Acoustical FAQ (Frequently Asked Questions)

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 Pro currently models only the first reflection from walls. This accurately models the "comb filtering" effects of walls. However, it underestimates the effect of "corner loading" subwoofers. For one wall, it is accurate. i.e. a subwoofer placed on the ground gives 6dB more SPL then a subwoofer in free space. However, for two walls (a wall-floor intersection) this first reflection model gives 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 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?

When the SPL of a loudspeaker is measured for MAPPOnline 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 wall material names (i.e. the "CH" in "concreteblockpaintedCH")?

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 MAPPOnline?

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). However, the best term we could come up with for the walls dialog was "walls" which is not as clear as we would like.

Why wasn't (material name here) included as a wall material?

There are certain materials which we have not included because we want to measure their absorption values ourselves. Light weight materials over an airspace 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 can not be ignored.