Monday, December 22, 2008

Dynamic Loudspeaker Cones: What’s Best?

Often seen as the “final frontier” when it comes to the hi-fi playback chain. Can the judicious choice of the right dynamic loudspeaker cone material really do wonders for sound quality?

By: Vanessa Uy

As we headlong into the 21st Century, dynamic loudspeakers as a whole is probably the only hi-fi component that did most progress – sound quality wise. And yet the choice of the “perfect” cone material is still a contentious “political” issue when it comes to designing a loudspeaker that not only sounds excellent, but also displays good marketability and salability as well. The following are a sampler of the most widely used cone materials currently on the market.

Paper, as a loudspeaker cone material, has been around probably since the invention of the loudspeaker itself. Paper’s advantages are ease of manufacture, good cost to performance ratio. Its disadvantages are lack of stiffness - which could be a problem when the loudspeaker is forced to play louder than its intended design, generating unwanted resonance and harmonic distortions. Despite of paper’s disadvantages as a loudspeaker cone material, I’m very much in love with oil impregnated paper cones due to it’s lovely midrange tonality and excellent damping properties – provided they’re not played louder than their design intended. Though various schemes of paper composites – like aquaplas - had managed to make paper still one of the most widely used loudspeaker cone materials to date. Though potential hi-fi loudspeaker buyers with very deep pockets tend to avoid paper coned speakers due to its “old fashioned” image.

Polypropylene (later turned into mineral reinforced polypropylene or MRP cone) - commonly referred to as “plastic cones” - was developed during the start of the 1970’s to replace paper as a loudspeaker cone material. Hi-fi buffs fell in love with them because they can be played louder – in comparison to their paper counterparts - without distorting easily. The problem is that when polypropylene loudspeaker cones distort, they don’t distort in a musically consonant manner. Instead they produce a vulgar sounding “quack”. Thus the reason why you don’t see polypropylene cones being used as an electric guitar loudspeaker cone material. But in car stereos, polypropylene cones are often de rigeur.

When kevlar was first manufactured into a loudspeaker cone material, many in the hi-fi community hailed it as the perfect loudspeaker cone material given that it is stiff enough to be used in bullet-resistant body armor. But it is not cheap to manufacture and deteriorates fast when exposed to ultraviolet light, precluding its use outdoors and even in cars that frequent the beach. Though I love it’s neutrality of tone which is very useful when it comes to listening to a well-recorded jazz performance, many hi-fi buffs that I know of – who coincidentally are long-time professional musicians – tend to dislike loudspeakers with kevlar cones because they’re tonality is “too dry”.

Carbon fiber was also hailed by hi-fi buffs when it was first used as a loudspeaker cone material. It is stiff, lightweight thus very low inertia and unlike kevlar, carbon fiber is resistant to ultraviolet radiation – i.e. direct sunlight. Might carry a somewhat stiff price premium, but many seasoned “music lovers” tend to dislike loudspeakers with carbon fiber cones as having a dry tonality. But love them or hate them, carbon fiber coned loudspeakers have gained scores of accolades by respected reviewers and critics in the hi-fi industry and on loudspeaker systems that range from entry level price to the flagship models of seasoned loudspeaker manufacturers.

Thankfully for us in the Free World, aerogel technology wasn’t given to former Iraqi dictator Saddam Hussein during the 1980’s by former US President Ronald in order to “tweak” those Soviet-era Scud missiles. Known in the hi-fi community as high-definition aerogel, a speaker material with serious aerospace pedigree due to its air-like lightness and aircraft-grade aluminum-like stiffness. High-definition aerogel has been hailed throughout the 1990’s as the best – if not the best – loudspeaker cone material. Light, stiff, and tonally neutral to a fault it was supposedly the perfect loudspeaker cone material, but I still have reservations. Though I often “view” the “perspective” of paper coned loudspeakers as a “duller” version of reality, loudspeakers using high-definition aerogel to my ears sounds as if Mother Nature or God Herself were telling me “you are listening to an abomination of natural order”. I mean aerogel-coned speakers have this very, very, very, very low-level digital-esque “swoosh” / modulated white noise that is there to remind me that what I’m hearing is not the “natural sound” Mother Nature intended me to hear.

Although metal coned loudspeakers also started to become popular during the 1990’s, this technological concept was also cursed with the not-so-easily-acquired-taste syndrome. I mean metal coned loudspeakers are very, very good within their power handling / loudness envelope. But push them a tad too far and you’ll be greeted by the distortions of ringy metal. Probably due to the “oil can” resonance that they exhibit –i.e. metal domed tweeters resonate with a vengeance near 30,000 Hz. That’s why since the revival of the vinyl LP, I’ve been avoiding metal coned speakers – especially with metal dome tweeters – like the plague. Given that even low-cost LP cartridges are flat up to 40,000 Hz and I could still hear with extreme acuity sounds above 20,000 Hz, metal coned speakers are simply just not for me. Plus they also suffer high reject rate during manufacture making their retail price more expensive than their counterparts.

So there you have it, one’s choice for the “perfect” loudspeaker cone material is not just about hard science and engineering, but also of personal taste and artistic inclination. Though the progress in sound quality terms was mostly made via innovations in loudspeaker design toward the end of the 20th Century, designing an excellent sounding loudspeaker and selling enough of it to keep your company and your personnel gainfully employed is still probably the blackest of all arts.