Saturday, May 23, 2009

The Harman International Reference Listening Room

Last week I returned from the AES Munich Convention where I gave a paper entitled ”A New Reference Listening Room for Consumer, Professional, and Automotive Audio Research.” It describes the features, scientific rationale, and acoustical performance of a new reference listening room designed and built for the purposes of conducting controlled listening tests and psychoacoustic research for consumer, professional, and automotive audio products. The main features of the room include quiet and adjustable room acoustics, a high-quality calibrated playback system, an in-wall loudspeaker mover, and complete automated control of listening tests performed in the room. A copy of my Munich AES presentation is available here.


The first prototype reference room was built at the Harman Northridge campus in 2007. Additional reference listening rooms have since been built at Harman locations in the UK, Germany, with the fourth one being constructed in Farmington Hills, Michigan. We are in the process of measuring and calibrating the performances of the different rooms using acoustical measurements and binaural room scans, which will be evaluated for their perceptual similarity in sound quality.


With a standardized listening room and playback system, Harman scientists can conduct listener training, psychoacoustic research and product testing at different Harman locations throughout the world. The results from these different locations can be compared or pooled together since the room, playback system, and trained listeners are a constant variable. With this brings greater testing efficiency, flexibility, and new opportunities in the kinds of product research and listening tests Harman is able to do in the future. Already, we are using the unique features of these rooms to conduct very controlled listening tests on consumer in-wall speakers, and to research and benchmark the performance of various commercial and prototype loudspeaker-room correction devices.


You will hear a lot more about the Harman International reference listening rooms in the near future because of the pivotal role they will play in the research, testing and subjective benchmarking of new Harman consumer, professional and automotive audio products. Just thinking about these research possibilities makes me truly excited!

24 comments:

  1. Great listening room. Except too much bass absorption. Such a room is quite opposite to average european listening room where bass absorption is very low so one usually gets low freq RT60 in seconds. Will this be a problem when simulating average consumer listening room acoustics?

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  2. Sean,
    I noticed that you have your Phd. Is that recent or has have you been a Dr. for a long time? What was the subject of your discertation and what is your Phd in-acoustics?

    By the way, the room looks great. Are the speakers JBL Pro models-just curious.

    Randy Bessinger

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  3. Hi Randy:

    Yes, my PhD is relatively recent (2007) and is in Sound Recording from McGill University. My PhD dissertation was on "Interaction between Loudspeakers and Room Acoustics Influences Loudspeaker Preferences in Multichannel Audio Reproduction." I used binaural room scanning to measure how these interactions influence preferences, and how listeners adapt to the room acoustics.

    Yes, the loudspeakers in our reference room are professional monitors (JBL LRS6332) seen here
    http://www.jblpro.com/catalog/General/Product.aspx?PId=26&MId=5
    The four subs are consumer models: JBL HB 5000

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  4. Hi Vuki,

    Where are you getting your data regarding the higher RT60 times of average European rooms?
    Of course, the notion that you can even accurately measure the RT60 of small rooms is flawed based on the recent work of Toole. The definition of a diffuse field doesn't apply in small rooms because the size, dimensions and uneven distribution of absorption makes an isotropic field impossible. At low frequencies, the room modes dominate what you measure and this varies dramatically depending on the positioning of the source and receiver. We used several microphone and loudspeaker positions and spatial averaging to minimize these effects -- but I wonder how meaningful the RT60 measurements really are in small rooms?

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  5. Hi Sean,

    not being a scientist I don't have any kind of collected measured data. But, knowing where I live I'm sure that solid brick walls have much less LF absorption than drywall. Also having some listening expirience in "drywalled" rooms I usualy get the impression of (ironic-isn't it-) "dry" sound. One can gat very nice sounding bass in such room, but always a bit dry (to my ears). It could be that I'm accustomed to listening to room modes, but somehow I miss the "slam" compared to nice solid walls room.
    As you can guess I'm an audiophile and probably talking BS :-)

    Anyway thanks for the great blogs!

