Measuring sound levels

Aruffell

Aruffell

Aruffell

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Hopefully someone here can clarify.

I went out and bought a sound level meter today that does a range of 30-130dBA in the hope of measuring the noise of graphics cards and the like.

I've worked out that a rough ambient noise should be around 20dBA based off the type of house, area i live in (quiet with no busy roads etc...)

So upon measuring a graphics card at idle and load from around 10cm away, i was given the following readings:

Idle - 47
Load - 55

Am i right in assuming that the calculation should be simple as readout-ambient=noise of the subject in question (graphics card)

Meaning:

Idle is 47-20=27
Load is 55-20=35

This seems correct in my mind as looking on Google to see what others have got from this same card, it seems the results are VERY close by 1dBA either way so im assuming this is correct but i know that sound isn't linear, and is logarithmic so hoping to get some clarification on this.

Obviously the machine testing the graphics card is passively cooled in other areas therefore not contributing to the sound.

Thanks in advance,

Andy
 
For some reason I don't think that's correct, as when you have two identical sounds you don't add the two together, instead the general rule is you add 3dba.
 
Decibels are a logarithmic scale. Its complicated, but I do know that a doubling in noise means you add 3db.
 
saitrix said:
For some reason I don't think that's correct, as when you have two identical sounds you don't add the two together, instead the general rule is you add 3dba.
Click to expand...

Indeed, and obviously there is no way in hell that a graphics card fan pumps out 55 decibels of noise as that's as loud as two people talking whereas my calculation to 35dBA sounds more feasible as most fans are rated upto around 30 anyway.
 
Aruffell said:
Sorry i should have explained -THIS particular graphics card.

Andy
Click to expand...

Why not, tests are not standard and you will find lots of test from a much greater distance than 10cm some from meters. Making it almost impossible to compare components. Had this trouble when trying to find a quite PSU.
 
AcidHell2 said:
Why not, tests are not standard and you will find lots of test from a much greater distance than 10cm some from meters. Making it almost impossible to compare components. Had this trouble when trying to find a quite PSU.
Click to expand...

I was on the assumption that the level recorded from the component (Graphics card, or PSU or whatever) would be the noise of the component INCLUDING the ambient noise therefore i assumed the ambient noise reading would have to be removed to get the true result of the component itself.
 
Does look like it as the difference is so high, but makes little or no sense to me. sound as you know isnt linear so simple subtraction doesn't work.

http://www.menlh.go.id/apec_vc/osaka/eastjava/noise_en/1/page3.html

Section 3.3
3.3 Decibel Level Difference (Compensation for Background Noise)

To compensate for background noise, the difference in decibels is calculated. The formula is below. Background noise compensation uses L1 (dB) as the A-weighted sound pressure level sum of the targeted noise and the background noise, and L2 (dB) as just the background noise. It then estimates the targeted noise L3 (dB) by obtaining the difference.



As a shortcut to computing the A-weighted sound pressure level of background noise, it is stipulated to obtain the difference between the combined dB value and the dB value of the background noise, and reduce the compensation value by the dB value of the combined noise (Table 3-3, JIS Z 8731 Appendix 2 [ISO1996-1.2]). As can be understood from the table, if the background noise is 10 dB or more less than the combined noise dB, its effect on the targeted noise can be ignored. If the difference between the combined noise and the background noise is small (below 4 dB in JIS), there is the possibility of error, hence correct compensation is not possible.

Table 3-3 Noise level meter reading compensation for effects of background noise (Units: dB)
Difference between when there is
background noise and when not
Click to expand...
 
Well this may help, giving you an approximation on what levels to expect. These were done by using the SPL sound level meter app on my iPhone, this is what I came up with.

Dead silence 25DB
Original XBOX1 31DB
PS3 SLIM on Startup 27DB
PS3 SLIM warm playing game 31DB
Soundproofed PC IDLE 28DB
XBOX 360 NO GAME 37DB
XBOX 360 WITH GAME SPINNING 38DB
PS3 60GIG on START 29DB
PS3 60GIG warm playing game 33DB


My xbox360 at the time was a non slim. The new slim is much much much quiter. At a guess around 26-27db
 
Yes with dBs you just add and subtract them, when you convert it into linear units you cant just add and subtract.
 
thedoc46 said:
Well this may help, giving you an approximation on what levels to expect. These were done by using the SPL sound level meter app on my iPhone, this is what I came up with.

Dead silence 25DB
Original XBOX1 31DB
PS3 SLIM on Startup 27DB
PS3 SLIM warm playing game 31DB
Soundproofed PC IDLE 28DB
XBOX 360 NO GAME 37DB
XBOX 360 WITH GAME SPINNING 38DB
PS3 60GIG on START 29DB
PS3 60GIG warm playing game 33DB


My xbox360 at the time was a non slim. The new slim is much much much quiter. At a guess around 26-27db
Click to expand...

having heard an Xbox-360 startup, i can assure you that they're louder than 37dB. closer to 55-ish i'd say.
 
I used to handle a £3,000 decibel meter at a factory that went for adjustments every 6 months and was the same that was used by the Council.
Even standing in a quiet library the meter could reach 45db so whatever you're using to get a reading of 27db can't be working right.
You also have to stand a certain distance away for a correct reading (especially with machines and live bands).
And yes, as above, if 2 readings are the same you add 3db and if they aren't the same you only take the higher reading.
Imagine my band (and I have a decibel meter we use for setting up), I get the drummer to play and he's usually around 110db. I then get each intrument to the same level so the backline when playing all together should now be 119db and then my voice is added (not sure what that reaches).
 
dmpoole said:
I used to handle a £3,000 decibel meter at a factory that went for adjustments every 6 months and was the same that was used by the Council.
Even standing in a quiet library the meter could reach 45db so whatever you're using to get a reading of 27db can't be working right.
You also have to stand a certain distance away for a correct reading (especially with machines and live bands).
And yes, as above, if 2 readings are the same you add 3db and if they aren't the same you only take the higher reading.
Imagine my band (and I have a decibel meter we use for setting up), I get the drummer to play and he's usually around 110db. I then get each intrument to the same level so the backline when playing all together should now be 119db and then my voice is added (not sure what that reaches).
Click to expand...

Looking forward to going deaf?
 
read the title as masturbating sound levels :o

thought the op might have had a over enthusiastic room-mate >.<
 
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