|This article does not cite any references or sources. (October 2013)|
Jet engines, whether or not installed in aircraft, can be tested either indoors or outdoors.
- A hush house is large enough to accommodate an entire aircraft, which is backed into the test bay through hangar doors by a tug. The engine can be run while installed in the aircraft, which must be restrained by holdback devices resistant to a multiple of maximum engine thrust. Most hush houses also have thrust frames for testing of an "uninstalled" engine that has been removed from an aircraft.
- Indoor engine test cells are facilities designed for testing engines removed from an aircraft (referred to as "uninstalled engines"). The engines in such facilities are generally suspended from overhead thrust frames.
- Outdoor run-up areas are facilities where engines are tested outdoors while mounted on thrust stands, or where engines are tested outdoors while installed in an aircraft. They may, or may not, include provisions for noise control.
The air intake and exhaust systems of indoor engine test cells and hush houses are designed to block the transmission of noise, whilst optimizing the engine air flows. The engine exhaust, after having been thoroughly mixed with cooling air, is generally discharged through a vertical stack. The gas path incorporates acoustic damping panels (often containing fibrous insulation protected from gas stream erosion by metal mesh) to reduce the sound energy of the gas stream and attenuate the noise transmitted to the surrounding outdoor area.
Because the engine exhaust flow is "augmented" with a relatively large flow of cooling air induced by a Venturi effect into the exhaust silencing system, the exhaust muffler of an indoor test facility is generally referred to as an augmenter tube, although the term "detuner" is commonly used in the UK.