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!  


128x128diamonddupree
Well its 45 amps per monoblock X 2 = 90 amps total.....nothing to sneeze at especially with a most efficient Class D design.

Musical Fidelity is a stereo amp so most likely the peak is 140A total.

Again, specs never tell all the story, but in lieu of similar measured specs into 4 ohms, 140 amps peak alone is more grey. It’s not uncommon for amps to cite high peak current delivery but without measurements or specs indicating what that means into 4 and even 2 ohms, its harder to make a valid comparison. Not to mention one being very efficient Class D and the other less so Class a/b.

Measurements from an independent source is best. Bel Canto amps regularly get the full review and measurement treatment from Stereophile to add clarity.

Meanwhile every Class D amp I have heard matched properly to pre-amp delivers a vice like grip on the bass that might sound relatively lean to some. WHen I first turned on my ref1000ms, I thought the bass was totally gone. No exaggeration. THen once my ears adjusted I heard it all.....extended, detailed controlled and articulate, not as fat flabby and one note as before.

Meanwhile newer BEl Canto Class D amps claim stability into 3 if not two ohms. That’s pretty good! DO Minis imdepance go lower than 3-4 ohms at any frequency? How about phase? DOn’t know offhand but that would tell even more about how difficult a load they might be or not.
Hello diamonddupree,

     After my last post, I think you received some good advice from several members on the benefits of multiple subs and active crossover devices.  I  run my mains full range and have my 4 subs low passed between 40-50 Hz.  I don't utilize an active crossover because I didn't notice a significant sq improvement when I tried one and reduced the bass sent to them.  I believe this was because my class D monoblock amps provide ample power, 1,200 watts each into my 4 ohm main speakers, and ample current, up to about 30 amps.
     I just wanted to let you know, however, that I believe you may perceive a significant improvement in sq in your system  by using an active crossover device like the Shiit Loki or DSP Mini to reduce the bass duties of your Magico Mini IIs.   I believe both these devices operate in a very similar manner but I'm not absolutely certain.  
      I also wanted to make sure you understand that utilizing at least a pair of good quality subs are also crucial for providing the high quality bass that will no longer be provided by the combination of your Magicos and your current single sub. 
     It's useful to think of the use of the active crossover device and dual subs as 2 sides of the same coin; they're both partially responsible for seamlessly integrating the high quality bass performance of dual subs with the high quality midrange and treble performance of your Magico Mini IIs.  
     They go together like hand and glove, Mutt and Jeff,  eric_squires and millercarbon as well as Trump and incompetence.

     If you decide to take this path as an upgrade solution, I'll share some more useful info and tips, that may be useful to you, along the way.

Tim  
@mapman according to Valin, "the MAGICO Mini is a textbook-perfect load (never dipping below 4 ohms and staying about 6 ohms for most of its frequency range)."
@noble100 good stuff and much appreciated. I just ordered a MiniDSP HD and should have it in a few days. I'll see how that works out and go from there. Thanks! 
That’s good, but there is still not much to bank on with the MF amp regarding how it handles even 6 ohms nominal even with dips below that. So that still leaves things open perhaps to a significant extent. 6 ohms nominal may be a harder load than 8 ohms nominal with some dips...it all depends. You would have to try them with an amp known to be stable into 4 ohms which in most cases mean an amp spec’ed and preferably measured for 8 ohms that also doubles power as much as possible into 4. The MF might do that pretty well but there is nothing concrete to bank on that it would so far. If it could, you would think MF would document it and make the amp more appealing for more cases. Also the bass control offered by the very efficient Class D amps could still deliver a big difference alone. OR even a Class a/b with good documented performance into 4 ohms. Could even be Class A but that could get very big bulky and expensive to deliver the watts needed for headroom with less efficient speakers going louder.

On the other note, I have considered a miniDSP for use with my KEF ls50s and Klipsch sw308 sub and liked it very much so very interested in how that works out.

If we weren't such sound anal audio buffs we wouldn't even care about these details.  We'd just say hey we have a good enough system and call it a day.   Off course, no self respecting audio kook would EVER do that right?