First off most people can easily mount their Surround Speakers properly at 2'-3' Feet above their listening position regardless if their Direct Radiating or a Diffused Speaker. Because just mounting their Surrounds higher will create a more proper diffused sound as intended.
Second what percentage of movies use surround sounds directly vs diffused?
I see that their are some people on here still ignore this FACT.
The huge majority of movies (99%) use surrounds for Atmosphere (diffused), Which is why if your setting up for an Anomaly (direct), then you will be greatly depreciating the Accuracy of the sound stage and misrepresenting what most Sound Engineers are trying to accomplish.
You don't need special speakers or tons of money to properly place your speakers in an ideal location to accomplish having Diffused Sound. That's like saying it doesn't matter if you face your center channel backwards or forward. This is proper speaker placement. I'm sure I could even find a movie scene where a reversed center channel could be beneficial but that's just silly.
As you should know every 6dB is a perceived Doubling in Sound to the human ear.
http://www.sengpielaudio.com/calculator-levelchange.htmSo if your using the QS8's you should be using a 95hz Crossover, however most receivers will not let you be that accurate so using either 90hz or 100hz should work fine. I personally prefer the 100hz Crossover because it has a Flatter Tighter Freq Resp of (+/-3dB)
While a 90hz Crossover brings your Freq Resp up to (+/-5dB). Which is not a good thing if your going for a FLAT FREQ RESP.
This is why Paradigm speakers another Canadian Manufacturer uses such a tight Freq Resp on all of their Specs that's (+/-2dB) instead of Axiom which standards are (+/-3dB) which allows Axiom to cheat their loudspeakers specs thus achieving lower ratings for their low frequencies of their speakers.
So next time you look at specs between different companies keep in mind that sometimes the Loudspeaker that says it can play lower can be misleading if you don't understand the fine print.
Don't get me wrong i'm a huge fan of both companies which is why I own Axiom QS8's in the first place.
