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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!  


128x128diamonddupree
erik_squires
16,337 posts
 
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
erik_squires
16,337 posts
 
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
mapman's avatar
mapman
22,399 posts
 
Sounds like a plan.  I am very interested to hear how much different or not  the BCs sound from your current amps and how that pans out for you.

I'll go out on a limb based on my prior MF->BC Class D change which is similar but different and say the difference will be clear and noticeable, FBOFW. 
diamonddupree's avatar
diamonddupree OP
75 posts
 
@mapman based on what you were saying before about current delivery, with the BC's Peak Output Current @ 45A, wouldn't that be a little too low for the Minis? And much lower than the MF @ 140A? 
mapman's avatar
mapman
22,399 posts
 
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.
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