Noise and machines

[sleepy1235]

Noise and vibration in equipment is a concern in general engineering. Reading about the noise issues I thought I would give some general thoughts that people could use for their problems.

Noise and vibration for machines is a vast topic. There are issues of safety and comfort. There are issues of diagnostics of machine function. I am going to focus on some specific items that might apply to people who have noise problems.

1. Defective, worn, and broken machine parts cause noise. This is why mechanics often listen to engines. The sound is often specific to specific problems. In manufacturing there are defective parts, sub-assemblies and whole units that do escape the manufacturing process and are defective. So there are bound to be some CPAP machines out there that are defective. I haven't yet read anything about specifications for noise by manufacturers or their testing. I don't see a certificate of compliance for noise with the equipment.

Parts can prematurely fail. You can find the bathtube curve online somewhere. Your CPAP machine might have a part that failed prematurely. If there is a defective part, or defective assembly the problem will progress.

2. Objects have their own specific mechanical modes of vibration.

So first you could consider the surface that your CPAP machine resides on and how it would interact with vibrations in your machine. If the object just happens to have a resonate frequency with some frequency in the CPAP it might become noisy. I would recommend having the machine site on a rubber pad. This would dampen any vibration being transmitted into the table or support for the machine. Also it would tend to absorb vibration from the machine.

Make sure you don't have objects on the table or support themselves that vibrate sympathetically (resonance) with some vibration mode of your CPAP. Like a button or a penny.

3. Make sure the machine is level and doesn't have anything leaning against it. Make sure it is free standing, that is not against a wall or panel.

The machine was probably designed assuming it is level and there might not be a lot of engineering thought to make it robust to not being level regarding noise. When not level moving parts will tend to be applying some force lateral to the shaft. Make sure it is level.

If something is leaning against the machine, it can change the vibration modes of the machine and perhaps cause resonances that will be noisy. It also can represent a transmission path of vibration energy into the object leaning against the CPAP machine resulting in noise either from the object leaning against the machine or whatever the object is touching.

Similarly the machine against a wall or panel can have vibration modes not encompassed by the design of the machine.

Further the wall or panel might act as a sounding board. (have resonances.)

4. Make sure all parts are snapped into place. Loose parts change the vibration modes and themselves can have vibration modes that build up.

5. Make sure the machine is clean. Debris and dirt can cause the machine components not to fit together properly and so there is unwanted vibration modes.

6. Abatement.

If you are getting down to the point of abatement, you should really be considering that your machine is either defective in manufacture or design or it has broken and get rid of it.

However, if you are looking at abatement, you will find it is by trial and error. The placement of vibration absorbing material at strategic positions can absorb sound. It is a technique to put strips of rubber asymmetrically on plates to absorb sound to reduce the sound level of industrial equipment. In the case of the machine i would place your finger down on certain points and see if that reduces the sound and then place a soft rubber object on that point.

I am thinking a thin rubber strip between the humidifier and the main unit might absorb sound.

Make sure first that the whole machine is resting on something sound absorbing.

I have low expectations for this technique, but it might offer some relief as stop gap.

Of course I am not an expert and you do this at your own risk. If your spouse leaves you or asks you to sleep elsewhere and this is a bad thing for you I am not responsible.

[jzap]

I don't know about your machine, but my CPAP is a lot quieter than the fan that my wife runs at night...

[LSAT]

Noise and vibration in equipment is a concern in general engineering. Reading about the noise issues I thought I would give some general thoughts that people could use for their problems.

Noise and vibration for machines is a vast topic. There are issues of safety and comfort. There are issues of diagnostics of machine function. I am going to focus on some specific items that might apply to people who have noise problems.

1. Defective, worn, and broken machine parts cause noise. This is why mechanics often listen to engines. The sound is often specific to specific problems. In manufacturing there are defective parts, sub-assemblies and whole units that do escape the manufacturing process and are defective. So there are bound to be some CPAP machines out there that are defective. I haven't yet read anything about specifications for noise by manufacturers or their testing. I don't see a certificate of compliance for noise with the equipment.

Parts can prematurely fail. You can find the bathtube curve online somewhere. Your CPAP machine might have a part that failed prematurely. If there is a defective part, or defective assembly the problem will progress.

2. Objects have their own specific mechanical modes of vibration.

So first you could consider the surface that your CPAP machine resides on and how it would interact with vibrations in your machine. If the object just happens to have a resonate frequency with some frequency in the CPAP it might become noisy. I would recommend having the machine site on a rubber pad. This would dampen any vibration being transmitted into the table or support for the machine. Also it would tend to absorb vibration from the machine.

Make sure you don't have objects on the table or support themselves that vibrate sympathetically (resonance) with some vibration mode of your CPAP. Like a button or a penny.

3. Make sure the machine is level and doesn't have anything leaning against it. Make sure it is free standing, that is not against a wall or panel.

The machine was probably designed assuming it is level and there might not be a lot of engineering thought to make it robust to not being level regarding noise. When not level moving parts will tend to be applying some force lateral to the shaft. Make sure it is level.

If something is leaning against the machine, it can change the vibration modes of the machine and perhaps cause resonances that will be noisy. It also can represent a transmission path of vibration energy into the object leaning against the CPAP machine resulting in noise either from the object leaning against the machine or whatever the object is touching.

Similarly the machine against a wall or panel can have vibration modes not encompassed by the design of the machine.

Further the wall or panel might act as a sounding board. (have resonances.)

