Ariel's

[pre65]

Hi-i thought the KEF drivers you mentioned used Bexstrene (if thats how you spell it) which i thought was plasticy.

Philip

[pre65]

Hi-i was nearly right (funny what you remember sometimes)

http://www.kef.com/history/Hist1960.asp


Philip

[James D]

Do you rub the cone when its playing? Does it rub on anything when its playing? No? Then don't worry.

The plastic cone sounds dead and lifeless compared to running your finger over a paper cone because it is...

Why is trying to foist them on you? Why doesn't he wan them if they are so good?

Ok he may well be genuine and lots of people like pp cones but they are not the people who like their paper cones...

[andrew ivimey]

He is a genuinely original character certainly, and he already has a pair of polys, so like the smoker says, 'go on, it will do you good..'

I am happy with paper.

James I found some Dutch speakers (on the web!) called double quasars mk2. Any relation?

Bextrene it is - just got a pair of Calindas in Cash converters; £24.99. A classic and immediately recognisable sound.

[Cobblers]

The famous Kef drivers are indeed made of Bextrene, a stiffer though heavier cone material than Polypropylene. This is the material used in the still superb LS3/5a's.

Bextrene is a form of acetate plastic derived from wood pulp apparently.

It's maybe not a sound to thrill the senses (slightly slow and quacky sound) but it doesn't lack resolution.

5 1/4 drivers will be inherently stiff due to small size so polyprop's ok for small speakers and midrange, but I haven't heard many ported speakers with bigger than 6 1/2 inch polys that were great. dynaudio drivers being a worthy exception, possibly not the best for small tube amp's.

look at Harbeth, notice they still use polyprop's in their small 5 1/4 cone speakers despite waxing lyrical about their own stiffer injection moulded Radial (ultra stiff unique patented plastic) cones in the bigger better models.

Lynn Olson's article!
http://ai.kaist.ac.kr/~suh/DIY/feedback.html

[petercom]

Just to put this all in perspective.

For years drive unit manufacturers have tried to come up with the ultimate cone material. This has ranged from paper, naturally, to cast alloy (SEAS). Most plastic materials are derived from the packaging or culinary industry. Why? Well, take Bextrene (a material that used to be used for moulding packaging). At its height the loudspeaker industry, and this included Kef, Audax and a few others, would have taken the output of a Bextrene plant for one hour - and that's for a year's supply. Speakers don't use much material!

Bextrene was readily available when the BBC and KEF were formulating plastic cones. It can be made into a fairly stiff and not too heavy cone and is easily moulded. It is quite lively and yields a strong midrange peak, resulting in a 'quack' on vocals. This can be addressed in the crossover (Spendor BC1, LS3/5a, Heybrook HB2) and the lively nature can be damped by applying a layer of plasticiser. AFAIK Bextrene is no longer available in industrial quantities.

Polypropylene was 'discovered' by Dudley Harwood at the BBC (Bextrene cones were developed by Spencer Hughes at the BBC), who later founded Harbeth (in the same way that Spencer Hughes had founded Spendor) to commercially exploit the patent. Unfortunately for him the patent was not watertight and 'filled' polypropylene cones soon became commercially available from other companies.

PP is a naturally highly damped material so sounds 'dead' when you scratch it. In cone form it is not particularly stiff, so it either suits very heavy large cones or, more usefully, small light cones. Around 100mm is optimum for stiffness and good transient attack.

For optimum stiffness metal cones became all the rage in the '90s. A good metal cone has no breakup mode through the required bandwidth. Many of the cones that were formed from sheet aluminium had/have terrible breakup modes and sound, naturally, metallic as a result. The best metal cones are cast (SEAS) and have a strong resonance at high frequencies which can be dealt with by good crossover design.

At this point we have to question whether we really want a cone to be stiff at all. Most of the best sounding speakers have had cones with well damped breakup modes scattered through the useable bandwidth. This has the advantage that you can use a big cone and the breakup will allow it to only use progressively smaller parts of the cone for output as the frequency increases.

The problem is that, unless you control these breakup modes mechanically, the breakup can be audibly obvious as coloration, especially noticeable on voices. B&W have done extensive work on this with Kevlar cones. The option is to use this woven material to give a good combination of flexibility and damping.

