Audio Note speakers will do that.
The An-E is 95db effiend and goes from 18hz-23khz at ± 3db. Although they
say on thier website -6db which is just another way of saying it.
There is a Von Scheikert (sp?) model called the DB93? (I am really butchering this name here) that is very efficient and goes pretty low. It has a built in powered woofer section............ Any it looks very interesting. Maybe someone else can chime in on this with a bit more (accurate) info.
The Wilson Alexandria.
Nominal Impedance: 8 ohms
Woofer: One 15 inch - One 13 inch
Midrange: Two 7 inch (vented enclosures)
Tweeter: Ambience: One 3/4 inch Supertweeter
Tweeter: One Inverted Titanium Dome
95 Db @ 1 watt. Down to 18 Hz. Good luck with coming up with the coin for a pair. Pretty amazing that they are that efficent with the drivers they have.
Well, I guess my speaker is close to what your looking for. My Hyperion 938s are supposed to be flat down to 30Hz (depending on room size), 90dB, 6 ohms nominal. I'm driving it with a cheap 20 watt solid state all-in-one Yamaha tuner/CDP/integrated to levels that would wake up my neighbors at night. And no it's not what I normally use with these speakers, just waiting for my new integrated amp to arrive. And it's probably the most affordable so far mentioned at $4500 retail.
I believe Soliloquy 6.3i and 6.5is would both fit the bill and not break the bank. Unfortunately I don't know the status of the company, but there are usually a few used ones at reasonable prices. I have their 5.3's that don't quite make your cut, but are outstanding speakers by any account and offer great bang for the buck. Underwood Wally sells them new and B-stock at reasonable prices and is an excellent dealer.
BTW, I don't think I'd agree that "efficiency is the key" when it comes to speakers. Perhaps you are not stating this well. I've certainly heard ineficcient speakers that sounded great, and efficient speakers that sounded bad within specific respective systems. I think "synergy" would be a better word. With that in mind it may be good to be more specific about what you'd be pairing these off with and what exactly are you after that you don't have now.
Silverline Sonata II or III (95db, 25Hz)
Soliloquy 6.3 (90db, 28Hz)
Coincident are also said to be quite good.
Reimer too has speakers to fit the bill.
Other option: add a sub. Our ACI Titan blends seamlessly with our 53Hz Klipsch La Scala horns. I've had three people ask me, "Do you only use the sub selectively?" when it was on.
I've owned both the Silverline's & Solilquy's, and find
them both to be highly musical, non-fatiguing speakers
that completely disappear in the room. On the used market, they are a steal!
Best of luck,
On the used market:
Silverline Sonata II ~$2600
Soliloquy 6.3 ~$1500
Soliloquy 6.5 (22Hz) ~$3300
Bargains all, IMO. And they mate well with virtually any amp. That is, if you like the amp, you will like the sound. The speakers are that neutral sounding.
Von Schweikert DB99 is 99dB efficent.
Though not my taste, the old Klipsch K-horn is quite possibly the loudest speaker on earth. For those who want to rock... the entire block and maybee the sub-division accross the interstate and down the road.
Klipsch K-horn is quite possibly the loudest speaker on earth
I do like the K-horns when paired off with the right amp, and at 104db they are mighty efficient. They will not, however reach down much below 30hz in my experience. Tight bass is not their forte, though of the range of the older Klipsch Heritage line they do Bass the best of the bunch given the corners they were designed to be positioned in. Their specs indicate 33hz at the bottom. Fast dynamic midrange, crystaline clear, and yes, loud as you can take if that's your poison. If you are hooked on sub-30hz bass you will need a sub with K-horns (or any of the Klipsch Heritage line for that matter).
I also believe that speaker efficiency is very important. While I have also heard many non efficient speakers that also sounded great they don't IMO have the same type of life like dynamics that you get from good quality highly efficient speakers unless they are driven with huge power amps. Josep you didn't mention what your budget was as this might greatly narrow the playing field. If money were no object the choice would be easy, Wilson Alexandria. I am partial to JM Lab speakers as most models are quite efficient. I have a pair of JM Lab 946 Electra's which will dip below 30Hz. They are rated 32Hz-32KHz and -6db at 27Hz at 93 db efficiency, nominal impedance 8 ohms and minimal impedance 3.2 ohms. These speakers really rock! With the dual 10 inch woofers they deliver clean, powerful, tight, accurate bass that can really fill a room without sounding boomy or boxy. What I do like about them is that they really do play all types of music very well, including rock and you do NOT need a 500 watt amp to drive them and they also sound great at low volume. I previously had a set of Infinity's with 87 db efficiency that I drove with a 150 watt amp and what a difference the JM Labs made in dynamics and bass energy. There are many good speakers out there but most of them IMO sound quite lean on the bottom end even though they may be rated down to 30 Hz or so. There are very few if any that I have heard that better the bass performance of the 946 Electra's without sounding boomy or costing a LOT more money.
I have the Zu Druid Mk4 (although they were originally the Rune model that I had upgraded). Efficiency is 101dB, frequency response 35Hz to 20kHz, 12 Ohm nominal impedance (8 minimum) , 10" proprietary woofer, augmented by a proprietary 1" supertweeter with a split shelf high-pass filter network at 12kHz (as close to no crossover as none at all). Although not quite as low as what you're after, at the price ($2,800) they are a stupendous value. Add a decent subwoofer if you need more low end grunt and you'll be laughing.
I am driving the Druids with 2Wpc of tube power, which replaced 125Wpc of ss (which was also very good), and couldn't be happier. Still require some break-in on the upgraded drivers, but the music is already sweet and satisfying. Very even across the frequencies, mid-range is excellent. Bass is accurate and clean, although not the deepest. A decent sub will fill in the lowest notes if desired.