A full range speaker?

Here we go, a ceiling diffusion manufacturer:

https://www.oeler.com/wood-ceiling-panels/

A couple things about room treatments in general: it may look at first like it’s just a matter of picking out what you might think you might need from a vast forest of treatment products that are out there, pro or DIY. The one big problem with any of that is that it will in fact work to some extent. That is, whatever you pick out will work, but how much and at what frequencies? It’s great to say that we can absorb or diffuse by so much at X frequencies. But how do even know where the problem spots in the room actually are to begin with? Are we reducing the right frequencies at the right room locations? Are we in fact making things better or making things worse? We can’t know what to treat and what to leave alone if we haven’t yet done our homework and have visually mapped out where the problem areas in our room actually are...until we do that, then we’re just guessing...the odds certainly don’t favor guesswork simply because the behavior of the world of acoustics typically does not follow ’common sense’ logic...our best guesses are more likely to turn out to be wrong than right. There’s always experimenting, which is good, but measuring the room first is even better. But this can’t be done in a single sitting, it takes Many different readings. It’s tricky, and in the pro arena, when it’s time for that they call in the other pro’s: the acousticians. In the hifi world, that gets pricey, worth it maybe, but still pricey.

But, of all the things you mention above, the drapes idea seem to be maybe your best shot at your biggest bang for the buck here. I mean those very heavy sound-deadening curtains they use in studios, with a thinner outer covering to keep the wife happy. None of the you mention will really do anything to offer much control below 200 Hz, but above, those curtains would be good. But the best part is that you can control how much wall coverage and you can experiment easily by sliding them open or closed...a great way to experiment for yourself. Rugs on the floor if you don’t already have them.

AFA the ceiling is concerned, I’m not sure anything would be effective for the bass. Foam would help only so much in the mids and the highs, but the reason the mids and highs sound so compromised to start with is because of the bass. Too much folded bass energy in the small room creates not only a problem with the fundamental bass note, but also on all the harmonics of that note, as you go up in frequency (and down in amplitude). So you can put foam, fiberglass or curtains down to control the harmonics everywhere, but they are just band-aids. The real trick would be to try to gain room size and volume to keep the bass from bombarding the mids and highs into oblivion. Once the mids and highs are contaminated (mixed in with the harmonics), you can’t absorb your way out of the problem without reducing the good sound along with the bad...so, if you must do it that way, then reducing things by a judicious amount, and no more, is the about only hope there is of applying an optimal treatment, a limited compromise...but it does also help keeps costs sane, since any additional treatment after that point would only make things sound worse.

A speaker has to go flat to 30 hertz with large baffles and large drivers in a full size cabinet to be considered full range and if you can find one made prior to 1965 that is 16 ohms you will definitely hear a full range system unlike anything made today. The baffle should be twice the width of the woofer and three times the height of the woofer to be considered a full size cabinet so for a 15 inch woofer it would be 30 by 45 inches and the cabinet should be 1.5 to 2 times the depth of the driver so for the 15 inch woofer that would be 22.5 to 30 inches deep. When you get a speaker like this with the high quality drivers in it you will know what full range is and the need for a subwoofer will go away completely.

realworldaudio-

The brain makes sense of the fundamentals ONLY when the upper harmonic spectrum is correct. 

If true this would explain a number of things. It would explain whyTownshend Supertweeters improved the sound of instruments far lower in frequency than the Supertweeters output. It would explain why frequencies we cannot even hear as such nevertheless have an effect that can be heard. And it would account for the fact there are three times as many ear cells devoted to detecting these high frequencies than the ones we can hear.   

Maybe not explain, the question of why is always hard to crack, but it does for sure agree with all of these observations.

The bottom octave 20 to 40 Hz is critically important. You can not get the sense of a live performance without it. The breath and feeling of the music disappear. Drums and bass become two dimensional. Synthesized bass just dies. I have never heard a speaker system produce this correctly on it's own not that it is impossible but, it seems to be much easier with subwoofers. It takes more than subwoofers. You have to put them in the right places in a well treated room with additional room control and digital bass management. The subs have to have adequate power and be timed correctly. If not done well you have just mud and a detriment to the rest of the system. This is the most difficult part of the spectrum to get right and a zillion ways to get it wrong which is why there are so many opinions on the subject. A large part of the problem is room acoustics. Even with the best equipment the room can severely F up the bass. Rather, I should say that the room will F it up. +- 10 dB in an octave is not uncommon. The end result is what I call one note bass. There is no one solution to this problem. It helps if the room was designed as a listening room to begin with but most people do not have that option. So, you have to use multiple subs with a lot of power, room control and digital bass management with a two way digital crossover. Those of you who are digital phobic need to get over it. You are just shooting yourself in the foot.