Thursday, January 1, 2009

A Video on How We Measure Loudspeaker Sound Quality at Harman International

Part of my job at Harman International involves participating in audio dealer training and press events. This involves a 1-2 day field trip to Harman's R&D labs in Northridge where the visitors experience first-hand the listener training process, and participate in a double-blind loudspeaker listening test. Visitors usually leave our labs with a heightened appreciation and respect for the scientific efforts behind the development and testing of new models of Revel, JBL, and Infinity loudspeakers.

A few years ago, Infinity commissioned a video known as "Infinity Academy", aimed at  encapsulating  the 1-2 day training event onto a DVD. Chapter 6, the "Final Test," discusses listener training and the double-blind listening test, where trained listeners evaluate the Harman prototype loudspeaker against its best competitors. The goal is to achieve "best-in-class" performance, attainable only until  the prototype receives a preference rating higher than its best competitor. In the event that the loudspeaker fails on its first attempt, the listeners' feedback is used to re-engineer the loudspeaker, after which, it is re-submitted for another listening test.

The picture to the right shows three loudspeakers on the automated speaker shuffler in the Multichannel Listening Lab. The shuffler brings each loudspeaker into the exact same position within 3 seconds, so that any loudspeaker positional biases are removed from the listening test.

Chapter 6 can be downloaded in  MPEG-4 (H.264, 41 MB) or MPEG  (84 MB) formats.  The entire 6 chapters of the DVD are available here.


  1. "Loudspeaker positional biases"?

    Have you considered that a speaker that sounds great in one position may sound not so great in another? People spend hours positioning speakers, and you just consider this a bias? This is no way to compare speakers !

    It is not science when you ignore a MAJOR factor.

  2. The loudspeakers will interact with the room always. When you compare speakers keeping your self on axis and the speakers on the same physical position in the room (so boundaries reflections are "the same"), the interaction will occur to all speakers. Therefore you can compare individual speakers and see which performs the best.

  3. It is true that the sound of speakers will vary as you move around the room depending on how uniform it's off-axis response is. In our listening tests we test the quality of the direct on-axis sounds as well as the quality of the off-axis sounded which arrive at the listener via reflections. The best loudspeakers have a frequency response that varies very little as you move off-axis.

    Below 200-300 Hz, there will be variations in the bass depending on the positions of the loudspeaker and listener with respect to the room boundaries and how the source-receiver couple into the room modes. We control these interactions via our speaker mover and controlling the listener position. All speakers are treated the same in this regard so that the bass differences heard among loudspeakers are due to the speaker and not the room.