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Post by OziRiS on Mar 23, 2020 12:56:01 GMT
Hey all In these times of Corona virus and isolation, I'm forced to do my course work for school from home. It works well enough when I'm just doing written assignments, but the experimental side of the physics lessons is obviously a challenge, so we're pretty much limited to just doing calculations right now and that's hardly the fun part of physics class, now is it? At the moment, we're working on waves - standing waves specifically - and were supposed to do an experiment where you tie a string to a small speaker-like contraption that is then connected to a tone generator. The other end of the string has a hook tied to it that you can hang different weights off of and then the string is run over a pulley attached to the edge of the table. The aim from here is to create various standing waves and do a bunch of calculations on how the length of the string, the different weights and the frequencies affect each other. I'm thinking of building this string vibrator/standing wave generator myself, so I can actually do the experiment at home. The idea is to use a tone generator from the Internet and either a modified speaker or some sort of small DC motor connected to the 3,5 mm jack in my computer, but I'm not entirely sure what stuff I need to get this idea to work. That's where you guys (hopefully) come in. I know there are more than a couple of people here who would probably know or at least have an idea of how to build this contraption. Remember, it has to be built out of stuff I'd have relatively easy access to, as it's kind of hard to get stuff shipped from China or somewhere like that at the moment, so things I can get to by modifying or taking old stuff apart would be preferable. A few specs, so you know what I'm aiming for: - The thing has to be able to vibrate in at least some relatively broad part of the audible frequency range, so the PC can actually send out a usable signal. - It has to be sturdy enough to not fall apart while vibrating a string that's holding a weight of up to about 200g (just under half a pound) I found a video on YouTube of what it looks like when you use the contraption we'd have access to in our physics lab at school (minus the pulley and weight), just in case you've never worked with one before and my description sucks  : Hope you guys can help  |
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Post by GTCGreg on Mar 23, 2020 13:06:28 GMT
There are a number of frequency generator apps available for both PCs and smart phones. That shouldn’t be a problem. You won’t get enough power out of the line out of a computer or even the headphone output of a smart phone to adequately drive a speaker. You will need some type of amplifier in between or use a powered computer monitor speaker. You also want to find a speaker that has a relatively large throw to it. It doesn’t have to physically be that big, but should be one that is designed for low frequency output.
When attaching the output post that connects to the stream, to the speaker, all you really need is a long bolt and a fender washer. Glue the fender washer to the center of the speaker and that towards the outer rim of the speaker. There is more movement at the center them at the edges. Other than that, it’s a relatively simple project to build and I don’t think you would have much trouble making one. .
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Post by OziRiS on Mar 23, 2020 13:11:01 GMT
Okay, finding a computer monitor with built in speakers won't be easy these days, so what could I use as an amplifier if I'm forced to use the 3,5mm jack for audio output?
ADDENDUM: The speaker doesn't have to go that low in frequency. Somewhere in the 200-600 Hz range would be fine. I don't want the wavelengths to be either so long that the string has to be too long to fit on my dining room table, or so short that it's impossible to see the waves with the naked eye.
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Post by GTCGreg on Mar 23, 2020 13:15:51 GMT
Okay, finding a computer monitor with built in speakers won't be easy these days, so what could I use as an amplifier if I'm forced to use the 3,5mm jack for audio output? ADDENDUM: The speaker doesn't have to go that low in frequency. Somewhere in the 200-600 Hz range would be fine. I don't want the wavelengths to be either so long that the string has to be too long to fit on my dining room table, or so short that it's impossible to see the waves with the naked eye. Maybe you could find a used small guitar amp that someone is trying to get rid of. |
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Post by OziRiS on Mar 23, 2020 13:20:09 GMT
I was actually thinking of finding an old, sort of large computer speaker, cutting off the membrane, attaching some sort of screw/bolt to the middle of the speaker, like you said, and then laying it down on its back and clamping it to the table, so it doesn't move. I'm just worried it would be too fragile to take the load of the string and weights.
What do you say? Think that could be an option?
