Saturday, February 13, 2016

Is Your Audio System Cat-Friendly?

While early high fidelity audio systems got notoriety for “scaring away the horses” – is your current audio set-up cat-friendly?

By: Ringo Bones 

Maybe we should blame cellist David Teie for this given that his Kickstarter funded research into feline-centric / species-appropriate music that recently got scientific verification by a recent independent study conducted by researchers at the University of Wisconsin and published in Applied Animal Behavior. Also, Teie’s Music for Cats compositions recently got scores of positive testimonials by early purchasers who tested Teie’s cat music recordings on their own cats noting that it actually had a relaxing effect on their own pets. 

Cello player David Teie comes from a long line of musicians, composers and professional instrumentalists. Since 2014, he has been the conductor and music director of Washington D.C.’s premier chamber orchestra – the Eclipse Chamber Orchestra – and currently serves on the faculty at the University of Maryland’s School of Music. Teie’s career has spanned performing as a soloist with the National Symphony Orchestra under Russian maestro Mstislav Rostropovich. And also as the acting principal cellist of the San Francisco Symphony where Teie performed as cellist on Metallica’s 1999 album S&M. His research has been published in the Royal Society Biology Letters and in Evolution of Emotional Communication. His invention of species-specific music was described by the New York Times as the number one idea of 2009. 

According to cellist David Teie, cats were our first choice because they’re widely kept as pets which allowed us to easily share music with them. Given that cats can hear audio frequencies way above the human hearing frequency limit of 20,000-Hz, can cats even appreciate those upper octaves of Teie’s music given that most entry-level audio systems have trouble playing at significant volume – never mind proper phase linearity – of audio signals above 20,000-Hz? 

With the relatively wide availability and relative affordability of audio components and recordings capable of producing cleanly audio signals above 20,000-Hz – i.e. 24-Bit 192-KHz sampled PCM DVD Audio files and Super Audio CD recordings that can produce notes above 100,000-Hz and some moving coil cartridges like the Dynavector 17D2MkII Karat Diamond whose shorter 1.7-mm diamond cantilever allow it to have a high-frequency extension above 100,000-Hz and diamond coated tweeters that can cleanly play 100,000 Hz or higher audio frequencies – then it is now relatively easy to upgrade your audio system that can produce sounds that even cats, dogs and even bats can clearly hear. 

Maybe it was due to the fact that he hanged out with Metallica for a relatively long time during rehearsals in comparison to us mere fans back in 1999 or whether he is already a Metallica fan back when bassist Cliff Burton was still alive that got me wondering how much Metallica was an influence to cellist David Teie upon hearing of Cozmo’s Air – one of the tracks of his Music for Cats – that it reminded me of the ambient into of Metallica’s Damage, Inc. – the last track on the Master of Puppets album. Well, at least Teie managed to make his “cat music” also interesting to hear for us human music lovers which will probably give Pet Sounds a whole new meaning to audiophiles around the world. 

Monday, February 1, 2016

Transmission Line Loudspeakers: The Ultimate Domestic Hi-Fi Loudspeakers?

Given its ability to produce unbelievable amounts of bass for its size, are transmission line loudspeakers qualify as the ultimate domestic hi-fi loudspeakers?

By: Ringo Bones

As of late, there has been discussion on how come hi-fi audio designer Arthur Radford’s electronics – especially his EL34 based audio power amplifiers like the Radford STA25 - get more recognition in comparison to his transmission line loudspeakers which despite being manufactured 50 or so years ago can still manage to hold its own in a side-by-side comparison to more recently manufactured hi-fi loudspeakers. Arthur Radford did a lot of work, both theoretical and practical, on transmission line loudspeaker design during the 1960s.The Radford Studio 90 which was also sold in the U.S. in kit form during the late 1960s as the Audionics TL90 – a ¼ wavelength 3-way transmission line loudspeaker equipped with Radford sourced drivers and crossover circuit. The Radford Studio 90 was the first commercially manufactured hi-fi transmission line loudspeaker based on A.R. Bailey’s papers and there are even larger models based on the same design. Even though they were a bit pricey when they first entered the market, enough of them were sold in the United States to establish a “cult following” of this legendary loudspeakers. Despite their excellent subjective sound quality, why are transmission line loudspeakers relatively rare in comparison to competing designs? But first, here’s an introduction on the theoretical and practical principles of transmission line loudspeakers. 

Then and now, designers of closed-box / acoustic suspension and vented / bass reflex loudspeaker systems have long been able to make heavy use of computers, while transmission line systems had been designed by cut-and-try methods. Transmission line loudspeaker systems are more complicated to design because of their inherent distributed-parameter nature. By way of comparison, sealed / acoustic suspension and vented / bass reflex loudspeaker systems can be treated as a much simpler, lumped-parameter acoustic systems. Also, there is still a dearth of research literature regarding transmission line loudspeaker design to guide the prospective designer. But to those adventurous enough, they should check out Quick & Easy Transmission Line Speaker Design by Larry D. Sharp and those “white papers” published online by John Wright of TDL. 

Transmission line loudspeakers are known for their deep, powerful bass and the way they grip a room, filling it with a full scale performance. But they have their downsides too, notably the difficulty of tuning the line, which appears to be the blackest of arts in the audio engineering world. A practical transmission line has two main effects that are advantageous to loudspeaker design. Firstly, the sound venting from the end of a quarter-wavelength transmission line is 90-degrees out of phase with the signal from the back of the cone which drives the line, which itself is 180-degrees out of phase with the front radiation. This ensures that sound radiation at lower frequencies is progressively moving into phase and it will add, rather than subtract, to the forward low frequency response. Also a practical transmission line loudspeaker is lined with acoustic felt and wool, so that a majority of upper bass and midrange energy is absorbed before it reaches the end of the line and the outside world. Lower frequency bass energy gets through, making low bass apparent. In electrical engineering terms, a transmission line port is a low pass filter with a 270-degrees plus phase shift. 

An area where transmission line loudspeakers receive criticism is midrange coloration. To overcome this, various transmission line loudspeaker designers over the years adapted a number of sensible design features. If the transmission line vent length is made exactly ¼-wavelength in length, it tends to act like a tuned pipe which introduces coloration. Making the transmission line slightly shorter, a technique later adapted by John Wright of TDL during the late 1960s, reduces this coloration without adversely affecting bass quality.
In some transmission line loudspeaker designs where the line is folded quickly behind the cone, the strongly reflected sound wave from the cabinet wall can give that “clatter-type” coloration in the midrange. For this reason, in newer transmission line loudspeaker designs, the rear wall of the cabinet is kept as far back as possible and fitted with a generous covering of soft, absorbent carpet felt. 

One great thing about a transmission line loudspeaker is that once the cabinet dimensions have been optimized and fixed, it can be subtly tuned to give the bass quality you want in your listening room just by altering the amount and density of long hair wool in the line. This makes transmission line loudspeakers extremely versatile for home constructors, which combined with their subjective performance explains why they’ve been making a comeback since the 1990s hi-fi boom. 

Another great advantage, or possibly the greatest advantage, of transmission line loudspeakers – and probably why they’ve returned during the 1990s in conjunction with the zero negative feedback single-ended-triode audio amplification Renaissance of the period - is their highly damped impedance curve. Impedance varies little across the entire audio spectrum – especially in the upper bass and lower midrange region in comparison with vented / bass reflex and closed box / acoustic suspension loudspeakers. This makes transmission line loudspeakers much, much easier to drive with zero negative feedback single-ended triode audio amplifiers and other low feedback vacuum tube audio amplifier designs.