Do you need full-range speakers with great subs?

If you've got a couple of great subwoofers, do you need full-range speakers for the front and surrounds in a really big room? I currently have full-range floor standing speakers for every channel. The fronts are 6 ft tall with two 12 inch woofers per speaker and the rears are 5 ft tall with two 12 inch woofers per speaker. I'd like to reduce the size of the fronts and surrounds to large bookshelf sized speakers, but I don't want to compromise the sound quality. I'm currently running 5.1 and I'd like to go to 7.1 to take full advantage of the new HD sound formats.

I'm using one sub with 18 inc woofer.

My room is 70 ft long by 22 ft wide with a 22 ft ceiling. A pretty big room for a residence, but I'd rather not have 8 monoliths in the room. It is also my living room and not a dedicated theater.

The center speaker is 25 ft from my sitting position, the fronts are about 30 feet away and the surrounds are 25 feet behind me in a 5.1 set up. Because of seating, I cannot put the surrounds directly to the sides of the seating position as a lot of seating diagrams recommend.

When I go to movie theaters, the speakers along side the wall overhead don't seem that large, but there are a lot of them though. I think I counted about sixteen total speakers along side the walls and in the back.

Below are the specs of the speakers that I am considering for fronts, backs, and surrounds in a 7.1 setup.

Infinity Kappa 6


Cabinet dimensions: 25'' H x 15'' W x 10.5'' D.
Power handling: 150 Watts RMS.
Nominal Impedance: 4-6 ohms.
Frequency Response: 39Hz to 45 kHz.
Crossover Frequencies: 800 Hz and 4.5 kHz.
Emit Tweeters.
3" Polypropylene dome midrange
10" Injection Molded Graphite Woofer

I welcome your comments and suggestions.

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No, but you can cross the subs over lower with larger speakers.
I would not advise this - that 3" polydome mid was discontinued - it won't play loud enough for you space requirements - you will suffer terrible midrange compression and difficulty to hear dialogue on movies in such a large space or worse you will blow them up.

There is a replacement but it looks Mickey mouse

Have you considered panels to reduce the room size across the middle and hanging baffles from the ceiling - it is a very long room (like a tunnel) and you may end up with very long reverberations as you get in a church or gymnasium ( you say it is concrete). The mirror glass on one side will also act as a very strong reflector.

Narrow dispersion type designs or horns might be your best bet (you probably will benefit from limited dispersion and the higher SPL that horns can achieve)
What's your sub? It can make a huge difference if you have a 90 watt no-name vs an 18" 400 watt velodyne?
A few things. " taking advantage of the HD Audio formats" has nothing to do with 7.1.

Secondly, to take advantage of any HT audio format, you really want to match your center to your mains as far as driver types and sizes. It sounds like you have four full range monsters right now and no sub. Thats a problem for current audio tracks on DVDs as it stands, although I am sure the four channels sound great. The center channel, usually the dialog channel ---is key.

Anyway, movie sound tracks are engineered with a sub in mind, thus the ".1" in 5.1, 6.1 or 7.1.

So no you dont need full range speakers with subs and its not actually desirable for Home Theater. Most DVD sound tracks are designed to crossover at 80 HZ and thats the standard setting for most AV receivers. With fuller range speakers, including the centr channel, you could cross at 60 or even 40. My center channel extends to 45 HZ, so I could probably cross at 60 hz and be OK all the way around, including the surrounds.

Good luck.