Wednesday, November 2, 2011

Metal Coned Hi-Fi Loudspeakers: Wave of the Future?

It is probably the stiffest cone material currently manufactured for domestic high fidelity loudspeaker use, but are metal coned hi-fi loudspeakers truly represent the future of loudspeaker design?

By: Ringo Bones

Contrary to popular belief, it does not favor playing back heavy metal rock music and while discussion still continues on the pros and cons of metal-coned drivers, the number of designers and manufacturers using them does seem to be on the increase since the late 1980s, and it is not just the bass guitar amplifier maker Hartke that’s been famed for using metal coned drivers. In the United States, Platinum, NEAR, Joseph Audio and Thiel are well-known examples while in the UK, Acoustic Energy, Monitor Audio, JPW, Studio Power, B&W (in their up-market Nautilus), Musical Technology and even Mordant Short whose up-market Performance 6 loudspeakers got very favorable reviews back in 2005. In Norway, the popular driver maker SEAS were producing a range of aluminum and magnesium alloy units since the start of the 1990s while the famed metal-dome tweeter, despite its disadvantage of an oil-can resonance between 25-KHz and 30-KHz, is still currently being used in many commercially produced hi-fi loudspeakers and is still produced by a number of manufacturers worldwide despite of the advent of high-resolution digital audio and the vinyl LP revival whose wider-than-REDBOOK-spec-CD frequency response can easily reach the oil-can resonance mode of most metal-dome tweeters. Unlike Red-Book 16-bit 44.1-KHz sampled CDs whose bandwidth stops dead at around 22-KHz.

Fundamentally, the argument for metal hi-fi loudspeaker driver cones rests on its very high stiffness with the potential avoidance of any unwanted resonance or “breakup” in these drivers’ intended working frequency range. To optimize metal cone stiffness, special alloys are used. These are physically hardened and then reinforced by electrolytic anodizing which results in a thick coating of very tough “ceramic” made from the very oxide – i.e. aluminum oxide - of the alloy itself. This anodized surface lends itself to dye coloring, as in the case of Monitor Audio’s well-known “Gold” dome back in the mid to late 1990s. Both main drivers – i.e. bass midrange cones and tweeter domes benefit from the chemical reinforcement process.

When commonly used softer cone materials give or bend in their breakup frequency, and they generally do in their operating frequency range, their resonances must be carefully apportioned and controlled – i.e. damped – to try to attain the highest sound quality. Resonances do color the sound, and their presence is often seen as irregularities in the loudspeaker’s frequency response. Paradoxically, how these errors appear in the measured response may not always be a good indication as to how they actually sound. Like playing Classical string quartets on a typical metal coned hi-fi loudspeaker doesn’t always make the reproduced sound of the Classical string quartet recording sound as if it is always accompanied by a xylophone or by Zildjian and Paiste cymbals.

With softer damped materials – like fibrous paper or pulp card, Bextrene and Polypropylene plastic and bonded matrix composites – bending may be imperfect because these materials don’t act as perfect springs to begin with. A true linear spring recovers immediately from deflection or deformation with near 100% restitution after being stressed. In contrast, many composites and plastics show some memory effect, a slower recovery after bending, and some nonlinear compression with higher forces. This may result in a change in sound quality as sound level is increased. The nonlinear response to high bending forces, and the slowed recovery after bending – technically speaking, it is a form of hysteresis –is a factor in the overall linearity of the driver. In return for the favorable internal damping from a resonance viewpoint, non-metal-cone technology can provide a smooth response, nicely extended to the required upper limit, and then may often deliver a smooth acoustic rolloff beyond this point.

In contrast, the metal diaphragm or cone may be essentially perfect from its bass resonance to beyond the required range, and have no resonance whatever in its lower operating region. Potentially, it has a singular freedom from compression and hysteresis distortion. Subjectively, that manifests itself, if the overall system design is of sufficient quality and a great tonal neutrality, a sound with expressive dynamics and a high dynamic range. Clarity can be very high and low-level detail excellently resolved, in short, fine transparency is a typical of the genre.

However, there’s a price to pay. Like for like, metal cones are generally heavier than the alternative cone materials and magnet for magnet, this often results in reduced sensitivity, often a loss of 2 to 3 decibels. Metal cones are substantially more expensive than paper pulp or plastic equivalents – not to mention the seldom stated fact that metal cones destined for metal coned loudspeakers have a higher reject rate in their production in comparison to paper and plastic.

