Together again for the first time, eleven white papers written by Floyd E. Toole, Ph.D., Vice President of Acoustical Engineering at Harman International Industries, two papers by Todd Welti, Research Acoustician, and a Room Mode Calculator from Harman International.
Due to the fluid nature of the web, previous links to these papers no longer worked. Though still available on the Harman web site, these papers are hard to find so I consolidated them in one location.
Excellent reading for beginners and seasoned audiophiles. Enjoy.
Wayne
A New Laboratory for Evaluating Multichannel Audio Components and Systems**By Sean E. Olive, Brian Castro and Floyd E. Toole, Harman International Industries, Inc.
http://www.wghwoodworking.com/audio/HarmanWhitePaperMLLListeningLab.pdfThe design criteria, features and acoustic measurements of a new listening laboratory designed specifically for listening tests on multichannel loudspeakers and components are described.
Designing a dedicated listening room? This white paper will get you started with formulas to determine the perfect room including sections on room proportions, background noise, reverberation time, and control of early reflections.
Direction and Space – the Final Frontiers**By Dr. Floyd E. Toole, Vice President Acoustical Engineering, Harman International Industries, Inc.
http://www.wghwoodworking.com/audio/HowManyChannels.pdfHow many channels do we need in order to be able to believe that we are "there"
Audio - Science in the Service of Artby Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/AudioScience.pdf"… it turned out that most people, most of the time, liked and disliked the same loudspeakers."
Loudspeakers and Rooms - Working Togetherby Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/LoudspeakersandRooms-WorkingTogether.pdf"Problem is that there are no industry standards for either loudspeakers or rooms. In this paper we
will attempt to make the best of this imperfect system by identifying the major variables in the
loudspeaker/room system, and discussing methods for their measurement and control."
Loudspeakers and Rooms for Multichannel Audio Reproduction, Part 1by Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/LoudspeakersandRoomsPt1.pdf"Here we look at the basic theory of multichannel audio systems, leading us to understand why certain loudspeaker designs and room arrangements work better than others."
Loudspeakers and Rooms for Multichannel Audio Reproduction, Part 2by Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/LoudspeakersandRoomsPt2.pdf"Making a good loudspeaker - Imaging, space and great sound in rooms.
Loudspeakers can be designed to be “room friendly” so that they can sound good in a variety of different rooms. Controlling reflections can optimize imaging and spatial effects."
Loudspeakers and Rooms for Multichannel Audio Reproduction, Part 3 – Getting the Bass Rightby Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/LoudspeakersandRoomsPt3.pdfChoosing the number and locations of subwoofers, and determining where to sit, are fundamental to good bass. Multichannel
audio should be shared, so we try to get good bass at several locations. Acoustical knowledge is essential, but EQ can help.
Subwoofers: Optimum Number and Locationsby Todd Welti, Research Acoustician, Harman International Industries, Inc.
http://www.wghwoodworking.com/audio/multsubs.pdf"Intuition tells us that putting a large number of subwoofers at different locations in a room is likely to excite room modes in a more “balanced” manner, as compared to a single subwoofer. This idea has potential where there is not a single listening location, but rather a listening area."
Low-Frequency Optimization Using Multiple Subwoofers*
by Todd Welti and Allan Devantier
http://www.wghwoodworking.com/audio/low-frequency_optimization_using_multiple_subwoofers.pdfAt low frequencies the listening environment has a significant impact on the sound quality of an audio system. Standing waves within the room cause large frequency-response variations at the listening locations. Furthermore, the frequency response changes significantly from one listening location to another; therefore the system cannot be equalized effectively. However, through the use of multiple subwoofers the seat-to-seat variation in the frequency response can be reduced significantly, allowing subsequent equalization to be more effective.
Maximizing Loudspeaker Performance in Rooms - Part 1by Floyd E. Toole, Ph.D.
Why Loudspeakers Sound the Way They Do.
Maximizing Loudspeaker Performance in Rooms Part 2 - The Acoustical Design of Home Theatersby Floyd E. Toole, Ph.D.
Acoustical Design and Equalization
http://www.wghwoodworking.com/audio/MaximizingLoudspeakerPerformanceInRooms.pdfThis overview in four steps is intended to set a context within which readers can apply the more detailed technical information in the accompanying paper: “Loudspeakers and Rooms - Working Together”.
