Loudspeakers for Music Recording and Reproduction, by Newell and Holland

There are a number of cookbook and do-it-yourself guides to building loudspeakers, but few aimed at experienced builders and those already in the industry. And no, you can’t find everything on the Internet, and separating the gold from the dross of PR-speak “white papers” in the AES Journal pre-prints is a major project in itself.

If you are interested in high-efficiency, high-headroom loudspeakers and how they are used in modern studios, this is the book to get. More broadly, if you are interested the key technical parameters that affect the subjective listening experience, this is one of the few books that has a rigorous and comprehensive coverage of the subject, backed by the two authors’ decades of experience in professional audio. Dr. Keith Holland is a lecturer in electro-acoustics at the Institute of Sound and Vibration Research at the University of Southampton, and Philip Newell is an international consultant on acoustic design with over 40 years of experience designing hundreds of recording studios (this is his fifth book on professional audio).

In addition to loudspeakers - which are covered by an introduction on acoustics, and moving on to separate chapters for the main types of loudspeaker design, loudspeaker cabinets, horns, and crossovers, there are chapters on amplifiers and cables, loudspeaker behavior in rooms, interfacing loudspeakers with the rest of the studio, subjective and objective assessment (with particular attention to the effects of phase delay at low frequencies and the midrange), challenges in low frequency design and the effects of these choices on transient response, and a final chapter on surround sound.

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What happens when history falters? When brilliance is forgotten?  When a brilliant mind dies tragically in obscurity and secrecy? This is essentially what happened to Alan Dower Blumlein, a British electrical engineer who developed many circuits and concepts we take for granted today, yet is barely known.  This obscurity was compounded by a confluence of bad luck and unfortunate behavior which delayed the first biography of Blumlein until 57 years after his death. I’ve just finished reading one of the two biographies that appeared in 1999: The Inventor of Stereo: The Life and Works of Alan Dower Blumlein by Robert Charles Alexander.

Blumlein was truly an electronic genius, at least at the same level as Edwin Armstrong, yet had the bad luck of working in a company (EMI) that didn’t encourage publication (Blumlein only published two papers in his career) and discouraged publicity (only four photographs of Blumlein are known to exist), and died while working on an extremely top-secret project (centimeter radar) during World War II, resulting in his war work being buried in secrecy. His only tangible legacy (other than his designs and inventions, which were widely used) were his patents - over 120 of them - which trace the path of his short career.

Here is a thumbnail summary of Blumlein’s life and accomplishments:  He was born in London in 1903 of an Alsatian father and South African mother (of Scottish background). He was an intelligent child, but only learned to read at age 12 when he realized this was important.  He picked up an interest in electricity as a child, which lead him on a path to a degree from City and Guilds College in London, a respected technical branch of Imperial College. In 1924 he got a job at International Western Electric (later to become S.T. & C.) analyzing telephone line cross-talk.  As part of this work, he invented a balanced bridge that allowed sub-picofarad capacitance measurements on phone lines, which greatly facilitated efforts of cross-talk reduction. He also developed very sophisticated compensation networks for buried and undersea cables.

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The lifetime journey of an audiophile can be long and varied. From the first music you heard as a kid on a hand-me-down radio to the hair-raising experience of hearing a world-class esoteric audio system, the enjoyment of music can still exist at all levels of audio reproduction. If the sound you hear is the result of what you make with your own hands, an even higher level of satisfaction results. In a world where manufactured devices come from a far-away land and are increasingly dense and disposable, being able to make and control a key aspect of your musical enjoyment is a precious ability.

There are many reasons why DIY (Do-It-Yourself) audio is feasible and enjoyable:

• The human ability to process and enjoy sound is extremely complex and not fully understood. Subtleties in the reproduction of sound can enhance (or detract from) our enjoyment and these subtleties are often under the control of the experimenter.
• Old analog recording and amplification techniques from 50 or even 75 years ago still provide incredible musical enjoyment. These techniques can be readily constructed by a skilled amateur, unlike, say, movie or video techniques.
• Unlike someone interested in chemical experiments, electronic experimentation is free and uncontrolled (so far) and old surplus electronic parts and equipment are readily available, allowing experimentation on a budget.
• Some aspects of audio reproduction, such as analog amplification and mechanical design, are accessible to the amateur.  Fancy college degrees or expensive industrial equipment are not required.
• There are many facets of audio reproduction, each with a deep history and technology, allowing almost unlimited fields of exploration for the inquisitive mind.
• With sufficient knowledge and skill, it is possible to build an audio system that sounds better than any commercial system available.

