Speakers to perform their best MUST NOT MOVE AT ALL (meaning the tops should not wave around, even a silly millimeter!). So rubber is OUT! Spikes are best, but if you are on a wood floor, you have to be cunning about where you place the speakers relative to the supporting structure, in order to minimize the rocking motion that can result from the floor flexing (spikes won't help with that problem.)
So, how far apart are the trusses? |
Gammajo, here's the deal on speaker placement over joists:
Assuming the joists are running the short way across the room (and that you have your speakers facing the long way) take care to place the front and rear spikes of the speaker(s) as close to adjoining joists as possible. In other words, if the front and rear spikes were actually 12" apart, then the front spikes should be right on top of one joist and the rear spike on top of the next joist to the rear.
Or another example, if the F and R spikes are 16" apart, then the fronts should be 2" in front of one joist and the rear 2" behind the next joist to the rear.
You can locate the joists pretty easily with an electronic stud finder if you can't actually get under the floor and see them.
That is what I meant by "cunning" speaker placement relative to the joists. |
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Newbee, you raise an interesting point which I think is long overdue for discussion:
There are absolutely no vibrations or "resonances" to be DRAINED from a loudspeaker. And if there are, then its cabinet/enclosure (or stand) is poorly designed.
The object of using spikes/cones under speakers (as opposed to components) is to "mass-couple" the speaker to the ground. "Mass-couple" is just a fancy term for "hold it down tight!" and steel tie-downs with big bolts would work great too, if you didn't mind looking at them.
The only thing that should move/vibrate in a loudspeaker is the transducer(s) itself -- and 99% of those only move forward and backward. And the only thing the transducer should impart its vibrations to is the air -- not the cabinet, or the stand, or the floor.
With components, especially turntables, transports, and amps (because of tubes and especially transformers) it can be desireable to "drain off" micro-vibrations thru a mechanical "diode" like cones, or ball bearings, etc. But speakers do not require this. With loudspeakers, the use of cones and spikes is merely a way of securing the cabinet (or frame, in the case of electrostats) to the ground so that ALL the energy of the transducers is transferred to the air, and none to the cabinet, floor, etc. |
Fiddler, if this is what's happening in your case:
"All coupling does to many suspended floors is excite the floor which creates a delay in the sound traveling in the floor and it muddies the bass badly."
Then it's because the wood floor is flexing (what you call "excite") underneath the speaker allowing the woofer motion to rock the enclosure back and forth. Remember, it only takes 1/16" of deformation (flex) in the floor for a 5 foot tall speaker to rock back and forth as much as 3" at the top! There are three possible solutions:
1.) (the easiest) reposition the speaker so the front and rear spikes/cones/feet are on top of, or very close to, the (two closest) joists themselves (as discussed earlier)
2.) If (1.) isn't possible for some reason, then put blocking (little cross joists) between the two joists right under the speakers and/or put posts (or jacks) from the ground to under the floor where the speakers sit.
3.) If (1) and (2) aren't possible, the best solution (a bit of a hassle to do nicely, but works great!) is to run a brace (aluminum tube or plastic PVC pipe works well) from the top-back of the speaker to either the wall behind, or back down to the floor at least 4 feet behind the speaker, and secure it.
Any of these solutions will keep those woofers from rocking the cabinet instead of your ears. An additional benefit will be better highs and mid-range transients.
Hanging speakers can work also, except the chains or cables need to be splayed enough to insure that the speakers don't sway even a little. That's sort of an ugly tour-de-force don't you think? |
Fiddler, apparently you have a very under-engineered floor which is indeed being "excited" by the sound waves in the air! Is it an old structure? I have cured this problem for clients (I'm an architect) who had intolerably bouncy floors due to undersized joists put in by a shady builder (joists can be "up to code" to carry the load, but they usually need to be bigger than that to resist bending)
My solution in such cases (when none other was possible or practical) was to add a couple more layers of plywood subfloor, with the sheets staggered and edge and face nailed very well. This acts like a stressed skin and keeps the floor from bouncing excessively.
Frankly, I don't believe attaching the speakers elsewhere (like the ceiling) will keep the sound waves in the air from exciting the floor, as it is right now. |
Fiddler, I am an experienced builder as well as a licensed architect. I also have a minor in acoustics from MIT, and trust me, you don't begin to know whereof you speak, your limited personal experience notwithstanding. There are architects and architects; sorry you didn't find a better one.
As for your resonant floor, speakers coupled to the floor can't possibly move the floor for the simple reason that, except for down-firing subwoofers, transducers only move horizontally and floors only move vertically. So whether you say 'bounce' or 'resonate,' the floor would have to move; and if it doesn't, then perhaps the floor isn't the culprit; it could have simply been a standing wave between floor and ceiling created by an identical frequency peak in your previous system's response curve.
My guess, after all you've described, is that your new system's response is such that the natural room oscillation (standing wave) that got excited by the previous system, now doesn't occur. |
Fiddler, as in all professions, there are some incompetants, many bright ones, but few brilliant ones. The fact that your problem was solved with a speaker change and not with a construction project is what led me to my conclusion ;~)) |
Zargon, your case is the special exception I mentioned earlier, namely: you have a transducer (subwoofer) that moves up and down, same as the (only) direction the floor can move. So naturally it can mechanically excite the floor (grab it and shake it) in that direction at 34 Hz or whatever. But a normal forward facing transducer can't do that because the floor can't respond to its forward-backward motion. A woofer or sub can of course possibly excite strong standing waves in the air in a room (not the speakers' fault, just a factor of the room dimensions) and these standing waves can excite the floor to resonate. My point is that to decide how best to accomodate a speaker, one has to look at how it might want to move and then figure out how best to restrain it.
Gammajo's analogy doesn't really apply to loudspeakers for two reasons. First a vibrator's action is usually rotational (semi-omnidirectional), and loudspeaker transducers are reciprocal, whether they're cones or electrostats. Second, a vibrator is designed to transfer energy to another solid (your body). But loudspeaker transducers must absolutely NOT do that (transfer any energy to the enclosure.) ALL their motion must go into vibrating the air. That is why the speaker enclosure or frame must not vibrate (resonate) or be able to physically move (like rock back and forth on rubber pads or a rug or a too-flexible floor.)
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