Getting good sound in a room. How is it done?
- Step One: Start with a good room
- Step Two: Start with good loudspeakers – ones that are “room friendly”
- Step Three: Improving Bass Performance – working with standing waves
- Step Four: Improving Bass Performance – equalization does work!
Understanding Room Acoustics and Speaker Placementby Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/UnderstandingRoomAcousticsAndSpeakerPlacement.pdfThe room is the final audio component and, as such, it can make or break a truly satisfying listening experience.
Loudspeakers and Rooms for Sound Reproduction—A Scientific Review*
by Floyd E. Toole, Ph.D.
http://www.wghwoodworking.com/audio/loudspeakers_and_rooms_for_sound_reproduction.pdfJames Moir: “Finally, in my view, if a room requires extensive treatment for stereophonic listening there is something wrong with the stereophonic equipment or the recording. The better the stereophonic reproduction system, the less trouble we have with room acoustics.”
[This paper] is a review of acoustic and psychoacoustic research from disparate fields, put into a framework that is familiar to the audio community. The result is intriguing. It turns out that some of our common practices are less than optimum, and some popularly held notions might need to be revised.
The Harman Room Mode Calculatorhttp://www.wghwoodworking.com/audio/RoomModeCalculator.zipA tool to play with after reading the above articles. Part 2 of "Maximizing Loudspeaker Performance in Rooms" has detailed information on how to interpret the graphs.
The calculator uses Microsoft Excel or compatable spreadsheet for the calculations.
Toggle betwen WAVES and MODES at the bottom left of the spreadsheet.
*Articles added 7-04-10
**Articles added 5-15-12
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March 28, 2025
The science of acoustics has evolved since Floyd Toole did his ground breaking studies. Norman Varney of NWAA Labs is one of the people building on Floyd Tooles's work. The August 2022 Stereophile article
NWAA Labs: Measurement Beyond The Atomic Level is an excellent starting point to learn about room acoustics.
NWAA Labs: Measurement Beyond The Atomic Levelhttps://www.stereophile.com/content/nwaa-labs-measurement-beyond-atomic-levelYou need a big space to measure the effects of reverberation times of a room with and without absorption.
"At very low frequencies," Ron interjected. "NWAA Labs can measure accurately down to 25Hz because it resides in a floating room inside a floating room, separated from the outside world by roughly 25' of concrete. The room's background noise at 1000Hz is an astounding –43dB!"
A few tidbits from the article:
Absorption is the most common treatment used in listening rooms. The measurement of absorption was first described by Wallace Sabine, who compared the reverberation times of a room with and without absorption. This difference was then converted to units of absorption using this formula:
A = 0.9210(V*d/c)
where
A = equivalent absorption area in m2,
V = volume of reverberation room in m,
c = speed of sound at ambient temperature and humidity in m/s,
and d = decay rate in dB/s.
Most of what we think we know about absorption is wrong! Absorption calculations in use today can err by as much as 85%. The biggest error concerns how important the area of absorption is in the calculation of how much absorption is needed."DeGrandis has done some unbelievable research in the field of diffusion," Ron said. "He's come up with a computer program that allows him to simulate what happens to a design when he changes parameters. "We've done the same research with diffusion, where shape is again key. I'm sorry, but almost 90% of what's out there, theory-wise, is BS. For example, you can't use a block's length in a 'skyline-style' diffuser to determine the frequency range that it affects."
AV Room Services is the retail arm of NWAA Labs. Norman Varney has published 46 room acoustics articles, a great resource before spending spending thousands of dollars on room treatments.
https://avroomservice.com/articles/Danny Richie of GR Research and Ron Brenay of New Record Day posted two excellent video interviews with Norman Varney of A/V Roomservice discussing the importance of room and floor-borne vibration on the audio quality of high-fidelity systems and how the A/V Roomservice Equipment Vibration Protectors can really help to manage this imparted vibration to improve your system's overall audio quality.
Ron's interview:
https://youtu.be/7JmXXrIoJb8?si=1JHWW4VMO4DSjlZ5Danny's interview:
https://youtu.be/FrN9kFputwQ?si=gsn4FfHteCis__nuThe EVP's are available at AV Room Service
https://avroomservice.com/
