OEM 2013-2015 BMW X1 E84 Right Under Seat Subwoofer Woofer Speaker | eBay
X1 15 INCH subwoofer box plan - YouTube
IMG_0847 | Rog Mogale 'X1' Sub bass 6th order bandpass cabin… | Flickr
Light Harmonic Tesla Model Y Premium Sound System Stereo Kit | x2 Front Door Woofers & x1 Subwoofer | Perfect for High Bass & Loud Music | Music Lovers | Easy Install (3 Units) : Electronics