Noise level

[bababrown]

Ed and Matt,
I noticed on your home page under New Quieter Blowers that you state, "We have reduced the noise level of our blowers by 10 dB which represents a 50% reduction in noise level." It actually represents a reduction to 0.1 the original noise power (a 90% decrease) or to 0.316 the original sound pressure level. I notice that Bill Pentz made the same error on his site ; it's one of the very few technical errors I've found in his work. The 10 dB reduction is very significant.
bababrown

[arthurs]

Actually bababrown, a 10 dB change in *SPL* (sound pressure level) is considered by us sound engineers as a "halfing" or "doubling" of acoustic pressure level as perceived by the human ear, the emphasis here is on human perception (based on a lot of subjective tests). Technically, dB SPL follows 20log math, so for the sake of accuracy, 6 dB SPL change would be what a half or double amount of sound pressure would be. When calculating dB change in power (watts), you follow 10log math.

Nonetheless, the acoustical improvement gained of the new blowers is pretty significant, considering how simple the solution is.

[bababrown]

Arthurs,
I would have no problem with the 50% reduction value if it were stated as, " ... a 50% reduction in perceived noise level." Noise level and perceived noise level are different things.
bababrown

[arthurs]

Arthurs,
I would have no problem with the 50% reduction value if it were stated as, " ... a 50% reduction in perceived noise level." Noise level and perceived noise level are different things.
bababrownI guess it comes down to the nitty gritty details and being accurate in how we describe things.

Just so people have an understanding of how dB SPL changes are perceived, here's a simple chart (hopefully it looks ok):

dB SPL Change__|__Pressure Ratio__|__% of original__|__Subjective change

-1 dB__________|__1.12 to 1______|______ 89______|__Barely Perceptable
-3 dB__________|__1.41 to 1______|______ 71______|__Noticeable to most
-6 dB__________|__2 to 1_________|______50______|__ Very noticeable
-10 dB_________|__3.16 to 1______|______32______|__Twice as loud/soft
-40 dB_________|__100 to 1_______|_______1______|__About the maximum we can perceive in terms of change

[arthurs]

Also, for the sake of accuracy, when we are measuring machines for output noise level, not only should we be far enough away for the SPL meter to "hear" the machine in it's entirety (I generally measure at a distance that is 2 to 3 times the largest dimension of the noise source), but we should duplicate the measurement conditions as well, for "before" and "after" measurements--being the same distance away from the machine, and same distance from any neighboring boundaries.

Keep in mind that for every doubling of distance from your noise source, you will see a 6 dB drop on your SPL meter measurements! So if you measure the cyclone from 6 feet, and read 90 dB SPL, if you move the meter to 12 feet away from the cyclone your meter will read 84 dB SPL provided nothing else has changed in conditions. So when you say you're reading 93 dB SPL, please state what distance you are from the noise source so we can make meaningful comparisons!

Also, to keep things simple, set your SPL meter to "Slow" averaging, and "A weighting" (which is what OSHA uses as a standard for measurement in industrial application, even though I think it is a bit misguided at higher and/or more impulsive noise levels). For what we're doing, it should be close enough.

The iPhone has some useful sound measurement applications, but keep in mind that the built in microphone starts to crap out around 95-100 dB SPL, making the measurement of loud sources of noise very inaccurate, if not impossible.

[Matt]

So Do we need to change what we are saying? Are we way off base?

Matt

[bababrown]

Matt,
I had two concerns with the statement; one was accuracy and the other was for you to take full credit. If you change to " ...a 50% reduction in perceived noise level" it becomes an accurate statement. On the other hand I think you can fairly claim a 90% reduction in noise power level.
bababrown

[K9-mal]

Based on the improvements achieved by this device, I tried putting one of them on my wife. Any wagers on the results?

[Matt]

Based on the improvements achieved by this device, I tried putting one of them on my wife. Any wagers on the results?

ROFLOL I bet it didn't go well.

[arthurs]

On the other hand I think you can fairly claim a 90% reduction in noise power level.
How are you figuring out the math for that statement?

[arthurs]

So Do we need to change what we are saying? Are we way off base?

Matt
I don't think you're way off base, but qualify your statement with *perceived* as half as loud or something similar, and you should be fine.

[bababrown]

Arthur,
A noise power reduction of 10 dB means that the power is 0.1 times the reference level. So 0.9 of the original or reference power has been eliminated. The reduction is 10LOG(sp ratio squared) or 20LOG(sp ratio), where sp is sound pressure and sp squared represents sound power.
bababrown

[dwdrury]

Matt,

I think Richard and Arthur are onto something here. Putting a word such as "perceived" in it would, should, get you off any hook the competition might want to hang you up upon. Your "out" is the documented dB measurement. Perhaps one of those little "fine print asterisks" where you could provide some details of how the number was obtained, e.g.: "measured in back to back tests at a distance of X feet, 'A' scale,..."

Experience tells me installation of noise reduction devices applied to the wife strangely only increases SPL. So that's where my wager would go.

Regards,
DWD

[armstrr]

Ed and Matt,
I noticed on your home page under New Quieter Blowers that you state, "We have reduced the noise level of our blowers by 10 dB which represents a 50% reduction in noise level." It actually represents a reduction to 0.1 the original noise power (a 90% decrease) or to 0.316 the original sound pressure level. I notice that Bill Pentz made the same error on his site ; it's one of the very few technical errors I've found in his work. The 10 dB reduction is very significant.
bababrown


can you link or provide details on the changes to the blower? i can't find info on it.

thanks

[bababrown]

Look in Product Questions under Quieter Blowers. On the first page at the bottom Ed has a post with a link to a drawing that shows the added stick. Also, if you go to the Clear Vue site, in one of the videos Ed demos the new blower in a closet and makes some sound level measurements.
bababrown