1) The larger the diameter of a speaker RELATIVE TO THE WAVELENGTH OF
THE SOUND IT'S REPRODUCING, the more its output is beamed straight
ahead. This is very significant for tweeters (wavelength at 5 kHz is
2.7", at 10 kHz it's 1.35"), which is one reason tweeters should be as
small as possible. (Another reason is lightness--lower inertia enables
more rapid response.) It matters less for woofers, because bass
wavelengths are so long (11.3 feet at 100 Hz, 22.6' at 50 Hz, 56' at
20 Hz) that any speaker will be small enough not to beam.
2) The inverse-square law does not apply in normal rooms, because the
sound energy remains mainly in the room. Moving further from the
speaker does not much lower the sound level at your ear but lowers the
proportion of the sound coming directly from the speaker rather than
being reflected by room surfaces first.
This suggests a non-standard physics. The basic complaint is that
the floor vibrates, and we know the speaker cases are in direct contact
with the floor. HG now suggests that if the cases were separated from
the floor by a foot or two of (compressible) air the "floor and walls will
probably vibrate almost as much." We should be interested to learn
how this could possibly occur.
No - the basic complaint is that low frequency sound is heard either
above or below the room with the speakers. The theory is that this can
be reduced if the speakers are removed from direct contact with the
Car speakers are not directly connected to the exterior surfaces of a
car, yet low-frequencies are easily transmitted by those surfaces to a
listener dozens or even hundreds of yards away.
If the room's walls, floors and ceiling is made from compliant materials
(ie wood, sheetrock, etc) then it's quite likely that low frequency
sound from a suspended speaker will create standing waves that will
cause the walls, floors to resonate.
In this case, if indeed we are talking about a poured cement structure
(ie - modern multi-story apartment building) then that will be far less
But I still can't believe that a speaker sitting directly on a concrete
floor that is presumably 3 or more inches thick can possibly experience
enough of a vibration amplitude to be transmitted through the floor.
Presumably there is carpeting on this floor, which would decouple the
speaker to a great extent from the concrete floor.
A different and rather complex environment. The car is of smaller
dimensions and the bass wavelength are much larger than the car
dimension. In addition, there is little damping from the sheet metal.
And as previously mentioned, a 15" or larger woofer is more like to be
heard at a distance that an 8", this is roughly analogous to power
factor in house current. The "power factor" changes with distance from
the speaker. Just a "trick" to get more sound outside.
Unlikely to be significant. Such resonances that do occur seldom couple
out. Once more it is conductance that is of concern. A diffuse wave
bouncing off or being somewhat absorbed is not even coupling in phase.
Do the math or look at the geometry. The bass wavelengths are more on
the order of the room size.
Believe what you will. The theory and practice are against you.
A quick search for (better) floor speakers.
Note the feet. What do you think they are for?
isolation cones, note the minimal contact area:
Beats the hell out of me why you keep pursuing these theories of yours.
The physics is more than you think.
You can just wait for Andy to report back.
Who at one time spent a lot of time listening to room acoustics and has
friends with commercial recording studios.
An anechoic chamber built from the right absorbtive materials can
isolate the acoustic energy, if you are willing to build "a room within
a room". This is economically (and aesthetically) very, very unlikely,
but will achieve isolation even at subsonic frequencies.
Most recording studios have the opposite problem, and will use such
methods to isolate low frequency / subsonic noise (from air
conditioning, trucks, elevators, etc.) to prevent it from entering and
The techniques are neither new nor especially complex. A little Google
searching on these anechoic room / chamber techniques will show how it
My college dorm room was on the second floor of a steel-framed,
concrete-floored building. One of the guys in the basement below had a
Klipschorn. We could never hear his music, but with our shoes off we
could feel the beat.
Your floors may still vibrate to some extent if you decouple them from
the floor, but far less than they do now. Suspending your speakers
might reduce perceived bass because some of that bass energy will now
be pushing the speaker box back and forth instead of projecting it all
into the room. Setting the speakers at a different height from the
floor than the manufacturer recommends may make bass response uneven.
Placing the speakers lower than recommended will usually affect treble
response, because you're now listening off the tweeter's axis.
Whether subwoofers make the sound inaccurate or not depends on what
you mean by a subwoofer. If you have a packaged system with a small
bass box and even smaller satellites, that bass box probably is
probably just a woofer, reproducing frequencies below 100 to 250 Hz,
and probably cutting out well above 20 Hz. True subwoofers are
designed to augment speakers that already have decent bass, by beefing
up output in the 50~20-Hz range (sometimes even lower) and can make
the overall sound cleaner because the drivers handling the upper bass
and lower midrange won't have to deal with the bass at the same time.
Also, using a subwoofer lets you place the bass source wherever in the
room the bass propagates best while placing the rest of the system
wherever they sound clearest. (If the crossover frequency, where the
main speakers hand off the signal to the subwoofer, is well below 100
Hz, you'll never notice that the bass and treble are coming from
You know, that sounds like a good idea to try.
I could put some fabric around the rolls.
I have some leftover fabric with the U.S. Flag on it.
I may shorten the cardboard tube enuf so it doesn't act as a conduit
Well they do sell isolation cones (spikes) for just this purpose, but like
many things audio they are a lot more expensive than they are worth
(especially if you buy the ones with oxygen free metal).
For on the cheap, though, maybe make your own with some bolts and nuts?
I would do a little experiment first.
Send a friend to the apartment below,with a phone.
Then pick up the speaker(s) off the floor, and check by phone if
that makes any difference.Repeat until sure of the outcome.
If no reduction, isolation from the floor wont do anything.
But if it works well,get a nice 2 inch slab of stiff foamrubber, and put
that under the speaker.
So - you don't actually know how much sound is actually getting through
to the apartment below. ?
This isin't based on a complaint, or any direct knowledge if your
current setup *needs* to be modified ?
All of the vibrations will be directly transmitted to your head,
Your neighbors will be grateful...
If you have to ask how to reduce vibrations from speakers within an
apartment you have too much speaker for too little apartment...
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