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How loud is 'Loud' ?

There seems to be a consensus that 75-80db is safe for at least a couple of hours exposure, but how is this measured? I'm using an iPod app from Studio Six called SPL Pro, which has a number of modes.

Mode

SPL supports four standard ANSI decay times. All times are in terms of exponential decay, where the reading will decay by 20dB over the specified time.

SLOW -- this mode uses a 1-second decay time. Good for getting a general reading of the ambient sound level.

FAST -- this mode uses a 125ms decay time.

IMPULSE -- not used very much, normally Peak mode would be used. This mode has a 35ms decay time.

PEAK -- Peak mode show the peak value received since the last screen update.

Also, there is a mode call Leq. This mode does an equal-weighted time average of the incoming SPL level.
Click to expand...

Both slow and fast give similar readings, and at my normal listening level give readings up to ~80db. If I use Peak mode I get readings up to 20db higher. I understand why, but what is not clear to me is to which mode (if any of these) the guidelines apply. I don't believe it can be Peak, because if I adjust the volume so that maxima of 80db occur for this mode it is very quiet.

Also, should I use A or C weighting?

I expect some will say that an app is no substitute for a proper meter, but Studio Six make the claim that their app is more accurate than the standard Radio Shack meter. I'm not sure that the standard calibration they have supplied is suitable for a latest generation iPod mic. I'm interested in your comments on this aspect too.
 
zarniwoop said:
I expect some will say that an app is no substitute for a proper meter, but Studio Six make the claim that their app is more accurate than the standard Radio Shack meter. I'm not sure that the standard calibration they have supplied is suitable for a latest generation iPod mic. I'm interested in your comments on this aspect too.
Click to expand...

I use the Faber Acoustical Sound Meter app and find it correlates pretty closely to an old Radio Shack meter I also have. With both set to C weighting the averages look about the same, within a db or two as far as I can see, though the iPhone app is way faster than the old needle-meter on the Radio Shack so gives an indication of peaks too. I believe accuracy decreases with higher volume, i.e. the iPhone isn't really up to measuring gig volume etc. The think that surprises me is how high the peaks are above the mean level, e.g. if I'm getting a 73-75db average at the listening seat I can be seeing peaks up to 93db or so registering on the iPhone meter.

PS when using the iPhone obviously be aware that the mic is in the bottom, i.e. don't sit there taking a reading of your own wooly jumper! The Faber Acoustical app rotates so you can hold the iPhone with the mic facing the sound source.
 
Tony L said:
...the iPhone app is way faster than the old needle-meter on the Radio Shack so gives an indication of peaks too.
Click to expand...

I suppose that's the answer. Conventional anaologue meters will never respond sufficiently quickly to catch very short duration peaks, so they will always show a time-averaged value below that, and since it is likely that the guidelines were originally conceived with these in mind it's the averaged value that matters.
 
As the App is probably monitoring thje microphone electrical waveform, it is likely to be able to respond immediately to peaks within the limits of the microphone bandwidth and large signal handling. It is the latter which is going to be problematic in a smartphone - low bias voltage on the electret and low voltages powering any preamp and the ADC must limit the maximum volume where compression starts.
 
davidsrsb said:
As the App is probably monitoring thje microphone electrical waveform, it is likely to be able to respond immediately to peaks within the limits of the microphone bandwidth and large signal handling. It is the latter which is going to be problematic in a smartphone - low bias voltage on the electret and low voltages powering any preamp and the ADC must limit the maximum volume where compression starts.
Click to expand...

Thats an interesting point. I have a professional MicW i436 calibrated mic for iPad/iPhone use and the maximum SPL that can be measured is 102dB according to the manufacturer whilst my old Radioshack meter goes up to 126dB. The i436 goes lower at 34dB vs 50dB for the Tandy.

Just spotted that the i436 can measure up to 130dB if used with a special cable that has -20dB or -40 dB pad to lower the sensitivity. So its a iHardware issue. They also make a mic that can handle 160dB Ouch!

Cheers,

DV
 
I was at The Who Charlton concert, May 1976. 126dB at 32m, outdoors, Guinness record for about 15 years. Don't think my ears ever recovered.
 
pspcpog said:
That's phenomenal at 32m! What amps and speakers were they using? :D
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Lots of Crown DC-300's from memory, JBL stacks. Around 75 KW!

There are bootlegs of most tracks on youtube. "Won't get fooled again" even sounds loud on a laptop!
 
canonman said:
I was at The Who Charlton concert, May 1976. 126dB at 32m, outdoors, Guinness record for about 15 years. Don't think my ears ever recovered.
Click to expand...

Me too, but I don't remember it being that loud - I may have been a little further than 32m from the stage, and without walls or a ceiling I guess the sound level dropped off more quickly than in a regular theatre.
 
zarniwoop said:
Me too, but I don't remember it being that loud - I may have been a little further than 32m from the stage, and without walls or a ceiling I guess the sound level dropped off more quickly than in a regular theatre.
Click to expand...
Yes, probably right on that although Wiki confirms the sound level as being a record.
Funnily enough, I can't recall it raining! Some good memories here:
http://www.ukrockfestivals.com/who-ptbin-76-vftmud.html

Sensational Alex Harvey Band were also brilliant.
 
zarniwoop said:
There seems to be a consensus that 75-80db is safe for at least a couple of hours exposure, but how is this measured? I'm using an iPod app from Studio Six called SPL Pro, which has a number of modes.



Both slow and fast give similar readings, and at my normal listening level give readings up to ~80db. If I use Peak mode I get readings up to 20db higher. I understand why, but what is not clear to me is to which mode (if any of these) the guidelines apply. I don't believe it can be Peak, because if I adjust the volume so that maxima of 80db occur for this mode it is very quiet.

Also, should I use A or C weighting?

I expect some will say that an app is no substitute for a proper meter, but Studio Six make the claim that their app is more accurate than the standard Radio Shack meter. I'm not sure that the standard calibration they have supplied is suitable for a latest generation iPod mic. I'm interested in your comments on this aspect too.
Click to expand...

Do you know what A and C weighting are? Most standards affecting humans I believe still use A weighting. It has a sensitivity supposedly corresponding to human hearing i.e. Mid band frequencies are the high point and attenuation of higher and lower frequencies like a bell curve see http://www.engineeringtoolbox.com/decibel-d_59.html

measurement of equipment would be C or linear weighting.

Use slow/fast to taste and dare I suggest A weighting. Having said that not all affordable meters will offer both so you may end up talking different ways of measuring without both parties knowing so, apples and pears.

I hope that make sense.

If you really want to explore measurement check out Leq an averaging of sound over time, the opposite of peoples fascination with peak levels. Measurements of environmental and work place noise tend to be Leq and A weighted.

Further edit 70 dB A weighted is very different to 70 dB linear or C weighted. Back to the many views posted.

One more edit for those who ask what is loud https://www.osha.gov/dts/osta/otm/noise/health_effects/soundpressure_aweighted.html
 
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