Speaker in a sealed box - Page 1
Forum section: electronics / beginners

author: kcs
author_rank: Regular Contributor
timestamp: April 11, 2014, 03:32:21 pm
content: I got curious how speakers/piezo elements are used in water-resistant rated equipment? For example in industrial, military or even consumer equipment (Galaxy S5). There are no holes to prevent moisture from coming in, but at the same time sound is loud and clear. So how is it done?

author: miguelvp
author_rank: Super Contributor
timestamp: April 11, 2014, 06:03:17 pm
content: the box vibrates with the sound.sound doesn't need air, is just vibration of molecules, you can hear surface sounds inside water and you can hear also in water even if you hearing is not in direct contact with the water.Just good vibrations!

author: BravoV
author_rank: Super Contributor
timestamp: April 11, 2014, 06:06:08 pm
content: The box it self will transmit the sound/vibration generated by the piezo elements if it is attached firmly to it.

author: Holograph
author_rank: Regular Contributor
timestamp: April 11, 2014, 06:45:43 pm
content: Quote from: kcs on April 11, 2014, 03:32:21 pmI'm no expert on the construction of a piezo speaker, but with a traditional dynamic (cone) speaker, all you need to do is use a poly or metal coned speaker with a rubber surround (I guess foam COULD work too, but I think it would be worse) and it can be water resistant while being exposed on one side to open air. Technically there are coatings for paper cone speakers that add some degree of water resistance as well, but I'm not a fan of paper cones, personally.Now whether that would work for you really depends on how much water pressure you might subject it to and whether you'd want it to be usable underwater or if you just want it to not break if accidentally submerged.It's otherwise possible to, like the other posters said, conduct the sound right through the case of your device without leaving it exposed at all. Harder to get good sound quality, but how many phones (as an example) have good sound quality from their speaker? Not many.

author: kcs
author_rank: Regular Contributor
timestamp: April 11, 2014, 07:13:41 pm
content: I did a test with piezo element. At 50 cm I was getting 102-104dB, when I have placed it inside a sealed box and firmly attached it, I was getting 80-83dB. That's 4 times quieter. So 3-5 meters away I would barely hear it.I won't place this box in water, I want it to be protected from random splashes of water. I am not looking for sound quality, I am interested in max loudness.Btw, foam absorbs water.

author: Shock
author_rank: Super Contributor
timestamp: April 11, 2014, 07:35:39 pm
content: I've only seen a water resistant speaker a while back on a shower radio that I had. It had a plastic cone rather than a paper cone. No part of the back end of the speaker is exposed outside. You could splash water on it all day and it was fine.I'm not sure how much moisture could get in but I recall it had a waxed PCB.Another idea would be to use a thin gland behind a protective grill. This would allow more sound energy to be released.You can get fully waterproof speakers so I'm sure it's an easily solved mystery and all documented in the patents.

author: Jarrod Roberson
author_rank: Regular Contributor
timestamp: April 11, 2014, 07:47:35 pm
content: Quote from: kcs on April 11, 2014, 07:13:41 pmClosed cell foam does not absorb water.

author: kcs
author_rank: Regular Contributor
timestamp: April 11, 2014, 08:37:57 pm
content: I would prefer to go with piezo element as it is much more power efficient. But if speaker with plastic/rubber cone is the only solution, then I guess I need something likethisand 4W of power to match my tested piezo element.Quote from: Jarrod Roberson on April 11, 2014, 07:47:35 pmI see. I don't have that type of foam to test. It would be interesting to know how much does it limit the sound.

author: miguelvp
author_rank: Super Contributor
timestamp: April 11, 2014, 08:41:50 pm
content: Note however that sounds travels further in water than air (due to density).

author: Holograph
author_rank: Regular Contributor
timestamp: April 11, 2014, 08:44:12 pm
content: another possible option is a surface transducer, which focuses specifically on making a surface vibrate the sound. We - or at least I - weren't trying to imply that you can just stick a speaker in a box in any method. It needs to be installed in a way that it transfers as much vibration through the case as possible.Most don't sound good, but you said you don't need sound quality, so it could work, depending on how it's installed.Personally I think a poly-cone dynamic speaker is probably best.

author: SL4P
author_rank: Super Contributor
timestamp: April 13, 2014, 02:25:51 pm
content: Quote from: kcs on April 11, 2014, 07:13:41 pmConsider the audio spectrum you're trying to reproduce - that will give you an idea of the material for the transmissive surface (glass, plastic, other). That in conjunction with the resonant frequency of the driver, volume of the sealed box, and the medium (water) will tell you more about the best way to drive the transducer to get as vlose to your desired performance as possible.

author: Zero999
author_rank: Super Contributor
timestamp: April 13, 2014, 06:59:52 pm
content: Drill a hole in the enclosure and glue the piezo behind the hole with a waterproof silicone sealant.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 13, 2014, 08:22:38 pm
content: Moisture protection is simply a matter of using a water-proof barrier between the transducer and the outside environment. This could be as simple as a sheet of very thin plastic (like a plastic bag) between the speaker and the grille to the outside.Piezo transducers have notoriously poor frequency response. I doubt there are very many phones with piezo transducers for speaker, microphone, or even vibrator service. Speakers tend to be the traditional electro-dynamic (magnet + wire) kind. Microphones tend to be electret condensor (often the size of a match head), and vibrators again are usually electro-dynamic (either a motor and an offset weight, or a low-frequency "buzzer".)

author: lewis
author_rank: Frequent Contributor
timestamp: April 13, 2014, 08:40:34 pm
content: Water resistant speakers use drivers with the cone made of mylar like this:For true IP rating, piezo devices can be glued to the inside of an enclosure. No good for low frequencies, but adequate for noises and beeps.