This is a cover for HackRF Portapack H1 with two mini-loudspeakers. There is some air volume inside the cover intended to improve bass sound.

The two speakers are still monaural; Portapack H1 does not support stereo sound. 

To activate the speakers under the Mayhem firmware: Goto Options/Interface. The topmost clickbox must show a red "X". A loudspeaker symbol will appear at the top. Activate the loudspeaker (loudspeaker symbol turns green). Goto e.g. Receivers/Audio. Set the volume to 90 (at the extreme right of the second row from the top).

Speaker: Pair of 8 Ohm 1 Watt    28 x 9 x 4 mm
Connect them in series (2 x 8 = 16 Ohm)

I got mine via Aliexpress from the KY WIN ROBOT shop:
https://www.aliexpress.com/item/32923824898.html?spm=a2g0o.productlist.0.0.71ae25de7TZYOQ&algo_pvid=3460079d-0530-40c8-8761-bedaeda33767&algo_exp_id=3460079d-0530-40c8-8761-bedaeda33767-6

See also my other Portapack accessories:
https://www.thingiverse.com/thing:4892365
https://www.thingiverse.com/thing:4907118
https://www.thingiverse.com/thing:4924478