| stevenliddle |
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| Joined: 24 May 2008 |
| Posts: 27 |
| Location: Sweden |
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| I need help in understanding the way that EASE calculates Direct SPL.
For example, when EASE 4.3.8 is set to calculate SPL using the old multitone source, I have a horn loaded device which produces different and counterintuitive SPL values. All levels are set to flat max which applies different power gain to each 1/3 octave band, up to the maximum level allowed by the manufacturer's data - these are obviously the power gains required to achieve a flat frequency response according to the sensitivity of the device.
The following observatinos were made using Standard Mapping.
When I view a 1/3 Octave value at 500Hz for this device I get a value of 99.5dB at the on axis location. 4kHz gives 98.7dB. When I look at the broadband sum I get 97.6dB which is lower than either of the 1/3 octave values.
Reverting to the new pink noise source and applying flat maximum to the devices results in the power being distributed equally across the 1/3 octave bands so that the sum is equal to the power handling for the pass band. For example 1400W spread across 9 1/3 oct bands of 155W each.
The SPL which results are 500Hz 1/3 oct of 93.5dB, 4kHz 1/3 oct of 92.5dB and a broadband sum of 105.5dB, again all at the on axis location. This seems to be a more reasonable conclusion.
So my point is, using the old multi-tone method, the broadband sum was down by more than 6dB which leads me to think that the new pink noise source may be too optimistic or is the old method pessimistic or am I barking up the wrong tree? |
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