Guide resonance sounds and wobbling

The noise of electric motors itself is inaudible, however it is sometimes greatly amplified by resonant building materials. Once the source of the noisy operation of a ceiling fan has been identified there are several possibilities to tone down the vibrations. This guide will also tell you how to correct an unstable, wobbling running.
Total reading time: 9 min or skip directly to the summary

Contents:

Short introduction: Sound

Sound describes a spreading mechanical wave that is perceived in the ear conch and is passed on to the brain. Apart from normal household activities like cooking, cleaning and talking, electric appliances also create sound during their ventilation and operation process. The generated sound should be as quiet as possible so that the well-deserved atmosphere of rest and relaxation of the residents is not disturbed. The threshold to a disturbance is a sound level of 40dB(A), an in-between of whispering and talking indoors. Sounds below this value or usually not noticed consciously, however during rest periods or times of mental pressure even low volume can cause people strain. Constant exposure can even lead to stress-related illness such as a heart condition.

More information about sound pressure, comparative values and health effects in our guide "Sound and sound pressure".

Frog croaking
Older generations of washing machines, hair dryers, hoovers and dish washers sometimes reach more than 90 decibel – modern models are much quieter. Particularly instruments that used for longer periods of time, or operate continuously, such as fume hoods, ventilation systems, refrigerators and freezers are worth thinking about investing a bit more money into quiet units. Often they also come with the added benefit of low energy consumption. Energy-saving fans are equipped with a DC motor that makes them run so silent that they can even be set up in bedrooms and operate during the night. For this reason you should always pay attention to decibel specifications when purchasing a new device, and compare the values with everyday noise to get a better understanding: For example, 10 decibel correspond to leaves falling from the tree, 20dB are similar to a clock ticking and 60dB are like croaking amphibians. Otherwise, a seemingly exceptional bargain might turn out to be a frog, not a prince.

Croak – Disputes between neighbours because of garden ponds and the disquieters they attract often end up in courtrooms. Looking harmless and innocent, a frog produces up to 90 decibel.


What are resonance sounds?

Guitarist
Resonance – the reverberation of a vibration – is occasionally much stronger than the original source. This effect is used in music. Hollow bodies are integrated in musical instruments to create the sound of full, melodic sounds. Motor-powered appliances are also able to cause resonance, however this sound results in much less pleasure.

Every electric motor generates vibration that is not perceived by the human ear in its pure acoustic form. In many countries they are known as mains hum that is caused by the mains supply in AC and EC motors. If the amplitudes meet solid, resonating materials such as metal, wood or drywall they are intensified, just like it would happen with a guitar.

Identifying the source

Correctly fitting the ceiling mount prevents resonance sounds
The fan’s ceiling mount transfers vibrations of the motor to the building materials where they are intensified in some cases.
Apart from resonance sounds there are other things that can cause irritating buzzing in a ceiling fan:
  1. Audible noise after installing a ceiling fan for the first time is in no way an indicator for a faulty product. The parts and components of the brand new device simply might not have had time to properly run in yet. Leave the device on for 24 hours non-stop in summer mode (cooling motion) to reach the essential service performance. Afterwards the fan usually operates without further problems.
  2. Inner parts of the motor have fallen into the housing during the installation and now move back and forth with each movement of the motor. You can easily test this by lightly shaking the fan to see if any screws or other small parts are causing rattling sounds. If that is not the case, the next step is to hold the motor in your hand and let it operate without the blades (not possible with energy-saving DC direct current models). Please take note of the safety instructions according to the manual. If the motor unit operates smoothly and quietly, there is no damage on the motor. Instead, the bracket on the ceiling has caused the noise. This can be stopped with our tips in the following chapter.
  3. Continuously variable dimmers (wall controllers) are not suitable for ceiling fans unless it has been specifically indicated that they are compatible. This could be another reason for the irritating operating noise. Our product range includes wall controllers that allow you to individually regulate the fan’s rotation speeds.

Tips for a smooth running

The place of installation is a crucial factor when it comes to smooth operation of the ceiling fan. Preferably, try to fix the unit to a crossbeam, piece of lumber or structural element. In case of suspended ceilings it is recommended connect the wooden or drywall ceiling to the higher solid ceiling, therefore interlocking them both and transferring the resonating surface further up. Long screws and threads that reach into the main ceiling reduce a potential resonance and thereby resonance sounds. With the help of a special suspension system, available in different sizes, it is possible to bridge the gap as well.

In case the device is already put up, you can place a piece of foam rubber in between the hanging (semispherical upper part of the rod) if the model has a suspension rod. On devices without rod simply but the rubber between the ceiling and the ceiling mount. As long as the inlay between metal and solid ceiling is soft and elastic you can also use small pieces of carpet or other textiles instead of rubber. The objective is to eliminate all rigid, fixed spots between the fan and wall that may transfer vibration.

Eliminating wobbling

A visible wobbling or jerking of a ceiling fan can result in irregular noise that is perceived as disturbing in living and working environments. This noise does not actually count as resonance sound, nevertheless it should be addressed anyway.

After the recommended 24h running-in period the distance of each blade to the ceiling should be identical. The measurements can be taken with a ruler or folding rule. First of all, check if the ceiling mount is fixed properly and securely to the ceiling on all sides. When the screws have not been tightened evenly this could already be the cause for the imbalance, in which case readjusting the blades will not help much. If everything is in order though, and there is still a visible difference, the alignment of the metal blade holders can be corrected by gently pushing them into place. Never bend the blades themselves, instead gently move the holder upwards or downwards until all blades are in the same position.

Fixing the unit to uneven wooden beams or pitched ceilings can also make it difficult to align the fan properly. Fans that are suitable for installation on angled ceilings are specifically identified as such in the item description. The maximum angle that is stated in the specifications should be exceeded.

Likewise, bulky pieces of furniture that take up a lot of space in the room impact the fan’s airflow negatively (uneven supply of in-coming air). Check if moving the cupboard helps to stop the wobbling of the blades.

Interested? Our reading tip:

The refrigerator is buzzing, the computer is ventilating and the radiator is gurling? Some noises at home can be eliminated by a couple of professional adjustments, others however you will either have to endure or replace with newer, more modern technology. Still, some noises are generated by street traffic, neighbours or housemates and they have a more or less obviously noticeable impact on our well-being. Read more about how to soften background noise in our new blog entry “Leading a quiet life“.

Short summary

Strip of foam rubber
Resonating vibrations coming from the motor of the fan can be dampened quite easily if they are intensified by adjoining builidng materials. Elastic foam rubber exists in many different colours so there will be no noticeable difference to the colour of your ceiling. The material can be cut with a normal pair of scissors, it barely ages and is available in crafts stores and big supermarkets at a low price. Carpet leftovers can also be used, they are just as ideal to stop the motor from transferring vibration as the rubber. Simply take a pair of outdoor shoes and walk over parquet floor and a rug in comparison and you will notice that basic textiles are much more efficient than you might think at first.

Enjoy the silence. If you have any further questions about our ventilation appliances, please give us a call or send an email – we are happy to help.

Image sources:
creoven.de
Guitarist: RyanMcGuire , pixabay.com/ CC0 Public Domain

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