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General question about speaker impedance and amps

I was recently told my Dunlavy Sc IIIs present a difficult amplifier load due to their impedance which fluctuates between 5.5 ohms and 3 ohms., in general i am trying to get an idea of how to match amps with low impedance speakers, some basic questions i have:
generally speaking are amps which double there power into a lower load good with low impedances? does it necessarily present a harder load when a speakers impedance fluctuates? in general are class A biased amps particularly good with low impedance speakers, i am under the impression tube amps are not suited for this purpose is this correct?(once again, in general). Also my speakers have an efficency of 91db so i was thinking of trying a lower powered amp that would work well with a low impedance, any recommedations? for example a yba or gamut with 70w to 100w, i would like to compare an amp such as this to the DNA -1 i recently bought so i can decide if i want to send it in for revision or go with the lower powered amp as i've found in the past i have prefered to higher powered amps though i have just started to experiment with the dunlavy's
mkaes

Showing 2 responses by gregm

gregm
3,395 posts
 
From specs, an yba passion (~200W) has a much heftier PS than its equivalent Gamut (~200W). I'm not saying one's better or worse: ultimately you'll decide if that question arises. However, if 3ohm is the lowest your speakers go, it shouldn't be a problem for any well-designed ss -- and that includes the PS as Audiopile notes above. OTOH speaker EFFICIENCY is usually rated as db (spl) @ 1kHz / 1W. IF your speakers' impedance were 8ohms, you'd need 2,83Volts and 1amp (current) from your amplifier. If your speakers were 4ohms you'd need 2 amperes to achieve this, etc. As speakers' impedance varies with frequency, and music has all sorts of frequencies integrated at any moment, the amp has to be capable of providing required voltage & current in order to drive the speakers adequately: the bass as loud as it should be in correlation to the mids, the highs, etc, i.e. it must amplify the input signal so that the speakers make it sound (as far as they can) like it was at the amp's input.
That's one reason why many people buy ss amps with large wattage -- it immediately means the PS is hefty. OTOH, please note that many SS amps have excellent specs only at FULL power. At the levels we listen to, distortion figures can go up quite dramatically -- another reason (among many) why it's good to listen before you buy
gregm
3,395 posts
 
Audio, I agree that the wattage "doubling" specs can serve as an indication when it comes to SS amps. But there's a limit to how far this doubling can go: the PS and the amplification device. Because, in order to keep energy constant as your amperes go down, you either have to lower the volts or increase the watts (A=W/V). Take a look at a very well presented case here. The VA product of the PS has to be humongous (and very heavy -- PS weight is a good indicator!). Furthermore, specs CAN be misleading (not false, mind you). In the thread above, s/one stated that an amp specs a whopping 72amperes (peak-to-peak)!!! Wow, and they're not lying! looking closely, you notice peak-to-peak: i.e. peak current is 72/2 and rms is 36x0,707= 25A. Excellent -- assuming this is per channel.
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