I'd go with Bluecube speakers. I have used the same designs under a different brand name, and I have supplied Bluecube to other DIY installers with good results.
Yes, the rear speakers should be closer together than the sides. You'll be using a mix of genuine 6.1 and 7.1 soundtracks from Blu-ray with simulated 7.1 created using Dolby PLIIx. The speaker positions are determined by angle and distance from a centre listening position.
It could be argued that extending the distance of the rear speakers would eventually lead to a position that is in-line with the side surrounds, but that overlooks the huge increase in power required to overcome the sound dissipation over distance (look up Inverse Square Law) to provide a balanced sound field at the listening position. The consequences start to multiply: Will the amp be capable of driving the speakers effectively; how much sooner will the amp go in to clipping (run out of power) on those channels, or do you plan to install an additional power amp just for those channels; how will that affect the power to the other channels; what extra distortion will be introduced as the amp clips and how soon will it result in damaging the speakers (blown tweeters first); how much more distracting will it be for other occupants not in the main seating area to hear those rear speakers playing so much more loudly than the others; how soon will the power to the rear channel be over the maximum rating of the speakers?
In summary, you can put your speakers anywhere you wish, but it doesn't mean you'll be able to drive them effectively or safely. Most AV receivers can't maintain a high and sustained power output to all channels despite what the specifications say. My own tests reveal that 105W/Ch from an AV Receiver running Pink Noise at reference 85dB is matched by 50W stereo amp running the same tone and at the same level. So, despite the paper spec suggesting that the AV receiver is over twice as powerful, in the the real world it's current delivery that counts. In-ceiling speakers are, by design, going to direct most of their sound at the floor first. The sound reaching the listening position is a combination of the off-axis direct sound and the reflected sound bounced from the floor and other non-absorbent surfaces. It stands to reason then that the power demands placed on the amp from in-ceiling speakers will already be higher than for conventional forward-firing speakers of the same efficiency. Adding to that load by positioning the speaker where they'll require even more power simply reduces the lifespan of the equipment.
Yes, the rear speakers should be closer together than the sides. You'll be using a mix of genuine 6.1 and 7.1 soundtracks from Blu-ray with simulated 7.1 created using Dolby PLIIx. The speaker positions are determined by angle and distance from a centre listening position.
It could be argued that extending the distance of the rear speakers would eventually lead to a position that is in-line with the side surrounds, but that overlooks the huge increase in power required to overcome the sound dissipation over distance (look up Inverse Square Law) to provide a balanced sound field at the listening position. The consequences start to multiply: Will the amp be capable of driving the speakers effectively; how much sooner will the amp go in to clipping (run out of power) on those channels, or do you plan to install an additional power amp just for those channels; how will that affect the power to the other channels; what extra distortion will be introduced as the amp clips and how soon will it result in damaging the speakers (blown tweeters first); how much more distracting will it be for other occupants not in the main seating area to hear those rear speakers playing so much more loudly than the others; how soon will the power to the rear channel be over the maximum rating of the speakers?
In summary, you can put your speakers anywhere you wish, but it doesn't mean you'll be able to drive them effectively or safely. Most AV receivers can't maintain a high and sustained power output to all channels despite what the specifications say. My own tests reveal that 105W/Ch from an AV Receiver running Pink Noise at reference 85dB is matched by 50W stereo amp running the same tone and at the same level. So, despite the paper spec suggesting that the AV receiver is over twice as powerful, in the the real world it's current delivery that counts. In-ceiling speakers are, by design, going to direct most of their sound at the floor first. The sound reaching the listening position is a combination of the off-axis direct sound and the reflected sound bounced from the floor and other non-absorbent surfaces. It stands to reason then that the power demands placed on the amp from in-ceiling speakers will already be higher than for conventional forward-firing speakers of the same efficiency. Adding to that load by positioning the speaker where they'll require even more power simply reduces the lifespan of the equipment.