Finally, while there are no resonances in their primary frequency range, when a metal cone does finally give up and resonate, it lets go with a greater exuberance than a paper or plastic coned driver. So severe is the first resonance that it can rise 10 to 15 decibels above the main response and with sufficient energy to suck power out of the adjoining frequency bands. Thus, a 6.5-inch metal coned driver might resonate at 6-KHz – desirably higher than the 1-KHz typical resonance of a good paper or plastic coned driver – but it does so with such amplitude that the cone output decays prematurely into a pre-resonant suckout, tailing of above 2-KHz. This makes the crossover design of a metal coned hi-fi loudspeaker much more awkward.

This means that if the crossover rolloff isn’t sufficiently fast – i.e. not enough high ordered crossover slope – some of that 6-KHz peak may pop up into the treble band, roughening both the tweeter’s sound and its measured response. Some hi-fi loudspeaker designers resort to anti-resonant traps: electrical filters that seek to notch out the resonance and remove it from the system’s sound. This may seem like a brilliant engineering solution, but it limits the loudspeakers’ compatibility with power amplifiers – i.e. single-ended triode amplifiers with a low damping factor doesn’t like these kind of speakers.

Ultimately, it is up to the loudspeaker designer to make the best choices in the overall system build, regardless of the cone technology employed. Excellent sounding high fidelity loudspeaker systems have been produced over the years that use every conceivable combination of driver technology. Just hope that if you finally found your ideal hi-fi loudspeaker, sound quality wise, it is within your range of affordability.

Plastic Coned Hi-Fi Loudspeakers: Brilliant Engineering Solution?

First touted supposedly as an ideal solution against cone break-up inherent in early paper coned hi-fi loudspeakers, do plastic coned loudspeakers offer a brilliant engineering solution?

By: Ringo Bones

Maybe is it because on my first-hand audition of supposedly high-tech Bextrene and Polypropylene (MRP – Mineral-Reinforced Polypropylene) high fidelity loudspeaker cones whose drive units are well enough engineered to give smooth string tone, but on orchestral crescendos suffer from timbral muddle and tonal quack; I mean an overwhelming majority of them – i.e. ones within my price range – display a degree of plastic quack that was apparent with violins, plus a little nasality, just enough to add character when played at sound-levels of a typical violin or a Classically trained singer performing live sans electronic amplification. Fundamentally, the argument in favor of plastic cones over paper cones rests on plastic’s high stiffness in comparison to paper, with the potential avoidance of any unwanted resonance or cone “breakup” in the intended working frequency range. But were plastic coned hi-fi loudspeakers really has more flaws in comparison to the paper coned loudspeakers they are intended to replace?

Use of heavy, well-damped plastic cones that display a great measured performance – frequency response flatness wise – but little else in terms of subjective purity of tone and timbre (i.e. sound quality) came about as a result of a research into loudspeaker cone materials started by the BBC that culminated in the early 1970s. Thus prompting established high fidelity loudspeaker manufacturers of the time to switch from paper cones to plastic cones – i.e. Bextrene and Polypropylene. When other established hi-fi loudspeaker companies with bigger R&D budgets like B&W, KEF, Celestion and Wharfedale equipped themselves with sophisticated research facilities during the early 1970s eventually merely confirmed what the BBC had discovered a few months before, thus taking to plastic cones with enthusiasm. But to the ears – and wallets – of long-time hi-fi enthusiasts, too many top line monitors with plastic coned drivers brewed up in Britain between the early 1970s up to the early 1990s have sounded perplexingly poor in relation to their enormous engineering input for questions not to have been asked.

Fueling me and other hi-fi enthusiasts growing suspicion on the capabilities of plastic coned loudspeakers was back in 1995, when the well-established loudspeaker company called Mission produced the 731 LE whose better performance was largely due to switching from the use of plastic to a doped paper cone on the main driver. Even though there are scores of loudspeaker manufacturers – mainly in Britain – who swear by performance of plastic coned drivers – i.e. Spendor, Rogers, KEF, etc. But more often than not, plastic coned loudspeakers are still viewed by an overwhelming number of veteran hi-fi enthusiasts as something that’s good enough for mainstream pop and rock music, not for music that demands a little more precision and soulful rendition.

Friday, September 16, 2011

Paper Coned Hi-Fi Loudspeakers: The Best Hi-Fi Speakers?

