the placement of any speaker depends a lot on the belongings of the room. For Apollo i recommend a minimum distance between 1m and 1,2m to the backwall (baffle, not the backside of the woofer- cabinet) but there are also customers who are satisfied with a closer distance, then i recommend some damping on the backwall. The longest wavelenght which is effective produced by the o.b.`s in room (depending on room and placement) should be shorter than the distance to the rearwall under ideal conditions. The speaker- placement regarding the best imaging is the first way to follow: When both panels are fully parallel to each other that there is a focus in the middle, the place where solo- voices rise in height is the best regarding the distance to the backwall, this depends a lot on the resonances of the room. Then you can adjust the size of imaging by changing the distance inbetween the baffles to the point where the focus in the middle is not sharp anymore, go back a little and Apollo will fill the whole room with music and produce the middle and voices in a realistic size.
Then you can start to tune the basses, which is done very quick by setting phase, frequency and volume on the plate- amps. In some cases when the distance to the sidewalls of your room is too small you can place Apollo in the same angeled way like your Beveridges, the imaging also will be good in comparison - but not the same quality like the imaging you get from parallel placement.
The measurements in the review are done from 15 degrees to 60! degrees out of axxis in nearfield. Also the Prometheus MKI slot- tweeter is measured in nearfield with horizontal and vertical angling (although you only get horizontal angling in listening- position, a slot- driver is not made for vertical angling). The two last curves for the widebands show the addition of frontside and backside of the baffles, the others not. The lower end of the wideband- response is also measured in nearfield without the influence of the room, the in- room the behaviour at the lower frequency- end is more flat and extended. The frequency- response is very flat for a crossoverless 12"- wideband when the backside- response of the o.b. is added. The range of flat response is between 20 and 40 degrees horizontal angling. On axxis the graph is a little rising in the 2-5Khz- region but even when you sit on axxis they sound ok. and then the performers are closer to the listener in this (on axxis) position. The dispersion of the Prometheus MKI was relatively uniform in the crossover- region, the wideband- driver does not beam like other big drivers when used above the break up- point of the cone and on listening- position measured between the tweeter and the wideband angeled between 20 and 40 degrees there were no big differences between the drivers. The Prometheus MKII and also the Apollo are a little better than the MKI.
The acoustic phase is also measured nearfield and it shows the common behaviour of a 12"- cone breaking up at 2Khz. Fullrange- speakers and widebands show this behaviour, too. The 12"- wideband of Prometheus breaks up like other cones (but controlled) and to higher frequencies there are only small areas of the cones moving, the areas are changing with the frequency and when the areas change you get a nearfield- measurement like this, a measurement with a little more distance between cone and microphone will result a very different graph.
There are so many aspects in speaker- behaviour, maybe it is the most complexed theme in hifi and also there are not enough measurement- methods used by far (dynamic measurements and laser- testings on the cone at different frequencies are imho also very interesting). Most published measurements are amplitude- curves, sometimes you find an additional Mlssa waterfall- graph added but this is only half of the truth - which everybody knows - is the real lie! So the most important point is to listen with an open mind trusting the own ears only, please let me know how you like the Apollo- sound after your second contact!
Regards
Robert Bastani