The result of these is that home-built or -modified audio equipment can be a fascinating and enjoyable hobby.  However, my appreciation of this has been dulled over the last few years as I have become more involved in consulting on commercial designs (mainly for Artemis Labs), and the increasingly high-quality, and in some ways, uncompromising high-end systems I have been exposed to. When your audible senses have become fine-tuned and almost any system shows various flaws, it is easy to fall into a superior, dismissive attitude to lesser systems. I have never been a believer in the one, ultimate “absolute sound”, but I was beginning to adopt an elite attitude about audio equipment, thinking that most systems “sucked”.  This attitude is readily reinforced by attendance of trade shows like the CES where (for a variety of reasons) the vast majority of the sound actually really does suck.

I had a pleasant reminder of my DIY audio roots, however, during a recent visit to Thailand, where my friend, Kamon, spent a day to bring me around to visit various audio DIYers he knew in Bangkok.  For example, here is Kamon and Mr. Pae (described in my posting from October 2007) discussing the system in his house in the outskirts of Bangkok:

Note: The following pictures can be seen at higher resolution if you click on them.

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For the first time in three years I attended the Consumer Electronics Show (CES) as well as the concurrent T.H.E. Show in Las Vegas. The CES has been the largest trade show for the consumer electronics industry in America for years.  It used to alternate between the coasts and Chicago, but the main show has been in Las Vegas since at least the mid-1980s, when I first attended it. This posting will give my overall impression of these shows, with no guarantee of completeness, fairness, or impartiality.

The bulk of the show is in the huge convention center halls and in the Sands Convention Center - the size and crowds earned this part of the show the name “the zoo”.  Showing off high-end audio requires acoustic separation between vendors, and the usual way to do this is to set up the equipment in hotel rooms that have had their beds removed.  As a result, the high-end audio part of CES was always separate from “the zoo”.  Over the years, dissatisfaction with the CES management plus the high cost of rooms caused an alternative show to be created: “T.H.E. Show” (The Home Entertainment Show). Up until 2007, the high-end audio part of CES was held at the Alexis Park Hotel, off the strip and quite far south of the convention centers.  T.H.E. show was held in the adjacent St. Tropez hotel, so it was easy to walk between the two high-end shows.  Both of these hotels are low-rise “garden”-style designs, spread-out, with no casino or slot machines (!). However, in 2007, the CES moved the high-end exhibits to the upper floors of the Venetian, a huge hotel/casino right on the strip, and part of the Sands complex.  T.H.E. Show then moved into the Alexis Park, which, although nice, was a long shuttle bus ride from the Venetian.  The slow economy has reduced the number of exhibitors, especially at T.H.E. Show, and lots of people I met at the Venetian didn’t even know of the existence of T.H.E. Show or didn’t spend the time to visit it.  It’s too bad, since I found the Alexis Park much more relaxed and convenient than the Venetian.

One of the first things you see when approaching the Alexis Park is this remarkable steel sculpture that plays music and follows you around! It is the creation of Solar Sound Sculpture, basically two men from the San Francisco Bay Area who work in an old steel shop in Oakland along with other large-scale sculptors.  I had a good talk with Justin Grant who built most of the sculpture and he explained that this had initially been shown at the 2008 Burning Man festival.  The speakers on the top have infrared sensors and servos that make the speakers track the closest person.  It is huge - at least 20 to 30 feet tall, and quite striking.  It can be run off solar panels, but in this set-up was running off storage batteries. Very impressive!

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The last update on my music computer system was just over two years ago; it is time for a new update.  The main music computer is still the same AMD Athlon in the TNN-500 case but the hard drives have been upgraded.  The sound I/O card is the Lynx Two.  The OS is Windows XP SP2 updated with the most recent patches.  The programs used are basically the same as reported earlier:

Exact Audio Copy - for ripping CDs
Sony Sound Forge 7 - for recording from records and for general sound editing
FLAC - for lossless compression
Ogg Drop - for lossy compression
Tag&Rename - for editing meta fields
Foobar2000 - for playing back files
Windows XP/Windows Explorer - for organizing and accessing sound files

As the number of sound files has grown, I’ve ended up using Windows Explorer and the Windows file system to organizing the files.  I use the hierarchical file system as follows:

• Top level: Type of file (Books, Music, Lectures, etc.)
• Music Category
• Album Title
• Resolution (for high-res files only)

The following screen shot shows the hierarchy in action:

I’ve drilled down to the individual tracks (each one a FLAC file) in the 96-24 folder under Scientist_…, under Reggae~dub, under Complete Albums.