Despite their faults – and there’s a lot of them – do paper coned hi-fi loudspeakers truly deserve the title as the best of its kind?

By: Ringo Bones

Maybe its just because I’m a loud electric guitar music kind of guy or was it the glut of entry-level hi-fi loudspeakers during the 1990s that got “best-buy” status - -i.e. the doped paper-coned Mission 731 LE back in 1995 - when they were equipped with paper-coned loudspeakers that fueled the prejudice in me and thousands of others in our first-hand auditions that the paper-coned hi-fi loudspeakers are the best of its kind. To avoid being accused of being economical with the truth, paper-coned loudspeakers have their own share of nasties – i.e. cone break-up at high listening levels can result in a tonal coloration which can jar the senses. But given that other alternatives – i.e. mineral-filled polypropylene, high-definition Aerogel, Kevlar, carbon fiber, aluminum and magnesium metal cones and even diamond coated ones – are not entirely free from coloration and are somewhat pricey, does this mean that paper-coned loudspeakers have a unassailable cost advantage from an engineering standpoint too?

Influential personalities in the field of hi-fi equipment design and the contemporary music industry all have their share of praises for the paper-coned loudspeaker. Back in 1994, Ken Ishiwata – chief engineer of Marantz – tells the hi-fi press at large that the best way to treat paper cones for use in hi-fidelity loudspeakers is to soak it in oil for 48 hours to give it a gorgeous tone and dark inter-transient silences. But the process of manufacturing Ken Ishiwata’s oil-impregnated low tonal coloration paper-coned hi-fi loudspeaker is definitely not a technique that lends itself well to contemporary mass production.

In the loud electric guitar playing world, guitar god Yngwie Malmsteen has a now-famous “tone testament” on the paper-coned Celestion G12T-75 electric guitar speaker saying that it compliments the violin-like tone and feel of his guitar playing. Malmsteen also says that he has used Celestions ever since the early days of his guitar playing career in Sweden.

And famed High End hi-fi equipment manufacturer - Yamamura Churchill - uses a rare paper sourced from select hand-made bamboo pulp from Japan on the cones of their top of the line loudspeakers. The “reign” of the paper-coned hi-fi loudspeaker could ultimately blamed on the seemingly immortal runaway popularity of loud electric guitar music of hard rock and heavy metal music, don’t you agree?

Thursday, April 7, 2011

It’s The Power Supply, Stupid!

Mainstream audio engineers as usual may beg to differ, but how much does power supply design and topology affect audiophile grade audio amplifier sound quality?

By: Ringo Bones

Charles G. Whitener, Jr., president of Western Electric Audio Products wrote his views on this particular subject matter which got published in the December 1997 edition of Stereophile magazine which goes: “We have come to this really arrogant conclusion: When tubes are removed from the chassis, the amplifier becomes nothing more than an expensive power supply.” There may be some truth to what Whitener had said – whether vacuum tube based or solid-state designs, it has been experienced by seasoned audiophiles time and time again that that power supply design and topology does play a role in the empirical assessment of sound quality of a typical audio power amplifier marketed to audiophiles. But is there really something more going on here?

The topic of power supply design and topology and its effect on the subjective sound quality of a “well-engineered” audio power amplifier – like the design and topology of the analog output stage of a universal CD / DVD player – has always been and probably will always be a politically charged topic to “mainstream” audio engineers. The issue is often seen by mainstream audio engineers like a mandatory sexual harassment / gender sensitivity training aimed at their machismo driven chauvinist little corner of the universe. But given that audiophile grade audio amplifiers – unlike mobile phones – are aimed at hi-fi / audiophiles who listen to them with their own two ears instead of connecting them to a 22,000 US dollar Fast-Fourier Transform audio analyzer, should mainstream audio engineers pay more attention to the power supply design and topology of audio power amplifiers?

Ever since the latter-half of the 1980s, audio engineers who still care about the sound quality of their designs and final products have come to conclude that the overall impedance of the power supply is a much bigger problem than anyone has previously thought. Electrocompaniet’s Per Abrahamson in a January 1998 edition of Stereophile magazine interview says that the power supplies of 99% of the amplifiers on the market are designed with big capacitors, big transformers, big everything – without taking into account the frequency response of the power supply.

