amplifier has low source resistance. However, this applies only for the same loudspeaker basket (motor) with the same coil configuration (coil height, coil weight, overlap area in the magnetic gap).
As such, we can say that in the case of the DT Classic range, if the signal voltage is the same, the volume decreases as impedance increases.
Thanks to an innovative configuration, with the same signal voltage the Stellar.45 driver can develop more sound pressure on account of a higher flux density. What’s more, unlike the dynamic driver, the STELLAR.45 driver captures virtually all magnetic field lines on account of the longer coil. This results in a stronger drive force.
What else do I need to bear in mind when purchasing headphones?
In addition to the way that the headphones are worn (over-ear, on-ear and in-ear), the design (closed-back, semi-open-back and open-back) and features such as Bluetooth® and Active Noise Cancelling (ANC), it is also important to consider the technical values on the headphones’ data sheet. So, before you buy any headphones, think about which devices you’re mainly going to be using them with.
And if your music playback devices at home cannot supply the required power, an additional headphone amplifier can seriously enhance the sound. A portable DAC (digital-to-analogue converter) with a built-in headphone amplifier could be a great option for when you’re out and about and on the go. As long as you bear all these pointers in mind, nothing will be able to come between you, your headphones and pure music bliss.
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