Past meetings of the Society
June 1998

Robert Rieder of International Jensen
Meeting summary by David B. Hadaway

Open Forum

David Hadaway mentioned the article by Tom Nousaine in the June 1998 Stereo Review entitled "Tweak versus Geek." Two systems were compared in a single-blind test: one fully tweaked with expensive interconnects and electronics, the other with very ordinary equipment. The same CD player and speakers were used in both signal chains. None of the listeners scored better than chance. Alvin Foster added that his own preamp and amp are 20-25 years old (older than his son) and still performing well.

Lou Souther announced the passing of his friend Peter Meisinger, a contributor to Audio in the early years. David Hadaway met Meisinger while living in Washington DC and was helped by him in an AES presentation.

Souther showed a Sungean DT300VW shirt-pocket-sized 4-band radio (AM, FM, Short-wave, and TV). It is about $75 from J&R Music World.

Bob Miller talked about two portable DATs made by Pioneer and Tascam with 96kHz sampling rates. The Pioneer has confidence heads (read after write) and is $1400. Micha Schattner said the Tascam has had some logic problems-it sometimes would freeze up for no reason. You could clear it up by turning it off for a while but "don't record a concert with it without a backup."

Micha said that the company Sek'D has a way of recording 20-bit audio on a regular DAT ("Don't ask me how"). There was some discussion as to whether 24 bits is worthwhile, or even exist. Real-world D to A converters always have less than the theoretical resolution. Extra bits are essential to maintain sound quality through several successive stages of DSP (digital signal processing) before the final 16-bit product.

Alvin Foster did some testing on Dan Banquer's new 6-channel preamp. He was surprised that his Sound Technology test setup with the inexpensive Turtle Beach Fiji soundcard could measure -100dB distortion and noise down to -106dB. [I also have a Turtle Beach sound card, a Monterey which I bought in 1995. Its audio quality is superb -- JSA.]

Alvin also ran distortion tests on his Wisdom Audio loudspeakers and burned up the ribbon in one speaker. The ribbon in the other speaker survived but was visibly wrinkled. To his surprise, the distortion had dropped to 0.1% at 90dBspl and 8kHz [warning: do not try this at home-DBH]. He tested the Mackie Mini-monitors (a professional powered speaker) and was impressed-at 90dB SPL, 4kHz had 0.3% distortion at 3 meters, and it was flat within 1dB from 200-20kHz.

Feature: International Jensen

Robert Rieder is the senior acoustical engineer at International Jensen (IJI). He is also an active recording engineer and has worked as a producer for Wisconsin Public Radio and Germany's Deutsche Welle. Finally, he is a freelance trumpet player and one of this country's few specialist performers on historic trumpets. He mentioned a BAS connection—his mentor Dick Greiner (University of Wisconsin) has written for the Speaker.

Rieder began with a genealogy of Biblical proportions. IJI traces its roots to 1910 when Peter Jensen emigrated from Denmark to develop a market for Poulsen wireless products in America. Shortly after this, he and another employee, Edward Pridham, left Poulson to form their own R&D firm, The Commercial and Wireless Development Company. They worked on wireless communications, audio amplifiers, and transducers. In 1915 they introduced their first production loudspeaker.

Interestingly, back in 1915 their loudspeakers received praise for their fidelity in contemporary newspaper accounts, yet their response was probably from 325 Hz to 3 kHz. So our standard of what constitutes "high fidelity" is always evolving. At that time, the term "loudspeaker" was not universally used-- Jensen and Pridham called their device the "magna vox," which is Latin for "great voice". Soon after, they changed the name of their company to Magnavox. Pridham remained with Magnavox until 1954.

Jensen and Pridham promoted their devices with numerous public demonstrations. One of the early installations was at the "Hoo Hoo House" night club which had two rooms, but only one group of musicians. The owner wanted to use the magna vox gear to reproduce music in the second room where the loudspeakers were arrayed in positions that corresponded to those of the five musicians. Each musician was reproduced through his own microphone/speaker channel. Apparently, this early stereophonic sound reinforcement system was dramatically successful until the Musicians' Union got wind of it and put a stop to it. Also, he amplified President Woodrow Wilson's League of Nations speech, since Wilson was in failing health and too weak to project his voice.

Western Electric eventually took over the public address market and Jensen's focus was changed to radios. In 1925 Jensen resigned and, in 1927, founded Jensen Radio Manufacturing Company. In 1929 he moved the company to Chicago and remained its president until 1940. After several years of consulting work, he founded Jensen Industries in 1943. He died in 1962. Jensen's loudspeaker company went through numerous corporate and ownership changes in the following years. Finally in 1988 the IJI management bought the company from Beatrice, [foods!--DBH] Inc. In 1996 the consumer division was bought by Recoton (which distributes every imaginable audio accessory), and the OEM (Original Equipment Manufacturer) division continues along with the automotive sound system division as a private company owned by Robert Shaw Inc. Their General Magnetic division in Dallas is the largest producer of loudspeaker magnets in the U.S. They have an alliance with Goodmans in the U.K.

Through all these changes they have maintained engineering continuity. Peter Jensen was with the company for 40 years. Jim Novak, who started with enclosure designs (in the early days you bought drivers and built your own box), was there from 1952 until his retirement in 1989. His seminal work led to the Thiele and Small papers that gave the mathematical analysis of box and speaker interaction.

