Which speakers will fill 5,000 cubic ft coherently

It seems I need to clarify something here. My comment above referred to **all** tube amps, not just Atma-Sphere (and FWIW, our MA-2 is quite comfortable driving four ohm loads).

However- what everyone in audio (and thats a lot) need to realize that there is a trade-off between sound and impedance. **FOR ALL AMPLIFIERS**

I highlighted that but I don't intend to be yelling... the point is, that even transistor amplifiers sound better on higher impedance speakers than they do on low impedance.

Steve McCormick is well-known for making rugged transistor amplifiers- has for years. In a recent email to Paul Speltz, who makes the ZERO autoformer, Steve reported that his amplifiers sound better driving 4 ohms *through the ZERO* than they do direct. In this case, the ZERO was loading the transistor amp at 16 ohms.

On hearing this, I asked several transistor amplifier manufacturers at CES what was up. Universally, they all responded, to paraphrase: 'Just because the amplifier is comfortable on 4 ohms does not mean that they sound best there- they sound better when you run less current through them. Yes, they do sound better into higher impedances'.

What this tells me is that 4 ohms is to get power as a tradeoff against sound quality. Everyone take note!

So I am amending my statement made some months ago above:

'If you are investing in an audio amplifier (tube or transistor), your investment dollar will be best served if the speaker used is at least 8 ohms or more (all other things being equal), if sound quality is your goal.'

To me, high end audio is **only** about sound quality.

While your amplifier might sound great on a given 4 ohm speaker (for example Magnaplanar tells me all the time that their speakers 'never sounded better' than on our MA-2), it will sound smoother and more detailed if you could magically change the impedance upwards without changing anything else.

Right now the closest we are to that is to use a set of ZEROs.

Interesting huh?

The Zu Presence weighs 80 lbs, has a 14 inch wide front baffle that narrows toward the rear at a 60 degree angle. It is biamped, highly efficient and sports a 16 ohm flat impedance curve. The owner of Atmasphere uses a similar Zu speaker with his amps. This suggests that he might think they work well as a combo. Zu has a return policy. If you keep them, you pay freight one way, just like any other speaker. If you return them, you pay freight the other way too. It's a small gamble.

Zu has a serious jump factor. Sound emanates effortlessly from the full range driver and the seamlessness of no crossover reproduction holds many of us in awe. They may not solve your problem completely but I would say they stand a better chance than most any other speaker, given your preferences and constraints.

Veddy interesting.... thanks for the clarification, Ralph. Of course, all other things are almost never equal ;~)

Atmashpere, in your opinion which is more important - the speaker's relative impedance or the smoothness of the impedance curve? For instance, would an amp rather see a speaker that rated at 16 ohms which actually varies from 12 ohms to 45 ohms, or a smooth 8 to 12 ohm load? Or is it something that can't really be expressed this simply.

BTW, your contribution to the Forums is invaluable.