Need help making a speaker quiet in daughters new toy

[ThatGuy]

My daughter has received a new toy this Christmas and it has a noisy door bell that they LOVE to push repeatedly. It wouldn’t be so bad but it’s really noisy and needs to be about half the volume.

I’ve used tape in the past to cover the sound holes, and packed the speakers with cotton balls, but I would rather be able to calculate a resistor value to put in series with the speaker so that it becomes quieter.

Can anyone help me out with the math behind this so I can have a starting point on what value resistor to use?

Merry Christmas!

[Jarrett]

Can you take it apart and take pictures?

[packetbob]

If it’s a normal 8 ohm speaker then possibly stickling an 8 ohm resistor in series should lessen the power to the speaker by 50%ish…

Or not…

[packetbob]

Turn Down Electrical Toy Volume

[JohnC]

Typically a speaker will have an impedance (resistance) rating printed on the back of it; typically 8 ohms but sometimes 2, 4, 16, or 32 ohms or even some other value (you can also find out using a multimeter). You can solder a resistor in series with the speaker to reduce its volume.

For example, if you have an 8 ohm speaker and you solder an 8 ohm resistor in series then the speaker will be supplied with 1/4 the amount of power that it did previously.

The audio signal is a certain voltage, and the equation for power is (V^2)/R. Since the total resistance connected to the amplifier is now 16 ohms, the amplifier will be providing half as much power as it did when only the 8 ohm speaker was connected. However, that power is now being divided equally between the speaker and the resistor, so the speaker puts out 1/4 the amount of power compared to without the resistor. The speaker converts electrical power into sound, and the resistor converts electrical power into heat.

Speaking of heat, when sizing a resistor make sure to take into account the power rating of it. For example if you have an 8 ohm 4 watt speaker and decide to use an 8 ohm resistor, make sure the resistor is rated for a minimum of 1 watt. If the speaker is rated for 1 watt, then using a 0.25 watt resistor is suitable (we have all kinds of resistors at VHS, as well as soldering equipment available to use. Lee’s Electronics also sells all of these supplies.)

[Janet]

@ThatGuy thanks for posting. This is the kind of thing we love to troubleshoot! Can you post the toy info and model

[winegummo]

would it be too low tech of a solution to open it up and put a small piece of tape over the speaker?

[Metal_Janet]

Often when we need to quiet or silence noisy equipment on film sets, we will put a little dab of hot glue or sticky tack on the speaker. Cotton batting also works.

[ThatGuy]

Sorry for the delay in response. It’s been a busy few days!

I took it apart and opened it up. It is an 8 Ohm speaker at a whopping 0.25 Watts (I’m telling you this little dog has a big bark!)

Thankfully there is seemingly endless amounts of room to play in this enclosure. I have a good selection of resistors kicking around so i’ll have a go at it here and see how it goes. I don’t recall what wattage resistors I have, I think 1 Watt… It may be a much higher wattage than it needs, but at least we know heat won’t be an issue

I agree, I could just tape it, I’ve done that in the past with great success, but then I wouldn’t learn anything new from the project and I feel like this would be a good project for the oldest (7 yrs) to help me with since she is always asking to help me with projects. It would be very simple, quick, and nothing to blow up like what happened on the last project that I did with her… Whoops!

…I guess I should explain the explosion a little bit more.
We were spending some quality Dady-Daughter time together and she was having fun with the electronics. Safety glasses on, but low voltage circuit kinda stuff. I preach safety when we do this and although she can be pretty anxious at times, I try to tread lightly on the subject so I don’t scare her off. I give her enough information so that she doesn’t try sticking things into an electrical socket. She was slightly nervous but with my words of comfort that this is a safe experiment, she wanted to keep learning so we get setup. I was playing around with an old oscilloscope I have laying around so we decided to look at different wave forms. I figuredI would show her how a bridge rectifier works, so we plug one onto a bread board and power it up. The wave form was really dirty so I decide to go one step further and add some capacitors to the circuit so she can see what those components do to a circuit. I figured it could lean in to a great discussion if she was interested, or at the least it would show her a different image on the screen and at this point she would be excited to see that too. A little 40VA, 24V transformer was supplying the power for this experiment, but it may have been a 240VAC input and I was running it off a 110V supply so it may have been only 12V output, I don’t recall to be honest, but thats neither here nor there…

I dig up some really old capacitors that I had in a spare parts bin, check the voltage and it looked like it would work with the circuit to provide some noticeable difference. Daughter is starting to lose interest at this point with me having to find capacitors, so I quickly plug them into the circuit and watch the display for a result. At this moment I still have my hand on the capacitor and I am telling her to watch the screen. I feel the capacitor quickly start to bulg in my fingers, then BANG!

At this point she’s freaking out, theres smoke, loud noise, me doing my best to hold my laughter back as I am just then remembering that capacitors are polarity sensitive components, and they fail quite spectacularly! She didn’t think it was quite as funny as I did at the time but I think by now I have earned her trust back enough that she will help me with this project

I deal with AC electricity frequently in my daily job, but when it comes to DC electronics, I am pretty much self taught. It’s just a different beast than the stuff I work on. I enjoy it a lot and I love to learn about it so I appreciate the help and advice that everyone has provided me.