One day the company was contacted by a Japanese audio magazine asking for an interview with Novak. It seems one of his old designs had developed a cult following. They ended up restarting the production line and making a run especially for Japan at $2000 each.

In the old days of prototype engineering, you would have as many as six iterations of the design. Now, with computer simulations, it can be done with one or two. This has been made possible by the use of FEA (finite-element analysis; used among other things for checking the performance of bridges), which models the speaker as a "wire" mesh. Involving the solution of 30,000 simultaneous equations, it was beyond the reach of small companies until recently (with the advances in PCs). Jensen wrote itsprogram to translate the FEA model into frequency and phase response and is currently doing FEA on speaker spiders. Another program Jensen wrote calculates the frequency response for any number and location of drivers on a baffle.

Another of Jensen's testing procedures -- modal analysis -- uses a laser to measure the velocity and displacement of the physical cone in order to analyze breakup modes. Rieder showed a slide of a speaker with the "motor" (magnetic structure) in front of the cone instead of in back. This allows the speaker to fit in half the space. The image of the speaker exists only in the computer.

Alvin Foster: "Do you design for a flat response?" Not necessarily- whatever the customer wants. The Jensen labs used to be full of racks of B&K and GenRad equipment. Nowadays a computer, monitor and a couple pieces of specialized gear are all that's needed. Jensen has two anechoic chambers, in Chicago and North Carolina, which are calibrated to each other. They are 18' cubes and are useful down to 125Hz. For test measurement and prototyping, a variety of environmental tests are used: heat, humidity, UV, IR, vibration, shower, salt spray and immersion. One chamber will power 3000 speakers at 30 watts each ("You don't want to be in that room!"). One customer wanted the speaker to be subjected to the particular size and shape of dust particles found on Mount Fuji, so that became known as the "Fuji test." High-temperature testing is extremely important for car use. Jensen tests to 220 degrees F and wants to go higher (David Weinberg has measured 160 degrees F in a car on a 70 degree day in Washington DC). The car industry has extreme requirements for reliability (100,000 miles) and IJI has a vanishing low return rate. [When semiconductors began to be used in quantity in cars, the semiconductor manufacturers were surprised to find that the reliability requirements of the auto industry exceeded the requirements of aerospace customers-DBH.]

Question: What is your tolerance for drivers, that is, how far can they deviate from the reference? Generally +/-3dB.

Comment: We visited Boston Acoustics and they reject any drivers outside of 1dB from the reference.... We make speakers for many different applications and price ranges. This implies a wide variety of performance requirements. A speaker that is completely unacceptable for one application may be perfectly adequate in another. Every time we reject a driver for any kind of shortcoming, we have to absorb or pass on that cost somehow. So we design and test to what our customers need, which is the same thing that BA or anyone else does. [What the audiophile customer needs is debatable, BA is obviously making a statement of quality independent of market "needs"--DBH].

Current research is in making more of the speaker out of plastic, which can be sonic-welded; gluing is a nuisance. Jensen has lines which can produce a speaker every 2.5 seconds, but also has a "cell" producing 108 per hour for more specialized customers.

Rieder He concluded this part of his talk with Rieder's Laws of Acoustics: 1. There are no substitutes for mass and volume 2. You can't produce sound without volume velocity. 3. No amount of advertising will ever change the laws of physics. (attributed to R. A. Greiner) 4. If bad sound was lethal, audio would be a leading cause of death (attributed to Don Davis) 5. We may not know how yet, but if you can hear it, it can be measured. 6. Anyone who builds a loudspeaker system will believe that it is the best-sounding loudspeaker ever created. (attributed to Leo Beranek) 7. It is almost always the case that there is, in fact, no new thing under the sun. (paraphrased from a quote attributed to Jim Novak) 8. Newton WAS right!

Rieder studied music and engineering and both are still active parts of his life. When he is doing engineering he is thinking about getting back to music and when he is making music he is thinking about engineering. Although he studied modern instruments, he has found a niche in playing the valveless baroque trumpet. It comprises 8 feet of coiled tubing and it was used until the late 1800's when it was gradually replaced by the valved trumpet.

It plays a natural harmonic series, so in the low registers only certain widely spaced notes can be played. As you go up in frequency the notes get closer together (and harder to play!). [For an example of what can be achieved by a skilled performer, check out The Hoffnung Music Festival Concert where Dennis Brain performs a Leopold Mozart alphorn concerto arranged for garden hose and strings--DBH]

Music composed before 1825 was written for valveless trumpets. The low notes are harmonically richer than on modern instruments, the high notes are very pure. Performance style on the older instruments allows for a great deal of freedom--modern style is mechanical by comparison. He generally plays in the Chicago area since he has a day job, but maintains a schedule as a guest performer with early music groups in various parts of the US and Canada. CDs have been issued with him playing solo trumpet on two recordings of Handel's Messiah, one with Apollo's Fire, the Cleveland Baroque orchestra (Onda Records); the other with His Majesties Clerkes (Narada Records). He recently recorded with the Washington Bach Consort for Newport Classic Records.

Question: "When do you find time to practice?" "Sometimes during lunch break I put on the mute with a mike and headphones and a DSP reverb program and pretend I'm playing in the Taj Mahal. People outside the office just hear a faint squeaking sound."