Nice job Alexc. Please keep us up to date.
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Alex: Nice job it truly shows how critical room correction is. Also, I compliment you on not trying to deal with the holes. It just doesn't work, unless it's a very small gain needed. I also appreciate your discussing our PARC with us. I wish we could have served you better in Venezula, but having a TacT dealer there, and we are just starting to distribute in South America I think you made the right choice. Dealer support (particularly abroad) is very important.
The only other comment I would make is about your subwoofers. I think they are very very good, and quite musical, but I agree they do not integrate well over 50 to 60 Hz. You might consider speakers that work near flat down to 40 Hz--although I'm surprised that the Sonus Faber speakers aren't filling the bill at 100 Hz--does the room have a severe suck out at this frequency, or is it a speaker issue?
Thank you for the kind feedback. I also wished I wold have been able to audition the PARC before taking the plunge with the TACT. As for my problems below 100Hz, these are very much room induced problems. The Guarneri's in my old room were capable of remarkably linear reposnse down to 45 Hz. In this room, I have sharp dip at 63 Hz and another one at 94 Hz, both in the 12 dB range. Further up the spectrum, I get another sharp dip of about 6 dB at 158 Hz. The rest is pretty flat indeed. The dips are symmetrical oand nearly identical on both speakers, os I think I am dealing with some nasty room issues (floor and stairwell at the lower frequencies, and perhaps the suspended plaster ceiling at 158??). Setting the X-over point at 50-60 Hz takes care of the worst of the lowest dip, since the RELs do quite well in this range, but if could X-over at 100 I would completely clena up the bottom end, and probably be able to correct part of the higher frequency dip. Given that I could not make these dips go away with repositioning, I chose to set up the Guarneri's at the optimum distance for driver integration and soundstaging. They are now 2.75 meters apart, 2.75 meters away from the sweet spot. Distance to the rear wall is close to 2 meters, and to the side walls about 1.5 meters.
I don't see how the REL would clean it up if it's room induced. You can of course increase the output of the subwoofer, but that will muddy up everything. You would need a sub that you could increase the output at 100 Hz--this would likely give you the same problems you had with the main speakers (although to a lesser degree). What are your room dimensions? 5.75 meters wide--that's 18.87 feet which would normally give a peak at 63 Hz--unless you are sitting at a null point. What are all dimensions--and can you tell us more about a "suspended plaster ceiling"? Also, have you measured the "hole" frequencies in various parts of the room to insure they aren't just nulls at the listening position, but are truly "holes".
OK, let me try to shed some more light.
- The room is 5.72 meters by 4 meters, with 2.72 meter high ceilings. The listening seat is dead center along the long wall, and about 18 inches away from the back wall.
- Backwall is treated with RPG diffusors. The first and second reflection points on the ceiling, front wall and side walls are treated with 4 foot tall RPG foam panels. The corners are treated with 4 foot tall RPG foam wedges (this is the RPG Studio in a Box kit).
- The level on the subs is adjusted so that the SPL between 16Hz and 85 Hz is no more than 6 dB down vs the midrange level of the mains. This level is still about half of the way to full output on the subs.This gives two broad peaks of about 10 dB fom 35 to 53 Hz and 62 to 83 Hz, which the Tact can easily suppress. The Tact can easily boost the output between 16 and 25 Hz as well, with no ill effct on the subs that I can perceive. The subs response exhibits similar dips to the main speakers, slightly shifted in frequency due to the different positioning and acoustical environment. Both subs show a dip at 54 to 62 Hz (this dip is the one that creates the humps described above when the output level is increased). The left sub dips again at 94 Hz, while the dip on the right sub is shifted to 108 Hz. The reponse on both subs then goes up to - 6 dB (vs the midrange) at 140 Hz, at which point the subs roll off.
- The ceiling seems to have been constructed by hanging a steel mesh from the actual roof (steel I beams covered with prefab slabs) using many welded steel rods. The mesh was then coated with plaster repeatedly to create this suspended plaster ceiling, which is about 2 inches thick. The space between the plaster ceiling and the concrete roof is hollow and about 18 inches deep.
- I should mention that all the walls are different. Behind the speakers, it is half flimsy sliding glass windows on the left and drywall over floor to ceiling glass panes on the right. On the right, we have plastered cinderblock. On the left, we have a 4 inch mdf sandwich over structural steel stuffed with compressed fiberglass. Behind the listening seat, we have plastered brick and of course the sliding hardwood door which covers one third of the wall. On this wall, above the listening seat, there is a huge AC vent, about 8 feet wide and 18 inches tall opening into a monster AC duct. The AC unit is way overpowered, so it stays off during listening sessions.
- THe sliding hardwood door opens pretty much directly onto a staircase leading down to the second floor. Althouh the door its solid, it is free floating on the rails and doe not provide a hermetic seal.
- The floor is made up of very long hardwood boards nailed every half meter or so onto a grid of 2 by fours, which in turn sit directly on the underlying concrete slab floor. This creates a shallow cavity under the floor.
As you can see, this room is basically a study in what NOT to do to create a good listening room. Just about every basic rule has been violated. It has, however, a few redeeming qualities:
1. Its MINE!! I can have as many cables on the floor there as I wish and my wife could not care less.
2. Its large enugh to allow the Guarneri's to be properly placed far away fom each other and the listener. My room in the US allowed only near-filed placement, and this is not how the Guraneri's show their best.
3. Its on the third floor of my apartment (OK, this is a very large penthouse apartment). All the bedrooms are on the second floor, and I have NO neighbors. So..loud music at 1 am is NOT a problem.
4. The view from the windows, which overlook the Avila mountain in Caracas is breathtaking. OK, you have to sort of kneel down to peer underneath the RPG foam panels I stuck to the windows in order to catch the view, but it IS there. :o)
5. In the room next to it (an informal dinig room opening up to the terrace) there is a full wet bar, so I can refill my scotch without walking to the kitvhen on the first floor.
6. Right outside the sliding wood door, there is a bathroom.
Hope this helps!
Alex: You haven't broken every rule. You still have at least 4 or 5 major ones you missed. But the ones you did break you did a really good job with them--crushed them more like it. I'm only kidding. Is it possible for you to take measurements in various locations in the room and see if you are in a null for those frequencies or if they are truly a "suck out" caused by the room. They are really big to be a suck out, but I can see certain positions where there could be a null. This architecture is fairly unusual as well (compared to the typical building we deal with)--I have some ideas on how it might react, but having not measured the in room response of a ceiling constructed in that way I'm not sure the theory is correct. It could be acting as a giant capacitive bass trap and could be why you have the holes (particularly the one at 94 Hz which corresponds to the room width). That's why I want to know if the 94 Hz is a null point or truly a hole.
I will try to take some measurements this weekend. The battery on my Rat Shack is dead. I also have the German AC Fish thingy sold by the CARA folks (ordered directly from the Fatherland!) whihc I'm sure its more accurate than the Rat Shack but have, so far, not managed to figure it out. My German is nonexistent and though I have copy of the manual in English it still makes no sense to me..plus the test/calibration CD is all in German too!