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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
16,382 posts
 
Hi OP:

The thing about a sub is that you aren't creating a speaker with sub, you are creating a brand new speaker system, of which the sub will handle the lowest octave.

So you are no longer just buying a new component, you are actively involved in speaker crossover design, and it's complicated. Crossovers are not absolute brick walls.  They have slopes and knee points and Q's, or knee sharpness. The idea that you can set your sub to 37 Hz and  your main speakers to 38 Hz is kind of funny. :)

I never said your speaker's were low efficiency.  I said they were going to be bass limited and with enough bass signal will show the original post was concerned with.  That is, they have limited dynamic range, but this range can be improved by limiting the bass the amp/speaker produces.

Do what you will.



Best,

Erik
onhwy61's avatar
onhwy61
5,255 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
22,456 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
22,456 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
22,456 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.
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