Sound insulation

I have range hood over gas range. There is wall mounted exterior blower and 8" diameter flex aluminum duct that connects from the blower to the hood. The hood and duct are concealed inside custom built wooden cabinet. The duct is really short, in fact it is no more then 90 degrees elbow. The blower is rather powerful and even if it operates at lowest speed it still causes quite noise in kitchen. I thought about putting some sort of inculation into cabinet that conceals the duct with hope to reduce noise from the blower. What kind of insulation provides maximum sound insulation? Are there any other steps that can reasonable be done to reduce blower noise?
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Sasha wrote:

I suspect most of the noise is coming from the blower and since it appears it is very close to the living area and has only a short air path, I don't think there is much you can do other than to opt for a quieter blower.
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Joseph Meehan

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Is it new or maybe old and has dirt (gunk) built up on the squirrel cage fan? Cleaning may help. Any small off balance of the fan will set up a vibration noise that maybe remounting the blower on cushions might help. It will resonate through the cabinat. I have a patio fountain pump that was noisy sitting on the plastic bottom that I put a piece of sponge under it and it quieted right down.
If it is wind noise, there is nothing you can do, that I have found. I have installed a few like that, seems like they were Thermador brand and they are just wind noisy but efficient and expensive.

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how about extending the duct, put in a right angle bend and move the blower down the wall, building some sort of exterior cabinet covered with siding etc to match the house.
David
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The blower is Broan brand, brand new and is mounted to siding outside if the house. There is no way to move it anywhere. The noise is a wind noise, no vibrations from duct, cabinet, etc. While I probably won't completely reduce noise, I can reduce it if I stuff good sound insulation into the cabinet that conceals the duct. The cabinet is not competely finished yet but even if I wrap it into duct foil unsulation I find there is les noise in the kitchen.
djenkins6 wrote:

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Sasha wrote:

If room permits change the 90 bend to two 45 bends. That should help reduce the turbulance. TB
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Sasha wrote:

If you can not or will not replace the blower, then I suggest reducing the flow restrictions. Use the largest possible ducts, make sure they are solid metal (no plastic or corrugated stuff). Consider adding non-flammable insulation around them and make sure any filters or grates that might restrict the air flow are as open and as large as possible.

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Joseph Meehan

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I agree with Joe, remove the flex duct and install hard duct. You may also want to install a speed control for the motor, why have this fan running at maximun RPM when you are just boiling water, or frying eggs. Why are you complaining? I thought everyone wants an industrial grade - super duper, "commercial cooking" set up in their home. Enjoy the sounds of a commercial kitchen, since in your case you can reduce the sound of moving air a little BUT it will never be what you were used to on your "basic no-frills" kitchen hood.
Joseph Meehan wrote:

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