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Old 8th September 2003, 02:26 PM   #11
Wizard of Kelts
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Quote:
Originally posted by Volenti
What's stopping the weight of the water from pretty much "bottoming out" the driver....
Good point. Okay, let's try something else then. How's the illustration below?

Both box volumes and water volumes are equal, but not connected.
Attached Images
File Type: gif water chamber speaker 6.gif (3.4 KB, 859 views)
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Old 8th September 2003, 03:35 PM   #12
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I think that there are better ways. Im not quite sure how the water would help as in effect its harder to move than air. A ballon with a gas with different properties from air might work. Whilst i was reading around this subject i came across what looks to be the solution.
http://www.kef.com/technology/acoustic/acoustic.html
It works by the activated carbon being able to adsorb (not absorb) some molecules from the air when the cone moves backwards and releases them when it moves forwards. This gives an effective increase in compliance and hence a better performance from the same size enclosure. Ive looked at the patents and the carbon needs to be treated really to prevent water absorption - but activated carbon isnt too hard to come by and if kept dry enough might be ok to use. I was considering building some speakers using this and a few other tweaks and seeing what i come up with.
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Old 8th September 2003, 04:03 PM   #13
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If I remember correctly, it was Cerwin Vega who had a speaker containing a gas filled bag. The gas was more easily compressed than air and made the enclosure seem larger than it was. Don't remember the gas.

I've read this entire thread and can't seem to find anything relating to the purpose of a water enclosure except some vague reference to and increase in effeciency.

Could someone clear this up for me?
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Old 8th September 2003, 04:22 PM   #14
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I don't see any possibility either than lowering the resonance of the driver by adding mass.
But that won't have any advantages over adding mass directly. And I don't see how it should be possible to increase efficiency this way.

Furthermore you can't accelerate water as much as you like. While there won't be much problems "pushing" it - "pulling" might cause cavitation.

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Charles
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Old 8th September 2003, 04:32 PM   #15
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The reason for a speaker's inefficiency is the impedance mismatch between air and the driver. The air has a very low Z, and the driver has a very high Z. (The speaker can act on the air with ease; the air can act on the speaker if wind gets up to hurricane speed.) Thus, the speaker moves back and forth large amounts and gets very little in return.

The idea is that the water could act as an impedance transformer. The area with which the driver interacts with the water could be small (15" woofer as an example) and the water could, in turn, act on a very large area of air.

I don't know that the water-air mismatch would be any better, but you might gain some improvement becuase the water would more easily be expanded to huge surface areas. (Imagine the surface area of a swimming pool moving up and down just 1mm--that's A LOT of displacement!)

The fact is, this is a huge can of worms, and a much easier solution is to just horn-load everything. Horn-loading causes the woofer to act on a much larger area of air, which brings the impedances closer to each other and increases efficiency.

For a permanent installation, a water-loaded sub (BTW, having a horn underwater is nearly useless, because the impedance mismatch is so much smaller) might be a useful and interesting way to increase output, but in the end, I suspect the practical problems would keep it from ever catching on. Horn-loading is a proven design and yes, it has its drawbacks (size, complexity, expense) and like all other things in speakers, there are tradeoffs to be made.

As part of the obligatory "DIY Driver" discussion, I think it would be really cool to make a totally waterproof driver that could be put in a water-loaded enclosure. If the walls of the room had watersubs in them, and the floor were just a grating over a couple inches of water that acted as the main woofer, you might get really good sound. Or it might just be a really expensive failed experiment.

I wonder if there's a grant out there that would pay us to build such a thing, just to find out....
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Old 8th September 2003, 04:33 PM   #16
ksl is offline ksl  Estonia
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i do not see the practical point in this design because the mass of water is big. and from my mechanics and physics lessons i remember that
F=m*a (where F is force, m is the mass and a is acceleration ) then the bass speed goes down, or am i thinking wrong

but if you are fighting with the pressure, what the driver gets when it's placed into the water (if you want to use a chamber with air behind the driver), then you should use a U-pipe like on the added picture
Click the image to open in full size.
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Old 8th September 2003, 08:32 PM   #17
Guss is offline Guss  Canada
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Could we use an Isobaric load to release pressure?
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Old 9th September 2003, 03:54 AM   #18
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Clever lad! Drivers that are waterproof on one side are easier to come up with, methinks, and isobarik loading would make 2 sides waterproof... (Butyl rubber + metal cone = CAR WOOFER THUMP THUMP THUMP) You might have a hard time finding this kind of driver with a low enough Qts so it wouldn't sound like it was going underwater. (Yuck. I bet the water makes Qts+2.)

The seal would still have to be REALLY good, but it could definitely be done. I still want to see someone come up with money so I can build a party hall on this premise.
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Old 10th September 2003, 02:26 AM   #19
Bull is offline Bull  United Kingdom
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How about these specially designed speaker which are waterproof and used for shower radios in the bathroom.

With a mylar cone, mylar surrond and mylar dust cap [all one piece,but corrated to make the surround.]Cone only 1 joing and thats joined at the edge,plastic frame.
The only catch is those type of speakers are always fullrange,not bigger than 51/4 inches and not bigger more than 20w rms[also used for burglar alarm bell boxes,and swimming pool speakers].


Also I heard there is a submergeable speaker called Lubell which can be used upto 12 metres underwater used at sealife centres to 'speak' to dolphins.
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Old 10th September 2003, 02:29 AM   #20
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www.lubell.com is the site for underwater speakers
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