This was my first attempt so not sure if i did it correctly.
1. . Made sure bass boost was off and lfe set to 0db.
1a. I set all speakers to 75db inc sub
(this left the sub at only 66 on the knob at the back? is this right as it only starts at 70 so 66 isn't turned up very much at all??
its at about 25 to the hour on a clock. Although the sub is quite close to the listening position.
2. Then, turned the amp volume down to the normal listening level position.
I'm assuming its a Velodyne HGS-15, if indeed thats correct you didn't mention the subsonic cutoff at the back of it (if its the model i think it is) there is a selectable 15/35Hz cutoff so if its currently on 35Hz that could explain why its not shaking the room apart.
If that doesnt apply, then run say a 15Hz or 20Hz test signal through it and look at the diaphragm movement, it should be fairly noticable even if its attenuated if it's being fed those frequencies. If its doing basically nothing at 15Hz the i could only guess that there is a cutoff somewhere in the system.
Dunno if this was helpful, please give more info if not.
EDIT: One thing to bear in mind, at those subsonic frequencies the wavelengths are several meters long. Your room doesnt seem that large so you wont notice them as much as say for example if you were at the opposite ends of a long room.
The confusion arises as the Excel spreadsheet that everyone is downloading from the snapbug site has HGS-15 as it's title and whilst everyone is using the spreadsheet, no-one seems to be changing the header.
Ah my bad ! I have heard one of those in action, they certainly have more than enough capability to shake a room about (better hold on to that beer). I'm thinking like Rob says it could well be positioning due the extreme length of wavelengths involved. Authough i still think it would be a good idea to look at diaphragm movement, that will speak 1000 words as to what kind of a signal its getting- i cant help but feel its not receiving much in the way of subsonics.
Unfortunately i am limited in sub position due to WAF.
Could possibly put it where i was standing when i took the pic of the sub (the doorway into the kitchen). May try it here when i'm next allowed (!) and post a new graph.
Room length is 13m x 13.5 wide so not the biggest but possibly big enough??? The pictures make it look a lot smaller than it actually is.
If it has to stay there, would a BFD be able to sort out a peak that large???
If your peaks and troughs are caused by room modes then the first point of attack is to move sub. If you can't then the other thing is to move the seating locations out of room mode peaks.
I don;t know whether these modes are from width, length or height modes. Probably length. Moving forward 3 feet should knock a big junk out of that peak and if the trough is a length mode it will help smooth it out too. Of course it will also probably move you in to problem areas from other modes.....but that's half the fun!
Put your test tone disc back in and stick on the nutter peak tone and then move your meter forward 3 ft see what happens. Or just turn up the volume and walk around and you'll hear the peaks and troughs of that mode.Try to move your own seating location to where it's neither loud or quiet. Then measure again.
""I don;t know whether these modes are from width, length or height modes. Probably length.""
The room is basically square (13 x 13.5') I'd imagine this is why the peaks/troughs are so big, and so centred around 2 freq's..
Looking at the photo's I'd say swap the sub with the cd rack ? / bookcase ? in the corner (where the black triangle thingy is) for a start, then see if SWMBO notices as it creeps rightwards towards the left main speaker..maybe even widen the mains and try and squeeze it in between the mains and the tv....
WAF doesn't look to be too much of an issue, going by that centre channel placement
i will get some pics up this week but basically now the sub is inside the front left speaker firing towards the front of the listener at the front of the soundstage as oppposed to firing inwards from the rear of the left hand side wall onto the left ear of the listener.