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Topic: How to properly isolate hum noise (Read 7029 times) previous topic - next topic
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How to properly isolate hum noise

Hello,

I have a serious problem with with. It is not audio hardware related, but is IS audio related.
I tried about everything, but still the problem is still there and really loud/annoying.

Problem is as follows. I have an aquarium (800 litres, with an Eheim 2080 canister filter).
Under my aquarium (Ferplast Star 200) is a cabinet that houses the filter. I had to remove the bottom because of the size, but even with the bottom in, it makes no difference.
The filter has been placed on 2 heavy paving stones. On top of that rubber isolation mats and the cabinet is padded with isolation acoustic foam. The tubing is isolated also through sponges so it does not come in contact with the cabinet.

When I turn the filter on in my house there is a loud hum noise almost everywhere in the house. I can even hear it on the 1st floor (aquarium is at ground floor). My net frequency is 50HZ (Europe).

Even stuffing the cabinet full of isolation foam has practically NO effect, it goes right through. Probably I need some heavy materials to keep the hum noise out. Foam is not the answer, it's not high pitched sound.

At this point I'm looking out for shops to buy heavy "lead" bitumen adhesive material to put inside the cabinet, but I have no idea if that is giving us any effect. By the way that material is quite expensive, I need quite a lot of it to seal the cabinet.

PS. I drove to Eheim myself with the filter to have it tested. They tested it on a concrete floor with no cabinet. In that situation the only thing you hear is the water running through the tubing, no hum. But in my situation the filter _must_  be placed in the cabinet under the aquarium.

Could anyone PLEASE give me some answers? I've really tried about everything I can imagine.

Re: How to properly isolate hum noise

Reply #1
Hello,

I have a serious problem with with. It is not audio hardware related, but is IS audio related.
I tried about everything, but still the problem is still there and really loud/annoying.

Problem is as follows. I have an aquarium (800 litres, with an Eheim 2080 canister filter).
Under my aquarium (Ferplast Star 200) is a cabinet that houses the filter. I had to remove the bottom because of the size, but even with the bottom in, it makes no difference.
The filter has been placed on 2 heavy paving stones. On top of that rubber isolation mats and the cabinet is padded with isolation acoustic foam. The tubing is isolated also through sponges so it does not come in contact with the cabinet.

When I turn the filter on in my house there is a loud hum noise almost everywhere in the house. I can even hear it on the 1st floor (aquarium is at ground floor). My net frequency is 50HZ (Europe).

Even stuffing the cabinet full of isolation foam has practically NO effect, it goes right through. Probably I need some heavy materials to keep the hum noise out. Foam is not the answer, it's not high pitched sound.

At this point I'm looking out for shops to buy heavy "lead" bitumen adhesive material to put inside the cabinet, but I have no idea if that is giving us any effect. By the way that material is quite expensive, I need quite a lot of it to seal the cabinet.

PS. I drove to Eheim myself with the filter to have it tested. They tested it on a concrete floor with no cabinet. In that situation the only thing you hear is the water running through the tubing, no hum. But in my situation the filter _must_  be placed in the cabinet under the aquarium.

Could anyone PLEASE give me some answers? I've really tried about everything I can imagine.

The source of any sound in this system is usually the pump. What about it?

Re: How to properly isolate hum noise

Reply #2
I don't understand what you mean with that answer.

That pump is needed to keep my fish alive. The hum get transfered to the cabinet (I guess) and is quite loud. Even after numerous things I tried to keep te noise down. I know that the pump is generating the hum, that is obvious. I cannot prevent that.

The source is there, but I need a way to keep it in the cabinet some way...

The pump has been checked by Eheim and is working normally according to them.

Re: How to properly isolate hum noise

Reply #3
What kind of floor is it resting on (floorboards, concrete, etc.)?

Re: How to properly isolate hum noise

Reply #4
You would usually try to mount the source of the hum in an elastic way so that the vibration isn't getting transferred to other items that may act as a sounding board.

Is the pump bolted down or attached rigidly? If so, is there a possibility to mount it using some kind of elastic fixture? Of course this assumes that the pump itself is the hum source. Transformers, however, can also hum.

In general, go as close to the source of hum as possible, and try to change the mounting there.

Re: How to properly isolate hum noise

Reply #5
There are many industrial vibration systems available. But they have to be selected based on the weight of the item and the frequency range of the vibrations.
Do a search for 'vibration isolation'
Kevin Graf :: aka Speedskater

Re: How to properly isolate hum noise

Reply #6
Quote
They tested it on a concrete floor with no cabinet.
And, I assume you have a wood floor?   Do you think the cabinet is "amplifying" the noise?

You might try some springs or foam rubber padding between the pump and the floor to minimize the amount of vibration that's mechanically transmitted to the house floor/frame.   Since the pump didn't make noise on the concrete floor, I assume pump is vibrating the floor (or cabinet) and that's where the noise is coming from.

 If the cabinet is vibrating and "amplifying" the noise, it might help to add stiffening/bracing to minimize the vibration.     It might also help if you can stiffen/brace the floor.

Re: How to properly isolate hum noise

Reply #7
50 Hz is not very audible. It is possible that what you hear is mainly harmonics.

If you hold the pump in your hands, how loud is it?