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Post by GTCGreg on Mar 23, 2020 13:23:51 GMT
I would leave the speaker cone intact. It helps keep the voice coil centered around the magnet pole. Without it, the voice coil could rub. Besides, you may want to be able to hear the tone you are generating.
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Post by OziRiS on Mar 23, 2020 13:27:32 GMT
I would leave the speaker cone intact. It helps keep the voice coil centered around the magnet pole. Without it, the voice coil could rub. Besides, you may want to be able to hear the tone you are generating. If you leave the cone and membrane intact, how would you attach the screw/bolt? I just poked a bit at my PC speakers and it seems like the cone is just a loosely stretched out "sheet" that covers the coil inside. I imagine that if you attached anything directly to that, the membrane would end up breaking apart anyway, which is why I was thinking of taking it apart from the getgo and attaching the bolt directly to the coil underneath. Or does that coil not move, but merely produce movement in the membrane...? |
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Post by GTCGreg on Mar 23, 2020 13:43:51 GMT
I think we’re talking about two different parts of the speaker. The cone as I refer to it, is the large paper or fiber disk that connects the center of the speaker out to the edge of the metal frame. I think what you are referring to is called the dust cap. It’s a small circular disk in the center of the speaker. There should be no problem cutting that away to accommodate the head of a bolt.
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Post by GTCGreg on Mar 23, 2020 13:48:43 GMT
Also keep in mind that the metal part underneath the dust cap is magnetized. You don’t want your bolt head to get stuck to it. Maybe look for a nylon bolt or use a large enough fender washer to keep the bolt head separated from the magnetic pole piece.
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Post by OziRiS on Mar 23, 2020 13:53:18 GMT
I think we’re talking about two different parts of the speaker. The cone as I refer to it, is the large paper or fiber disk that connects the center of the speaker out to the edge of the metal frame. I think what you are referring to is called the dust cap. It’s a small circular disk in the center of the speaker. There should be no problem cutting that away to accommodate the head of a bolt. Yeah, sounds like I'm just not up on my HiFi equipment terminology Now that we have that little misunderstanding out of the way, I have a set of these that I've been thinking of swapping out for a new set anyway:  You think those would be up to the task if I clamped them to the table, or would I need something sturdier? |
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Post by GTCGreg on Mar 23, 2020 13:55:01 GMT
Those look perfect. All you need is a large flat head screw and glue it to the center
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Post by OziRiS on Mar 23, 2020 13:59:32 GMT
Those look perfect. All you need is a large flat head screw and glue it to the center Awesome! Way easier than I was expecting! Thanks |
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Post by GTCGreg on Mar 23, 2020 14:01:30 GMT
He sure to let us know how it works out.
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Post by OziRiS on Mar 23, 2020 14:02:48 GMT
He sure to let us know how it works out. I'll be sure to take some pictures and let you know if it works |
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Post by the light works on Mar 23, 2020 14:08:21 GMT
indeed. it sounds interesting. I'm now having visions of scaling it up to Adam and Jamie's giant car speaker.
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Post by OziRiS on Mar 30, 2020 16:15:00 GMT
The project has unfortunately been put on hold, as every place that has the speakers I want at a price I'm willing to pay seems to be closed for the foreseeable future  Not really willing to take apart my old, fully functioning speakers without having something to replace them with, so it'll have to wait. |
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Post by the light works on Mar 30, 2020 16:51:11 GMT
The project has unfortunately been put on hold, as every place that has the speakers I want at a price I'm willing to pay seems to be closed for the foreseeable future Not really willing to take apart my old, fully functioning speakers without having something to replace them with, so it'll have to wait. the curse of bad timing. |
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Post by GTCGreg on Mar 30, 2020 17:51:05 GMT
The project has unfortunately been put on hold, as every place that has the speakers I want at a price I'm willing to pay seems to be closed for the foreseeable future Not really willing to take apart my old, fully functioning speakers without having something to replace them with, so it'll have to wait. Yeah, most of the electronic suppliers, such as Fry's and Best Buy, are closed here. Amazon still seems to be doing pretty much business as usual. I've received a number of purchases from them since the so called lock-down. |
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