WHat about four speakers.......

Mythtrip -

Let's take a look at what's going on in the concert hall, and then come back and look at speakers that bring some of those elements into the listening room.

In the concert hall, the direct sound from the instruments arrives first (naturally), from which we get our directional cues. Then there's a bit of a delay before the reflections start to arrive. There is a great deal of diffuse energy in the reflections, which set up a very powerful reverberant field that actually contains many times more energy than the first-arrival sound (although the first arrival sound is louder, its presence is brief).

This powerful, diffuse reverberant field contributes to the rich timbre we experience in a concert hall. There is a tradeoff relationship in halls between precise localization of sound sources and ambience, just as in the home. Most concert halls excel at rich timbre and luscious ambience rather than "imaging".

Okay, now let's step into the typical listening room. Just as in the concert hall, the first arrival sounds give us our directional cues (and primary timbral cues). But then there is relatively little delay between the first arrival sound and the onset of reflections. And typically, the reverberant field in the home has a very different tonal balance than the direct sound (unlike in the concert hall), because loudspeakers' directional characteristcs change with frequency. Compared to the concert hall, the typical reverberant field in the home arrives too soon; often contains undesirable strong, distinct early reflections; isn't powerful or diffuse enough; has too much bass relative to the midrange and treble energy; and decays too quickly.

A surround sound system seeks to approximate the concert hall by reproducing delayed ambience energy from the rear speakers. Whether or not this is more realistic than a comparably-priced two-channel system is debatable.

The problem with using a second pair of speakers to the sides, without delay, is that the ear localizes sound primarily by arrival time, and secondarily by intensity. Unless the path length to the second pair of speakers is at least a foot longer, they will be perceived as distinct sound sources. And even if they are a little farther away, their "reverberant" energy arrives way too soon, and will still cause image shift. Unless the signal to the second pair of speakers is delayed, in practice it will probably do more harm than good.

Some speakers are designed to put a great deal of energy out into the reverberant field. Omnidirectional speakers do so, for instance. You might look at designs by Shahinian, Wolcott, and MBL, for example. The bi-polars from Mirage and Definitive Technology also generated well-energized reverberant fields.

If placed fairly far out from the wall, dipole speakers can create a good sense of ambience because the backwave contributes to the reverberant energy in the room, and the farther out the speaker is from the wall the longer the delay before the onset of that additional ambient energy.

Treating the first reflection points is a good idea, whether with absorption or diffusion. Remember that in a small room a little absorption goes a long way (because sound waves will bounce it many times in fairly short time interval), and that in general diffusion is the better approach because it preserves the reverberant energy as long as possible instead of swallowing it up.

I hope this helps a little.

Duke

Walt Disney (the man, not the company) first experimented with surround sound in the 1930s along with Leopold Stokowski, when they were mapping out Fantasia. Unfortunitely for them, the theater owners at the time were not interested in spending money on the needed upgrades.

Mythtrip, it sounds as if you and Dr Amar G. Bose have visited the same concert halls : )

Honestly though, his published theory as to how he came up with the design for the original Bose 901's is very similar to some of what you stated above. The main problem with his design is that it uses multiple drivers and suffers from severe comb filtering. In effect, the design creates almost as many problems as it tries to address.

As Duke stated, omni's are capable of producing a very expansive soundstage but are also more susceptible to reinforcement / cancellation from room boundaries. If you can get a good pair of omni's properly set up, the soundstage is pretty amazing. I have a pair of point source ( one driver per cabinet ) omni's and they produce a soundstage that literally "wraps around you" and "engulfs" you on some discs. I have never heard any other speakers ever do this. To be honest though, the electronics in this specific system also play a key part in this as these speakers have not always produced this effect. This is true even though i have not altered their position over the course of many, many component / cable changes.

Dipole's aka "planar's", "stat's", "ribbon's", etc... are capable of doing this, but not to the same extent ( at least in my experience ). They do tend to sound far more open and less "congested" than what most "boxes" are capable of as a general rule. The problem with a dipolar design is that the rear wave is out of phase with the front wave, creating an instant problem with cancellation. In comparison, the specific omni's that i have radiate in a 360* pattern while keeping the signal in phase. So that you have a better idea of what i'm talking about, here's a picture of what they look like. The specs as published are VERY incorrect though, so take them with a grain of salt. The only thing that the manufacturer got right is that you need AT LEAST 100 wpc to drive these. I have two pairs of these with one looking like the picture and the other having a slightly different design.

All i can add to the above is that once you experience a system that has a very expansive ( wide, deep and tall ) sound stage, you will find it hard to listen to "boxes". They will, for lack of a better term, sound very "boxy". Obviously, some designs are better at "disappearing" than others, but much of that will also be up to the electronics that they are connected to. Sean
>

see Dolby Digital 5.1 channel sound
see DTS surround sound
see DVDa multichannel sound
see SACD multichannel sound

All of these formats are competing for the multi channel music market (Dolby Digital 5.1 is mainly for movies).

Anyway, my biggest argument against multi channel music is all of the speaker cable or interconnect involved. Your either going to have to run some very long interconnects or very long speaker cables to 2 sets of speakers. This can have a serious impact on the sound quality of those speakers. Why would one want to listen to 3 premium sounding speakers then 2 speakers that were producing noticeably less quality of sound.

This dimished sound quality for rears is not as evident in movies due to the fact that most rear channel sounds are really not recorded terribly well. Most of the Movie sound comes from the L/C/R/ speakers.

KF

I agree with TWL. I think there is potential in multi-channel reproduction, but I have yet to hear it done "correctly".