Note that I have the Windows appearance set to the old Windows 2000 style.  I don’t like the default candy-colored, toy-style that comes with Windows XP.

Custom folder icons are used to differentiate different types of music: ripped CDs, music downloads, or LPs.  Folders with no custom icon mean that the meta-data editing is not yet complete.  For high-resolution recordings, I keep two sets of data: one for the original high-res recording, typically 96KHz/24bits, and a 44.1K/16bit version for use in my iPod. (I’ve discovered that my 5th-gen video iPod does a lousy sample-rate conversion if the file it plays is not already 44.1KHz.) Remember that I am using ROCKbox on my iPod, which plays the open-source formats.

As the music category folders get large, I plan to add another level to the hierarchy: composer for the classical categories, and artist for the others.

As some of you know, I now have a second house in Vietnam.  My main computer there is a Mac Mini that can dual boot into the Mac OS or Windows XP using “bootcamp”.    A Western Digital “Passport” drive holds all the music files, currently over 100GB.  When booted into Windows, I use Foobar2000 to play music, just like on my music computer.  However, I needed an equivalent player when booted up in the Mac OS.  After trying several, I’ve decided on “Cog”.  It is straightforward, simple, and like Foobar2000, it is free.

Notice that I am not using a database-type music player, such as iTunes.  This is because all the ones I’ve looked at either don’t support the formats I’m using or make it hard to sort by composer (the classical music problem).  Using Windows Explorer is clunky, but usable for now.  I’m keeping an eye on new software, but at the moment, my main task is to move my music to the computer and enjoy listening to it!

Here are a few reflections on the recent RMAF show here in Denver, Colorado …

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I missed the Rocky Mountain Audio Fest for the first time this year, since I spent the month of October in Vietnam. IMHO, this is the best high-end audio show in North America, so was sad to miss it, but Lynn Olson (who lives near Denver) went and he and others have made some good observations on the show.  A good overview is given on the following diyAudio thread: Rmaf 2008. Lynn expects to post more here on ClariSonus, but to whet your appetite, here are a few tidbits.

There were quite a few new speakers, many with really good sound. For example, here is the new RAAL omnidirectional speaker with ribbon tweeters, designed by Aleksandar Radisavljević from Serbia (click on the pictures for a full-sized display):

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My friend, John Nunes, pointed me to a very interesting paper on the distortion of op-amps (more on this later).  I started poking around the site it resided on and found an excellent “Notable Site” for Clarisonus! This is the SG-Acoustics site, created by Samuel Groner, a masters student at the Zurich University of the Arts in Switzerland. As with many of the other Notable Sites, this one is a labor of love by a single creator, where he has posted information or research for the world to see, with no immediate commercial gain involved.  Samuel’s crisp, clean site gives his parts selection criteria, some mic amp and discrete op-amp circuits, test circuits, power supply designs, etc. Some Gerber files (for PC board layouts) are included.  All Samuel asks is that you read and agree to his “Terms of Use” and “Disclaimer”, basically asking permission for any commercial use of his designs or information.

The high-light of the site is Samuel Groner’s paper “Operational Amplifier Distortion”, published Sept. 1st, 2008. With excellent Swiss thoroughness, Samuel takes the op-amp measurement criteria established by Walt Jung in 1986 and extends it, both in methodology and in covering contemporary audio op-amps.  The full test methodology is given, which only starts with measurements taken by an Audio Precision System One. MATLAB is used to crunch and present the data. For anyone who has casually dropped an op-amp into an audio circuit without much thought, this paper is a wake-up call.  He presents distortion mechanisms most engineers have not thought of, including:

• Transfer Linearity
• Common-Mode Linearity
• Output Linearity (effect of loading)
• Input Impedance Linearity
• High-Frequency Linearity (inverting and non-inverting)

Future tests envisioned will include PSRR non-linearity, input impedance non-linearity, and non-linear AC input bias currents. His test methods look solid. Anyone contemplating using op-amps in audio should read this paper!  The other data on SG-Acoustics is valuable, too.