When the impedance of the power supply is all over the place, the problem manifests itself as a problematic unnatural sounding midrange and high-frequencies in the finished audio amplifier during audition. The impedance of the power supply is a mirror into the subjective frequency response – but you won’t find anything wrong with the audio power amplifier if you measure the frequency response by sinewave measurements. No problem even via a 22,000 US dollar FFT test gear. If you do tests by auditioning with well-recorded music and via your own two audiophile-seasoned ears, you can hear that the power supply design and topology does affect the frequency response. Audiophiles, musicians or anyone who gives a rat’s ass can hear it but we can’t measure it with fancy 22,000 US dollar FFT gear.

So if you are fortunate enough to have the opportunity to peek into those audio power amplifier designs famed for their sound quality, I just hope that the ultrafast Schottky rectifiers or those 15-nanosecond HEXFRED diode rectifiers, banks of electrolytic capacitors instead of a single dustbin-sized 100,000 microfarad capacitor won’t pose as an audio engineering culture-shock. All of these hi-fi tweaks serve to make a relatively modern sensibly-priced solid-state audio amplifier aimed at audiophiles to sound like their tube-based Golden Age of Stereo counterparts.

Monday, February 28, 2011

Of Music Lovers and Illegal Music Downloads

Intellectual property legal precedents and economics aside, why do an overwhelming number of music lovers put up with the dubious quality of illegally downloaded music?

By: Ringo Bones

Once upon a time, we music lovers used to show our devotion to our favourite musician by making them obscenely rich. We even tried to be musicians ourselves in the hopes of becoming obscenely rich too without resorting to being a narco-trafficker or a despotic leader. Then came the dreaded Napster at the very tail-end of the 20th Century and thus financially ruining the whole music biz, musicians and wannabe musicians like me. Only musicians – ageing ones - with a back catalogue proviso on their record-label contracts manage to escape the Napster scourge. Intellectual property legal precedents and economic concerns (as in free music) aside, why do most of us music lovers – even me at some point – put up with the film-noir like rigmarole of illegal on-line digital music downloads?

From a hi-fi enthusiasts’ perspective, our hi-fi rigs – with front ends that range from a humble lathe 20th Century era portable MP3 player, i-Pod, snazzy vintage turntable and for the fortunate few a state of the art CD player that is as expensive as a South Korean made family sedan that can play your CDs sounding like vinyl LPs – is the primary tool that allows us to hear music as it was recorded. The better the hi-fi rig, the closer the approach or the sound quality to the master tape. Heck, even women’s fashion magazines Glamour and Cosmopolitan featured articles back in 1999 and 2000 about how Britney Spears and Christina Aguilera all used to record to big-ass open-reel analog master tapes in their way of spreading the concept of sound quality as a way swaying the hoi polloi away from Napster and their ilk. Sadly, it didn’t work.

Somewhat reminiscent of the adage of saving your hard-earned cash until you can afford to buy that particular tool that would do the job right, it is also the rationale of making the most of your investment in vinyl LPs, CDs and those hi-resolution digital formats like SACD and 24-bit 192-KHz sampled DVD-Audio. Play a full priced CD – at around 15 US dollars – on even a good Mainland Chinese manufactured boom-box and at the very most you’ll hear only 7 US dollars worth of fidelity. Spend a little more on a decent entry-level hi-fi separates – usually start at around 500 US dollars these days and is usually composed of either American or Japanese made universal CD/DVD player, an integrated amplifier and some speakers at around 150 US dollars each item and the rest on interconnects and speaker wire - and you’ll soon get 10 US dollars worth of fidelity.

Sadly, those supposedly “free” music downloads that are illegal from the music biz’s perspective is not exactly “free” from our perspective. I mean that is our very own money that we spent in buying our home computer set-ups – may it be portable lap-tops or desktop work stations. Our own money used to pay to the internet service provider or the hourly rates of your local internet café.

My most nasty encounter with those music download sites of dubious legality are not only virus/malware related, it can also prove to be a waste of time. Given that our friendly neighbourhood music store has never been “adventurous” enough to stock expensive rare and audiophile-quality CDs that range in price from 25 to 50 US dollars even though quite a number of locals can easily afford it. I asked a net savvy friend back in 2002 for a site offering the Queensrÿche remake of Simon and Garfunkel’s Scarborough Fair that’s only available on a 50 US dollar Japanese CD pressing of Queensrÿche’s Empire album. All I got downloaded to my first-generation portable MP3 player was 4 minutes 30 seconds worth of digital silence. Talk about a waste of time.