"Power hungry" speakers

I assume that you're talking about Apogee's based on your impedances and mention of ribbons. Having said that, you state that the speakers are 76 dB's yet only a few amps could drive them beyond 70 dB's. How is that possible? It would require less than 1 watt to do this based on your own figures. Was it due to "protection" circuitry kicking in? If so, you need an amp without protection circuitry.

Other than that, i agree that a low bias output stage / high efficiency amp works very well with loads like this. Due to the lack of duty cycle that the amp reproduces / reduced current & heat involved, some of these newer designs truly are an "answer to audio prayers".

As far as 95 dB's go, i consider that to be a "moderate" listening level. While some recordings ( acoustic based music, etc.. ) sounds very good ( even "loud" ) at that level, it just wouldn't cut it for large scale Classical or hard Rock music. Bare in mind i'm talking about spl's as measured at the seated listening position, not one meter from the speaker.

Sean, I generally listen to my Scintillas at levels around 75db. Maybe I'm paranoid, but I believe my hearing will be better preserved. I've attended scores of live events, from intimate acoustic to stadium extravaganzas. I'm comfortable with my listening levels. I reserve 90 db and above for the likes of Led Zeplin once in a very great while. My seating a orchestral events is generally a third back, or balcony. 80 to 90db approximates the gestalt to my memory.

As for my speaker's ratings, you say, "1 watt should do." Am I listing it's specs wrong? Or are you being fecicious? ;) I am aware of successful powering of the Scinny with an 85 watt home made expressly for the Scinny. I had dissapointing results trying respectable amps of five times more power rating. Amp design is very important when pushing difficult loads.

Brand new class D amps are unfazed by the load. I'm thrilled by the results. The speaker playing field has been greatly leveled. I like to describe the sound as tubes on steroids.

Getting back to the question of efficiency, do you not agree large driver surfaces, resulting in minute travel, is a valid solution to speaker distortion? I can put my ear right to the ribbons, and hear the music as clear as fifteen feet away. There isn't any of that low level high frequency fuzz I've heard on domes and cones.

You mentioned an spl rating of 76 dB's. At 70 dB's, this would allow you 6 dB's of headroom before you reached 1 watt of input. As mentioned though, i didn't know if you were measuring at 1 meter ( which is useless except for sake of comparisons to reviews ) or at the seated listening position. Given that most rock music only offers appr 5 - 6 dB's of dynamic range, you would be using 1 watt of power to produce the full dynamic range of such a recording based on the above information. This isn't to say that i was recommending such an installation or that it would work as well as theory dictates, i was just spouting off figures based on the math that "acoustic theoriticians" would tell us was sufficient. We all know better than that.

I was also wondering by what you meant by the statement that very few amps would drive them beyond 70 dB's??? Obviously, most any amp could generate 1 watt of electrical output relatively easily, so what's the fuss? As mentioned, the only thing i can see coming into play here is the low impedance / protection circuitry kicking in.

As to why the Class D amps work better, that has to do with the reduced duty cycle that the amp sees, the lack of sag in the power supply and lower levels of reflected EMF generated by the speaker. As you reduce the duty cycle of the amplifier, you also reduce the amount of drive applied to the speaker. Less drive equates to lower levels of reactance, which gives us less reflected power to deal with. This in turn allows the amp to load up more efficiently, which is just more icing on the cake. If the switching frequency is high enough, the power is delivered in very short and fast pulses, giving the power supply ample time to recover from the small amount of power drawn from during those bursts. If the switching frequency is too low, you can hear the "pulsing" of signal and it sounds fuzzy, choppy and lacks cohesiveness. A higher switching frequency limits the duration between pulses and the energy in the gaps is somewhat "filled in" by what is called "the flywheel effect". In English, the overshoot of energy initially applied keeps the forward or reverse momentum going until the next pulse is delivered. The potential for distortion with such a design is quite high, but with newer technology and MUCH higher switching rates, they are finding ways to get around this. Sean
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Thank you, Sean. Perhaps the 76db rating of the Scintilla is not the limiting factor in it's compatability with amps. I should add that the Scintilla is rated .8 ohm, or neary a dead short, which is what nearly all amps choke on.

Yes, class D modules engineers are having success getting around the switching speed devil. I use amps utilizing B&O's ICE module. I can't say I understand the white papers, but I can attest to it's amazing delivery.

Sean...I find that "large scale classical" pieces often run about 76 dB most of the time, with occasional louder passages. The way I determine this is by playing a concerto (for example: violin) or a vocal piece. I ask myself "is the violin louder than a real violin can play?" or a similar question for the vocalist. I often find that it is easy to crank the volume up higher than this criteria would allow. Perhaps this is because we are used to listening to "live" performances that are "reinforced". Amplification of an instrument above its true volume is like putting your girlfriend's complexion under a microscope. You will not like the result.

Down in New Orleans last week (I have almost sobered up) I spoke with some musicians who suggested a reason for the exaggerated bass that seems to be so prevalent. They suggested that the guys who do the audio mixing have been overexposed to loud music, and have lost LF hearing. (I thought it was HF that goes first, but they said No, LF). To these guys the exaggerated bass sounds right.