Room Acoustics

[Dylanl]

Is there a way for me to see how much my room is effecting (coloring) the overall sound quality of the music I am playing? I have heard that you can do this with known sine waves & SPL meter. I have tried this with a Radio Shack SPL meter but the chart that I plotted was so exaggerated. It also seemed to change depending on where the meter was placed.

[picky]

EDIT: I bow to the master......(artto follows):

[artto]

Sine waves are generally not used for measuring room acoustical properties. When they are used, usually a number of standardized selected musical frequencies are used, not every single frequency.

Inaccurate microphones with unknown response curves, such as that on the Radio Shack SPL meter are not reliable in showing what is really going on.

In any instance, an omni-directional mic should be used.

Your system should be run in monaural mode. You should be testing only one speaker at a time.

Noise actually does very good job simulating musical conditions. Usually a broadband signal such as white noise or pink noise is used as a signal source for taking measurements.

White noise is noise whose amplitude is constant throughout the audible frequency range. It is often produced by a random noise generator in which all frequencies are equally probable. White noise is defined as sound with equal power per Hz in frequency.

Pink noise is filtered to give equal power per octave or equal power per 1/3 octave. Since the number of Hz in each successive octave increases by two, this means the power of pink noise per Hz of bandwidth decreases by a factor of two or 3 dB per octave. Pink noise has relatively more bass than white noise.

Its best to use some sort of real-time spectrum analyzer to interpret/show the microphones response.

The room, the speakers location, the location of the microphone all relative to each other, as well as any objects in the room will affect the measured results, which will be especially noticeable with sine waves. If you're recording the results to a tape deck, do not move around the room as this will affect the results.

There are various software that can do the analysis, some of the more sophisticated ones even being able to remove the rooms acoustics from the equation, showing the speakers free-field response.

In your particular situation I would suggest as Picky did, positioning the RS SPL meter at ear height at the listening position. If you are going to use sine waves I suggest you use a test CD that produces selected tones. If you use sine waves, its probably easiest to take the signal out from the RS SPL meter and feed it to a tape deck and record it. You can then easily refer back to the tape decks meters for differences in level when playing the tape back. If you have access to a spectrum analyzer you can do the same thing with white and pink noise by feeding the recorded tape into the spectrum analyzer. Theres lots of inexpensive audio editing software that have a spectrum analyzer feature built-in. I record the recorded tape to my computers hard drive and use the spectrum analyzer In Sound Forge (note: the consumer version of Sound Forge, 'Audio Studio' does not have a spectrum analyzer, only their pro audio products do)

http://www.etfacoustic.com/modes.html

http://www.rhintek.com/cara/cara21desc.php