Noise reduction in hydraulic systems often involves isolating the pump/prime-mover assembly using flexible mounts (isolators). In these cases, the use of hose is necessary to maintain the isolation between the pump/prime-mover and the rest of the system.
The flip-side to this though is, although long lengths of hose can reduce structure borne noise, hose is actually an efficient radiator in the frequency range where most of the energy is generated, typically around 600, 900 and 1200 Hertz.
In terms of vibration and noise conductivity, a long length of pipe or tube is the worst configuration. A long length of hose is better than pipe or tube, but still bad. A better configuration is one section of pipe or tube connected to one section of hose. And the best configuration for noise reduction is one section of pipe or tube with a section of hose either side, that is: hose > tube >hose.
Two other negatives of hose are: its length changes with pressure, and when it is bent through a radius, it acts like a Bourdon tube; it tries to straighten as pressure increases. Both of theses dynamics produce forces which act on connecting structures. For these reasons, the best way to control noise when making bends with hose is to use a solid bend (90° or 180°) with a hose section on either side.
In case you're not convinced, during testing, the noise level of a hydraulic power unit with a 150 gallon reservoir and 40 GPM piston pump running at 1200 rpm and at a pressure of 750 psi was measured at 88 dB(A). The power unit featured a radiused pressure hose. When this pressure hose was re-configured so that it comprised two hoses separated by a 90° swept elbow, the noise level was reduced by 5 dB(A).
This may not sound like much, but the logarithmic nature of the decibel (dB) scale means that a 5 dB(A) reduction equates to a 44% reduction in sound pressure and a 68% reduction in sound power. Not bad when you consider that when compared to other possible noise reduction measures such as increasing mass and installing isolating mounts or acoustic filters, changing the configuration of the pressure hose is probably the simplest and cheapest option, and the easiest to implement.
As you can see, installing uninterrupted lengths of hose for noise reduction is a mistake. And to discover six other costly mistakes you want to be sure to avoid, get "Six Costly Mistakes Most Hydraulics Users Make... And How You Can Avoid Them!" available for FREE download here.