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What is Floyd Toole saying about extra amplifier power and headroom?

I've been reading Floyd Toole's "Sound Reproduction The Acoustics and Psychoacoustics of Loudspeakers and Rooms" and came across a passage that I wish he went into further detail about. It has to do with whether having amplifier headroom has any noticeable improvement in sq. He happens to be talking about getting the bass right in small rooms, but in doing so, he also touches on the use of a larger amp for extra headroom: 

Remedies for unacceptable situations typically included spending more money on a loudspeaker with a “better” woofer (without useful technical specifications, that was a lottery of another kind) and a bigger amplifier (for useless headroom ...

It's the last part ("useless headroom") that I'm curious about. I have notoriously hard-to-drive speakers (Magico Mini IIs). Although the recommended amplification is 50w - 200w, in my experience, that's a bit of an underestimation. I'm driving the Minis with a Musical Fidelity M6PRX, which is rated at 230w @ 8ohms. (The Minis are 4ohm.) The combination sounds excellent to my ears at low to moderate listening levels, but I notice a slight compression in the soundstage at higher levels. My listening room, while small, is fairly well treated with DIY panels made from Rockwool, sound-absorbent curtains, and thick carpeting. So I don't think I'm overloading the room. But I have wondered if an amp with far more power than what's suggested (more headroom) would drive the speakers with a little less effort.

Those of you familiar with Toole or with driving speakers with power to spare, what are your experiences? If I went with, say, a pair of monoblocks that drive 600w @ 4ohm, would the extra headroom address the compression I'm hearing at higher levels? Or am I wasting my time and, potentially, funds that would be better spent elsewhere? 

Thanks!  


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onhwy61's avatar
onhwy61
5,252 posts
 
Using an SPL meter, how loud are you listening when the compression in the soundstage?  Dynamic compression is more likely a problem with your loudspeaker, alterations in soundstage width and depth at high volumes are a problem with your room acoustics.
mapman's avatar
mapman
22,408 posts
 
Diamond,

That’s a function of the amp. I don’t see specs or even better test measurements like Stereophile typically does for your amp into 4 ohms? Generally the beefiest amps capable of driving the toughest loads and delivering current as needed will double power output from 8 to 4 ohms and largely again into 2 ohms. So hard to say exactly where your amp stands in that regard. In general, it is less common for integrated amps to be able to do that but some can. More common with Class D integrated amps than class a/b but the best class a/b integrated amps may still do that quite well.
mapman's avatar
mapman
22,408 posts
 
What atmasphere said about effects of heat on speaker dynamics is certainly true but different speakers address that differently with different levels of effectiveness using technologies like ferrofluid, etc. Ohm is a good example of a speaker that handles power and current very well! I can vouch for that! I would expect the same of the Magicos but can’t say for certain. These are Magico Mini IIs, correct? Though wonderful speakers ( I recall auditioning them well) they are stand mount monitors and were low in the Magico line in their day and could have output level limitations. Not uncommon for many very good monitor speakers.

I have read of claims from Musical Fidelity for that amp to be able to deliver over 100 amps of current which would be very good, but at the same time no measurements or even published specs I can see to verify that. That would be quite exceptional for a Class a/b integrated amp I would say. Too good to be true? Don’t know.

If the speakers are the limitation, adding a separate powered sub and active crossover to limit the low end extension of the Magicos would be a practical thing to try to  offload much of the work from the monitors and make them not have to work so hard.

mapman's avatar
mapman
22,408 posts
 
In my case, just for comparison, I moved from a Musical Fidelity A3CR stereo amp, 120w/ch 8 ohm, 210 into 4ohm spec amp to BEl Canto ref1000m monoblocks, Class D, 500 w/ch 8 ohm, 1000 into 4. The difference in bass control and articulation at all volumes was night and day....simply transformative. This was with both large Ohm 5 and smaller Dynaudio Contour 1.3 mkII monitors, both notorious power and current hungry products.

Class D amps have a reputation in general for vice like bass control, hence their popularity in powered subs.
millercarbon's avatar
millercarbon
12,531 posts
 
Toole is right, headroom is useless. Literally. Headroom is by definition more power than you need. Translation: power you will never use. Translation: useless. 

You have made the rookie blunder of buying speakers that are hard to drive. Its not that they are 4 ohm. My Tekton Moabs are 4 ohm too. They are so easy to drive they sound marvelous with my little 50 watt tube amp. They would probably sound pretty darn good driven by my iPod. So (trigger warning!) you can forget impedance.

Buying speakers and amps is so easy. Yet it is not so easy some audiophile can't make it darn near impossible. All you do is eliminate from consideration speakers less than 92dB sensitivity. I know nothing about your speakers, except for having heard the name Magic and knowing that means they are crazy expensive and have a well earned reputation for being hard to drive. So without looking I will guess they are somewhere down in the mid to high 80's. [Fact check: 87dB. Tol ya so!] Which in itself is low enough to all by itself be a problem. 

Sorry, I only kind of glanced at the earlier posts, just enough to know you feel stuck with or married to those speakers. Oh well. Its not current. Its not headroom. Its not tubes or solid state or heat or ferrofluid or any of the other missing the point ideas. Those speakers simply eat power like its going out of style. The answer like I said is remarkably simple. Unless you yourself want to make it darn near impossible. 
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