Revenue and geographic information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 260,119	$ 208,398	$ 966,663	$ 864,069
Wireless speakers
Disaggregation of Revenue [Line Items]
Revenue	104,626	93,867	401,994	453,185
Home theater speakers
Disaggregation of Revenue [Line Items]
Revenue	89,660	66,732	388,902	283,952
Components
Disaggregation of Revenue [Line Items]
Revenue	48,135	42,283	137,539	113,530
Other
Disaggregation of Revenue [Line Items]
Revenue	17,698	5,516	38,228	13,402
Americas
Disaggregation of Revenue [Line Items]
Revenue	145,612	122,982	520,684	447,705
Europe, Middle East and Africa (“EMEA”)
Disaggregation of Revenue [Line Items]
Revenue	88,151	75,585	383,537	374,790
Asia Pacific (“APAC”)
Disaggregation of Revenue [Line Items]
Revenue	26,356	9,831	62,442	41,574
United States
Disaggregation of Revenue [Line Items]
Revenue	134,924	113,558	481,888	409,701
Germany
Disaggregation of Revenue [Line Items]
Revenue	20,636	18,512	96,775	95,720
United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	19,810	17,930	90,036	88,421
Other countries
Disaggregation of Revenue [Line Items]
Revenue	$ 84,749	$ 58,398	$ 297,964	$ 270,227