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Shootouts With Meaning: Here's How

Everyone wants to know which loudspeaker is best for their applications. What could be more natural than to line several models up and listen to them? This is called a shootout.

A Meaningful Shootout

What can you do? Here's a method that combines the measurement and listening processes to truly reveal the differences between your loudspeaker candidates. This process can be combined with a conventional shootout to identify the most appropriate loudspeaker for your application.

  • Reserve some time in your listening space when the room will be empty and quiet. It is imperative that this be the venue where the loudspeaker will actually be used because the acoustic environment will have a profound impact on the results. A high directivity loudspeaker may not sound as “musical” at a close distance or in a dead room as a lower directivity design. But take both of them into a reverberant space, and the higher Q device will produce superior speech intelligibility and music clarity.
  • Limit the attendance to yourself and a few helpers. Lots of people milling around will affect the results.
  • Select an audience area for the test, ideally away from room boundaries. It should be deep enough to evaluate the longest expected throw distance for the design.
  • Place the device-under-test onstage at ear height. Better yet, a lift can be used to elevate it. Aim it down the center line of the audience area and at the back row.
  • Move to the back row and measure the distance to the device-under-test. This is the third test position.
  • Cut this distance in half and mark it. This is the second test position.
  • Cut this distance in half and mark it. This is the first test position.
  • Select three additional test positions at these same distances, but along the left or right edge of the seating area.
  • Configure the device-under-test with the appropriate settings, sound level, etc.
  • Measure a stereo impulse response at each test position. A simple method for doing this can be found at http://www.synaudcon.com/sacirex change.htm.
  • Once you have the IRs, here is how to evaluate them.

    Listen to the IRs convolved with anechoic program material using a software convolver. The freeware Gratisvolver is superb for this purpose (www.catt.se). I would start with a speech track, an acoustic guitar track, and a drum track.

    Use a measurement program to determine speech intelligibility ratings such as the C50 (the ratio of the sound energy in decibels before and after 50 ms) and speech transmission index for each test position (www.easera.com). Forget about frequency response. For reasons I mentioned earlier, you cannot get a valid transfer function for a loudspeaker in a casual setup. Be content with the time domain data that describes the energy ratios that affect speech intelligibility and music clarity.

    This is the only practical way to determine how each loudspeaker will perform for an audience. You now have a data set that will be meaningful for either objective or subjective evaluation.

    Since you now have recorded audio system measurements in the real space, you may use a near-field monitor or headphone playback system to compare the WAV files made with Gratisvolver. You can move instantly to any position for any loudspeaker and listen to any type of program material. Try that in a typical shootout.

    The room noise will be absent if the IRs were gathered correctly. My experience has been that when evaluated in this manner, the result is often a different winner than would be selected by a group of listeners at a typical shootout.

    The performance of a loudspeaker is not independent of the listening environment, and the method that I have described will factor this into the equation.

    Pat Brown is president of Synergetic Audio Concepts (Syn-Aud-Con) Inc. and Electro-Acoustic Testing Company (ETC) Inc. Syn-Aud-Con conducts training seminars in audio and acoustics worldwide for those who operate, install, and design sound reinforcement systems. ETC performs precision loudspeaker testing for the audio industry. Pat can be reached at pbrown@synaudcon.com.



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