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  6. Hi Vuki,

    Thanks for the compliment about my blog. I don't think you are talking BS even if you are an audiophile :) You are in fact correct: brick walls, concrete basements, and stiff double-layer drywall construction will provide less bass absorption or damping of room modes than the single layer gypsum walls used in our Reference Rooms. We did this to minimize the subjective effects of room modes at low frequencies. This was a conscious decision we made to provide a better quality of bass reproduction in the room since a neutral, high quality room was needed for training listeners as well as evaluating audio algorithms and in-wall/on-wall/computer desktop Ipod speakers,etc. With that being said, lots of homes use single layer gypsum wall construction, so in that sense, our room is quite typical.

    If you have stiff massive walls you will simply have to work harder to control the energetic low frequency room modal effects at the listener location. Fortunately, you can partially do this through judicious placement of the loudspeaker-listener(s), and employing single or multiple point equalization at the listener location(s). We recommend the use of multiple subwoofers to cancel energetic room modes based on the principal of acoustical destructive interference. This gives a more consistent bass response over a wider listening area. Harman has a patent on this technology known as Sound Field Management (SFM), and we are employing it in all of our Reference Listening Rooms.

    If you like "slam" effect of your bricked walls room - there is no reason why this couldn't be simulated via the loudspeaker-room equalization.

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  7. Hi Sean,

    Great blog. I'm a big fan of Harman's approach to designing speakers.

    In your reference listening room, shouldn't those JBL speaker being used for surround duty be higher? A couple feet above the listener's heads?

    Looks like an awesome room.

    Dan

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  8. first thanks for this blog its great

    will your paper be available throw AES "new reference room"

    cant find it in the AES library

    I am constructing my reference room which by the way has a pair of LSR6332 and a pair of 4645c subs and lsr6325 for sourruonds (have to buy the center lsr6332) I have read almost all your pappers and Mr Toole pappers and new book its great

    your papers on your (harman) past listening lab have been a good referece hope to have your new specs soon.

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  9. Hi Valentin,
    Thanks for your comments. The AES preprint on the Harman Reference Room should be available on the AES site by October, or you can purchase their 126th Convention CD-ROM http://www.aes.org/publications/conventions/.

    Cheers
    Sean

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  10. Blogs are so informative where we get lots of information on any topic. Nice job keep it up!!
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  11. Blogs are so informative where we get lots of information on any topic. Nice job keep it up!!
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  12. The 2C3D Reference Listening Room was developed through years of experimentation and evolution by a group of high end audio manufacturers. It included WallDamped Isolation walls and TubeTraps plus great electronics.

    Does any of your present work reference the old 2C3D listening rooms?

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  13. Hi Arthur,
    Sorry, I am not familiar with the old 2C3D listening rooms, so I guess the answer to your question is "no". I Goggled the term but could not find a definition of the 2C3D room specification." If you could provide one I would appreciate it.
    Cheers
    Sean

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  14. today you are presenting a paper at AES NY 127 convention

    about 5 different room correction systems i hope you can share with us soon some of the results i will buy the paper once its up in the aes library

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  15. thank you very much for your information helped me understand things I did not know because

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  16. Hi Sean,

    For the listening rooms what was the deciding criteria for choosing the LSR6332 over the LSR6328 or, using Revel speakers that are available to you? Also, what stands are being used to support the 6332s in the pictures?

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  17. I have been a regular visitor of this site and I love reading blogs posted here. They are truly very well written, precise and to the point. Thanks.

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  20. Well This is true. A meaningful loudspeaker specification would naturally weed out the good products from the bad ones - and the manufacturers who couldn't meet the new quality specification would fall to the wayside. thanks for the sharing this great and very interesting topic with us.
    Team Sportswear

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  21. Whenever i see the post like your's i feel that there are still helpful people who share information for the help of others, it must be helpful for other's. thanx and good job.

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  22. Thanks for sharing the precious blog post.

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  23. Thanks for all the useful information in your blog.

    Why did you choose HB5000 subwoofers instead of LSR6312SP?

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  24. Hi Ruy
    We tested a number of 15-inch power consumer subs that Harman made and at the time JBL HB5000 had the highest undistorted output down to 20 Hz. The JBL 1500 Array was another good choice as being ported it has more output above 40 Hz but less output below that.

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