It is questionable, however, as to whether damping is desirable. For years speaker manufacturers thought that an optimally damped cone was the answer, hence PP. However many find the resulting sound very dead and lifeless, and you need a lot of amplifier power to bring it back to 'life'. Compare this with a soft pulp paper cone which has a wide number of resonances scattered throughout the useable bandwidth. These tend to sound lively, musically enjoyable and need very little power to sound good.

Of course you can relate 'lively' to 'resonant and colored' but it doesn't have to be so. The most lively transducer on the market is the NXT panel. This positively encourages resonance modes. The concept is to encourage so many resonance modes that they all fit together to produce the required sound in such a way that the actual piston movement can be very small. You could class a good full range paper cone - Lowther/Fostex - as doing something similar but with smaller levels of resonance and higher levels of pistonic motion.

The advantage of paper is that it is very easy to experiment with, can be doped with all sorts of other materials, and is simply formed into a variety of cone shapes. The drive unit designer is therefore able to trial many different cones to get the right sound.

Take the WD25 speaker. Many have asked how a 10" unit can cross over to a 1" dome. The answer is that the breakup modes are scattered through the 400 - 800Hz region so the active area of the cone becomes progressively smaller as frequency increases. It's a good cone!

[Paul Barker]

Originally Posted by petercom

However many find the resulting sound very dead and lifeless, and you need a lot of amplifier power to bring it back to 'life'. Compare this with a soft pulp paper cone which has a wide number of resonances scattered throughout the useable bandwidth. These tend to sound lively, musically enjoyable and need very little power to sound good.

Yes I found that MY Ariels (which were totally different to OP's) needed masses of SE power to start to sound good, but I threw in the towel when I found that simpler se amps got the result in your second half of the paragraph with "better" drivers. It took me a long time to realise it but I'm happy now.

Anyhow Ariels are so well received by so many and the net is full of rave opinions I'm sure OP will sell his, and maybe I'll get round to selling mine.

Should have bitten Greg's arm off before he heard Peter's speakers at Bristol!

[James D]

Andrew,

The Quasar MK.2 was developed by Bert D. in Holland who co-developed the Quasar with me. I did the baffle shape and design and he developed the filter and series connection. We swopped our ideas and philosophies and found we were after the same thing so we came together to create it.

Bert then developed his own bass unit to match the Oris horns and wanted to build a Quasar around them as he had some issues with supply of the Supravox unit - the Mk.2 is the result. It uses two BD 15" bass units and a Fostex 206E or AER Mk.1 fullrange driver. It is also bi-amped using a 'plate' amp to drive the bass units. I like the look of them but my wife wouldn't touch them! I also suspect mine would sound better as the series connection and passive filter exploits several tweaks to optimise the integration of the drive units to each other and to the baffle shape that need a lot of electrinics to replicate - and I really don't like the sound of active eq or digital filters...

James

[petercom]

It is fascinating to look at the spread of the Ariel mythology. In essence it is a nice, small driver, 2-way with careful attention to detail. There is no reason why it shouldn't be a nice speaker to live with.

What I don't understand is why it is so beloved by the valve amp fraternity. I can see that the designer recommends valve amps, but then who wouldn't? But its subjective efficiency, with the Vifa PP unit, doesn't seem to be in the region that valve amp users beg for. The designers stated 92dB is disengenuous. This is for 2.83v into a 4 Ohm load - useful only to transistor amp owners with good power supplies. The equivalent SPL per W (ref 2.83v/8 Ohms), which is more relevant to valve amp users, is closer to 88dB.

Perhaps an avid user can enlighten us as to the strengths and weaknesses of this design?

[Paul Barker]

Yes I'm using your series connection of driver design with your PMQ's, where the capacitor of the tweeter crossover is parallel with the woofer and the inductor of the woofer crossover is parallel with the tweeter.

In my home there is a lovely integration between the pair, you said also this is to do with the drivers sharing a baffle.

I have come up with so many ideas to alter your design, but you have come back with articulate reasons why not to, but like a gentleman (all be it an above average one).

I have hankerings to biamp, but you know what I know I'll lose the seamless integration.

there is always a catch 22, these are not perfect, but they are good enough for the budget alocated. They work at home for my music tastes. I'll not mess with them.

Oh what the heck I'll probably tinker and wreck them.!