Hi Laco, and welcome to the forum!
Sorry to only be arriving on your thread so late, but hopefully I can still be useful!
Yamaha HS7 monitors rear ports not suitable for soffits?
Yes they can be soffit mounted. Almost any speaker can be successfully soffit mounted, if the right precautions are taken in the soffit design. The only ones that absolutely cannot be soffit mounted, are speakers that have active drivers on the sides, top, or bottom of the case. But ports and passive drivers are not a problem. Some speakers are hard to mount in soffits, because of their physical shape (eg, deeply beveled faces, non-rectangular cabinets with more than (or less than) six sides, highly rounded shapes, etc. But even then, it is usually possible. Even the famous Genelec "eggs" can be soffit mounted, successfully. The HS7 is not a problem, and can be soffit mounted.
The manufacturer recommends placing monitors 1.5 m or more from the rear and side walls.
... if the room is big enough, then the can be away from the walls, yes. But the room has to be quite big, and the distance greater than 1.5m. As Jennifer and Starlight have mentioned, the problem is SBIR. If your speakers are within a certain range of distances from the front wall, then the SBIR dip and related artifacts will occur at frequencies that are very noticeable, and very hard to treat. For small rooms, the best location is usually up against the front wall.
I don't want to analyze yet, the room has an echo.
That is the
best time to analyze the room! When it is empty, untreated, and sounds terrible. That's when you SHOULD do the first acoustic tests... to capture the true natural response of the room, exactly as it is. Then you can use that information to plan your treatment accordingly. If you wait until the room already has some treatment, then you won't know if what you are measuring is due to the room, or the treatment... Then it is too late to know what the real problems with the room are. Always do your first REW test with an empty room.
I test how low frequencies behave, I move the speakers and the listening position
To do that properly, these are the two procedures you should follow for doing that.
How to calibrate and use REW to test and tune your room acousticsThe "walking mic" test, using REW I have a fairly large table,
I would suggest that you replace that with a smaller table. As small as possible. The table can have a big effect on the acoustic response of the room, especially with things like early.early reflections, and comb filtering.
I'm sending a few photos for an idea.
When you do your REW tests, take all of the guitars out of the room. They produce resonances that can affect the response graphs.
I just downloaded your MDAT, and I'll take a quick look....
- Stuart -