Re: How to properly isolate hum noise

Reply #8
Quote
50 Hz is not very audible.
In that case I guess I can throw-away my subwoofer!   :P   ...50Hz is within the audible range and with a large surface vibrating "mechanically" (like a wall or a floor) it could be annoying.

But there is a chance that the frequency is more related to motor/pump rotation than to the power line frequency.

Re: How to properly isolate hum noise

Reply #9
Quote
50 Hz is not very audible.
In that case I guess I can throw-away my subwoofer!   :P   ...50Hz is within the audible range and with a large surface vibrating "mechanically" (like a wall or a floor) it could be annoying.

But there is a chance that the frequency is more related to motor/pump rotation than to the power line frequency.
50 Hz is barely in the audible range. That is why you need a large surface (such as a subwoofer) vibrating in order to hear it well.

Re: How to properly isolate hum noise

Reply #10
50 Hz is not very audible. It is possible that what you hear is mainly harmonics.

If you hold the pump in your hands, how loud is it?

Came here to ask this.  How loud is it in your hands?

If its quiet in your hands, get some vibration isolating foam or Sorbothane sheets to decouple it from whatever its mounted on.  That or just buy a quieter pump.  I used to have a 300 lph eheim that was dead silent.  Couldn't even tell if it was on without touching it.

Re: How to properly isolate hum noise

Reply #11
50 Hz is not very audible. It is possible that what you hear is mainly harmonics.[{/quote]


 It is my impression that this is often factored into the design, whether intentionally or not.

Quote
If you hold the pump in your hands, how loud is it?

Good question, but also it is possible that the individual pulses of air are carrying the noise.   An in-line muffler may help.

Re: How to properly isolate hum noise

Reply #12
The floor is wood indeed, but the floor is not the one that is transfering the hum noise. I'm quite sure about that. I think it's the cabinet.

I cannot just hold the pump in my hands. This thing weighs about 35 kilograms when filled up. It not easy to just place it outside the cabinet, because I have to cut off all the tubing, drain the system, (co2 reactor, UV etc) then move it and connect it with new tubing.

I'm quite confident that the cabinet is taking over the hum noise, possible throught the air (is that possible) or via the 3 tubes connecting the pump, but even that is isolated, so could it be just through the air?

I hardly hear any hum noise when I put my head in the cabinet, but from a distance it becomes very audible.

Last night I put a rubber isolation 100cm x 50cm x 1cm on top of the pump and that did help a bit. The hard thing is that the pump has 3 tubes on top so I cannot just put rubber around it.


Could it be de resonance frequency of my cabinet is around 50hz?

For the people that think 50hz is barely audible, just play that tone with foobar on a full range audio system, preferably with a subwoofer. Then add a little distortion also to make it even more comparable. It's not only hearable, it's "feelable". that tone just passes through everything .

Re: How to properly isolate hum noise

Reply #13
Is it possible for sound/vibration to enter a structure or system at one point and leave it somewhere else? As I write, the idea of taking two cans and a piece of string to make a child's "telephone" system occurs to me: you can't hear the sound of voices from the string, but you can from the cans.

Is it possible, then, that vibrations may enter the wooden house structure structure under the pump, and be "transmitted" to some other point, where something is acting as a sounding box, or even some loose thing is converting the movement into sound?

Walk around the house with a screwdriver, holding the tip against things and the handle against the ear?

Just wondering...
The most important audio cables are the ones in the brain

Re: How to properly isolate hum noise

Reply #14
Is it possible for sound/vibration to enter a structure or system at one point and leave it somewhere else? As I write, the idea of taking two cans and a piece of string to make a child's "telephone" system occurs to me: you can't hear the sound of voices from the string, but you can from the cans.

Is it possible, then, that vibrations may enter the wooden house structure structure under the pump, and be "transmitted" to some other point, where something is acting as a sounding box, or even some loose thing is converting the movement into sound?

Walk around the house with a screwdriver, holding the tip against things and the handle against the ear?

Just wondering...

Well, when I put my head in the cabinet the most right (the pump is on the left, 3 door cabinet) the hum is just as loud as the first cabinet. There is definitely some resonance transfered.

I contacted 2 (car audio - tuning) companies that should sell (In Dutch Zelfklevend Bitumen), don't know the word in English, but it is heavy adhesive stuff that is also used inside car doors to dampen the sound. Unfortunately neither of them responded to my request....

Re: How to properly isolate hum noise

Reply #15
Well, when I put my head in the cabinet the most right (the pump is on the left, 3 door cabinet) the hum is just as loud as the first cabinet. There is definitely some resonance transfered.

I contacted 2 (car audio - tuning) companies that should sell (In Dutch Zelfklevend Bitumen), don't know the word in English, but it is heavy adhesive stuff that is also used inside car doors to dampen the sound. Unfortunately neither of them responded to my request....

Ask ebay. People do DIY car damping: the materials are available.

It has already been mentioned that there are industrial-strength absorption mats and feet available. I had a dancing washing machine, and google found me a whole heap of vibration absorbers. I ended up with Silent Feet, which, at least made the machine dance on the spot instead of flinging itself around. For you, one of the mat solutions I saw might be more appropriate.
The most important audio cables are the ones in the brain

Re: How to properly isolate hum noise

Reply #16
Try pressing on each of the surfaces of the cabinet. If one or more result in a significant reduction in noise then you have found a panel that resonates. Try stiffening them by adding a cross brace on the inside.