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Old 1st November 2001, 08:39 PM   #1
Ignite is offline Ignite  Canada
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This eludes me... There doesn't seem to be information anywhere on this. How does one calculate max SPL given wattage and driver sensitivity? Also how does one calculate theoretical excursion at a given frequency and power?
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Old 1st November 2001, 11:00 PM   #2
Freddie is offline Freddie  Sweden
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If I remember this correctly, each time you double the amplifier power you'll get a 3dB increasement.

So If you have a driver with 90dB/W sensitivity, it means that with 1 W you will will get 90dB. With 2W 93dB, with 4W 96dB, 8W 99dB, 16W 102dB, 32W 105dB.... So If you are want to play really loud, go for drivers with high sensitivity. It will probably be a lot cheaper than buying a bigger, more powerfull amp.

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Old 2nd November 2001, 12:10 AM   #3
f4ier is offline f4ier  Australia
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.... and here how to estimate Xmax given SPL, Sd and frequency.

Xmax = (0.00118*pi*(10^(SPL/20))) / (Sd*f*f)

where:
pi = 3.1415926535897932384626433832795
SPL in dB
Sd in square meters
f in frequency
Xmax in mm

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Old 2nd November 2001, 01:25 AM   #4
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f4ier has the correct equation for calculating excursion, but I would just like to point out some additional qualifications to the units. SPL is the rms value, in dB, even though excursion is given in peak value,and these calculations are based on the SPL in 2pi (or half) space, not 4pi. You would need twice this excursion to gennerate the same SPL in free field.
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Old 3rd July 2006, 05:22 AM   #5
exuviae is offline exuviae  United States
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Default So

Ok i am a bit slow, is there some calculation given an amount of watts and sensitivty that tells you a theoretical max spl? For example I have SoundStream Tarantual series T4-15 with a 91db at 1 watt at 1 meter, and will be pushing those with a 2000 watt rm Picasso PCA200D amp also from soundstream. Without sitting there figuring out exponents (2, 4, 8, 16, 32, 64, 128,256,512,1024,2048) i know this because of computer programming lol. By your calculations i would only hit around 124db. I think that is right, 11 double in power, 3db gain for a total gain of 33db added to a sensitivity of 91db = 124. However on 1000 watts and 2 10" in a ported box i hit 138.9 on a term lab meter (official meter of db drags) and the box was to small for the speakers, and the starting sensitivity was only 82. Something just don't add up, with 2 15"'s seeing 2000 watts i should be in the 145-150 on the term-lab meters.
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Old 3rd July 2006, 05:36 AM   #6
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sensitivity + 10log(power)

eg

91 + 10log(2000) =124.0103
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Old 3rd July 2006, 07:04 AM   #7
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If we are talking SPL drags then we are talking inside the cabin of a car. You'll have cabin gain amongst other things.
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Old 3rd July 2006, 07:59 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
are we really talking about 25db to 27db of cabin gain?
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Old 3rd July 2006, 08:44 AM   #9
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In my experiance cabin gain is maybe 4db/oct from 80hz or lower depending on the size of the car, you only get that sort of gain at very low frequencies. I do think the car this was for had a leeky boot though.
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Old 3rd July 2006, 05:23 PM   #10
soufiej is offline soufiej  United States
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Could this possibly be what you need; http://www.myhometheater.homestead.c...alculator.html

This takes into account the number of speaker enclosures in the room and room gain.
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