I just thought I'd collect my thoughts and experience regarding low and anomalous volume when using the PXC 550's in both Bluetooth and wired (non-USB) mode. I believe Sennheiser has included an inordinate amount of signal processing which effectively limits the maximum output of these devices so that no matter how loud you turn up the volume, they are always within a pre-determined distortion range. I believe this strategy/features can be negated to some extent.
Here are my notes for defeating these 'features':
1) Using the CapTune application, introduce a custom EQ curve with all values maximized. - This will result in a straight line across the top of the EQ window. I believe that as opposed to 'boosting' all frequencies, this has the effect of 'reducing the limits' across all frequencies. It doesn't 'add'... it just 'subtracts less'. I personally find that with maximized EQ, I get excellent volume and bass response where I hadn't previously; and without any negative impact on the overall balance and sound profile of the headphone.
2) When attempting to use these in a 'wired' configuration with analog audio input (not the USB cable) it is important to note that the PXC 550 circuitry is 'Active' as long as the battery has charge. You can disable Bluetooth and Noise Cancellation but the limiting circuits (described below) are still ON as long as the unit has charge. Also note that when 'Active', these have a relatively high impedance of 490 Ohms, requiring a beefy headphone amplifier.
3) When 'Active', the PXC 550's use an IFE/PA volume protection strategy which is designed to limit maximum volume when operating in a wired (non-USB). This circuitry constantly reduces volume below some magic threshold but, importantly, NEVER raises/restores it again. It isn't until you've reset the headphones (by removing them and twist-clicking them off and then on again) that maximum volume is restored. The intent of this feature is to keep flight attendant PA announcements from blowing out your eardrums while listening to the In Flight Entertainment. But the implementation is poor; resulting in ever-reduced volume over time as loud passages continue to trigger the limiter.
And... The only way to run these headphones in 'Passive' mode is to fully discharge the battery! (What, Sennheiser?!?) This property is described in the user manual (page 39 in the English version) under the subheading 'Using the Audio Cable'.
So in short:
* Maximizing the EQ can help achieve more volume without negatively affecting the characteristic of the sound when operating in Bluetooth or USB modes
* If using these with a wired headphone amplifier (analog, non-USB), run the battery down first so they run 'Passively' and present a 10x reduced load (46 ohms) on the amplifier and the IFE/PA limit circuitry is defeated
Enjoy the music!
Here are my notes for defeating these 'features':
1) Using the CapTune application, introduce a custom EQ curve with all values maximized. - This will result in a straight line across the top of the EQ window. I believe that as opposed to 'boosting' all frequencies, this has the effect of 'reducing the limits' across all frequencies. It doesn't 'add'... it just 'subtracts less'. I personally find that with maximized EQ, I get excellent volume and bass response where I hadn't previously; and without any negative impact on the overall balance and sound profile of the headphone.
2) When attempting to use these in a 'wired' configuration with analog audio input (not the USB cable) it is important to note that the PXC 550 circuitry is 'Active' as long as the battery has charge. You can disable Bluetooth and Noise Cancellation but the limiting circuits (described below) are still ON as long as the unit has charge. Also note that when 'Active', these have a relatively high impedance of 490 Ohms, requiring a beefy headphone amplifier.
3) When 'Active', the PXC 550's use an IFE/PA volume protection strategy which is designed to limit maximum volume when operating in a wired (non-USB). This circuitry constantly reduces volume below some magic threshold but, importantly, NEVER raises/restores it again. It isn't until you've reset the headphones (by removing them and twist-clicking them off and then on again) that maximum volume is restored. The intent of this feature is to keep flight attendant PA announcements from blowing out your eardrums while listening to the In Flight Entertainment. But the implementation is poor; resulting in ever-reduced volume over time as loud passages continue to trigger the limiter.
And... The only way to run these headphones in 'Passive' mode is to fully discharge the battery! (What, Sennheiser?!?) This property is described in the user manual (page 39 in the English version) under the subheading 'Using the Audio Cable'.
So in short:
* Maximizing the EQ can help achieve more volume without negatively affecting the characteristic of the sound when operating in Bluetooth or USB modes
* If using these with a wired headphone amplifier (analog, non-USB), run the battery down first so they run 'Passively' and present a 10x reduced load (46 ohms) on the amplifier and the IFE/PA limit circuitry is defeated
Enjoy the music!
