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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If it were me that owned the Magico Mini’s like any very good speaker, I would do anything I could ie throw the kitchen sink at it as needed to allow it to perform at its best before adding anything else.

That’s what I did with my big Ohm 5s and it payed off 100%. No subs!!

I never felt a need to add a sub even with the Dynaudio Contour monitors, though for some more extended recordings it would certainly have helped.

I do use a sub with my kef ls50s. Those are the smallest monitors I have run regularly but wonderful within their limits and with a sub they are top notch, up to a certain SPL level that is more than satisfactory in the small room they are in. THe kefs + sub cannot compete with the much larger Ohm 5s in a much larger room with no sub in terms of going loud and clear.

The Ohm 5’s with the 500 w/ch Class D Bel Cantos are the bomb. You turn up the volume and they keep going louder and clear until you reach those very high SPL levels that eventually get uncomfortable and can even cause damage to to the ear no matter what. THing is you never realize how loud the things are actually playing until you try to talk to someone and hear. That’s always a good sign from a distortion perspective! I know Ralph would agree with that. Compression is not an issue.

My goal was to be able to do that. It took the 500 w/ch Class D BEl Cantos to do that. The previous 120 w/ch Musical Fidelity was no match. Nor the 330 w/ch Carver amp prior to that (voiced like a tube amp, limited current delivery into 4 ohms). The Carver did very well with the Magnepans I had prior to the big Ohms though.

Magico Minis.....those are very good standmount speakers.....larger than many if not most.   I would not expect them to compete with larger speakers of similar quality in terms of ability to go loud, but would expect them to be more than capable alone in a small to modest sized room driven to their max.  Again, would be nice if other Magico mini owners would chirp in with their actual experiences trying to crank up the minis.
@barts thanks, lots of customization with that unit. Are you familiar with the MiniDSP? Any thoughts on how they compare? Much appreciated. 

@mapman I'm going to try rolling off the Minis closer to 80hz or thereabouts with an active crossover and see what that does before I get a second JL sub, which I may do at some point down the road. I also want to demo the Bel Cantos from my local dealer and possibly some Simaudio monoblocks. I'm still not sold on Class D for mains but willing to give them a shot. Thanks for your responses! 
Hi OP:

The Loki was offered as a tone control, in case you just want more bass as an alternative to buying a subwoofer.

Yes, the ceiling can be part of the issue. At louder volumes reflections and the resonance time matters a lot more.

miniDSP is an active crossover with EQ capabilities. Some JL Audio subs include automatic integration/crossovers and so I highly recommend them as they include all the expert knowledge in configuring your mains and subs, plus I like the results.

I know what you were trying to do, but without measurements it’s hard to tell what the right HP or LP setting is correct. Often crossover filters are offset to match both in phase and amplitude. Your speaker doesn’t go down to 38 Hz. it has a -3 dB response at 38 Hz (usually how this is spec'd, some use -6 dB), below which it drops around 12 dB/octave. So something like this:

-3 dB @ 38 Hz
-15 db @ 18 Hz


However this is the anechoic response. Who knows what it’s doing in your room without measurement? :)

One quick test I forgot to mention was the 2' test.

Sit in front of your speakers, around 2-3' and listen when you hear the problem.  Is the problem still there close up?

If yes - The problem is your room.

If no - The problem is the speaker or before.


Best,

Erik
The Minis go down to 37hz. Sounds like the active crossover will give me more precise control of the LP freq so maybe it's worth the price, and actually a deal compared to new monoblocks with extra headroom. Am I on the right track? Really appreciate your responses!



Absolutely.  Not only that, once you are into this, you can add EQ to the bass to tame room modes. :)

Best,

Erik