The small USB speaker “MINI EXTERNAL USB STEREO SPEAKER”, SKU #ADA3369, has crackles and pops, and USB disconnects when volume put to full using CLI command alsamixer
Works perfectly OK with a different USB speaker (Dell AC511 soundbar) - so I know the Pi and Operating system is at least capable of handling full volume output.
So I suspect the USB speaker is faulty hardware, or a faulty USB speaker driver.
running Raspbian GNU/Linux 9 (stretch)
TROUBLESHOOTING OUTPUT
pi@raspberrypi:~$ lsusb
Bus 001 Device 029: ID 1908:2070 GEMBIRD
pi@raspberrypi:~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
Subdevices: 7/7
Subdevice #0: subdevice #0
Subdevice #1: subdevice #1
Subdevice #2: subdevice #2
Subdevice #3: subdevice #3
Subdevice #4: subdevice #4
Subdevice #5: subdevice #5
Subdevice #6: subdevice #6
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 IEC958/HDMI [bcm2835 IEC958/HDMI]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: ALSA [bcm2835 ALSA], device 2: bcm2835 IEC958/HDMI1 [bcm2835 IEC958/HDMI1]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Device [USB2.0 Device], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
pi@raspberrypi:~$
SYSTEM LOG:
Oct 22 15:59:02 raspberrypi kernel: [ 318.848113] usb 1-1.2: USB disconnect, device number 26
Oct 22 15:59:02 raspberrypi kernel: [ 319.042730] usb 1-1.5: USB disconnect, device number 24
Oct 22 15:59:02 raspberrypi kernel: [ 319.042752] usb 1-1.5.2: USB disconnect, device number 25
Oct 22 15:59:03 raspberrypi kernel: [ 319.802303] usb 1-1.5: new high-speed USB device number 27 using dwc_otg
Oct 22 15:59:03 raspberrypi kernel: [ 319.941933] usb 1-1.5: New USB device found, idVendor=05ac, idProduct=1006, bcdDevice=96.15
Oct 22 15:59:03 raspberrypi kernel: [ 319.941959] usb 1-1.5: New USB device strings: Mfr=1, Product=2, SerialNumber=3
Oct 22 15:59:03 raspberrypi kernel: [ 319.941971] usb 1-1.5: Product: Keyboard Hub
Oct 22 15:59:03 raspberrypi kernel: [ 319.941981] usb 1-1.5: Manufacturer: Apple, Inc.
Oct 22 15:59:03 raspberrypi kernel: [ 319.941990] usb 1-1.5: SerialNumber: 000000000000
Oct 22 15:59:03 raspberrypi kernel: [ 319.944513] hub 1-1.5:1.0: USB hub found
Oct 22 15:59:03 raspberrypi kernel: [ 319.944909] hub 1-1.5:1.0: 3 ports detected
Oct 22 15:59:03 raspberrypi kernel: [ 320.262220] usb 1-1.5.2: new low-speed USB device number 28 using dwc_otg
Oct 22 15:59:03 raspberrypi kernel: [ 320.413656] usb 1-1.5.2: New USB device found, idVendor=05ac, idProduct=024f, bcdDevice= 0.74
Oct 22 15:59:03 raspberrypi kernel: [ 320.413670] usb 1-1.5.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
Oct 22 15:59:03 raspberrypi kernel: [ 320.413677] usb 1-1.5.2: Product: Apple Keyboard
Oct 22 15:59:03 raspberrypi kernel: [ 320.413685] usb 1-1.5.2: Manufacturer: Apple Inc.
Oct 22 15:59:03 raspberrypi kernel: [ 320.424360] input: Apple Inc. Apple Keyboard as /devices/platform/soc/3f980000.usb/usb1/1-1/1-1.5/1-1.5.2/1-1.5.2:1.0/0003:05AC:024F.0010/input/input15
Oct 22 15:59:03 raspberrypi kernel: [ 320.496799] apple 0003:05AC:024F.0010: input,hidraw1: USB HID v1.11 Keyboard [Apple Inc. Apple Keyboard] on usb-3f980000.usb-1.5.2/input0
Oct 22 15:59:03 raspberrypi kernel: [ 320.503489] input: Apple Inc. Apple Keyboard as /devices/platform/soc/3f980000.usb/usb1/1-1/1-1.5/1-1.5.2/1-1.5.2:1.1/0003:05AC:024F.0011/input/input16
Oct 22 15:59:03 raspberrypi kernel: [ 320.573445] apple 0003:05AC:024F.0011: input,hidraw2: USB HID v1.11 Device [Apple Inc. Apple Keyboard] on usb-3f980000.usb-1.5.2/input1
Oct 22 15:59:03 raspberrypi mtp-probe: checking bus 1, device 28: "/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.5/1-1.5.2"
Oct 22 15:59:03 raspberrypi mtp-probe: bus: 1, device: 28 was not an MTP device
Oct 22 15:59:03 raspberrypi kernel: [ 320.692242] usb 1-1.2: new full-speed USB device number 29 using dwc_otg
Oct 22 15:59:04 raspberrypi kernel: [ 320.833160] usb 1-1.2: New USB device found, idVendor=1908, idProduct=2070, bcdDevice= 1.00
Oct 22 15:59:04 raspberrypi kernel: [ 320.833174] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
Oct 22 15:59:04 raspberrypi kernel: [ 320.833181] usb 1-1.2: Product: USB2.0 Device
Oct 22 15:59:04 raspberrypi kernel: [ 320.833189] usb 1-1.2: Manufacturer: Generic
Oct 22 15:59:04 raspberrypi kernel: [ 320.833195] usb 1-1.2: SerialNumber: 20130100ph0
Oct 22 15:59:04 raspberrypi mtp-probe: checking bus 1, device 29: "/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.2"
Oct 22 15:59:04 raspberrypi mtp-probe: bus: 1, device: 29 was not an MTP device