This is the second part of a series of articles on the history and application of different power line frequencies. The first part is here.

NATIONAL GRIDS AND UNIFORM STANDARDS

As more and more power plants were built, linking and synchronizing them was found to greatly increase overall reliability. If one generator went down, others on the grid could continue supplying power. At first, alternators within a single power-house were linked, then power plants within a single power company’s territory, then between power companies. Of course, all the linked power plants had to be on the same frequency. This put lots of pressure to conform to national or at least regional frequency standards.

From everything described so far, it would seem that 25Hz was ready to become the North American standard. However, by the 1910s, sentiment was swinging away from 25Hz. AC transmission theory was becoming well advanced, and it was realized that by adding capacitance to the line, inductive reactance could be cancelled-out. (In these early days, this was rarely done with actual capacitors, but rather with over-excited synchronous motors, which had the same effect of adding capacitance.) Sending 60Hz power long distances was no longer as much of a problem. Rotary converters and induction motors had become more sophisticated and the problem of commutator sparking became manageable. By 1918, when the paper “The Technical Story of the Frequencies” was published, the sentiment was to go with 60Hz as much as possible and use rotary converters and the newly-available mercury-pool rectifiers for conversion where needed.

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As promised earlier, I plan to post articles on the history of electronics, power, audio, and radio. I’ve always been interested in technological history, especially in the process of how technology we take for granted today came about. Over the years I’ve collected text books and old magazines and have done research in technical libraries and on the internet. What I will be writing for ClariSonus will be a series of monographs on various subjects. The first one is on the frequency of the power that comes from an outlet.

[A note on the research for this article: I've been reading early issues of the Transactions of the American Institute of Electrical Engineers (AIEE) and the British publication, Journal of the Institution of Electrical Engineers (IEE), both available from Google books in pdf format. In particular, a very good reference article about frequencies is: "The Technical Story of the Frequencies" by B.G. Lamme in the January 1918 issue of the Trans. of the AIEE. Also quite helpful are the various Wikipedia articles linked within and this one on utility frequencies.]

[Another note: given that my research sources are English-language, the emphasis here is on the history in North America. The situation in Great Britain and Europe will mentioned, but not in as much detail.]

The frequency of the power we get out of our electric outlets has been fixed since time of our grandfathers or great-grandfathers, at least in the developed world. Yet we are aware that there two standards in the world: 50 and 60Hz, and we may have heard of other frequencies, such as 25Hz, 400Hz, and even DC. One country, Japan, even has both 50 and 60Hz. Where did these frequencies come from? Is one better than the other? What explains the geographical distribution of these frequencies? This article will give the history of the frequencies and try to answer the questions above.

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As most of you know, the Rocky Mountain Audio Festival is returning to Denver (close to where I live) on October 10 through 12. As in the previous 2 years, I’ll be there, most likely wearing a Press badge, taking photos, and posting them either here or in the Loudspeaker forum of DIYAudio.com.

Two years ago, I had big plans to produce the Karna amplifier. but gremlins with the filament supply put that on the back burner - maybe some day. Later that winter, I had the Big Accident, which sidelined me for quite a while - six months to be allowed put any pressure on left leg, another two or three months to learn to walk again, and another several months to get proficient enough not to require a cane.

Those of you who saw me at last year’s RMAF probably saw me with two companions - Alexander of RAAL, and my cane. I’ve outgrown the cane, and Alexander will not only be back, but exhibiting his astonishing new omnidirectional loudspeaker.

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My friend René Jaeger turned me onto a huge site of service data and scematics: eServiceInfo.com. The front page is somewhat intimidating, but there are good tools for browsing and searching. It covers everything electrical and electronic. There is a facility to request data, there is a forum for asking questions, and a way for registered users to upload schematics and manuals. Since the data is essentially user-contributed, the quality varies, but the few manuals I downloaded were good-quality scans. All downloads are free (although limited to a maximum of 50 per day and 500 per month) with the site apparently supported by Google ads.

eServiceInfo appears to be based in Bulgaria and its users and contributors are world-wide, so there is a very international cross-section of devices and data offered. As a user and provider of web-based information sites, I’m sensitive to the details of site organization and find that eServiceInfo is one of the best I’ve seen for providing data downloads. Check it out! By the way, the audio directories are here.