The Bowers and Wilkins PX7 headphones have bluetooth, USB-C, and 3.5mm TRS connections to audio sources. These are battery-powered high-sensitivity headphones that are known to work well with ALSA using the analog and USB-C connections.
This article describes using a USB-C source with ALSA. See Bluetooth_headset for bluetooth connection information. The described configuration and testing use alsamixer, aplay, and speaker-test (from media-sound/alsa-utils) for testing, and media-video/smplayer and media-video/mplayer for audio playback.
The PX7 V2 is a newer model with different connections. It is unknown how well these instructions work for that model.
These USE flags are set:
media-plugins/alsa-plugins ffmpeg mix usb_stream media-video/mplayer alsa
When the PX7 is plugged in to a USB port and powered on, multiple USB devices are created. This article uses this device (trimmed output shown):
lsusb -v -d 19b5:0025
Bus 001 Device 010: ID 19b5:0025 B & W Group PX7 Bowers & Wilkins bcdUSB 2.00 bDeviceClass 0 bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 idVendor 0x19b5 B & W Group idProduct 0x0025 bcdDevice 14.69 iManufacturer 1 iProduct 2 PX7 Bowers & Wilkins Interface Descriptor: bNumEndpoints 1 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming AudioStreaming Interface Descriptor: wFormatTag 0x0001 PCM AudioStreaming Interface Descriptor: bSamFreqType 7 Discrete tSamFreq[ 0] 96000 tSamFreq[ 1] 48000 tSamFreq[ 2] 44100 tSamFreq[ 3] 32000 tSamFreq[ 4] 22050 tSamFreq[ 5] 16000 tSamFreq[ 6] 8000 Device Status: 0x0001 Self Powered
The PX7 has proximity sensors that detect when they are being worn. When not being worn there is no audio, so testing while not wearing the headphones will appear to fail. Since these have a high-sensitivity, low-level input signals produce a higher than usual sound-level. Make sure to set the device volume to a lower level using alsamixer before starting. A starting value of 20 or so was useful when using speaker-test.
The headphone's volume controls do not control the volume of audio coming from USB or analog sources.
The PX7 USB connection runs at USB full-speed (480 MBit/s) and uses the USB Streaming protocol with S24_3LE format samples. The hardware reports support for many sample rates (e.g. 44100Hz) via
lsusb, but the only rate that produced usable audio was 96000Hz.
The headphone drivers appear to always be powered from the battery even when connected via USB. The internal battery charges through the USB connection even when playing audio.
Even the though the USB speed is 480 MBit/s, the device must be plugged into a USB 3 port or better.
The quality of the USB cable may be a safety issue 
|Device||Make/model||Status||Vendor ID / Product ID||Kernel driver(s)||Kernel version||Notes|
|Wireless Headphone||B & W Group PX7 (Bowers & Wilkins)||Works (USB & Analog)||
||snd-usb-audio (when built as a module)||5.19.3||Enable kernel option SND_USB_AUDIO in the kernel.|
The only installation requirements are:
- USB-3 Port (Type A or C). An extension cable of 6ft (2m) was successfully used.
- A kernel with approriate modules (esp. usb-audio), no extra firmware required.
- media-libs/alsa-lib and media-plugins/alsa-plugins with the above mentioned USE flags set.
- Packages for testing: media-sound/alsa-utils.
- Audio/video playback software, in this case media-video/smplayer and media-video/mplayer.
Device Drivers -> Sound card support -> Advanced Linux Sound Architecture -> USB sound devices -> <*/M> USB Audio/MIDI driver
Note that there have been times where not having all of the sound-related modules configured as modules has caused failures.
emerge --ask --verbose media-libs/alsa-lib media-plugins/alsa-plugins media-sound/alsa-utils
For the playback apps used in these instructions:
emerge --ask --verbose media-video/mplayer media-video/smplayer
Testing the hardware
Plug the headphones into a USB-3 port and turn them on. Use aplay -L to see that the device is seen by ALSA. Use alsamixer to unmute and set the device's PCM volume control to a low level. Use F6 to select the device Bowers & Wilkins PX7. A suggested starting level is 20. A high-level will produce very loud sound in speaker-test.
speaker-test -Dplughw:Wilkins,0 -c2 -r96000
This selects stereo output (
-c2) with a 96KHz sample rate (
-r96000). speaker-test appears to produce S16_LE samples which requires conversion to S24_3LE. Additionally the sample stream needs to be converted to the USB Stream protocol. Using
plughw in the device specification makes this happen. Using
hw does not work.
Make sure to wear the headphones so the proximity sensors will enable output. Pink noise should be heard alternating on the left and right sides.
Since the headphones may not always be plugged in, no configuration for setting the headphones as the default device is suggested. These instructions were all done with no /etc/asound or ~/.asound.rc present.
Playback using smplayer
smplayer needs special configuration to select the correct device and set the sample rate to 96KHz.
Setting the audio output:
Preferences >> Audio >> Output Driver >> Custom alsa:noblock:device=plughw=Wilkins.0
Setting the sample rate using the resample filter (passed to mplayer by smplayer):
Preferences >> Advanced >> Audio Filter resample=96000
The fliter only accepts S16_LE sources. CD's, WAV, and MP3 sources are usually output in this format
No audio output -- first steps
- Make sure the kernel has the usb-audio module configured, and if a module, loaded
- Make sure media-plugins/alsa-plugins is installed with the required USE flags
qlist -IC alsa-plugins
- Check the connections on the computer and the headphones
- Make sure the headphones are turned on
- The headphones must be worn to enable audio output
- Check the device muting and volume settings
No audio output in speaker-test
- Proximity sensors disabled audio
make sure of a good fit
- Sample format issues in speaker-test:
Various messages, including no support for s24_3LE -- use an empty /etc/asound A short burst of buzzing and then silence -- use a 96KHz sample rate
No audio output in smplayer
Use View >> Mplayer/mpv log to see error messages
- Make sure the output device is custom and uses plughw for the Wilkins device
- Make sure the resampling filter has been specified for pass through to mplayer
- Check the application muting and volume level. Gradually increase to the maximum.
Low volume / large variation in volume between sources
- Increase the device master volume to 33 in alsamixer
- Set the application volume level to middle to start, then adjust
- Different sources just have different volume ranges, adjust the volume as needed
- We tested 43 old USB-C to USB-A cables. 1 was great. 10 were dangerous . Retrieved on September 22nd, 2022.