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Old 05-22-2000, 01:36 AM   #1
dB Don
 
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Is there a real acurate way to convert PSI pressure into an approximate SPL reading. I am haveing alittle difficulty understanding the conversion. Is there a formula to follow, if so can you tell me it?
 
Old 05-22-2000, 04:13 PM   #2
Jim
 
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db don,
I have read somewhere that 170 db would be 14psi, I am not sure how it was figured or if it is even correct. Just what I have read befor and had the same question as to how you wouyld figure that.
 
Old 05-22-2000, 05:37 PM   #3
dB Don
 
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I would like for Richard to give some insite on the topic soon.Thanks for the reply jim.
 
Old 05-22-2000, 06:05 PM   #4
PoundMutt
 
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SPL = 20 Log(p/p ref)
p = pressure in pascals
p ref = reference pressure in pascals = 2 x 10^-5 Pa (pascals)
to convert psi to pascals you need this:
Pa/psi (approximately)
so take your relative PSI value convert it to pascals and dump it back
into the above formula.
2 psi = 13638 Pa
SPL = 20 Log [13638/(2x10^-5)] = 176.7 dB acoustical
More dB SPL versus PSI
dB
acoustical - PSI
50.7 - 0.000001
56.7 - 0.000002
60.2 - 0.000003
62.7 - 0.000004
64.6 - 0.000005
66.2 - 0.000006
67.6 - 0.000007
68.7 - 0.000008
69.7 - 0.000009
70.7 - 0.00001
76.7 - 0.00002
80.2 - 0.00003
82.7 - 0.00004
84.6 - 0.00005
86.2 - 0.00006
87.6 - 0.00007
88.7 - 0.00008
89.7 - 0.00009
90.7 - 0.0001
96.7 - 0.0002
100.2 - 0.0003
102.7 - 0.0004
104.6 - 0.0005
106.2 - 0.0006
107.6 - 0.0007
108.7 - 0.0008
109.7 - 0.0009
110.7 - 0.001
116.7 - 0.002
120.2 - 0.003
122.7 - 0.004
124.6 - 0.005
126.2 - 0.006
127.6 - 0.007
128.7 - 0.008
129.7 - 0.009
130.7 - 0.01
136.7 - 0.02
140.2 - 0.03
142.7 - 0.04
144.6 - 0.05
146.2 - 0.06
147.6 - 0.07
148.7 - 0.08
149.7 - 0.09
150.7 - 0.1
156.7 - 0.2
160.2 - 0.3
162.7 - 0.4
164.6 - 0.5
166.2 - 0.6
167.6 - 0.7
168.7 - 0.8
169.7 - 0.9
170.7 - 1.0
171.5 - 1.1
172.2 - 1.2
172.9 - 1.3
173.6 - 1.4
174.2 - 1.5
174.7 - 1.6
175.3 - 1.7
175.8 - 1.8
176.2 - 1.9
176.7 - 2.0
180.2 - 3.0
182.7 - 4.0
184.6 - 5.0
186.2 - 6.0
187.6 - 7.0
188.7 - 8.0
189.7 - 9.0
190.7 - 10.0
191.5 - 11.0
192.2 - 12.0
192.9 - 13.0
193.6 - 14.0
194.2 - 15.0
194.7 - 16.0
195.3 - 17.0
195.8 - 18.0
196.2 - 19.0
196.7 - 20.0
197.1 - 21.0
197.5 - 22.0
197.9 - 23.0
198.3 - 24.0
198.6 - 25.0
199.0 - 26.0
199.3 - 27.0
199.6 - 28.0
199.9 - 29.0
200.2 - 30.0


[This message has been edited by PoundMutt (edited 05-23-2000).]
 
Old 05-22-2000, 07:58 PM   #5
shootme
 
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Damn, poundmutt, I can't believe I didn't remember that one. I knew I learned it somewhere, sounds like thermo. With that kind of conversion, seems like the 12-15 psi to break your hand would be just about impossible, eh? Hence, doubt the window could be broken!
 
Old 05-22-2000, 08:32 PM   #6
bostonbmw328is
 
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resonant frequency=broken glass (opera singer/wine glass)
 
Old 05-22-2000, 11:55 PM   #7
Richard Clark
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dB don--i did an article on this subject for car sound a couple years ago --- anyway your request for a "real accurate" way is the tough part--for example 194 dB is equal to about 15 psi, and you can halve the pressure for every 6 dB reduction, putting 175 at about 1.5 psi--but the accuracy problem at these pressure levels has to do with the difference between static pressure and what happens in a system where the pressure is constantly changing--this is the difference between what happens in a truly isothermal system and an adibatic system---a car would lean more towards the adiabatic system-- the difference could be several decibels---anyway the nonlinearity of the air also makes things difficult as well, as it matters a lot wheather you mean rms or peak--this can also mean a few db difference at very high pressures--for instance the difference between rms and peak at 160db is about 3 db and at 194db the difference is 6 db--this is due to the fact that at higher pressures the nonlinearity of the air does not allow a pure sine wave to be generated--therefore the distortion of the waveform causes extra variables--so you can forget about a "real accurate" way unless you can define the exact conditions of measurement in extreme detail

[This message has been edited by Richard Clark (edited 05-23-2000).]
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Old 05-23-2000, 01:08 AM   #8
mrflamboyant
 
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i reckon my comment has nothing to do with this post directly. however, indirectly i recall something to the effect of 15 psi is enough force to break a human bone.(doubtful) in comparison to a fist breaking a window.(ouch)
either way, when it comes to broken windows and high pressure levels, i think a broken window has more to do with resonant frequencies. (i could be wrong)

but then again.....why is it that an opera singer is associated with a breaking wine glass? and not a baritone?

how do i find the resonant frequency of my rear windshield? do i turn it up to full volume, to see if it breaks or not?

by just looking at the behavior of the windshield, how far can it flex before it breaks or pops out?

what really breaks glass? sheer force? or resonant frequencies? both? how much of either will cause broken glass?
 
Old 05-23-2000, 03:21 AM   #9
dB Don
 
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Richard is there any info or website that you can direct me to about isothermal and adibatic systems. why do the higher pressures not alow a pure sine wave to be generated? How does the extra distortion cause extra variables? And why at 194 dB will the sound start to modulate? I have much to learn and I could use a little help or a direction to go. THANK YOU!
 
Old 05-23-2000, 06:48 PM   #10
PoundMutt
 
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quote:
Originally posted by mrflamboyant:
either way, when it comes to broken windows and high pressure levels, i think a broken window has more to do with resonant frequencies. (i could be wrong)
YES

but then again.....why is it that an opera singer is associated with a breaking wine glass? and not a baritone?
HIGH RES. FREQ. OF WINE GLASS

how do i find the resonant frequency of my rear windshield? do i turn it up to full volume, to see if it breaks or not?
TAP IT AND MEASURE HZ. OF THE SOUND.



 
 


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