What to expect when switching from a high efficiency speaker to low

[Sunsanvil]

My trio of M&K MPS2510 (aka S-150THX) speakers, even though they are 4ohm (3.5 min), are stupidly efficient (92dB spec, though measured as 'low' as 89.5...which is still crazy good). And so I've been "spoiled" for decades, getting by just fine with mid-tier receiver power.

I need to replace them though. The center, at a full 13" tall, is getting in the way of our next screen-size upgrade. We need something lower-profile (and I cannot find a decent S-125C in Canada, at least any willing to ship).

I really really like what KEF is doing in terms of design philosophy, by my goodness they are the worst case scenario for an amp: 4ohm (min 3.2) and perhaps more notably a paltry 85dB efficiency! Unfortunately there are no brick and mortar stores (of any kind) within driving distance so any purchase I make will be something of an act of faith. I'm wondering if anyone had thoughts on what to expect with that sort of loss of efficiency? Right now I'm on a Denon AVR-X3800H in a very small (<1000 ft3) room, subwoofer is a given, but ~6dB drop in efficiency means 4x the power needed for a given output. Scary!

 

[Nopiano]

You’ll have to turn the volume knob up! ;-)

The thing is, there are so many flavours of every speaker type that it’s impossible to generalise, but I’m going to do that anyway, in a moment. First, a tiny bit of context: I bought my first hifi over fifty years ago, and spent 15 years working Saturdays in a local hifi store in England. We mostly sold popular bookshelf designs, but had various larger and more exotic kit too. For example, Quad ELS57 & 63, ESS with the Heil tweeter, Tannoy dual concentric, umpteen Wharfedale, Leak, B&W, KEF, Misson and suchlike.

So, generally the less sensitive ones are often smoother and can sound better integrated between frequency ranges. The more efficient ones can sound more ‘live’ with greater apparent dynamic contrasts, but often have more colouration on e.g. human voice. Ok, all utterly subjective, but you can read specs all day and not find an obvious theme that you seem to seek.

Hopefully others we’ll chip in, and maybe you can say what music you generally listen to, and how loud? A diagram or pic of the room may help too. If you don’t want stadium rock then you may be fine with the Denon. (I’ve run 85dB ATCs with a Pass 25watt amp, though only out of curiosity at home). I have an instinctive bias against AV receivers because there’s so much gubbins in them that doesn’t contribute to stereo sound, and often they seem a bit bland compared to a regular stereo amp (all subjective of course), but I’ve heard stunning Yamaha and Sony AV kit, so anything’s possible. (My old Denon AV went crackly after a decade and still sits in the box somewhere!)

I like modern KEFs, so you’re looking in the right place, imho. If I had to choose a brand without hearing them, they’d be amongst my favourites. Hope this helps a bit, if lacking in the science department.

 

[Ruediger]

It will for sure make the Denon run even hotter.

Maybe get an external class D poweramp? It's not a big investment and easily does the job while being lean on power consumption.

 

[Uter]

Most likely, your assumptions and expectations to be proven incorrect.

 

[jcarys]

Personally, I wouldn't worry about it. If you must get new speakers, then try them with the Denon and if you truly need more power, then go buy an amp. Watts are quite cheap these days, but you may find that all you need to do is crank the volume some.

Before that, is it possible to get a stand that allows the M&K to work in your planned setup? Getting a custom made stand is far cheaper than replacing all the speakers. If that doesn't work, there are tons of center speakers from other brands that could knock the height in half.

 

[Skeptical_Aus]

I went from Klipsch Heresy IV's to March Audio Sointuva AWG (95dB to 83dB) and the need for more power was obvious. I sold my tube amp at the same time because it was not going to drive the March speakers well.

So what was the transition like? I have the March Audio P482 amp and a topping A90D in preamp duty and volume is exchanged for clarity and tone. Even with plenty of gain the raw volume of the Heresy IV is not really achievable, but the sound is spectacular and loud enough for me.

I miss the look of tubes and horns, but their function is Audio not visual.

 

[pablolie]

85dB isn't THAT hard to drive. The LS50 are that, and they're perfectly good with a 50W D-class amp that "xovers" at 80Hz to sub(s). And can play annoyingly loud.

 

[kemmler3D]

The real question is how loud you want to listen? 89dB efficiency is high, but most people consider 90dB SPL to be "too loud" anyway. So instead of using 2-5w on your receiver, you might use 20-50, to reach the same volume level, but you'd still be fine, and too loud is still too loud.

 

[mhardy6647]

My trio of M&K MPS2510 (aka S-150THX) speakers, even though they are 4ohm (3.5 min), are stupidly efficient (92dB spec, though measured as 'low' as 89.5...which is still crazy good). And so I've been "spoiled" for decades, getting by just fine with mid-tier receiver power.

Not terribly sensitive at all (the "dB SPL" rating is one of sensitivity, not efficiency). The louspeakers (using vintage Altec drivers) that I use (ca. 16 ohm nominal impedance) will produce about 100 dB SPL per watt (4 V into 16 ohms) at 1 meter.

Lower sensitivity loudspeakers are capable of very good performance, but will require gobs of power available to achieve it.
Admittedly "gobs of power" isn't hard to come by, even inexpensively, nowadays -- but there's something to be said for letting the loudspeakers (which are the actual transducers in the room, after all) do the work. EDIT: Not a mass-market approach any more, but still a viable approach.

The KEFs will sound fine -- whether they'll produce anything like natural-sounding dynamics without something bad happening to them (or just plain sounding "strained") can only be determined empirically.