4. Make sure all parts are snapped into place. Loose parts change the vibration modes and themselves can have vibration modes that build up.

5. Make sure the machine is clean. Debris and dirt can cause the machine components not to fit together properly and so there is unwanted vibration modes.

6. Abatement.

If you are getting down to the point of abatement, you should really be considering that your machine is either defective in manufacture or design or it has broken and get rid of it.

However, if you are looking at abatement, you will find it is by trial and error. The placement of vibration absorbing material at strategic positions can absorb sound. It is a technique to put strips of rubber asymmetrically on plates to absorb sound to reduce the sound level of industrial equipment. In the case of the machine i would place your finger down on certain points and see if that reduces the sound and then place a soft rubber object on that point.

I am thinking a thin rubber strip between the humidifier and the main unit might absorb sound.

Make sure first that the whole machine is resting on something sound absorbing.

I have low expectations for this technique, but it might offer some relief as stop gap.

Of course I am not an expert and you do this at your own risk. If your spouse leaves you or asks you to sleep elsewhere and this is a bad thing for you I am not responsible.

i\

If your S9 is noisy...take it back. It's got a 2 year warranty. S9 is an extremely quiet machine.

[chunkyfrog]

I generally sleep on my left side, the good ear.
I take my hearing aid out at night, so I can hear even less on my right.
I live within 300 feet of a major rail corridor.
What machine noise?

[JeffL]

In the last few weeks, my S9 started making a weird noise at about the 2 year mark. It was kind of a whirling noise that followed my breathing. It became loud enough to wake me up one morning. The problem was, it was intermittent, and I could not control when it would come and go. Fortunately, I have a hand held digital audio recorder. I put the recorder on my nightstand, and when the noise started up, I got a good recording of it. I emailed the recording to my DME, who at first tried to brush it off, but said they would take a look at it if I brought it in. I took it in, and of course, just like a car that won't misbehave in front of the mechanic, the machine would not make the noise on the tech's work bench. They did however, call ResMed, and they said they would replace it, so, I walked out with a brand new machine. When the old machine did not make the noise, it was nearly dead quiet, the new one seems to me, to be a little louder (the fan sound), but my wife says that it isn't. At any rate, it is well below any noise level that I would find objectionable.

After doing some research, I have a suspicion that the new noise from the old machine may have had to do with the humidifier, possibly a bad seal. When I packed it up to take it to the DME, the entire lid lifted right off of the humidifier, and it was a little tricky to put it back in place. I did tell the tech about it. I would have liked to check it out further, but since they exchanged it, I didn't have an opportunity. Also, I believe the new humidifier had a thicker seal than the old unit. The new lid is a bit harder to close, and has a thick rubber seal on the lid, that fits around the tank, that I don't remember seeing on the old unit.

I think the new unit also has a small power brick, with a two prong plug. I think the old unit had a three prong plug.

[Iowamv]

If your S9 is noisy...take it back. It's got a 2 year warranty. S9 is an extremely quiet machine.

Not to be difficult about this, but my s9 is completely silent only when I'm not breathing. When people talk about how quiet that machine is, they are separating the sound of breathing coming from (both ends of) the tube vs. what is actually generated by the machine, right? If it weren't for my breathing sounds, some of which seem to be coming from the machine, my s9 is virtually silent. But the breathing sounds take some time to get used to, maybe especially for spouses. Something about the whole setup together gives it a sort of quiet version of Darth Vader. THAT is normal, right?

[oak]

Ioamv: yup. normal.

[JeffL]

If your S9 is noisy...take it back. It's got a 2 year warranty. S9 is an extremely quiet machine.

Not to be difficult about this, but my s9 is completely silent only when I'm not breathing. When people talk about how quiet that machine is, they are separating the sound of breathing coming from (both ends of) the tube vs. what is actually generated by the machine, right? If it weren't for my breathing sounds, some of which seem to be coming from the machine, my s9 is virtually silent. But the breathing sounds take some time to get used to, maybe especially for spouses. Something about the whole setup together gives it a sort of quiet version of Darth Vader. THAT is normal, right?

That's how I remember my first machine. If I were to hold my breath, I don't remember hearing anything. With the new one, the sound is almost constant, but not louder than the sound that followed my breathing with the old machine. Now I'm wondering if they set it up differently. Oh well, it does the job, and like I said, it's well below the annoyance level.

[sleepy1235]

I never said in my original posting that my S9 was noisy. It is quite quiet.

As an engineer who is somewhat familiar with sound, I thought I would share some general purpose thoughts on noise.

Then some how the thread became something about the noise level of S9 machines.

[oak]

yup. stuff happens.

[chunkyfrog]

Materials to put under any equipment to absorb sound:
1) the resilient material for under heavy machinery in factories
2) food service fatigue mat
3) rubber floor pad made for horse stalls
4) High density foam floor mat they put in weight rooms
5) stiff foam carpet padding
Any of these products can be obtained on the cheap in a sample size--just enough for below the blower.

[robysue]

If your S9 is noisy...take it back. It's got a 2 year warranty. S9 is an extremely quiet machine.

Not to be difficult about this, but my s9 is completely silent only when I'm not breathing. When people talk about how quiet that machine is, they are separating the sound of breathing coming from (both ends of) the tube vs. what is actually generated by the machine, right? If it weren't for my breathing sounds, some of which seem to be coming from the machine, my s9 is virtually silent. But the breathing sounds take some time to get used to, maybe especially for spouses. Something about the whole setup together gives it a sort of quiet version of Darth Vader. THAT is normal, right?