A question about decibels

[ben4watches]

Coulds someone answers this for me.

If for arguements sake something makes a sound at 50 decibels and another at 60 decibels, is the combined decibel level 110 or is it just 60 decibels, as this just eats up the lower 50 decibel level.

[seadog1408]

AFAIC ben, it would only come out at 60 decibel.


cheers
mike :wink:

[Saint-Just]

Coulds someone answers this for me.

If for arguements sake something makes a sound at 50 decibels and another at 60 decibels, is the combined decibel level 110 or is it just 60 decibels, as this just eats up the lower 50 decibel level.

My 2p, and waiting to b proved wrong: it depends on many things.
It can even be quieter in certain circumstances. See sine wave, and how they can add-up

[lysanderxiii]

The Decibel is a base 10 logrithmic scale, so the two do not add so simply.

a 50 dB noise on top of a 60 dB would probably result in a 60.5 to 61 dB noise.

If you are really interested read here, about half-way down the page:
http://www.epd.gov.hk/epd/noise_educati ... tro_5.html

[docd]

The Decibel is a base 10 logrithmic scale, so the two do not add so simply.

a 50 dB noise on top of a 60 dB would probably result in a 60.5 to 61 dB noise.

If you are really interested read here, about half-way down the page:
http://www.epd.gov.hk/epd/noise_educati ... tro_5.html

+1

What he said - they are additive but logarithmically.
As an aside +10db results in an approximate perceived doubling in sound level.

[hogthrob]

OK, so can someone explain why no matter how loud I have the TV, I can never hear it over the sound of my wife talking on the phone, yet at the same time, I can't hear her if she speaks [s:2fimpmrn]at[/s:2fimpmrn] to me?

[Gruntfuttock]

Two lots of 60dB is double the power, so 63dB. 50dB+60dB would be a bit less than that.

[WORKSIMON]

OK, so can someone explain why no matter how loud I have the TV, I can never hear it over the sound of my wife talking on the phone, yet at the same time, I can't hear her if she speaks [s:3sqa1bft]at[/s:3sqa1bft] to me?

I have the same problem but for me it's tone's and pitch that I have difficulty with. I used to pump the telly up and still could not hear it properly when there was other noises around. I then played with the settings and reduced the bass and increased the treble and hey presto its much easier to hear.

[swanbourne]

It's not that simple, every 3dB gain is a doubling of sound/signal. If you get an antenna amplifier with 3dB gain, it doubles the signal, 6dB doubles it again and so on.

Eddie

[Gruntfuttock]

OK, so can someone explain why no matter how loud I have the TV, I can never hear it over the sound of my wife talking on the phone, yet at the same time, I can't hear her if she speaks [s:2jmyl50t]at[/s:2jmyl50t] to me?

This is an acquired medical condition common amongst husbands known as selective deafness. :lol:

[adrian]

OK, so can someone explain why no matter how loud I have the TV, I can never hear it over the sound of my wife talking on the phone, yet at the same time, I can't hear her if she speaks [s:3t5kaiog]at[/s:3t5kaiog] to me?

http://www.coolest-gadgets.com/20051209 ... e-control/

I don't need one yet but if you test it let me know how it works, one can never know.

[docd]

OK, so can someone explain why no matter how loud I have the TV, I can never hear it over the sound of my wife talking on the phone, yet at the same time, I can't hear her if she speaks [s:nf4wagos]at[/s:nf4wagos] to me?

Sounds like a special audio filtering technique: I know of high pass, low pass, band pass even parametric filters but I'm new to adaptive wife filtering :lol:

[Rod]

You would just hear the 60db noise mingled in with the 50db sound. It wouldn't sound any louder.
In amplifier power, to double the power of 40watts per channel you need a 400 watt per channel one (as previously mentioned it's a logarithmic change). This would only represent 3db's difference in sound level which is a mere whisper. So why would someone need a 400 watt one then? Reason - speaker efficiency. If you have a speaker efficiency of 91db and one of 88db the amplifier power requirements double in power. Most, if not all that power is frittered away as heat in the voice coils.

Rod

[magirus]

The DSU (Distress Signal Unit), attached to a BA (Breathing Apparatus) set used in the Fire Service in the UK, has to sound at a minimum of 90db for not less than 1hour when activated. So there. :wink:

[ben4watches]

WOW. I did not know sound was complicated :shock:

Thanks for your replies guys :wink:

[cannedheat]

As Gruntfuttock said, it would be a little less than 63 dB, exactly 62.3866 dB ( decimals are meaningless in this case, you are right )

Regards

[JasonG]

As Gruntfuttock said, it would be a little less than 63 dB, exactly 62.3866 dB

Nope. Depends greatly on frequencies, phase, etc. Sound is measured using a weighted, ballistic meter movement (or a software simulation of such).
Assuming different (incoherent, as coherent sounds are most unusual in the real world) frequency and phase, a sound at 50dBA added to one at 60dBA would come out at a bit under 60.5 dBA.

Keep it low.

[seadog1408]

so after all you scientists have gone on about waves/sines and everything else, i was right in laymans terms :D :D

[cannedheat]

Nope. Depends greatly on frequencies, phase, etc. Sound is measured using a weighted, ballistic meter movement (or a software simulation of such).
Assuming different (incoherent, as coherent sounds are most unusual in the real world) frequency and phase, a sound at 50dBA added to one at 60dBA would come out at a bit under 60.5 dBA.

edit:

I found my mistake JasonG, you are right. Mathematical - magnitude one. I had used (50/P0+60/P0)^2 inside the logarithm, and I should have used ((50/P0)^2+(60/P0)^2). The magnitude involved is not sound preassure, but the square of the division of sound preassure by the treshold of hearing. This is the magnitude to be added, not original sound preassure.

You are absolutely correct, a bit less than 60.5, 60.4139dB.

Thank you very much for making me understand it a little better.

Regards.

PS. and thanks lysanderxiii for the link!

[JasonG]

so after all you scientists have gone on about waves/sines and everything else, i was right in laymans terms :D :D

Yep, just for all the wrong reasons! :wink: