The optimal speaker is a one way. A single driver is the only approach that allows optimal phase and therefore time response. It is fortunate that the human hearing is relatively insensitive to the serious transgressions and errors introduced by multi driver speakers with crossovers.
It has been pointed out for many years that crossovers separate the fundamental frequencies from their harmonics, and the transgression is massive. The fact that hearing is relatively insensitive to these gross errors does not mean they are insignificant and should be dismissed out of hand.
The ideal moving coil loudspeaker should have one single cone. No lesser person than the great audio engineer
Paul Voight realized this in the early thirties and developed a high fidelity full range driver and loaded it with a corner horn. This came into production in 1934. It is widely recognized as the worlds first high fidelity loudspeaker.
In the early fifties GE briefly got into the speaker business and produced an 8" aluminum cone full range driver, that was quite good, and was used in the Decca corner horn designed by Dr A.R. Bailey and Ralph West.
One of these was the second speaker I built. It is actually not a horn, but a folded Voight pipe. It was successful enough that it launched the Transmission line project at Radford audio in the early sixties.
At the same time because of the success of these full range drivers, and the fact that Peter Walker's Quad electrostatic speaker had taken the audio world by storm interest in better speakers really picked up.
Quad ESL 1957
At Goodmans loudspeakers their chief engineer Ted Jordan developed a 4" aluminum coned full range driver with a unique suspension. The cone weighed 6 grams. Unfortunately the owner of Goodmans died and the company was sold and turned into a junk brand and most of the employees including Ted were fired.
Ted went into business with the company accountant Leslie Watts and produce the driver. I heard it in 1959 and was smitten with it. Unfortunately the drivers had a life of about 20 minutes. Ted was a brilliant audio engineer but not a good mechanical one. I guess I consider myself an intuitive mechanical engineer and worked with Leslie Watts for around 14 years or so improving the driver and marketing it in Canada.
At our little Eagan residence we have converted a small bedroom into a small sitting room/ listening area and game room for the grandchildren. I'm using just one of these Jordan Watts drivers per side, 2 drivers in all.
The sound is smooth with good detail and depth of image. The bass is much better than other speakers of similar size, in fact F3 is mid forties. In that small room you would actually vow there was a sub.
Fortunately these drivers and Ted Jordan's subsequent designs have not been forgotten. These drivers and speakers had a strong market in the Far East, probably because rooms are much smaller.
In the last years Mark Audio have been producing drivers based on Ted's principles.
The problem with these drivers is power limitation (15 Watts) and oil canning of the cone due to over excursion.
Mark Audio have now been helped by some very good transducer engineers and further developed this driver and found a way to prevent damage from over excursion.
Because of the problems of crossovers, especially in the speech discrimination band, I now detect a renewed interest in wide band drivers. This has always been a goal at B & W in their 800 series, bit until their new D3 series the mid range driver has been plagued with cone break up at the upper end of the pass band.
Recently Dennis Murphy has produced a
three way design using this
novel 3" full range driver from the UK as a wide band mid range.
So the essence of all this is that no crossover is the ideal and in small rooms is a very viable solution.
Two ways built with wide band bass/mids can be very successful especially if the crossover can do minimal violence to phase and therefore time and make for a seamless transition.
Three ways are very often problematic, because the mid has nowhere near the bandwidth required, so both crossovers end up where the ear is most sensitive and you end up with multiple problems. Power handling of a lot of mid range drivers is also frequently inadequate. A good mid range needs a bandwidth of at least 4 octaves and be able to be crossed around 350 to 400 Hz on the lower end, and preferably at 4KHz on the top end. Those are few and far between.
The development of more good full range drivers to be used as mid range drivers will make this much easier. They will also improve two ways by raising the crossover out of the speech discrimination band.
Lastly you can get excellent bass from smaller drivers, but not good bass and high power handling. If you want good bass and high power then it makes the case for a three way, or a good two way and a sub.
In a small room I think you can make the case strongly for full range drivers. In small rooms you tend to often be close to the speakers, and so driver integration issues can be a problem with close proximity. For a small room I think either a full ranger or a two way is most appropriate.