Noise reduction for speakers

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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.
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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 still probably vibrate almost as much." We should be interested to learn how this could possibly occur.
--
Don Phillipson
Carlsbad Springs
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Don Phillipson wrote:

No it doesn't.

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 floor.

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 likely.
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.
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On 12/11/2010 7:56 PM, Home Guy wrote:

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.
http://www.google.com/products/catalog?hl=en&safe=off&q=speaker+on+floor&psj=1&um=1&ie=UTF-8&cid …79874328502500108&ei=9l8ETfHMC8T_lgeZ5YmwCQ&sa=X&oi=product_catalog_result&ct=result&resnum=3&ved DcQ8wIwAg#
http://www.bestbuy.com/site/Polk+Audio+-+Triple+5-1/4%22+2-Way+Floor+Speakers+%28Each%29+-+Black/8825505.p?skuId ˆ25505&ci_src110944&ci_skuˆ25505&ref&cmp=RMX&loc&id07352527510
Note the feet. What do you think they are for?
isolation cones, note the minimal contact area:
http://compare.ebay.com/like/260666843734?ltyp=AllFixedPriceItemTypes&_dmd=Gallery&var=sbar&rvr_id 3310057019&crlp=1_263602_304692&UA=WXF%3F&GUIDp09d4cd12a0a02652d34f93ffefe4ea&itemid&0666843734&ff4&3602_304692
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.
Jeff Who at one time spent a lot of time listening to room acoustics and has friends with commercial recording studios.
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On 12/12/2010 12:52 AM, Jeff Thies wrote:

http://www.google.com/products/catalog?hl=en&safe=off&q=speaker+on+floor&psj=1&um=1&ie=UTF-8&cid …79874328502500108&ei=9l8ETfHMC8T_lgeZ5YmwCQ&sa=X&oi=product_catalog_result&ct=result&resnum=3&ved DcQ8wIwAg#

http://www.bestbuy.com/site/Polk+Audio+-+Triple+5-1/4%22+2-Way+Floor+Speakers+%28Each%29+-+Black/8825505.p?skuId ˆ25505&ci_src110944&ci_skuˆ25505&ref&cmp=RMX&loc&id07352527510

http://compare.ebay.com/like/260666843734?ltyp=AllFixedPriceItemTypes&_dmd=Gallery&var=sbar&rvr_id 3310057019&crlp=1_263602_304692&UA=WXF%3F&GUIDp09d4cd12a0a02652d34f93ffefe4ea&itemid&0666843734&ff4&3602_304692

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 destroying recordings.
The techniques are neither new nor especially complex. A little Google searching on these anechoic room / chamber techniques will show how it is done.
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Largely done with double wall construction, at least the ones I've seen. Where there is minimal connection between the two walls.

Excatly.
Jeff
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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.
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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 different places.
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Obviously, I meant "if you decouple THE SPEAKERS" from the floor.
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wrote:

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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 for vibration.
Andy
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On 12/11/2010 8:46 AM, Jeff Thies wrote:

Invite friends over, let them lay on the floor put the speakers on their backs and tell them it's a free massage. :-)
TDD
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On 12/11/2010 8:54 AM, Andy wrote:

Set them on heavy duty bubble wrap.
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Workable, but I have a 7 yr. old grandson who visits. :-)
Andy
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Andy wrote:

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?
Jon
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On 12/11/2010 7:54 AM, Andy wrote:

Don't know the cost of their stuff but you might call them for expert advice:
http://www.polycrystal.com/pc-mainframe.htm
TDD
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Andy wrote:

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.
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wrote:

The apartment below me is empty.
Thought of asking the manager to let me test different volume levels to see what can be heard on the bottom floor.
Andy
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Andy wrote:

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 ?
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Headphones...
All of the vibrations will be directly transmitted to your head, bypassing the floor...
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...
~~ Evan
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