BowersWilkins PX7

Resources

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.

Note
The PX7 V2 is a newer model with different connections. It is unknown how well these instructions work for that model.

Software

These USE flags are set:

FILE /etc/porage/package.use

media-plugins/alsa-plugins ffmpeg mix usb_stream
media-video/mplayer alsa

Hardware

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):

user $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.

Note
Even the though the USB speed is 480 MBit/s, the device must be plugged into a USB 3 port or better.

Tip
The quality of the USB cable may be a safety issue ^[1]

Standard

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)	`19b5:0025`	snd-usb-audio (when built as a module)	5.19.3	Enable kernel option `SND_USB_AUDIO` in the kernel.

Installation

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.

Kernel

KERNEL

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

root #emerge --ask --verbose media-libs/alsa-lib media-plugins/alsa-plugins media-sound/alsa-utils

For the playback apps used in these instructions:

root #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.

user $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 plug or 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.

Configuration

ALSA configuration

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:

CODE

Preferences >> Audio >> Output Driver >> Custom
    alsa:noblock:device=plughw=Wilkins.0

Setting the sample rate using the resample filter (passed to mplayer by smplayer):

CODE

Preferences >> Advanced >> Audio Filter                                                       
    resample=96000

Note
The fliter only accepts S16_LE sources. CD's, WAV, and MP3 sources are usually output in this format

Troubleshooting

No audio output -- first steps

Make sure the kernel has the usb-audio module configured, and if a module, loaded

user $lsmod

Make sure media-plugins/alsa-plugins is installed with the required USE flags

user $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

user $alsamixer

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

References

↑ We tested 43 old USB-C to USB-A cables. 1 was great. 10 were dangerous [1]. Retrieved on September 22nd, 2022.

[1] We tested 43 old USB-C to USB-A cables. 1 was great. 10 were dangerous [1]. Retrieved on September 22nd, 2022.

[1]