2. amps-preamps
  3. 162140-151413

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
mapman's avatar
mapman
22,399 posts
 
My understanding from quick read is the minidsp device can function as an active crossover and it’s internal implementation is digital. Crossover goes between pre amp and amp, both analog. So the digital crossover must then first do Analog to digital conversion, then work its magic digitally then convert back to analog for output to amp. That is a different function in the system than the DAC. The DAC takes a separate digital source and converts to analog for an analog input into a pre amp.
So the digital part of the minidsp is really a black box. It all happens internally and being digital that enables many potentially marvelous things not possible with analog. How marvelous or not? The only way is to try and hear. It either will make things sound better or not depending how you use it. I would not get hung up on the extra conversions between digital and analog it does. That just an ingredient in the final results. It’s the final results that matter. Personally it sound like a very smart design and I may try it myself possibly someday unless I spot something that sounds even better by then.
atmasphere's avatar
atmasphere
11,928 posts
 
DBAs add complexity and would also likely take more time and effort to get right initially as a result. If it were me I would solve one problem at a time....resolve the problem at hand first with existing sub then consider adding DBA after that is resolved, but only if worth it for you.
Actually in practice a DBA is easier to set up than a single sub, since you don't have to work so hard getting the bass right at the listening chair! When I installed my setup, I already had speakers that made deep bass (flat to 20Hz) so I only added two subs. I only placed them once. Only hooked them up once (IOW didn't play with phase). I used cheap speaker cable. I didn't mess with the amplifier crossover settings more than once. It worked perfectly the first time. By comparison I have a single sub in my bedroom, and moving that thing around so I finally got bass where I wanted it (and not all the bass is there, its a bit of a compromise) was a bit of a pain, plus the sub is sitting in an obvious space, but where it would be convenient doesn't work- no bass in that location.

Well its 45 amps per monoblock X 2 = 90 amps total.....nothing to sneeze at especially with a most efficient Class D design.
Uh- can we do a bit of math here? If 45 Amps, giving the amplifier the benefit of the doubt, so driving a 1 ohm load. The power formula is Power = Isquared x R where

power is in watts
I is amps (in this case 45) and squared

R is the resistance of the speaker

This means that if the amp makes 45 amps it also is capable of 2025 watts. If we are talking 4 ohms, then the output power is 8,100 watts. Clearly this isn't happening. A speaker that only dips to 4 ohms isn't going to need that sort of current in any event. The OP simply has no worries in this regard. The fact that the amp is class D is irrelevant in this regard and will behave as an ideal voltage source driving this speaker.

mapman's avatar
mapman
22,399 posts
 
Yes but the topic was total amps not power so # amps per channel x 2.

Class D amps are most efficient by a large margin. That’s their biggest claim to fame. So they are inherently better at delivering more power and current than others. Just like more efficient speakers are better at going louder with less.

You will have to take that argument up with bel canto and their published specs for PEAK amps and power onto both 8 and 4 ohms. That power double couldn’t happen without the hefty # amps to enable it. If more than enough, then better safe than sorry. Right now the OP still sounds sorry so maybe better to be safe.
audiorusty
284 posts
 
Proper installation of your MiniDSP would be between your preamp and amps. IOW you would connect the left and right outputs from your preamp to inputs 1 and 2 of the MiniDSP. You would then send two of the four MiniDSP outputs to the inputs of your Musical Fidelity amp and one of the remaining MiniDSP outputs to your sub. Technically you could send both of the remaining two outputs of the MiniDSP to the your sub as long as the sub has both a left and a right input but I doubt if you would notice any difference. 
diamonddupree's avatar
diamonddupree OP
75 posts
 
@atmasphere the JL sub that I have makes it very easy to set up with auto room correction. It comes with a mic that you place at the listening position, run a test sequence and the sub's internal DSP corrects for the room modes. I've never had a problem setting up the sub anywhere I've placed it. In corners, against wall, midwall. Once I run the room correction software, from the listening the position, there are no nulls, peaks or modes as far as I can tell. 
More to discover