Economical OB design

[James D]

Chaps,

Whilst hunting around driver alternatives for an OB design with bass helper I ran across this Visaton design based on the B200 driver (the beastie I was considering). It's called the NoBox BB and looks quite nice. I haven't found a cost yet but based on the driver prices and filter design shown I would say £400 plus cost of building the baffle. This is just under double the cost the Fostex FE167-Eminence Beta 15 but there are those who will tell you the B200 is a better driver than the Fostex - I don't think it is on voices - particularly female voices... but the B200 is mellower so might suit Max more :-)

The baffle design is very close to the Quasar dimensionally so I can readily believe the response graph.

ciao

James

[Max N]

Hi James
Thanks for the link. I am a bit concerned as to their suitability for small SE amps. What do you think? They are quoted as 90dB, nominal 4 ohm impedance. Also they recommend an impedence linearization module upstream of the crossover for use with 'critical tube amps' - would this drop the sensitivity further?
Cheers
Max

[James D]

Well 4 ohm by itself is neither here nor there providing that your OPT has a 4-ohm tap. 90dB/1W/1m is marginal by my reckoning if you intend to use baby SETs i.e. less that 8- 10Watts a channel.

But impedance linearisation networks for SET use do indicate that they aren't 4 ohms for much of their spectrum as the graph shows. They have a really nasty peak at the crossover point and a strongly rising impedance after that - really a typical voltage driven crossover filter loudspeaker response - horrible! And I have always found that the impedance correction networks rob the music of some life (microdynamics) when used... so I don't like that aspect of their design at all... and I don't design the filter networks for my OB designs that way because of this...

To me its a compromised design that is more aimed at conventional ss amps than SETs but it is an interesting choice of driver and the WAD PP amps would sound very nice on it.

There is also the possibility of redesigning the filter network to work better than their design and I hope to investigate this a bit too (don't know when I'll get to it...). I thought it was interesting to see other people succeeding with a similar design.

BTW the inspiration and pattern for the Quasar design was the Supravox Planneau design which goes back to the 1960s in their catalogue! Both Bert and I found this independently and started work on it before combining our efforts.

James

[Scottmoose]

The B200 is a killer with T-amps. Take a look at my friend Dan Mason's thread about just this, chillingly entitled 'The Gravity Well of a Dark Star' (Dan's humour -he likes this sort of thing): http://www.audiocircle.com/circles/i...&topic=19253.0 100 pages and counting. Omega Speakers are in the process of making a commercial Dark Star.

6moons review of Red Wine Audio T-amp based system with B200. I've heard a similar setup and it blows 99.9% of other systems I've ever heard out of the water. There is magic about the sound you can get from these things, I kid you not. http://www.6moons.com/audioreviews/r...roadtour5.html The B200 also responds to tweaks very well -Dave Dlogos's phase plugs are the most immediate tweak.

Best
Scott

[James D]

It was echanging emails on PB design with Dan that got me looking at the B200 - well that and the excitment on the German boards about the B200. I heard one a couple of times and it was nice - and good with a T-amp. However I thought it lacked detail, microdynamics, vocal quality and air compared to the better Fostex - it benefit was that it had a better Qes for OB use - although the use of a bass helper negates this advantage. This isn't to say that it is a long way behind them. It is mellower than the Fostexs - but that isn't a benefit in my book with a proper amplifier although it is an advantage with a T-amp... but to some extent this is personal taste and I go for neutrality, accurate voice, detail and microdynamics everytime.

I do wonder what it would be like in Quasar style system with an optimised filter and driven by a good SET. I suspect it would benefit from a good super tweeter though..

James

[Scottmoose]

Depends what you call a 'proper' amp -have you seen RWAs new Signiture 30? 30wpc, low DF, lead-acid battery coupled, so no mains interference. This thing is a giant-killer. I tend to prefer Nelson Pass's class-a power-amp designs, but there's not much in it any more.

Agreed about some of the minor issues with the B200. I still love them though because they are one of the two cheapest routes to a high-end sound that I know of. £200 outlay (drivers, a couple of sheets of MDF, 4 piano hinges and some veneer), and you have an open baffle, using direct-coupled FR drivers ideal for this application (shed-loads of excursion, bomb-proof build and perfect Q, as you mention), that with some crafty design will get you down to about 50Hz. They've got to be the biggest steal in audio. Not ultimately as capable as your Quasars, still less a Linkwitz Orion of course, but for the outlay you're laughing. They respond well to the tweaking too -phase plugs, a mild zobel, some damping to the rear of the basket etc.