[JB63]

Those pumps say they are made of cast iron. You could probably watch the rust develop. Also mounting pumps above a tank is not a good idea. It is hard to get water in them to start the flow. It can be done but it is a PITA.

Another thing to remember is that sound travels better in water than in air. The speed of sound is about four times faster in water than in air.

It is true that sound speed is faster in water than in air (sound speed = sqrt (Bulk modulus / mass density)). This has to do with the compressibility (bulk modulus) of the medium (water is less compressible than air, though more compressible than steel). However what we need here is the "radiation efficiency" in air vs in water. There have been underwater sound experiments done by eg the US Navy where sounds travels for very long distances underwater because there is very little dissipation/absorption.

It is easy to make a room (air) quieter by adding some sound absorbing panels and so on. It'll be more difficult to make a volume of water quiet.

The approach I'd take is to work more on the source (noise generation) as opposed to the symptom (noise reduction). For this, I'll take a dual approach:

1. Reduce structural vibration excitation: (vibration creates sound and vice versa) Here we'd need a balanced pump, mounted on soft rubber feet to a heavy mass. Flex couplings between the pump and pipes. Heavy pipes (the heavier the less they vibrate and the less they create noise)...

2. Reduce In-water pressure pulsations: Pick a pump that has as smooth as possible a flow rate, usually a large number of impeller blades, and carefully designed inner chamber (none of this is available today as chamber/impeller geometry is very primitive) .... so there is a lot we can do ... question is, who's going to start (ie which pump manufaturer is going to develop quiet pumps ?)

 

[d_link]

Sorry Jason I hope you don't think I'm high jacking your thread but you sparked a great topic. JB63 great info would you say maybe a pump with the impeller modified kind of like a ships propellers would be quieter then lets say a paddle wheel?

 

[BlackGrandPrix]

No problem at all. I said discuss

 

[JB63]

Sorry Jason I hope you don't think I'm high jacking your thread but you sparked a great topic. JB63 great info would you say maybe a pump with the impeller modified kind of like a ships propellers would be quieter then lets say a paddle wheel?

Yup, there is a lot we can learn from submarine impellers the Navy has designed. the best impeller geometry would be that of a "scooping" where the blade is pushing on water "continuously" as opposed to straight blades. It may be beneficial though to add some sort of in-line helmholtz resonator that would be tuned to the blade passage frequency (number of blades times pump RPM). Those devices are often used in duct acoustics and bass speakers but rarey in aquatic applications .. need to look further there.

 

[d_link]

How would you tie a helmholtz resonator into an impeller? Are you using the helmholtz resonator to oppose the sound or resonate it? I'm not to familiar with a helmholtz resonator but from what I read it would create sound and make it louder correct? Also submarine impellers and how they silence the motors before nuclear subs came along may lead us to an answer. Also are there any members that might have worked on a submarine that could lend a hand?

 

[JB63]

How would you tie a helmholtz resonator into an impeller? Are you using the helmholtz resonator to oppose the sound or resonate it? I'm not to familiar with a helmholtz resonator but from what I read it would create sound and make it louder correct? Also submarine impellers and how they silence the motors before nuclear subs came along may lead us to an answer. Also are there any members that might have worked on a submarine that could lend a hand?

The Helmholtz resonator would be tied as close as possible to the pump's out, not the impeller. The principle is that the resonator puts out a pressure wave that is exactly out-of-phase with that from the impeller, bringing the total fluctuation to something very small. It's the same principle (but in reverse) of those ports (openings) you see in audio subwoofers.

As for subs, the main issue with the old generation (diesel) is that the combustion process of the diesel made a lot of noise. In addition diesel needed air (oxygen) to burn. With the nuclear submarines, heat is used to generate steam which pushes on pistons/turbines, hence no combustion/explosion and that is why they're very quiet.

The propeller design in nuclear subs is designed to minimize the wake turbulences and create no cavitation (tiny bubbles due to negative pressure next to impeller blades). The propeller is much efficient if it is moving through laminar (non-turbulent) flow. The geometry of all powerheads we use creates a lot of turbulence and hence inefficiency.

I acn talk about this on and on ... stop me if I did too much

 

[Bsbarton]

It is obvious that we introduce noise to our tanks. Also it is good to eliminate or reduce it. Reading this thread I wonder how noise impacts the fish and coral. Shallow water animals that we keep will be subject to much more noise that deep sea aminals.

I read this:

"Well, fish can click, squeak, whistle, peep, grunt, croak, and make lots of other noises. With all that fishy underwater racket, it would be kind of silly if fish couldn't hear!

Your question isn't silly though. After all, there are no ears on a fish's head. Ears that stick out (like yours and mine) would ruin a fish's streamlined body shape and slow the fish down.

But fish have ear parts inside their heads. A fish's body picks up sounds coming through the water and sends them to the inside ear parts.

A fish also has a special organ--called a lateral line--that runs along each side of its body. This organ helps the fish sense movements in the water, including vibrations made by sounds. And it gives clues about what direction a sound is coming from."

Anyone have any info?

 

[bigdane36]

mine sounds like a harley lol i need to get that fixed -devil

 

[d_link]

I'll borrow some instrumentation from work and do some basic NVH measurement ... I'll keep y'all posted. Goal: some dB level?

Did you get the equipment?

 

[liquidskys]

our main return is in the sump/fuge which is in a dffrent room of the house... (so Im guessin that may cut down on some of the hum from that pump..)

but we have 2 maxijet 1200's in the display for added flow and man its definitly humming in there..

on top of that forsome reason out lights hum a little too.. its not the ballast it seems to be coming from the bulbs themselves.. but regardless it makes the canopy hum which is sitting on top of the tank..

I honestly dont think the fish or inverts really mind or get stressed..
maybe at first when they are are first added.. specially if they were wild caugth..

however I think the stress in out little reef's are way less then if they were still in the wild.. (other predators, lack of food or atleast hvaing to search for it) this being said if your reef is healthy and well maintained..