Acoustical FAQ (Frequently Asked Questions)
Measured Arrays
| OMNI Loudspeaker | Surfaces
| Sound Field Scaling |
Frequency Response Scaling
Loudspeaker Data | SPL
Calibration | Low Frequency Polar Data Acquisition | Acoustical FAQ
When I "corner load" a subwoofer, I only get a 10dB increase in SPL. I thought a corner increased a subwoofer output by 12dB?
As mentioned in the "Acoustical Information," MAPP Online Pro currently models only the first reflection from boundary surfaces. This accurately models their "comb filtering" effects. However, it underestimates the effect of "corner loading" subwoofers. For one boundary, it is accurate. i.e. a subwoofer placed on the ground gives 6dB more SPL then a subwoofer in free space. However, for two boundaries (a wall-floor intersection, for example) this first-reflection model shows an increase of 10dB, which is less than what is expected from a two-dimensional " theoretical corner loading", i.e. 12dB. In three dimensions, (which MAPP Online Pro does not currently model), the SPL of a corner-loaded subwoofer increases 18dB. Note that this ONLY works for low-frequency sources placed very close to corners. It does NOT work for higher frequencies, when sound starts to become directional. (source: Acoustical Engineering, H.F. Olson, 1954).
- Why does a UPA seem louder than a CQ in MAPP Online Pro?
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When the SPL
of a loudspeaker is measured for MAPP Online Pro it is driven with
full-spectrum pink noise at the onset of limiting. Because a CQ covers
a wider frequency range (more low frequencies) than a UPA it limits
earlier for full-spectrum pink noise than a UPA. If you were to drive
both speakers with A-weighted pink noise, a CQ would be louder than
a UPA. Meyer Sound is in the process of developing a method of measuring
the maximum SPL of each loudspeaker on a per-octave basis.
- What are the
initials at the end of surface material names (i.e. the "CH" in "concreteblockpaintedCH")?
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The initials at
the end of the material name indicate which text book they are from:
CH = Cyril Harris, "Handbook of Acoustical Measurements and Noise
Control", Third Edition, Acoustical Society of America, 1998.
LB = Leo Beranek, "Acoustics", Acoustical Society of America, 1996.
KF = Kinsler, L, Frey, A, et al., "Fundamentals of Acoustics", Fourth
Edition, John Wiley and Sons, 2000.
- Why are there
no ceilings or floors in MAPP Online Pro?
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Every effort has been made to avoid labeling any part of the sound field up/down/left/right/top/bottom so that you can feel free to think of it as either a floor plan (four walls) or a section plan (two walls a floor and ceiling).
- Why wasn't (material
name here) included as a surface material?
-
There are certain
materials that we have not included because we want to measure their
absorption values ourselves. Lightweight materials over an airs pace
are intended to achieve some of their absorption by resonating (especially
at low frequencies). We expect that this will effect the phase to
a large enough extent that it cannot be ignored.
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Release Notes
Legacy XML Reader
Java and OS Tips
MAPP Pro
User Guide v2.8.54
(16 Mb)
RELATED PAPERS
MAPP: Predicted &
measured frequency
response
Curvilinear arrays
and MAPP Online
Low Frequency
Polar Data Acquisition
For questions or more info:
MAPP Online Pro support
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