Q: How do you equalize a room?

A: With a hammer.

In October, Sam Berkow of SIA Acoustics led a joint meeting of the Boston AES and the Boston Chapter of the Acoustical Society of America. Mr. Berkow works with the Walters-Storyk design group and is the creator of SMAART acoustical measurement and analysis software. His informative and lively presentation addressed "äthe interaction of sound systems and rooms" and discussed his thoughts about audio reproduction system optimization.

Sam pointed out that one should not think of tuning or equalizing a sound system by simply turning knobs, faders, sliders and other electronic devices. Rather one should consider how to optimize sound system performance in conjunction with a particular room; and refine this by measurements once installation is complete. He presented very useful approaches to optimize "systems" (rooms and sound systems) using both acoustical measurements and critical listening. The goal is to optimize or "tune" a system so that the perceived subjective quality by listeners is both "accurate" and pleasant. He suggests that in order to optimize a system the designer should not only perform an analysis of the sound system but also analyze the room acoustics, and that while you can not use your ears for an accurate analysis, the results of optimization should be consistent with positive auditory perception..

Traditionally sound systems have been tuned using single channel measurements of frequency response. His talk discussed how dual-channel FFT measurements provide a more useful measurement because the signal arriving at the measurement microphone can be compared with the original signal. Sam demonstrated this dual-channel technique with a microphone, audio input device, a laptop computer and software developed by Sam's company SIA software.

The two main types of acoustical measurements that Sam uses in his work are impulse response and frequency response measurements.

Two real-world examples of how to use these measurement tools were presented. The first example showed the methods he used to optimize a movie theater sound system. The frequency response of the system met criteria but listeners complained that the system did not sound right and intelligibility was compromised. By measuring the response of one loudspeaker and comparing this with measurements of separate crossover regions of the loudspeaker a particular resonance above the crossover point of the low-frequency device was found and minimized with only one small adjustment to an equalizer. However, this small adjustment was all it took to correct all the complaints about poor sound quality and speech intelligibility!

The second example showed how an impulse response measurement was used to find a problem with build up of low-frequency energy for listeners seated under the balcony in a 1200 seat auditorium. This measurement showed tonal imbalances in the room and that acoustical treatment would better optimize the system rather than tuning the sound system.

After the presentation a couple of measurements were made using a small sound system and loudspeaker. Both music and pink noise were used as measurement stimuli and other features specific to SMAART software were demonstrated. One improvement to earlier versions of the software and a very useful feature is the ability to make fixed point per octave measurements (FPPO). FPPO provides the same precision per octave so that fewer measurements are required. 24 data points per octave are indicated on the screen with a frequency response transfer function measurement. Those of you who have performed FFT measurements without FPPO are familiar with the frustrating lack of measurement resolution in the lower octaves.

Sam gave a very friendly and personable talk and encouraged the audience to get involved with the presentation and to ask many questions. And as plenty of discussion followed, I would judge his talk a great success.

--Matt Moore