How do you chose speakers based on room size?

Gentlemen,
Timely topic. I've got an open plan listening area--my my living room--that is roughly 15' long and 11'3" wide with a "mostly" open wall on the longer side (that is, from the back/listening end wall, the open wallspace extends about 11-12' toward the speaker end). 7'6" ceiling. I am using B&W CDM7se floorstanders.

If there is a problem presently it is with a weaker lower end. (Duke hit the nail perfectly.) Overall positioning has been tweaked to the point where I am happy with the sound but I cannot seem to get past the bass issue. On most recordings I really don't notice (but imagine that there is still an effect that will be appreciated if the issue is corrected) while on others the lack is clearly noticeable.

We've got carpet on the floor and upholstered loveseats at both the closed side and at the listening location. I'm guessing these don't help the bass but the rest of the frequency range sound so good I'm in a quandry.

The wife and I would like to put in hardwood and to replace the loveseats (the cats are slowly shredding them) with leather but I am really nervous about "hollowing out" what is now an otherwise very rich sound (absent some degree of bass).

My speakers of choice (the next upgrade) would be the larger B&W 803D which also have the benefit of better (and additional) drivers and B&W's diamond tweeter. (http://www.hometheatermag.com/floorloudspeakers/1005bw/#) I'd been concerned that the size was a problem but Duke has suggested otherwise. Any comments on current setup or proposed changes (gear or room) would be greatly appreciated.

I always said that the more the room acoustics become a challenge. You have to try a listening triangle in that room as a starting point and choose your speaker type.

This is a great thread !

I was wondering if we could take this a step further ?

Is there some aspect of speaker build/design that one should look for in those small room/nearfield situations that would be different than the larger rooms and visa- versa ? Something that would not be placement specific .

In the larger room one will want to turn up the volume so as to pressurize the room while sitting farther away from the speakers . But in a small room one will want to turn down the volume because there is less area to pressurize and you are sitting closer the speakers .

Newbee addressed speaker types , Duke talks about spreading the bass sources and reducing the port frequency in a tight space , mapman suggests tight driver integration for small rooms and bigger drivers for large rooms . But then J Bailey speaks of single drivers for easier driver integration and uses 3 way big woofer back loaded horn speakers in his small room .

Are there some simple guidlines for design as well as size ?

Thank you .

Saki, Speaker placement (including the rooms that they might work well in) is critical for just about every speaker design.

Some folks pursue set up diligently until they have optimized it, some more than others until their significant other or their own sense of asthetics takes over, some not at all and everything in between.

Your suggestion raises the toughest and most common (I think) situation facing the majority of audiophiles. Good sound in a small room. Tough under the best of circumstances and especially so if your expectations are demanding, but to exclude placement as a consideration presumes that there is a speaker with audiophile pretensions which will sound good no matter where you put it or where you sit when you listen to it.

I don't know of such a speaker, let alone provide 'simple guidelines' or advise, apart from getting a pair of sealed enclosure cone driver monitors that can be placed near a wall or on a book shelf, a sub woofer to fill out the bottom end, and an equalizer of some sort to balance out the very uneven sound that would be likely. Not very good advise IMHO unless you don't care about things like a balanced FR at the listening position as well as a full (wide/high/deep) sound-stage.

FWIW.

Saki70, you have very good questions. I'm going to avoid getting too specific here because I don't want my post to cross the line and become an "ad".

Driver integration is dependent on driver vertical spacing, crossover frequency & slope, and listening distance. Briefly, the ear is poor at resolving the height of a sound source below about 1 kHz, improves dramatically between 1 kHz and 4 kHz (where it peaks), and then actually decreases a bit at higher frequencies but remains pretty good. Steep-slope crossovers give better driver integration (less vertical smearing) at close range than shallow-slope crossovers. In my experience, having a suitably low crossover frequency is more beneficial to driver integration than is close inter-driver spacing. Perhaps Clio09 will post here, as he's the one who really opened my eyes (and ears) on this subject.

Saki70, you mentioned that in a larger room we want to crank it a bit but in a smaller room we want to turn the volume down. One factor that comes into play here is the thermal modulation characteristics of the drivers. Usually the tweeter is more efficient than the woofer so it's padded down, and it normally gets a lot less power anyway. So many speakers run into the problem of the woofer's voice coil heating up more than the tweeter's voice coil, so the woofer has more thermal compression as we turn the volume knob higher. This voice coil heating is virtually instantaneous; a 100-watt transient is like touching a 100-watt soldering iron to the voice coil. Anyway, if the woofer's voice coil is heating up faster than the tweeter's it will have more thermal compression at high input levels. The designer then has to choose an input level at which the drivers are balanced relative to one another, and he will probably choose a fairly high level, let's say 90 dB/1 meter for this example. If we go to 100 dB, the tweeter will get loud a bit faster than the woofer because its thermal compression is less, so the speaker will sound a bit bright on peaks. If we go down to 60 or 70 dB, now the tweeter is softer than the woofer so the speaker sounds a bit dull and lifeless. I think this phenomenon is behind the fact that many speakers do not really "come to life" until you crank 'em up a bit.

So to sum up the preceding paragraph, it's not uncommon for a speaker's tonal balance to change with the input power level, going from dull at low levels to "just right" (the Goldilocks zone) to too bright at very high levels. If a speaker is going to work well at a wide range of power levels, either the woofer and tweeter need to have very similar thermal compression characteristics or their departure from linearity should happen at higher input power levels than we're likely to see in the home.

On a related note, low thermal compression correlates with speakers that convey emotion well. Musicians use variations in loudness to convey emotion, and it's nice if the speakers can preserve those dynamic shadings. If a speaker is compressing the peaks by 2 or 3 dB, well then ou lose emotional impact.

So anyway in order to meet the requirement that a speaker work well at low levels in a small room and also at high levels in a large room, a lot of issues have to be addressed. I think it's easier to address them with prosound drivers, but won't claim that's the only feasible approach. But large-diameter prosound woofers and high quality constant-directivity horns & waveguides combine good directional control with the ability to move a lot of air should they be called upon to do so.

I don't think it's possible to design a speaker whose characteristics in the bass region do not change significantly as its position in the room (and/or the room itself) is changed, so I think the best we can do is build in a reasonable amount of adaptability that will hopefully cover most situations.

Duke