Funny what you said about do they really just jeep installing drivers until they sound good. I have no idea what they were doing. Bit I like to think they were trying g to just be over the top and sound good. Maybe they all need the kind of receiver or amp they cane with and to play music from that era. I mean for a large majority of them they were using quality components. So it wasn't being cheap.How they aren't the best sounding soeakers on the planet is beyond me.
It was a cheap 'n dirty way to increase output and power-handling from small, fragile mids and tweeters of the day. High efficiency was the name of the game here, in order to extract as much sound as possible from the average 25wpc tube and early solid-state amps of the 1960s without making speakers that were the size of a small fridge*. It also meant that you could build a full lineup from the same parts bin, adding extra drivers to make the next model up the chain (drastically reducing R&D and manufacturing costs). However, there are a lot of drawbacks to just adding extra mids and tweeters and supertweeters. Sound waves radiate outward from a speaker cone (both forwards and backwards), so if you have two speakers playing the exact same signal, you have two "bubbles" of energy coming towards you. Remember the movie "Ghostbusters", where they warned about not crossing the streams? That's what happens here, and so these "bubbles" start overlapping. Depending on the exact frequency, they can cause constructive interference (the signal becomes louder), or destructive interference (the signal becomes quieter, or even cancelled out). These leads to a jagged response called "comb filtering", which is further aggravated by the fact that these two identical soundwaves will arrive at your ears at different times, as they're emanating from at least two different points. If you're listening in the ideal "sweet spot", then none of this will matter and the speaker sounds excellent, but the sound will change dramatically if you move a muscle. Having a many-way crossover also introduces it's own issues, as each crossover can induce a phase shift, and provide more opportunities for drivers to overlap at the crossover points. All speakers suffer from these issues from one extent or another, and you can skirt around it with extremely careful designs (ie: line arrays) or mitigate it by listening further away from the speakers, but generally it gets worse and worse the more drivers you add. Hence why you rarely see anything more than a 3-way speaker these days, and some audiophiles swear by full-range drivers or coaxial/point-source speakers. And truth be told, there is something magical and cohesive about a really good full-ranger, even if they don't come close to reproducing the full spectrum of sound. Give a pair of KEF Q150's, or even a nice clock radio, a listen, and you'll see what I mean.
*There's a traditional rule in the loudspeaker business, known as Hoffman's Iron Law, which states: "Bass Extension, Efficiency, and Size. Pick two." You can create a small speaker with lots of bass, but it'll be need gobs of power. You can create a small speaker that screams on one watt, but it won't make any bass. You can create a speaker that will peel paint from the walls and damage your foundation, but it'll be absolutely ginormous. Modern technology's made this less of an issue, but the rules still apply to one extent or another. The Hoffman in question was the "H" in KLH, who built their reputation on the KLH Model Six, a reasonably-sized and reasonably-priced two-way acoustic suspension loudspeaker that was wildly popular in the late 1950s and 1960s. It was flat from 40Hz through 16kHz, which was more than competitive with the gigantic corner horns and full-rangers that dominated the HiFi market of the 1950's, and played a big role in helping make stereo practical and affordable to the average person (I'd be remiss if I didn't mention the Acoustic Research AR3A and Dynaco A25 here). However, while those corner horns can sing on just 3 watts of tube power, the KLH's need at least 20. Those acoustic suspension "bookshelf" speakers sparked the demand for higher power amps and really used them to their highest potential as they can soak up power like a sponge, whereas the screaming 'suis tend to compress audibly if you start packing on the power.
