OVERVIEW: Klipsch SLM-3400-C Shallow Depth In-Ceiling Speaker One of the most compact in-ceiling speakers on the market, the SLM-3400-C features a shallow depth (50mm) with a fully enclosed back box. Along with premium acoustics straight from the legendary Klipsch Reference 3000 architectural series, the SLM-3400-C brings high performance acoustics in an extra slim package - for great sound where installation space is limited.