6. Introduction to acoustics: Reflections

This is an intuitive explanation of the effects of a perfect acoustic reflection at a single listening position when the source is within 1 wavelength of the reflecting surface. Note that all of the acoustical effects that you hear in this video are actually happening because of the surroundings. No extra artificial effects were added. For the video portion, the microphone and Sound Pressure Level (SPL) meter are 10 m from the reflecting wall. The microphone is a DPA 4011 condenser cardioid. The two frequencies used in the demonstration were 43 Hz and 55 Hz - but this really doesn’t matter... The signal was generated using Cycling74’s Max/MSP running on an Apple Macintosh, connected via HDMI to an standard AVR. (The reason I do this is that the AVR can act as the sound card and power amplifier all in one.) The loudspeaker driver is a 13“ Scan-Speak woofer in a sealed cabinet made of 25 mm MDF (one of the old prototype woofers left over from the original BeoLab 90 development