You should start with a test CD, Stereophile test CD 2 or 3 have test tones. You can use this in combination with a Radioshack SPL meter and graph your room/speaker response. Sean did a very good post on the corrections for the Radioshack SPL meter--it's not linear. You should be able to do a search and find it, but if not I can repost it. I copied it for future reference it was so good. Most likely you are getting a bump around 40Hz from the 15 foot wide wall. That will make the bass bloom---way to much. Unfortunately, problems at that low frequency are not well compensated for with room acoustics. They generally only work at 80-100 Hz and above. They can help--but they won't be the cure. The cure in severe problems is active eq. A notch filter where you have that bump. I know it almost sounds like heresey to use an eq--but there are audiophile grade eqs (TACT, Sigtech) and you might be able to get by with a simple yet high quality notch filter (not the sophistication of the TACt or Sigtech--but might do the trick).
First make sure that it's NOT the equipment. Using a test CD monitor the AC voltage at different frequencies. If that's OK check the speakers. This is a little tougher. Best would be outside if you have long enough cable, otherwise in the largest room. Using only one speaker and an SPL meter monitor the level at different frequencies. The meter should be very close to the speaker. Also check with Avalon about any impedance anomolies at the offending frequencies. Also the resonant frequency of the speaker / spike / floor combination could be an issue. Get the exact measurements for the room and calculate areas that would be likely to give you a problem. If the room measurements are OK than it's not the room. Bad floors are a possibility too. Contact me back in a few days after you've tried some of my suggestions. By the way, a good SPL meter and all purpose electrical meter are indespensible. Also get all of the cheap test discs that you can. You never know when one will come in handy.
What is your wall made out of. If it drywall on stud it usually acts like a drum near the frequency you are describing.
If you do have that kind of drywall simply thump the wall in various areas and listen to the thud. Compare it to the pitch of the blooming artifact from the speakers. That might be helpful.
This is similar to the floor artifact you are describing bu thas a pitch nearer to what you are describing
With the Eidolons, you may want to move them slightly away from or closer to the wall. This shouldn't substitute for troubleshooting the source of the noise. I have a pair of Avalons, and they are very picky of room position. I had a similar phenomenon, and I found that some loose flooring / rafter bracing in my house was the cause. There was a weekend when we were replacing carpet that I went around my living room, sinking a 5lb box of decking screws every 3 in in the subfloor; Went down stairs while the wife was jumping on the floor and marked all of the locations where I heard noise, and secured all of the bracing with glue and screws. I put R25 insulation in the floor joists with 5/8 drywall below the listening room. All of this including the carpet cost less than my interconnects, and made the whole room much more quiet. After I was done, I heard more noise, which turned out to be a bush on aluminum siding, rattling soffet, and some tin lamps on the wall. I would guess that the addition of granite slabs under the speaker will not fix your problem, but it is not a bad thing to try... Good luck!!
I have a very funny graphic idea of that day in your house with your wife jumping up and down and you drilling screws into nearly annything that moved o rmade noise....sort of right out of bugs bunny or something
$4700 retail in ASC traps and still a bass problem? Is there something wrong with that picture?
....some good suggestions though from those up above...good luck.
JDWEK -- It was kind of a funny scene... I am also a fan of Bugs and it could have been good 'toon material. I also caught the business from more than one that saw a screw every 3 inches... My floor doesn't make any noise any more...
Mes -- One thing I forgot -- are these Eidolons new, or not played often, or have been disconnected, moved, ect?? If so, let them break in for 500 hours and not worry about it(unless the bass sounds distorted or is breaking up). Avalons are by far the worst speaker to break in, requiring a lot of power and time. They will also get "cold" if not played at least once a week for a good listening session.
Agree that an active EQ trim at the problematic frequency can be an effective fix, if you've covered the other fundamentals (speaker placement, securing vibrating room elements, etc..
Rooms all have their own resonance, and few approach near neutrality, while many are simply problematic even when you do all the dirty work, spend a bunch on tube traps, etc..
Sometimes just a little trim at a problem frequency is so much more of an easy fix than infinately fussing and frustrating yourself...or, lighten your bass tone control slightly, if you have one. Yes, it's not purist to use tone controls, but you are looking for the overall best effect, and if improves things more than worsens them (hopefully much more), don't be too religiously against it.
Digital EQ should have the least negative effect, especially on phasing, but also a high quality analog EQ is not something to rule out. Used sparingly, mostly for cutting peaks (dips are often hard to add gain to, as they often are due to out of phase signals). Try to use it very sparingly, and only on the bands where it truly sounds good to use. Try keeping your adjustments to about 3db or less for least negative effects. I picked up a beautiful and really quite transparent Rane EQ at the Flea Market for $60. Rane makes alot of pro gear, and their analog EQs are quite nice.
Alternatively, try some different interconnects and maybe speaker cables. Some are lighter on bass than others, and the right one might just rid you of the bass bloat you are getting. If all else fails, remember that 99% there isn't so bad, and think of all the people putting up with all the pops, ticks, and warbles they get with their vinyl, and they still find the ability to love the heck out of it.
I know exactly where your coming from once you mentioned having your speakers on a suspended floor. While J_K did a "bang up" job on describing a good plan of attack, that will still not keep the joists themselves from flexing. While it might not fit in with the decor in the basement, installing some bottle jacks and / or 4 x 4's to lift or brace the joists that flex the most will do wonders.
If i can remember correctly, i also think i remember a review in Stereophile talking about these speakers being the hardest to position and achieve good bass as compared to every other speaker that they have tried. Please correct me if i'm wrong and i DON'T mean this as an insult to you or your speakers in ANY way. I'm simply stating that you may not be alone in having this problem with those specific speakers. Sean
Thanx to the above. The problem is at 80-90 Hz on test CD's.The house is nearly 90 yrs old, tudor, built l like a tank with non-suspended floors concrete and walls concrete and plaster. You can jump up and down with no give and squeeks. Unfortunately, the basement ceiling is finished, making access to the floor above impractical to say the least. Sean, no offense taken, I've heard that some rooms just aren't compatable with the Eidolons. Highdecibel-precisely, thats exactly what I've been thinking. Switching IC's, SC's, front end and amps hasn't made a significant difference. Maybe my room and speakers are like Bruce and Demi, not made to stay together for long. Anyone want some quilted cherry mint Eidolons cheap? Thanx for the comments, much appreciated. Mark
I have a pair of eidolons and the ascents before them and I have found them difficult to position so they are at their best for bass extension. That is not quite what you are referring to but I have found peace of mine by using a sigtech for the same amount of money and significantly better WAF than the tube traps. Before you really consider getting rid of the speakers why not try a Tact or some other such system. Tact has a 3 week trial period with money back.
The only negative of the sigtech is that it ruined alot of my tinkering that I kind of enjoy doing. On the other hand I think I enjoy listening more now.
80 to 90 Hz is your floor to ceiling dimension. You already have carpet, but it might not be the best for absorbing these waves. While I stated that active EQ might be the way to go (I had to do it), it's always good to try to do as much as possible without active EQ. As another poster said--make sure everything else is right first. If the short shag carpet is not very dense, it might not be absorbing the bass waves. You may consider replacing it with denser natural fiber carpet. (probably cheaper than another pair of ASC bass traps).
If you sell your speakers, let me know!