Cheers!

PS: Is this forum on Tapatalk? That is my primary forum interface (I know, it sucks, but it’s SO much more convenient!) and it would be so much easier for me to follow these threads if it was on there.

[ThatGuy]

Well wouldn’t you know it, I think this toy has the same speaker as the one in R2D2!

I have a feeling the driver may be different so I will probably need to use a different resistor value to determine a volume that works for this toy. Thanks for the link!

[ThatGuy]

So I have an 8 Ohm speaker, and I’ll try adding an 8 Ohm resistor in series with the speaker.

Would it serve any benefit to put an additional 16 Ohms in parallel with the speaker/resistor so that the circuits total ohms remains at 8 ohms?

The only thing that brings that question up is a comment on the R2D2 link above where someone suggests changing the resistance can have a negative effect on the amp or driver for the speaker. I would have thought it could only cause damage to an amp if the resistance was reduced, for example a 4 Ohm speaker installed on an amp rated for an 8 Ohm speaker… But if a 16 Ohm speaker was installed on that 8 Ohm amp then wouldn’t it be ok?

I’m sure for this project it won’t matter but I’m thinking ahead to other projects where it may make a difference. This is all about learning for me. I prefer to learn how to do it right so I can decide where I break the rules, instead of breaking the rules without even knowing they are getting broken.

[JohnC]

That’s correct. It won’t harm an amplifier to connect a higher impedance speaker, but it might if you connect a lower impedance speaker.

[Metal_Janet]

Ah, 7 is a great time in a young girl’s life, so many possibilities opening up as the motor skills solidify. Slightly off topic, forgive me, but down the road if you ever want to do a daddy-daughter welding lesson, give me a shout. It’s officially a Disney Princess skill now, after all. My little sister tried out TIG when she was 9…

[ThatGuy]

Off topic is fine with me, the post stayed on track long enough to get the answers that were needed besides, friendly conversation only strengthens the community. I’m all for it!

You are Awesome! and I thank you for the offer! I will definitely let you know as she approaches that comfort level. Sparks and heat scare her right now but i’m working on it with soldering and cutting with grinders. In fact, I’ve been working on it since she’s been little. Not just with building stuff but with everything in general. I built a small ropes course in the back yard for her to play on, dug a trampoline into the ground, put up a zip line. Free play kind of stuff that they can push themselves to their own limits as they feel comfortable. Every year I try to add something new to it. Next year my goal is to build a rock climbing wall and beef up the zip line with stronger cable. She’s still pretty timid on the structures, some of her friends will climb laps around her, She is most certainly all ‘Girl’ right now despite my attempts to influence other activities, but she’s been getting brave on the structures and has asked me to install a horizontal bar for her to practice doing flips on.

My goal for the rock wall is to help her get comfortable with heights since that still scares her quite a bit, and to get familiar with getting roped into a harness.

I’ll be getting her into the shop more as we go through next summer. I’ll have to find some projects that she could do with wood, and start her off easy. She does ask to help every time i’m building in there and I do everything I can to include her with the projects when I can. I have such a small space to work though its not really safe to get two bodies in there so it is hard, and I am limited to mostly wood tools right now.

I was given a stick welder but I don’t have a power source to run it yet, and I’m not really sure what i’m doing with it. Its an old piece of equipment but I think it still works… i’m really not the one that should be teaching her though considering my lack of experience with it. Brazing I can do, stick welding… its been quite a while since i’ve done any of that

[ThatGuy]

Oh, I’ll post project photos a bit later, they are not much, its a cheep toy and the repair falls in line with the price, but may as well show the results none the less.

[ThatGuy]

I found 47 ohm resistor was a noticeable result but still too loud, so I tested a 100 Ohm and found that was much better, but might still be annoying for others if they were working on a computer, so I ended up using a 220 Ohm resistor to bring it down to a level where they can comfortably play with it without disrupting everyone else in the house… I may need to up the volume a bit by going back to the 100 Ohm later, but I’ll wait for feedback from the kids and see if it is too quiet for them.

This is where it gets a bit ugly… I was going to use heat shrink but i figured for all intent of purposes, a couple wraps of electrical tape will suit this toy just fine. It’s not typically my style but the tape was closer and much easier to get, so it won.

Thanks everyone for your help with this!

Happy New Year!

[Metal_Janet]

That’s excellent. Just so you know, TIG has no sparks, and heat is just something that you put in one place and then use pliers if you need to pick it up (at least that’s the case with steel… aluminum conducts like crazy and has taken me by surprise more than once). within industry, TIG welding is considered to be an area where women traditionally excel. Autogenous outside corner welds are definitely easy enough for a kid. If she gets comfortable with heat… and wants to try her hand at sparks. Plasma cutters are basically light sabres. The youngest I’ve taught that to so far was a 13 year old girl.

I generally avoid charging for kids, because I find it very rewarding to watch a young person attack the scrap bin knowing that nothing is safe from them, lol.

Anyways, you know where to call when she gets to that special age where a girl has only one thing on her mind… mastery of fire and steel.