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How accurate are these cheap sound meters?

I'd expect those cheap meters to be accurate to something like ±5% of the actual value. Good enough for relative comparisons, but not good enough to put a lot of faith in the exact numbers.

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18 minutes ago, BobVonBob said:

I'd expect those cheap meters to be accurate to something like ±5% of the actual value. Good enough for relative comparisons, but not good enough to put a lot of faith in the exact numbers.

I just noticed that all of those cheap meters are measuring starting from 30dB, but the point of the test I want to do is to see if my PC is silent and I will need levels below 30dB as well. Do you think I can find a meter that measure below 30dB as well? I couldn't find any (from those cheap ones)

 

Or I'm exaggerating and I don't need to measure below 30dB?

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Edit: Looks like there are apps for iPhone/Android that can actually measure dB, might give it a try

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30 minutes ago, Filingo said:

Is it accurate enough?

 

Do you know of any cheap meter that is also accurate?

Unfortunately in this area, accuracy costs $$$. The chances are, they're not that bad and is good enough for a relative measurement that is not used for business or legal reasons. Absolute measurements will require you to have access to a reference sound source for calibration, and those reference sources should be checked every year or two. This is almost certainly total overkill for this use case. It's a lot of cost, and that gets you absolute accuracy to 1dB unless you pay silly amounts.

 

BTW in past employment, making sound measurement was a major part of my job function.

 

12 minutes ago, BobVonBob said:

I'd expect those cheap meters to be accurate to something like ±5% of the actual value. Good enough for relative comparisons, but not good enough to put a lot of faith in the exact numbers.

Sound meters usually measure in dB, and getting accurate to 1 dB is considered good enough for most use cases. 1 dB is equivalent to 12% of level. Be careful not to treat a log measurement as if it were linear. Taking 5% of the dB numerical value would be nonsense. 

 

6 minutes ago, Filingo said:

I just noticed that all of those cheap meters are measuring starting from 30dB, but the point of silent PC fan is also the noise below 30dB.. you think I can find some that measure below 30dB as well? I couldn't find any (from those cheap ones)

Electrical self noise of the microphone and circuitry makes it difficult to measure lower levels. It gets expensive really quick if you want to go there.

 

Note you can work around this to a degree by moving the microphone closer to the noise source. A rule of thumb is that sound level decays with distance, 6 dB lower for doubling distance. Going the other way, it is 6 dB higher if you halve the distance. So if you measure closer to the noise, it will be louder and you can get it within your measurement range. You will have to be careful though, the above assumes there are no sound reflecting surfaces nearby, which can reflect sound and vary the level. Pick a consistent measurement location if you're making changes to see what happens.

 

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4 minutes ago, porina said:

Unfortunately in this area, accuracy costs $$$. The chances are, they're not that bad and is good enough for a relative measurement that is not used for business or legal reasons. Absolute measurements will require you to have access to a reference sound source for calibration, and those reference sources should be checked every year or two. This is almost certainly total overkill for this use case. It's a lot of cost, and that gets you absolute accuracy to 1dB unless you pay silly amounts.

 

BTW in past employment, making sound measurement was a major part of my job function.

 

Sound meters usually measure in dB, and getting accurate to 1 dB is considered good enough for most use cases. 1 dB is equivalent to 12% of level. Be careful not to treat a log measurement as if it were linear. Taking 5% of the dB numerical value would be nonsense. 

 

Electrical self noise of the microphone and circuitry makes it difficult to measure lower levels. It gets expensive really quick if you want to go there.

 

Note you can work around this to a degree by moving the microphone closer to the noise source. A rule of thumb is that sound level decays with distance, 6 dB lower for doubling distance. Going the other way, it is 6 dB higher if you halve the distance. So if you measure closer to the noise, it will be louder and you can get it within your measurement range. You will have to be careful though, the above assumes there are no sound reflecting surfaces nearby, which can reflect sound and vary the level. Pick a consistent measurement location if you're making changes to see what happens.

 

Wow thank you for the detailed answer, I will get one and see!

 

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8 minutes ago, Filingo said:

Edit: Looks like there are apps for iPhone/Android that can actually measure dB, might give it a try

Worth a try and see how you get on with it. Again in my past job, I was tasked at one point at trying out various apps for iOS because the company wanted sales people to have a basic measuring capability. From memory the best one at the time was by Faber Acoustical. Their offerings have changed since then, but they currently offer SoundMeter X. I just installed it on my iPad. For free, you get a sound level meter with the basic options you'd expect from a dedicated unit. I can't speak of accuracy, but given Apple devices are far less variable than Android ecosystem, it should be ball park usable.

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